Energy efficient electric heaters

Do energy efficient electric heaters really exist?

Some will tell you that energy efficient portable heaters are the most efficient form of heating around – that they’re 100% efficient, even 300% or 400% efficient for heat pump electric heaters.

But most non-renewable electricity sources (coal, natural gas, nuclear) involve burning a fuel, and converting at best 45% of the heat produced into electricity. So even with a 100% energy efficient electric heater you are getting only 35-45% efficiency from the heater when total energy consumption is factored in.

Even geothermal electricity only converts about 35% of its heat source into electricity. So unless your electricity comes from solar, wind, or hydropower, you can’t come close to the efficiency of a typical modern forced air furnace.

What’s the truth? The truth is that electrical heat is almost always the most expensive and least efficient form of heating (unless your electrical rates are heavily subsidized), and that people who are stuck with electrical heating systems are some of the most motivated at finding other ways to conserve energy, for example by improving sealing and insulation, in order to offset the higher cost.

As for energy efficient electric heater ratings (for example ENERGY STAR or the Canadian EnerGuide ratings), there aren’t any. Why? Because all resistance based electrical heater elements are 100% efficient at converting electricity to heat. There’s no point in rating them. It’s the the poor energy conversion at source that’s the problem.

So if you’re looking for the most efficient electric heater, you can stop now. Instead, read on to find out what can make an electric heater effective for your needs.

How do electric heaters work?

Here’s how most heaters work: a current passes through a wire that provides electrical resistance. This resistance converts all of the electrical energy into heat. That’s why energy efficient electric heaters are all 100% efficient.

But wait, you say – don’t some of them have fans blowing the air around, so at least the energy to power the fan doesn’t turn into heat?

Actually, it does turn into heat, eventually. The fan moves air molecules, and the increased friction between the air molecules turns into heat. It’s the law of entropy – all forms of energy tend to move to a more disorganized state, and heat is the most disorganized form of energy there is.

It’s important to consider how energy efficient electric heaters stack up against the competition. Yes, some energy is lost in generation – at least 55% of it in the case of coal fired plants. Transmission losses add another 2-6%. So a 100% energy efficient electric heater powered by coal is at most 43% efficient.

Meanwhile, an 80% efficient natural gas furnace really does convert 80% of the source energy into heat to warm your home.

The exception to this 100% efficiency rule for electric heaters is a heat pump, which I briefly describe at the end of this article. Heat pumps provide more heat output per unit of electrical energy input than resistance-based heaters, so this leads some heat pump marketers to refer to them as more than 100% efficient, but this is somewhat misleading, as we’ll see.

Types of electric heaters

Strictly speaking, any resistance-based electric heater is an energy efficient electric heater. But different electric heaters spread the heat in different ways, which can be more or less effective for the job at hand. So rather than speak of energy efficient electric heaters, we should perhaps speak of the effectiveness with which these heaters meet your needs.

A central electric heating system usually involves a forced-air electric furnace with ductwork and room vents, or a forced-air electric boiler with radiators in each room.

For a forced-air electric furnace, a heating element heats air that is forced through the furnace by a fan, and the hot air is then pumped through ducts throughout the house, much as in a forced air natural gas furnace.

For a forced-air boiler, the boiler contains a heating element that heats water which then circulates, either on its own or with the help of an electric pump, through radiators through the home.

If you have one of these units you may be paying a lot for your heating. Such units are often installed in houses that previously had a forced-air oil or natural gas furnace or boiler, and the switch can usually be attributed to a time period when, or state/province where, electricity was substantially cheaper, per unit of heat available from it, than natural gas or oil.

The bad news for central electric systems is that you may be spending a lot more to heat your home than if you used natural gas, since electricity rates in most jurisdictions have been going up as state-owned utilities begin to apply more market pricing to electricity.

The good news is that converting to a natural gas furnace or boiler isn’t hard – if there’s a gas main nearby. You already have the ductwork or rads you need. Do a payback analysis to see how soon the savings will earn back the furnace purchase price. Chances are the payback will be under ten years.

You may be able to turn your central electric system into a more energy efficient electric heater by adjusting the fan to start blowing at a lower initial temperature, and to stop blowing after the heating elements stop receiving power, again at a lower temperature.

These adjustments are recommended by heating experts. The adjustments let heat flow through the house sooner, and more heat to be extracted from the furnace and delivered to the house after the heating elements go off.

A baseboard heater spreads heat using both conduction and convection. Conduction is the transfer of heat from a heated surface to a gas, in this case from the heating element to the air. Convection happens when the heated air, which expands and becomes lighter, rises out of the heater and draws colder air in from below. Air currents from this convection draw the heat up into and around the room.

Baseboard heating is more common than central electric heating, for houses originally built with the entire house being heated by electric heating. Baseboard heaters are inexpensive, unobtrusive, and require no ducting. They do of course require additional electrical work but it is usually easier to run a few extra wires than add an entire ducting system when building a new home.

Note that one drawback of a house entirely heated with baseboard heat is the tendency of moisture to build up on windows, as there is less circulation of the air within the house compared to forced air systems, and combustion-based heating systems (natural gas, oil) sometimes use internal air to feed the furnace or boiler, which draws out moisture. (See my article Energy efficient dehumidifiers for tips on moisture control.)

Movable energy saving space heaters can operate by convection or radiation. Note that movable space heaters are a major cause of home fires, causing up to 25,000 residential fires each year in the US according to the Consumer Product Safety Commission. So if you go with a movable space heater, be very careful to keep a close eye on it, and follow the product documentation to minimize risks.

Also, note that energy saving space heaters plugged into ordinary outlets can draw a considerable amount of power – 1,000 to 2,500 watts depending on the model – so make sure your wiring and fuse or circuit breaker for that circuit is up to the task!

The common types of movable space heaters are convection and radiative. As you already know, both are 100% energy efficient electrical heaters.

A movable convection heater is much like a baseboard convection heater, except that it may be enhanced with a fan to propel the heated air in a particular direction and improve distribution of the heat through the enclosed space. And of course you can move it to provide the heat wherever it’s needed.

A movable radiative heater has a very hot heating element, usually enclosed in a glass tube much like an incandescent light bulb. Behind the tube is a reflective strip of metal which directs most of the radiative energy from the element out the front of the heater.

This energy is in the form of infrared radiation (don’t worry – it’s perfectly safe!). Some of this infrared radiation is converted to heat when it strikes a solid object (a chair, a wall, a person), and some is reflected further. Eventually all of it is converted to heat.

Cold air passing by a radiative heater does not get heated by it. Only the solid objects that absorb the infrared radiation are heated. For this reason, a radiative heater may be a good choice for a cold room such as a garage or outdoor workshop, where you only want to heat the specific area of the room you are working in, and where insulation and weatherproofing may be poor or nonexistent.

But be aware of the risks – a radiative heater can set an object on fire if the object is too close, is exposed for too long, and is flammable.

Efficiency of passive and active electric heaters

Although all resistance-based electrical heaters are 100% energy efficient electric heaters at converting electricity to heat, we can think in terms of how effective they are at getting that heat to where it’s needed, and not sending it where it isn’t.

The more passive an electric heater is – the more it depends on heat rising, or natural airflows, to spread its heat – the more its effectiveness is subject to its placement within, and the properties of, the room or house it is in.

For instance, if a baseboard (a passive source of electric heat) is located on an outside wall with poor insulation, that wall will get hotter than the ambient air of the room, and some of the heat will escape through the wall.

In the same room, an active convection heater such as an energy saving space heater with fan, would not heat the outside walls as much, because it propels its heat forward. The lower heat differential between the inside of the wall and the outside would produce less heat loss.

A floor vent for a forced air electric furnace would also result in less heat escaping from the walls, because the heating element is centrally located in a well-insulated furnace, and the floor vent is (probably) not running hot air against an outside wall.

Of course none of this would matter much if the walls were very well insulated – little heat would escape out the back of a baseboard heater, so nearly 100% of it would be available to heat the room itself, as with a floor vent or movable heater.

The most energy efficient electric heaters for keeping one person warm are active heaters, either radiative or convection. For example, if you get cold feet when working in a poorly insulated den, a ceramic heater at your feet may be all you need. (That and a sweater.)

Time-of-use billing: meet the storage heater

If your electricity rate depends on time-of-use (e.g. you pay more for electricity at peak, such as during the weekday when industry is a big user, or on cold winter nights when many homes are using electric heat), then the most energy efficient electric heaters, at least from a cost perspective, may be storage heaters that let you save up the heat produced during low-cost times, and broadcast that heat during high-cost times.

Storage heaters use clay bricks, or other ceramic material, as a heat sink. These heaters can direct the heat from the heating element to the air (if heat is required, electricity is cheap, and no heat is stored in the bricks) or to the bricks (if no heat is required, the bricks still have heat storage capacity, and electricity is cheap). When electricity is expensive, louvers open so heat from the bricks can transfer into the air.

Storage heaters can have automatic or manual controls. Automatic controls allow you to set a thermostat and have the room heated at all times to the desired temperature, with the heater determining when to store heat, when to emit stored heat, and when to heat the room directly with electricity.

On cheaper, manual models (which are less energy efficient unless you can master the controls and have the time to keep tweaking them), the heater determines when to charge up the ceramic material with heat, based on time of day rates, and you control when and how much heat is emitted.

Automatic models are typically 15-20% more efficient than manual models, unless the person using the manual control is very good at controlling it!

Energy efficient electrical heaters with heeat storage can save you up to 30% if your utility offers lower rates at night, and if you heat your house to a typical comfort temperature during the day. These heaters can store up enough energy for the higher-priced peak periods in as little as 8 hours of off-peak operation.

Since the cheapest electricity rates tend to be at night (except on very cold winter nights, when rates spike), there is less of a benefit to your using storage heaters if you don’t require much heat during the day.

For example, if the house is vacant all day on weekdays, you can use regular energy efficient electric heaters and a setback thermostat to keep the temperature considerably lower during the day, in which case there is less value in having storage heaters that emit heat during the day when little heat is needed.

Still considering the low cost of individual storage heaters (as low as $200 for a one-room unit), the speed with which they can charge up at night, and the fact that few people set their programmable thermostats to a large gap between vacant and occupied temperatures, these units are a sensible investment for anyone adding or upgrading electrical heaters in their home.

Pretend you have time-of-use billing!

Even if you don’t pay for electricity on a time-of-use basis, acting as if you did is a good way to reduce the amount of greenhouse gases you contribute to the atmosphere. Why? Because the times of highest demand for electricity in winter, when electric heat is used, tend to be:

• During regular work hours, because industrial and commercial operations use a large amount of electricity
• During extremely cold nights, when everyone using electric heat has their heaters running hard to keep their houses warm.

During these peak times, the percentage of electricity added to the grid that comes from fossil fuels is high, because electricity from coal and natural gas can be brought online quickly to meet short-term demand. If you heat your house a little warmer during off-peak hours, and let it coast down below the ideal temperature during peak hours, you’ll reduce demand for fossil-fuel-based electricity.

Of course this depends on your having an energy-efficient storage system for your heat. At the very least, this would be a well-insulated house. There’s no point in overheating a house to take advantage of off-peak electricity, only to have that heat escape within the hour because the home is poorly insulated.

Do-it-yourself storage heating for time-of-use scenarios

While I wouldn’t recommend that you try to create your own full-fledged heat storage system based on the above principles – unless you’re an engineer and an electrician – there are ways you can take advantage of the ability of masonry or water to absorb and then emanate heat. The two key points are to heat when it’s cheap, and to build thermal inertia into your home.

Heat when it’s cheap: set your thermostat higher when electricity is cheap, and lower when it’s expensive. You can do this using a setback thermostat and a knowledge of the time-of-use periods from your utility.

Thermal inertia; give your home thermal inertia, by (A) insulating to the hilt to keep heat inside, and (B) including lots of masonry or sealed liquid in its construction.

For example, if you incorporate a large masonry fireplace with a sealed wood-burning or gas stove into your living room, the masonry will help stabilize your indoor temperature by soaking up heat when it is cooler than the interior air temperature, and by heating the living room when the living room is cooler.

You don’t ever have to have a fire burning to take advantage of the fireplace’s heat absorbing and emanating properties, but obviously fireplaces tend to be big partly so that the extremes of hot and cold that come from burning a fire and letting it burn down are evened out by the masonry.

Or, if you have to rebuild or add an interior wall, you can add to its thermal inertia by putting bricks, or 2-liter plastic drink bottles filled with sand in between the studs. (I don’t recommend water, although it’s easier to come by from sand, because you might drill or nail through those walls later to hang a picture, and you don’t want a 2-liter water bottle popping on you behind drywall!)

You can also fill plastic bottles with water and leave them under your bed or in other out of the way areas.

One benefit of building thermal sinks into your home – whether formal ones such as a masonry wall or fireplace, or simple ones such as plastic bottles – is that they work both for heating and cooling. In summer you can run the AC on high when electricity is cheap, and heat will be drawn out of the thermal sinks. Then during pricier times the thermal sinks will absorb heat and this will cool your home.

And don’t forget to leave the bathtub full after you’re done your bath in winter – until the water has fallen to room temperature. There’s no point in letting all that expensive heat go down the drain, especially if you heat with electricity.

Choosing the right addition to your home

If you want to add new energy efficient electric heaters to your home you first need to determine whether you’re going for built-in baseboard heaters, or portable electric heaters.

Built-in baseboard heaters

If your house is heated with electric baseboard heaters and you want to upgrade to more energy efficient ones, I suggest you look instead at other energy efficiency upgrades that can reduce the amount of heat escaping from your home – your baseboard heaters should already be at 100% efficiency (in terms of converting electricity into heat).

If you definitely want to buy new heaters (for example, if the old ones stopped working), then go for a storage heater. Even if you aren’t paying time-of-day usage now, the chances are very high that you will be within the next five years. And the gap between peak and off-peak electricity rates will only get worse in the future.

Depending on the model, baseboard heaters can be controlled by a built-in dial and perhaps a timer control, or by a wall-mounted thermostat.

If you buy baseboard heaters make sure you get the timer control or a wall-mounted programmable thermostat. Electric heat is too expensive to heat each room the same temperature all the time. With a timer control or programmable thermostat you can drop the temperature when the room is sure to be unoccupied.

Wall mounted electric heaters

We keep our heat down at 66F – and stay comfortable with sweaters and slippers. But taking a shower can be a chilly process, at least until the hot water has fully kicked in. This Stiebel electric wall heater helps: it can heat a bathroom or bedroom in under 5 minutes and it is a solidly built, German-manufacturered heater that takes no floor space and very little wall space.

The Stiebel wall heater can be installed with less effort than a baseboard heater and its fan helps spread the heat very quickly. It also comes with a 60-minute timer so that if you just want to heat the bathroom during your bath, or the bedroom long enough that you can warm up under the comforter, you can let it run a short period and have it shut off by itself.

Portable electric heaters

You can’t just look for the highest-rated portable energy efficient electric heater for that chilly basement room, back porch office, or spare bedroom over the garage. Why? Because, as we discussed, all electric resistance heaters operate at the same efficiency level. Instead, I recommend you decide (A) whether you can switch to a different form of heat, and if not, (B) what use of the room is driving the need for heat.

Switching to a different heat source: If your house is heated by a forced-air oil or natural gas furnace, and there is one poorly heated room, consider having an HVAC specialist improve the ducting to that room.

For example, the previous owners of our house added a kitchen extension with a crawl-space below. They installed baseboard heaters to heat the extension. After we moved in (and got our first winter electricity bill), we removed the baseboard heaters and had an HVAC company branch a circular duct pipe off the main basement duct, to direct heat up from a floor vent.

This cost only about $200 at the time and based on the drop in our electricity bills after that first winter I would guess the renovation paid for itself in under three years. We also added as much extra insulation in the crawl space as we could to reduce the amount of heat escaping out the kitchen extension floor.

Another option is to improve airflow between the cold area and warmer areas of your house, so that you can draw warmer air into the cold room. Strategically placed fans can be useful in this case. For an unheated back porch that has been enclosed and converted into an ‘indoor’ room, there may be an old window between the main area of the house and the porch; opening this window when the room is in use will improve airflow.

How will the room be used? Decide if the entire room needs to be heated, or if you only need to heat a single area, based on how the room is used. Also decide whether the room needs to be heated a large portion of the time, or only occasionally. To heat a single area, a radiative heater or a small convection heater with a fan is the best bet.

If you’re heating the room only occasionally, then an energy efficient electric heater is less of a concern than if you’re heating it all the time. For continuous heat, you will save the most on your electricity bill if you focus on making the room as well-sealed and well-insulated as possible.

Heat pumps

A heat pump does not so much produce heat as move it from a colder (outside) location to a warmer (inside) location. A heat pump can be 3-4 times more efficient than an electric resistance heater in terms of how much heat you get for the electricity the unit consumes.

Manufacturers may refer to their heat pumps as 300% or even 450% efficient, which is misleading. Compared to an electric baseboard heater, the same amount of electricity used by a heat pump, under ideal conditions, produces 3 to 4.5 times as much heat indoors.

But heat pumps are not converting energy from electricity to heat – they are converting electrical energy to mechanical energy, and using this mechanical energy to move heat from a colder to a warmer location.

Another way to put this is that electric resistance heaters are 100% efficient all of the time at converting their electricity to heat, while heat pumps can appear to be 300% to 400% efficient, when compared to electric resistance heaters, provided the heat pump is operating under ideal conditions.

The “ideal conditions” that lead to a heat pump reaching 4 times as much heat output per unit of electrical input as an electric resistance heater, usually involve an atypically small differential between the indoor and outdoor temperature. Heating to 18C when the outdoor temperature is 12C (64F indoors and 54F outdoors) can get you to this level of efficiency.

But if you heat your home to 18C (64F) when the outside temperature is -18C (zero Fahrenheit) you will not do any better in terms of heat output for electricity input than with an electric resistance heater.

In fact, because of condensation that occurs on the heat pump at these low temperatures, the heat pump must sometimes switch to cooling mode, cooling the indoor air so it can warm the coils and melt frozen condensed water from them.

For colder climates, you also need a backup heating source to go with your heat pump, so that when the outdoor temperature falls low enough that the heat pump can no longer supply adequate heat, or can no longer do so as efficiently as the backup source, the backup kicks in.

Obviously, the climate in many areas, or through the heating season for even moderately cold areas, falls between the two extremes of minimal heat differential (high coefficient of performance for an air source heat pump), and extreme outdoor cold (performance no better than electric resistance heating), so the relative apparent efficiency of heat pumps versus energy efficient electric heaters will vary.

Energy saving geothermal heat pumps avoid this high-differential problem, by extracting heat from deep underground, where temperatures never fall much below 12C. Thus they can reliably deliver 3+ times more energy output in the form of heat, per unit of electric energy input, because the ground temperature, being very close to the desired indoor temperature, reduces this differential.

While air-source heat pumps might not be suitable as your only heating option in a cold climate, they are a sensible investment if you also need air conditioning. For example, some portable AC units, and some ductless minisplit air conditioners, operate as air conditioners in hot weather, and as air-source heat pumps in cool weather. Some can also act as dehumidifers, so you get three appliances in one!