Before you buy, look at other options

A crawl space heater may seem like the right solution to cold floors above a crawl space in winter. Heat the crawl space, and that will make the living room warmer too. Heat rises, so you’ll have a toasty warm floor and the cost of heating the living space itself will go down. Right?

Yes, up to a point. Heat from the crawl space will rise into the home. But heat will also escape out poorly insulated crawl space walls, or through any gaps between the walls and the ground, through wall cracks, and through drafts on any windows and doors.

So while a crawl space heater may solve the problem of cold living area floors, it probably shouldn’t be the first thing you try. You could save a whole lot of money – and find a better solution to your problem – by looking at other options first.

What if the problem is high craw space humidity or crawl space condensation in winter? Heating the crawl space will reduce moisture there, but once again you’ll be better off to solve the source of the moisture than to try to band-aid the problem with a crawl space heater.

In this article I’ll try to give as many reasons as possible for why you shouldn’t buy a crawl space heater – at least not until you’ve tried everything else. A crawl space heater is a big financial commitment if you don’t do your homework on the crawl space heat envelope first, because you’ll be running that crawl space heater for many hours through cold weather, and electric heaters are very expensive to operate. (I strongly advise against a combustion-based crawl space heater because of the fire risks.)

Crawl space heater

Not the best use of your hard-earned money
Photo by Knitting Zeal, via FLICKR

But if you only want to see what crawl space heaters are available, you can just jump to the last section where I look at some of the available heaters.

Keeping the cold out

Before you try warming up your crawl space with a crawl space heater, you should do what you can to keep the cold out. That cold air is what’s making the upstairs floors cold in winter. And air circulating from outside into the crawl space, which you might think would help dry out the crawl space and keep moisture from entering the house, may well be having the opposite effect. (More on this below.)

Are there air leaks to the outside? This is the first thing to try fixing. Putting a crawl space heater into a drafty crawl space just means you’re paying to warm up the out of doors. Close off any major air gaps by repairing the exterior walls or shoring up crumbled masonry under the above-ground walls. If the crawl space has exterior openings (doors or windows), make sure these are properly weather stripped and that they close tightly and stay closed. Cracked window panes should be replaced with energy saving thermal windows. Better yet, if the crawl space doesn’t need natural lighting, you should just close off any leaky or broken windows and insulate and seal the openings.

If your crawl space walls are wood framing over masonry, check that there are no gaps between the framing and masonry. Remember that any bond point between the framing and masonry needs to have a sealed barrier such as 6 mil plastic to stop moisture and termites. You can inject expanding insulation foam between the foundation masonry and wood framing from the inside of the crawl space (but not from the outside, as this insulation degrades quickly in sunlight).

Many crawl spaces built to older building codes were built with outside ventilation on opposite walls. The idea was that air would flow in one vent, draw moisture out of the crawl space, and then flow out the vent in the opposite wall.

Unfortunately, things don’t really work this way. If there is any way for air to rise from the crawl space into your home – which there surely is – the cold air entering from outside is warmed in the crawl space, and since heat rises, this warmed air rises through the floor into your home, drawing in more cold air from both crawl space vents. While this stack effect is now well studied and well understood and some building codes have been revised to take it into account, there are still many areas in North America where the building codes still require venting on opposite walls of a crawl space.

Instead of using vents, you need to properly seal your crawl space against air leaks from the walls and humidity from the ground. See the next section for help on sealing your crawl space. Don’t close the vents without also sealing against humidity, or you’ll be inviting humidity in without giving it a way out.

Are the walls of your crawl space insulated? In the crawl space under my kitchen extension, the exterior walls consisted of two-by-fours 24 inches apart, with wood siding nailed onto the outside. So of course the kitchen extension was freezing cold in the winter. But sticking a crawl space heater in there would just have meant sending most of that heat through the wood paneling to the outside. So first I insulated.

Insulation will not only help your crawl space stay warmer, reducing the need for a crawl space heater; it will reduce the problem of humidity condensing on cold outside walls, since the walls won’t be a direct contact point between the cold outside air and the warmer inside air.

Ensure that the exterior facing has no cracks or holes. Then add fiberglass insulation or a mineral wool such as Roxul between the joists. Add a vapor barrier, tape it, and cover with 3/8″ plywood.

Between sealing for air leaks and insulating the walls of your crawl space, you’ll be well on the way to keeping the outdoor cold from leaking into the crawl space and cooling the living areas above it. And while a crawl space heater uses up energy – and your hard-earned money – every time it starts up, a well-insulated, well-sealed crawl space doesn’t cost you anything to keep warm, if the crawl space stays warm all on its own.

That’s how things turned out for me – once I sealed and insulated, the breakfast nook floors stayed toasty warm and there was no need to install a crawl space heater. In fact, we were even able to get rid of the baseboard heaters in the breakfast nook.

Note that crawl spaces typically involve a wood frame sitting atop a masonry foundation, in which case you should probably try to insulate this juncture well.

Getting the moisture out

Condensation can be a big problem in a crawl space

Condensation can be a big problem in a crawl space if it is sealed but not insulated
Photo by Ken Douglas, via FLICKR

Another popular reason people have for buying a crawl space heater is that their crawl space is too moist. There may be signs of excess humidity such as black mold or a mildew smell in the crawl space, moisture damage to floors upstairs, or damage to baseboards or the base upstairs walls. Particularly if the edges of the floor or the upstairs walls are uninsulated, cold air can draw heat out from the bottom of the upstairs walls, leading to condensation which in turn can cause the drywall to grow mildew or mold. Finally, you may have actual signs of water in the basement: water dripping from joists or condensing on walls, damp crawlspace floor or soil, heavy moisture build-up on exposed pipes.

Before you consider installing a crawl space heater, make sure you’ve got this moisture under control. Follow these steps to control crawl space humidity:

1. Find any water sources and deal with them. For example, handle leaks coming from pooled rainwater on pavement or soil outside the foundation by providing proper drainage outside the foundation. If you find water leaking in from walls or from the bond between masonry and framing, first check for leaking gutters or overflowing downspouts on the roof above, then seal or patch where the water is entering.

If humidity is coming up through the soil because you have poor drainage around the crawl space foundation, you may want to dig around the foundation and install drainage tile. (You won’t have to dig that deep since it’s just a crawl space.) If there’s a lot of water in the below-ground soil or you can’t get good drainage around the foundation, install a sump pump.

2. Seal the crawl space from the earth. You need to install a high-quality vapor barrier over the soil underneath your crawl space to keep moisture from the soil – and drafts, believe it or not – from entering the crawl space from below. Use a plastic crawl space liner. These liners are made of a thicker plastic than the standard 6 mil poly film used in vapor barriers, and are stronger and last longer. It’s just too easy to damage 6 mil film when crawling around in there, or to tear its edges away from the walls. A 15 or 20 mil crawl space liner will last longer and be less prone to damage.

Before installing the liner make sure you remove any sharp pebbles, discarded nails or screws, or any other objects that may cause the liner to be punctured from beneath when someone crawls around on top of the liner. The liner should seal off the ground completely and connect to the vapor barrier for your walls. In fact, you can insulate the walls and cover with plywood, then place the liner on the floor of the crawl space with enough material to spare so that you can run the liner all the way up the walls. Seal all seams with mastic tape.

3. Seal the vents. You should already have plugged any leaks in the walls or masonry / wall bond, and in any windows. Now that the floor is properly lined, seal the vents to keep outdoor air from being drawn into the crawl space. You will see conflicting advice on this on some other web sites – and from contractors in your area – because the notion persists that the right way to deal with crawl space humidity is to use vents to increase air flow through the crawl space and let the moisture out. But as explained above, what actually happens is that the stack effect pulls cold air into the vents and then up into the house, and the cold air, crawl space moisture, and airborne dust and mold spores come into your living area.

Caution: If you have a combustion appliance in your crawl space – a gas water heater or space heater for example – don’t seal the vents without first checking that there is an adequate air supply for the combustion. A combustion air supply directly to the appliance will provide it with the air it needs without causing the entire crawl space to cool down. Also make sure you have a carbon monoxide detector with battery backup for any crawl space that has a combustion appliance.

Once you have sealed your crawl space from outside air and moisture, and insulated the crawl space walls, it’s time to look at the next problem: cold in the floors above.

Staying warm upstairs

If you have properly insulated the walls of your crawl space and have encapsulated the crawl space so that no air can enter from walls, the ground, or any windows or doors, the crawl space should stay considerably warmer in winter. Still, you may find that the floors above the crawl space continue to feel cold. If cold feet is your only concern, I suggest you start by insulating the floor above the crawl space. But do not use a vapor barrier – you already have one around the walls and floor of the crawl space, so you definitely don’t want one above. Add batt insulation between the joists, and cover with 3/8″ plywood.

If you have heating ducts running through your crawl space to warm the living areas upstairs, it’s a good idea to seal and insulate the ducts (see Heating duct insulation). There’s no point in the heating ducts heating the crawl space if you can just insulate the ceiling to keep cool crawl space air from getting into the living areas.

Keeping the crawl space from freezing

The next concern is freezing pipes within the crawl space. If the pipes run between the joists, first insulating the pipes with foam pipe wrap such as Armaflex insulation, and then insulating the joists as described above (along with the encapsulation and sealing of the crawl space itself) may be enough to keep the pipes from freezing. During cold spells, letting a tap drip to keep water moving through the pipes will reduce the risk of freezing as well.

But if you do think freezing pipes are a real concern, you can install electrical pipe tape around the pipes. This tape contains a heating element that keeps the pipes above freezing. Here are a few pipe heating products you can buy directly from

Depending on your climate, you may be able to boost the temperature in the crawl space to keep it above freezing, simply by installing incandescent lights that are controlled by a thermostat. Remember that incandescent lights are only about 10% efficient at converting electricity into light – because the other 90% gets converted to heat. So using incandescent bulbs to heat your crawl space is not substantially less efficient than installing a crawl space heater, and is probably a lot safer.

You may also be able to use low-wattage infrared lights, provided you have at least 18 inches of space between their location and the nearest solid object the main beam of the infrared light reaches. One advantage of infrared lights is that their energy is only converted to heat when it strikes a solid object. So if you have a drafty crawl space, you can shine lights on the ceiling and the pipes to keep those warm, without sending a lot of heat out the openings that cause the draft. But be aware that infrared lights do pose a greater fire risk than standard incandescent bulbs.

One inexpensive possibility for a home-built crawl space heater is to buy a thermo electric switch such as the Thermo Cube TC-2, which provides power to attached devices when the temperature is below 30F / -1C. You can install plain light fixtures with 100 watt incandescent bulbs in the ceiling of the crawl space (close to the pipes), wire them through a plug to the TC-2, and plug the TC-2 into a wall socket. This way you will only be heating the crawl space when the temperature dips enough below freezing to risk bursting the pipes.

Just don’t use compact fluorescent bulbs for this job – you’ll save energy for sure – but you won’t be heating the crawl space at all, and it’s the crawl space heater effect, not the light, that you’re after. And remember that in many areas, standard incandescent bulbs are being phased out to force people to switch to CFLs. While I agree that getting people to switch to CFLs where there is a real energy savings, it’s unfortunate that this heavy-handed approach is necessary, as there are situations, such as building your own crawl space heater, or lighting a crawl space where you will only be in there a few minutes each year, where an incandescent bulb makes more sense.

Another option to keep the crawl space from freezing – without installing a crawl space heater – is to circulate air between the house and the crawl space. If you have properly encapsulated the crawl space to remove air flow and moisture from outside and from the soil, there should not be a problem with circulating air between the living areas and the crawl space, provided you properly filter it and deal with pressure differences. (Remember that in an unencapsulated crawl space, this air flow is happening constantly anyway, and is usually going one way – from the crawl space into the house.)

A crawl space ventilator is not the right tool for this job. Crawl space ventilators are designed to circulate air between the crawl space and the outside, which is exactly what you are trying to avoid by encapsulating your crawl space. A crawl space fan that draws unconditioned air into the crawl space from the rooms above may do the trick, provided you can install an air filter on it to keep dust and other airborne particles from the crawl space from entering the home.

Remember that if you use a crawl space fan to inject air into the crawl space from your living area, or to suck air out of the crawl space into your living area, you need to provide a return air flow elsewhere in the crawl space, or you will create a high-pressure crawl space or a vacuum (if the crawl space is properly encapsulated). Either way, this will create problems. If there are combustion appliances in the crawl space, a vacuum can be extremely dangerous, and either high pressure or a vacuum can increase the likelihood of air leakage to the outside even in a well sealed crawl space.

A crawl space fan is also not appropriate in summer if the house has high humidity levels (for instance, you live in a humid climate and don’t use air conditioning). You do not want to be circulating humid air into the crawl space. Instead, use a crawl space dehumidifier such as the SaniDry crawl space dehumidifier.

Many basement and crawl space repair companies recommend the Crawl-O-Sphere air system over a standard crawl space fan. This fan draws only 18 watts (that’s 157 kilowatt hours per year if running 24x7x365, or about $16 if your electricity cost is $0.10 per kwh). The Crawl-O-Sphere is designed to be installed in an encapsulated crawl space. However in reviewing information on the Crawl-O-Sphere, while I found they consistently stated that the Crawl-O-Sphere conditions the air flowing between the crawl space and living areas, they didn’t give any indication of how the air was conditioned or why a regular crawl space fan could not do the job. And of course every site recommending the Crawl-O-Sphere was also selling them.

So you really want a crawl space heater?

If you read the sections above, you will know that most of the reasons that lead people to look for a crawl space heater can be addressed by other methods – methods that won’t result in a decades-long commitment to higher energy bills. Electric heaters are very costly to operate, combustion heaters are a risky proposition for an airspace you seldom visit, and everything you can do to reduce airflow and heat loss in your crawlspace will help you avoid needing a crawl space heater at all.

To reduce the risk of fires in your heated crawl space, you may want to install a remote thermometer probe in the crawl space near the crawl space heater, and the wireless thermometer itself in your living area, so you can periodically check the crawl space temperature close to the heater.

It turns out that there really is no such thing as a crawl space heater – a heater specifically designed for a crawl space. Instead, choose an electric space heater that is suitable for the volume of the crawl space in question. You can install any convection-based electric heater in a crawl space provided you run it on a circuit that has adequate amperage, and that any extension cord you use is high enough amperage to carry the load. In terms of sizing, remember that a crawl space can have a far smaller volume of air than a room with the same square footage in your house, and that with proper encapsulation and insulation you should not need much additional heat.

Because heat rises, putting a convection heater in a crawl space with a very low ceiling does present a fire risk. For this reason you may want to install a fan-blower heater and build ductwork to carry the heat through the middle of the crawl space and distribute through various openings in the ductwork.

For more information on choosing the right space heater, see my most popular article, Energy efficient electric heaters.

47 replies
  1. Christine
    Christine says:

    Well I have an encapsulation done in my crawl space. I also have a dehumidifier, an industrial one, and still it is cold, not to the point of freezing, but it is cold. One half of my house is over crawl space and other half has a basement. The crawl space is very large, all the bedrooms are on top of the crawl space. The bedrooms are carpeted, the hall is wood floors, and I have baseboard heat, boiler heat which I love. But the builder had no heat going to the crawl space. This seems to be very strange to me. The builder is deceased so nobody knows anything. Well it is still cold now. What kind of heater can I use down there so I do not use up a lot of electricity and have a high bill? And my crawl space is very nice very white and clean, great storage space in a lot of it too but still cold and not to say the least great for cold beer/wine.

    • Robin
      Robin says:

      I recommend insulating your crawl space as much as possible, both the exterior walls (to keep outdoor cold out of the crawl space) and the ceiling (to keep crawl space cold away from your floors), before you give any thought to a heater. My crawl space has about 8 inches of insulation in its ceiling and the floor doesn’t get that cold in winter, even with temperatures dropping to -20C / -4F outside. You may find that if your crawl space is properly insulated (and properly sealed – but yours is encapsulated so should be well sealed) you won’t have as much of a problem with cold floors and won’t need a crawl space heater.

      If you are looking to not spend much on electricity, that is the best way to start. The better the insulation and sealing, the less you will spend heating the outdoors.

      As far as an appropriate heater, you first need to determine what heat output you need, which would require a heat loss calculation by an HVAC specialist. There are just too many factors (air volume, surface area of exterior walls, thickness of insulation, how much of the crawlspace is below grade, outdoor minimum and average winter temperatures, etc.) for me to advise you on what capacity heater to get. But most 120 volt space heaters have a maximum output of 1,500 watts; you could start by installing one space heater at that wattage and see what difference it makes (see my space heaters page for some recommended ones). Assuming your electricity costs you $0.15 per kilowatt hour, a 1,500 watt heater will cost you $0.23 per hour to operate, so even if it runs 24 hours a day your daily cost would be under $6. Try that for a month and see what difference it makes to your comfort and to your electricity bill.

      As far as efficiency, all electric heaters have the same efficiency, because they turn 100% of the energy in the electricity into heat, thanks to the law of entropy. So the main things you would be looking for are safety (you want one that won’t fall over), durability (e.g. based on customer reviews), and a thermostat that lets you set the temperature. You can set the thermostat to something as low as 60F, as that will cost less than setting it higher and (assuming the heater is powerful enough for the space in question) will give you relatively comfortable floors.

      Another solution you could consider – it is costly in terms of installation but will be cheaper to operate – is radiant floor heating. Since you already have a boiler, an HVAC installer could possibly install radiant floor heating in the floors above your crawl space (and if your floors aren’t insulated, could probably add that heating from within the crawl space). That would give you very comfortable floors and would be heated by your boiler which is probably cheaper to operate, for the heat provided, than any electric heater.

      • Bruce
        Bruce says:

        “daily cost would be under $6”
        Note: that’s $180 per month on your electric bill… for just that one appliance.
        Set the temp on the space heater as low as possible, and consider having a convenient way to turn it off at night.

        • Robin
          Robin says:

          Right, but my statement was “Even if it runs 24 hours a day” which is unlikely.
          Most space heaters don’t offer really low settings – ideally you want around 5C/40F. For that I’d recommend a Thermo cube temperature-controlled plug which will cut power to the heater when the temperature rises above 7C/45F.

  2. Peter
    Peter says:

    I have a cottage with an uninsulated crawl space. Within the crawl space is a framed/insulated area that is about 3’high, by 4’wide and 25 ‘ long. Very difficult to get into. This area holds the water lines.

    I have insulated the main exterior walls with 2″ ridged foam board as well as spray foamed the gaps. There is also insulation between the joists.

    My concern is the pipes freezing. What do you think about a hot water circulation system. I have read that it pushes hat water through the cold water lines.

    • Robin
      Robin says:

      I think heating the entire crawl space to prevent the pipes from freezing is overkill. You would be better to buy a pipe de-icing cable and wrap it around the pipes; the cable will keep the pipes from freezing all winter long, but will not waste energy heating the entire crawl space. You should then insulate around the pipes so that the heat from the pipe de-icing cable doesn’t just dissipate into the crawl space.

      I’m not familiar with the hot water circulation system you’re referring to. Again it seems to be overkill to circulate hot water through the pipes to prevent them from freezing; all you need is water that is above freezing temperature. Another issue with that system (based on my limited understanding of it) might be that it must either be a separate set of pipes that surround the existing pipes (in which case you are using more energy to keep the existing pipes from freezing than you would with a pipe heating cable), or it will not be able to circulate through pipes that are not arranged in a circuit. Such a system would need a pump that pumps water down one end of a pipe, with the water returning up the other end. Anything that is not in that circle would not get much if any hot water and could still freeze.

      • Machold
        Machold says:

        A hot water re-circ pump will eventually open pin holes in the copper because of a chemical reaction between hot water tank, water and copper.

    • Cel
      Cel says:

      I installed one, and, unless it is installed incorrectly, it did not work to keep my pipes from freezing. I had several conversations with the seller — so no I would not recommend.

  3. Denslow
    Denslow says:

    We live in a rural area and I’m looking for a way to keep the pipes in the crawl space from freezing in really frigid weather when the electricity isn’t working. This is not so uncommon here (once or twice a winter). So electric pipe wrap won’t work. The crawl space is dry, and about three feet high. I’ve read the arguments against it but wonder if, for a 2-3 day emergency period and with a bit of venting, a propane heater might do the trick.

    • Robin
      Robin says:

      If you are living there during the power outage, a propane heater in the crawl space might work okay. I would check the safety instructions for the heater before you buy though. I worry about the heat produced, in terms of the heater being quite close to the top of the crawl space (since it is a crawl space, not a ‘walk’ space). The other issue is that the thermostat needs to support very low temperatures of active heating, since you really only need to keep the crawl space around 5 degrees C.

    • francis
      francis says:

      I am just reading your question. I thought I would tell you what I have done to my crawl space. I did install a ventless 20k propane heater. It runs almost at the pilot setting when it gets cold down there. I have insulating board above it and when I turn it on I have a muffin fan blowing on it to move the air. It uses very little propane. I have had this setup over 5 years. I never shut the pilot off, it keeps it from rusting. I hope this gives you some ideas.

  4. gwyn
    gwyn says:

    I put an electric tape onto the pipe and covered it with more insulation. Covered all of the pipes near the tank for the well. The weather hits 15 degrees today and all of the water freezes again. I am in a mobile home that I have changed over to conventional home items such as the a/c and propane hvac, gas water heater, Tyvek and hardiplank with extra insulation and double pane low e argon windows and doors. How to I stop those pipes from freezing? Don’t want to put an electric heating element that might catch fire. The crawl space is at least 3 feet and the skirting is stone, wood set on some concrete. Suggestions?

    • Robin
      Robin says:

      It seems to me that the factors that determine whether or how quickly your pipe freezes are: for how long the temperature in the crawl space gets below freezing, how much below freezing, how much you can offset that with insulation and a pipe wrap heater, and how long the exposed section of pipe is. This last is particularly important, because the longer the section, the more electricity it will take for pipe wrap to keep it warm, and the more opportunities there are for it to freeze.

      My sister has a cottage that is fed by a well, in northern Ontario where the temperature often drops to -10F or lower. The water line from the well is buried below the frost line so the only part of it that is exposed is a four-foot section coming out of the ground and going straight up into the cottage. That section has a pipe wrap heater and insulation and is enclosed in a wooden frame underneath the cottage.

      In the short term (meaning this winter) there’s not much you can do to reroute the water line from the well, but longer term if you can find a way to bury the line at least 4 feet below ground (or wherever the frost line is in your neck of the woods) and have it surface only just below the entry point into the cottage, that will reduce the exposure to cold. Longer term you may also need to install a pipe melter inside the pipe – this is a heating element that runs down the center of the pipe in sections where it might freeze, and can be turned on – typically for five minutes – to thaw the pipe. That gets pretty pricey in terms of installation cost though.

      For now really all you can do is: make sure the crawl space is as airtight and insulated as possible; provide a heat source to the crawlspace to keep the temperature from dropping too low; make sure the line is as insulated as possible; provide a heat source to the line. It sounds like you have done most of that already and it may be just a question of how much better you can make the insulation or how much more heat you provide to the crawlspace or the line.

      The one other thought is: if you’re there and you know the temperature is going to drop overnight, leave the tap on a little. The water coming out of the ground should be substantially higher than freezing, so keeping a bit of flow through the pipe will bring heat in and increase the time it takes to freeze in the exposed section.

  5. Leah
    Leah says:

    We have a three family in slab and with a crawl space. the drain pipes freeze so tomorrow we are going to insulate the walls and the pipes? Is that enough?

    • Robin
      Robin says:

      It’s hard to know if it’s enough as many factors affect the situation. How often do the drain pipes freeze? Only on the coldest nights of the year, or routinely? If it happens rarely, then insulating the walls and pipes will help. If you can pinpoint causes (e.g. cold night combined with a certain activity involving water in the house) you might be able to plan for that by changing behavior (e.g. on really cold nights, run a hot bath, and let the hot water drain out before you go to bed so the last water going through is hot).

  6. Jon Donaldson
    Jon Donaldson says:

    My crawl space is half under/half above ground. cement walls, I have insulated the joist bays at top. Have THICK plastic lining earth floor and going up about 1 foot on wall. Previous owner/remodeler ran pex lines up outer wall and they freeze when outdoors gets to about 11 degrees. There are already hot radiator lines running through the crawl space to one unit on 1st floor, and an old capped line.

    I found a thin 3.5 radiator that I was planning on attaching to capped line, hanging from the joists to assist warm air flow in the area. Not to necessarily heat it, but help floor heat in the extremity of the house, and hopefully enough warm air up the back wall soffit to keep pex lines from freezing. Thoughts on this?

  7. Jon Donaldson
    Jon Donaldson says:

    previous homeowner/remodeler put pex lines through crawl space and up outer wall. They freeze and I have no access to them without cutting open walls.

    There is a hot water radiator line going to a 1st floor unit and a capped line in the crawl space. Doesn’t seem like too much extra cost to hang a hot water radiator (small – 3.5 inch thick) in the crawl space to assist with warm air flow to help pipes and extremity of back 1st floor?

  8. Jon Donaldson
    Jon Donaldson says:

    What about hanging a 3.5 inch thick hot water radiator in the crawl space? There is capped line in the crawl space and I have new water lines to a 2nd floor bath that the previous owner ran up the outer wall and they freeze.

    There is already a feed/return line to the hot water radiator system going through the crawl space…

  9. Brian
    Brian says:

    I have a completely encapsulated crawl space at our cottage/home on Lake Huron. Crawl space walls are spray foamed and also the floors with 3″ of closed cell foam. Crawl is 24′ x 42′ approx. 30″ high. I currently am drawing heat into the crawl with a Humidex fan which then expels the heated air through a 6″ vent from the crawl to the outside. My question is can I (now that I have spray foamed the crawl space floors and walls) re-circulate that heat from the crawl back in to the main floor? Seems like a waste to send that heated air outside. Would appreciate any advice you could offer.

    • Robin
      Robin says:

      If you have spray foamed the crawl space floor and walls you won’t be picking up any moisture from the ground, so I would think recirculating the air back to the house would be fine. Crawl spaces normally have a vent to the outside to ensure humidity doesn’t build up. With the sealed space you won’t have this issue. The only suggestion I have is to make sure any outside accesses to the crawl space are thoroughly weatherproofed, because you’ll now be drawing air from the crawl space back into the house, and any air leaks to the outside become air leaks to the house interior.

      • Brian McCann
        Brian McCann says:

        Hi Robin: an update from this last post. I have installed a fan on the main floor to draw warm air from our propane fireplace into the fully encapsulated crawl space. Crawl was much warmer this winter. Should I install a vent in the crawl so this new source of warm air doesn’t build up in crawl?

        • Robin
          Robin says:

          If you install a vent in the crawl space after venting warm indoor air into it you’ll just be heating the out of doors. It’s not the warm air you need to worry about building up in the crawl space but the humidity, assuming the air from your fireplace is coming from within your living space where it will pick up ambient humidity from human activity, water surfaces like toilet bowls / full sinks, shower steam etc. I would get a humidistat and just monitor the crawl space humidity for a few weeks. If it behaves itself, you can quit. If it starts to go up you might want to install a low-temperature dehumidifier in there with a drain line. The nice thing about the dehumidifier is that although it’s consuming electricity, it does help warm the crawl space so it’s doing double duty, and electric and propane heat are not that far off in price (since propane is the costliest form of heating other than electric).

  10. Terry
    Terry says:

    My question is : Will I have to provide heat to the crawl space to keep my sump pump operating through the winter?
    My situation is:
    We are building a new cabin with a wooden crawl space about 4′ deep. It will have the floor and walls of the crawl space encapsulated with 6 mil poly. The crawl space walls will be insulated. Foundation will be a minimum of 4′ below grade. We will have a HRV system operating off a humidistat for the crawl space/ cabin. We will also have a sump pump system working throughout the winter. The water lines will all be drained during the winter and the heat will be off. I will insulate the Sump pump well and the discharge line within the crawl space.

    I appreciate any comments, suggestions or related experiences. Thanks

  11. Ben
    Ben says:

    Had the crawl space encapsulated by basement systems solutions this fall and what a difference. House smells better and the temp was 46° when the outside air was 13° cooler and the ground pretty cold. I installed a remote temp and humidity gauge and can check it wirelessly with an app on my phone so I’ll be checking throughout the winter. Our pipes have frozen 4 out of the past 7 winters so I am hoping this makes the difference.

  12. Linda
    Linda says:

    I have a 1-1/2 story home built in 1946. It is on a crawl space – concrete blocks and dirt floor – about 4 ft high. Ten years ago I had an eco-energy audit done and the recommendation was to blanket wrap the walls and cover the floor with polyethylene sheeting. The four vents – two on west side, two on east side – were left uninsulated. I seal up the vents each fall on the outside with Styrofoam insulation, plastic sheeting and wood braced with bricks – the vents are about 18 inches by 6 inches. I have covered the water pipes with the electric tracing and the recommended insulation. There is no insulation on the ceiling of the crawl space, just the wood that supports the house floor.

    My house (935 sq feet) is heated with a Napoleon gas stove (30,000 BTU), with floor vents to second floor (no ducts in house at all). The stove is in the northeast corner of the main floor. The second floor rooms are at 70 F and the bathroom (southwest corner) is a mite chilly at 68 F during the winter. The stove has a blower and there is a ceiling fan to help move the heat around.

    Real estate agents have indicated that I need a “real” heating system since buyers don’t believe the gas stove is sufficient. I have a Samsung ductless split air heat exchanger on the second floor, but it is not efficient when the temperatures drop below 32 F. It is a great air-conditioner/dehumidifier in the summer. Is there a “real” gas furnace that could be put in the crawl space (access hatch is only 16 inches x 14 inches) with minimal duct work?


  13. peter hague
    peter hague says:

    hello.we have a 400 sq. ft. cavco park model home in cascade idaho. winter temps often at around 0 dg.the crawlspace is insulated with about 2.5 in. thick foam insulation all around inside of skirting. Would a ceramic heater be sufficient to keep the temp above freezing. area approx? 18-20 inches ground to floor clearance.

    • Robin
      Robin says:

      Zero degrees Fahrenheit is pretty cold. With 2.5 inches of foam insulation a 1500 watt ceramic heater would be just barely enough to keep the space from freezing at that temperature. To compute this I used a heat loss calculator and entered these specs:
      – 20×20 foot room
      – R10 insulation (which should be roughly right for 2.5 inches of foam insulation)
      – 4 square foot metal insulated door (you didn’t specify any door so I assumed there would be a small access door)
      – Basement slab (below grade) – there wasn’t a choice for ground level as this calculator is for a room not a crawl space
      – Good infiltration category (meaning well sealed against drafts)
      – 33 degree temperature differential (since you’re at 0 degrees and want it to be at least 33 degrees to stay above freezing)
      The result was 1251 watts which is about 20% less than a typical ceramic heater.

      Note that you’re also getting heat from up above, so one heater may be just enough. I would suggest getting two, for safety, and using a Thermocube to control the heater so it switches off once the temperature reaches 45F, that way you’re not wasting energy heating the space hotter than you need to.

  14. ray
    ray says:

    have a 30 in crawl with heater hard wired in just want to set it at home is only 7 years old full crawl everything in place live on west coast Vancouver what do you think thermostat should be set at

    • Robin
      Robin says:

      For Vancouver the main goal would be to keep things from freezing on the rare days when the temperature drops below zero. I would suggest ensuring the crawl space is well insulated, and set the thermostat to about 7 degrees.

  15. Albert
    Albert says:

    I am building a cottage and would not be there in Winter. Temperatures could go down to minus 30 Celsius. There is no power. I am concerned about frost getting in/under the foundation. The foundation walls are insulated from the in and outside. The crawl space bottom has a 2 ” concrete line with a some gravel and plastic below it. The bottom of the inside foundation is 2 1/2 feet below the 2 inch concrete liner. Any concerns that frost could get into the foundation? The main floor is a normal wood floor.

    • Robin
      Robin says:

      You’d need to figure out what your frost line is. In Toronto, for instance, the frost line is 48″ which means that all buildings with a foundation need to be at least 4′ below grade.

      That being said, if you’re not at the cottage, the main time you need to worry about frost in your foundation is during the first season after construction while masonry/concrete is still curing. Once it is fully cured, and assuming you have drained all plumbing, I’m not sure why you would need to worry about this. Summer cottages in Ontario routinely go down to 30C indoors in winter.

  16. Gina Watson
    Gina Watson says:

    I read this article with the hopes of finding a safe way to keep the pipes under my mobile home from freezing (especially while I’m away). It’s almost impossible to seal up the underneath of a mobile home to keep it water, cold, and condensation tight. Skirting can only do so much. In the past I have used a work light with a halogen bulb just to heat up the area where the water enters the pipe system to ensure the ground water doesn’t freeze. You ask, why not heat tape… tried that too, but each year I cannot seem to keep any heat tape warm enough when its super cold (-10). Heat tape doesn’t seem to work well on PVC, and PVC requires a specific type of heat tape to keep it from melting. This year I’d like to leave for a weeks vacation, but as I have cats (which will remain inside with someone checking on them), I don’t want to “winterize” my house. I want an easy solution that will ensure my mobile home and animals are safe. Got any thoughts…like to hear from ya. 🙂

        STEVEN K-BROOKS says:

        Thank you! This sounds like what I have been visualizing and trying to find. I am now reading all of the material, but it looks like you have hit on an excellent solution… at least for my problem, which is supply pipes that run through a crawl space and freeze when the outside temperature gets into the single digits.

  17. Greg
    Greg says:

    I live in Newfoundland in a 41 yr old poorly insulated 2×3 constructed mobile home. Except for a few minor upgrades before I purchased it, such as flooring or paint, it’s complete with original aluminum windows, aluminum siding and roof.

    The furnace finally failed after 4 breakdowns within 2 months of moving in. I’ve since installed a Fujitsu 12RLS3H Heat Pump. Of course, now I was left with cold floors and potentially frozen pipes. To make matters worse the center section of insulating panels the full 64′ length of the home were torn down or fell down over time. Luckily it was mid-March and the coldest days were behind me but I still had to address the issue of cold floors as the mini-split is a wall mounted model, not ducted.

    Pondering my options, one of the heat pump installers recommended installing lightbulbs under the flooring as he does at his cabin to prevent broken pipes over the winter. I could have simply run electric pipe tape and still have cold floors but I was warry of the safety concerns based on all the caution with the product. While I do have pipe tape on the main water line as it comes out of the ground into the house, that’s the only location.

    Since the furnace failure I’ve installed 4 industrial cage fixtures with 100w rough service bulbs and 1.5″ DOW Styrofoam insulation panels to close in the full length of the house between the beams. This worked okay for the winter of 2016-2017 though during a cold period ~ -20°C/-29°C windchill, temps recorded on a wireless outdoor thermometer within the partially sealed floor space would dip as low as -3°C. When temperatures would hover around freezing under house temps would be around 4-6°C depending on the wind.

    Over the Summer of 2017 I was able to pull the fiberboard and R7 pink fiberglass batts on one complete 4×64′ wing of the house. The rim joist is now insulated above R20 with R22 Roxul batts between each joist and the bottom now sealed with 2″ R10 DOW Styrofoam rigid insulation for a total of R34.

    I’ve since mounted the cage lights horizontally as the recent 100w 5000hr rough service bulbs failed within 2 weeks with base up. I’m using four 69w Sylvania 8000hr traffic bulbs this winter.

    Despite the lower wattage, 276w vs 400w the previous year, the floor space is reading 6°C and will go as high as 8-11°C when it’s 0 to 1°C. It’s 19°C inside with the heat pump on fan speed setting 2 out of 5 where as this time last year it would be on steady between 3-5. Outside temperature is currently -10°C with a windchill of -20°C.

    While I still have the other wing of the house to reinsulate and to install proper insulated skirting around the entire perimeter, 4 incandescent lightbulbs are keeping my feet warm, the floor space heated and the pipes from freezing.

    Light bulbs might be the solution.

  18. Dave Bell
    Dave Bell says:

    Hi, I live on Vancouver Island and I have a crawl space that is approx. 24’x40′ and 4ft.high. The walls are concrete and the floor is as well, however when I put some plastic on the floor some water droplets appear in spots. It also has 5 vents to the outside. What can I do safely to warm the crawl space up.

    • Robin
      Robin says:

      If the water droplets appear under the plastic, that’s normal – you’ve blocked the flow of water vapor from the floor to the outside. Changes in humidity will cause water to flow into or out of the floor; if the floor is covered, any humidity trying to escape the floor is trapped by the plastic.

      If the water droplets appear on the top side of the plastic it’s likely condensation that arises in situations where the floor is cooler than the ambient air. Since your crawl space is vented this water should eventually evaporate.

      Warming the crawl space won’t solve the first problem (which isn’t really a problem because you’re keeping the moisture below the plastic). It will help solve the second problem since the heater will keep the crawl space, and by extension, the floor, from getting cold.

  19. Gordo
    Gordo says:

    Located in Ontario where our coldest outside temperature to date has been -39 C, I have tackled the freezing pipe problem by running the cold water supply line through a 3″ PVC pipe. I attached a 5″ duct fan to the 3″ pipe which gets its intake air from the bathroom floor through a floor vent and blows it 26 ft., where the water pipe rises into the kitchen to supply the kitchen sink, the dishwasher and a “point of use 10 gallon water heater. I Installed an indoor/ outdoor thermometer to monitor the air temp where the PVC pipe comes up through the floor. In 15 years of operation there has never been more than a 3C temp drop from bathroom to kitchen. I have had to replace the fan 3 times.
    To heat the difficult to access enclosed and insulated water entrance area, about 8’X6’X3′ high, which supplies the bathroom, I installed a 4” duct system to distribute warm air into the water entrance area as well as the rest of the insulated, but not encapsulated, crawl space, about 35’X25’X3′ high. Normally, the temperature readings from a probe suspended 1′ below the living room floor in the middle of the crawl space run about 14C. When the wind is blowing off the lake when it is very cold outside, I have seen the crawl space temp drop to 6C.
    This system seems to work. As a backup, I have an electric space heater in the water entrance area set to come on at minimum temperature, which I believe is 40F. I have a wood fired fireplace insert to heat the house with natural gas space heater backup. If there is a power outage, I have a spare fan mounted on a duct which I can place over the air vent intake opening and power through a power pack/ inverter, since the duct fan only draws about 40 watts.
    It may seem like overkill, but there is nothing worse than replacing frozen pipes in a crawl space unless maybe begging to use a neighbour’s shower and hauling water till you can do the repairs.

  20. Julie
    Julie says:

    We just moved into a 35 yr. old bungalow that might be 1000 sfF, if that. There is a 4 foot crawl space – the walls are made of blocks and the floor is just dirt. We’ve had a lot of rain and there doesn’t appear to be water seeping in through the walls and the dirt is ‘dry’. My concern is freezing pipes – we have the pipe from the well coming in, (it comes up from the ground just at the wall inside the basement,) and then there’s the pump, the pressure tank and a machine that runs once a week to lessen the iron/metal in the water, (no it’s not a softener). I have someone coming in to give us a quote on insulating the whole thing but there is no heat source down there at all and I am wondering if some sort of heat would still be needed even if the entire crawlspace was properly insulated. Living in Ottawa the winters can get biting cold – it’s not uncommon to have temps in the minus 20/s, with the odd -30/-40 in Feb There’s mention of heat wrapping and insulating the pipes. I’m wondering if that’s enough on it’s own without insulating the entire crawlspace. Keep in mind I’m only concerned right now with the pipes, not how cold the floors will be. The previous owners who lived there for 20 years claim the only thing they ever did was put batt insulation over the 4 outside vents in the winter. The interesting thing about that is there is a heat wrap lying on the floor and a couple of non-working baseboard heaters down there. What are your thoughts? Would I still need a heat source if it was completely insulated? Do you think heat wraps alone would work? How do I keep the equipment from freezing?…or should I just believe the previous owners?…would you?

    • Robin
      Robin says:

      I would consider putting a couple of plug-in heaters in there and using a cold-weather Thermocube which will send power to the heaters when the temperature drops below 35F and cut power when temperature climbs to 45F. That way you’re not wasting electricity heating the crawlspace when it is well above freezing. If the crawlspace is insulated, with ground below it and heated space above, it is unlikely to get cold enough to freeze the pipes as long as the heaters are running during cold spells.

  21. julie
    julie says:

    Thank you, Robin. That sound like an easy fix. The quote for insulating the crawlspace was ridiculously expensive. I’m going to check out the thermocube some more – I’ve never heard of it.

    • julie
      julie says:

      So I checked out the thermocube and I think we’re going to go that way. However I suspect that the heater will still be running virtually 24/7 at least in Jan. & Feb. I have been trying to find electric heaters that can run non-stop and I’m having a hard time. The closest I can find is a milkhouse style that was originally made to run all winter in barns, but that was 50 years ago. (As they say – they don’t make them like they used to.) Any suggestion on an electric heater that can run 24/7? I know I can get someone to come and wire in a baseboard heater but we’d much prefer a portable.

  22. Jeff
    Jeff says:

    I use a heat cord to keep my crawlspace water supply from freezing, but I am not sure of the best way to prevent the washing machine drain trap from freezing during cold spells here in NJ. I am vigilant about letting the family know not to use the washer when it is really cold to avoid a flood in the laundry room. I was considering using heat tape but I am concerned about evaporation in the trap which would allow for sewer line gas to come up the vent. Any suggestions?

    • Robin
      Robin says:

      If you can use heat tape plugged into a Thermo Cube, the drain pipe will only be heated when the temperature is low enough to risk freezing. The evaporation you need to worry about is just the drain trap. One way to address that, assuming the drain trap is in the crawl space, is to box it in and insulate the box with 2″ of foam, but not the space connecting the drain trap to the floor. Put the tape on the section of pipe that is NOT in the box. That seems like a way to keep water from freezing in the sections of pipe exposed to the cold crawl space, while reducing the chance of the drain pipe freezing.

  23. Anthony
    Anthony says:

    Hi Robin! I have been trying to solve the cold draft problems in my home for years now. Every year I do some extra work in the crawl space hoping the next winter will be better and I just can’t figure it out and now my heating bills are a huge problem.
    I have spray foamed all the walls (perhaps not good enough not thick enough or what), and have installed super thick vapor barrier even with a padding layer under that on the soil.
    Thing is there are 2 vents that I “seal” by closing them in the winter and opening in summer because I get a humidity smell in the summer if i dont open them.
    I did not totally seal these openings because I worry that I will trap the humidity in the crawl space and the moldy smell will fill my home above.
    There is some very old wool insultion on the ceiling of crawl space (under my home floors) but in many places its fallen or just missing so you can assume floors are not insulated….
    Anyway now i have all heaters blasted in the house and they can t keep up. theres always a cold draft in the house.

    1) I read your articles and your answers and i just wish i could pay you for an in person inspection with detailed recommendations . Do you offer inspection and consulting like this by any chance? because i give up! I live in montreal please say yes lol.
    2) if not, what can you tell me based on what ive said so far??

    Thank you so much in advance for your help.

    • Robin
      Robin says:

      I don’t offer home consultations. I would suggest contacting a local home energy auditor – just search online for “home energy audit montreal” and call a few businesses to find out what they offer. They can usually identify ways to not only cut the draft from your crawl space but to save energy in other areas of the home.

      It seems to me that the wool insulation is the first thing to address. Remove it all, and properly insulate the ceiling of the crawl space. I had 8″ joists in my new crawl space and had 2″ of foam sprayed on the floor, then installed 6″ of Roxul, then boarded that in with plywood, and my dining room above the crawlspace has toasty warm floors even on the coldest nights.


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