Find where the heat’s seeping out of (or into) your house

An infrared heat gun can give you a thorough understanding of where your home is losing heat in winter, or gaining it in summer.

For years, I’ve been a big fan of the Kill A Watt meter, which measures the energy consumption of anything you can plug into a wall outlet. As I explain in How to save electricity, a home electricity monitor like the Kill A Watt lets you measure the consumption of each appliance, so you know where the biggest savings can be found.

With an infrared heat gun, you can do something similar, but with your heating and cooling costs. Just wander around the inside and outside of your house on a hot summer day or a cold winter evening, and point and shoot at windows, doors, walls, roof, or anywhere that heat might be able to pass through the exterior of your house. Your infrared heat gun will quickly give you a detailed picture of where the winter heat is escaping to the outdoors, and where the summer heat is leaking in from outside.

Professional home energy auditors often use an infrared camera to provide you with visual feedback on where your house lacks adequate insulation or weatherproofing. But these cameras are prohibitively expensive for most homeowners. You can also buy infrared film for a standard 35mm camera, but not many people still have a 35mm camera, and you have to store the thermal film in dry ice.

An infrared heat gun doesn’t give you the same colorful graphic printout of an entire side of your house, but since you can buy an infrared heat gun for $50 or less, you can at least get the same useful information as you’d get from a full energy audit, admitedly without the pretty printout, but also without the expense of the audit, which often costs $250 or more.

Most infrared heat guns come with a beam angle of 1:12, which means that if you point the gun at a wall 12 feet away, then press the trigger, you’ll get a temperature reading for a one square foot area of the wall. They usually come with a laser beam as well, so that you can see exactly what spot the reading was taken from.

How to do your own thermal leak audit

I recommend starting your thermal leak audit from the outside. Before you begin, make sure all windows and doors to your house are closed. If you’re doing the audit in winter, the heat should be running; in summer, whatever air conditioners you normally would use should be running.

Start with a pad of paper on a clipboard, and draw a rough diagram of one side of your house in pencil, including windows, doors, chimneys, or any other relevant features. Standing 12 feet back, take a series of readings with your infrared heat gun to get an idea of what the baseline temperature is. You are looking for the coolest temperature in winter, or the warmest in summer when the AC is running.

The idea is that the less heat escapes from within your house in winter, the colder the outside walls should be, while the less heat leaks into your air conditioned house in summer, the more of that heat should be staying on the outside of the walls. You are trying to find a reference temperature representing the areas where you have the least thermal leaking.

If possible, avoid doing readings on a wall that is receiving direct sunlight – wait for the sun to move, do it in the evening or early morning, or wait for cloud cover. The sun’s heat will significantly skew your results.

Some infrared heat gun models include a Set Reference button: once you have decided on the baseline or reference reading, you can point the gun at an area that has that reading, and press the Set button. On these guns, all future readings (until you press the Set button again) will show green for a temperature close to the reference temperature, red for a warmer spot, and blue for a colder spot.

Write out each reading on your diagram. Take special note of window temperatures; you may want an inside helper to close all your window coverings once you’ve done the first set of readings for that side of the house; you can then do another set after waiting ten minutes, so you can see what impact your window coverings have on stopping thermal leaks.

If you find a reading on the wall itself that is considerably worse than the baseline (much warmer in winter, much cooler in summer), take more readings close by, to see if you can pinpoint the exact extent of the thermal leak. There may be a spot in your wall that lacks insulation, for example because of settling, poor installation work, a later renovation, or rodent activity within the wall. Once you are done, you should have a good indication of any serious problems such as poorly sealed window and door borders, window glass that does not effectively block heat transfer, wall areas lacking insulation, or small heat leaks due to openings for cables, pipes, etc.

Do each exterior wall in turn. If your house is two or more storeys it will be harder to get accurate or detailed readings of the upper stories, but you can still get a good understanding of upper storey thermal leaks when you move indoors.

Gauging thermal leaks from inside

Next go inside, and do a thermal audit of the exterior walls, floor, and ceiling of each room. I don’t think it’s necessary to draw a wall diagram of every room, but if you are so inclined, go for it. Otherwise, just note any temperatures that seem outside the norm, and where such readings were taken, so that you can consider possible remedies once you’re done all your readings.

For the interior, choose an interior wall baseline; in this case, all exterior wall temperatures will probably be cooler than the baseline in winter, or warmer in summer. Again, you are looking for thermal leaks on window glass, around windows and doors, through poorly sealed light fixtures, in cracks in drywall or plaster, or anywhere that is touching an outside wall or may have an air leak to the outside wall. Take close-up measurements with your infrared heat gun of any wall outlets or light switches that are close to the exterior, even if they are on an interior wall.

Check the temperatures all over your top floor ceilings. Particularly if you have blown-in attic ceiling insulation, it’s possible the insulation may not be evenly distributed if it has been there very long. For summer readings it’s best to do your ceiling readings twice: once very early in the morning, when the sun will have the least effect on hot attic air leaking in through the ceiling, and once in the afternoon, when you can see just how much heat in your upstairs is coming from your attic.

I’ve got all these readings – now what?

If you’re lucky, you’ll discover very few significant thermal leaks. Windows with their window coverings opened are likely to show the biggest temperature difference from the norm, as even the most energy efficient windows have a much lower R-value than most walls or ceilings. You can address this in three ways: replacing old windows with newer, more energy efficient ones; adding energy saving window coverings such as thermal curtains or blinds (actually, almost any window covering will help to some degree); and applying energy efficient window film to the glass itself.

Other than window glass, the areas that will likely show the biggest thermal leakage will be areas where drafts are passing between the inside and outside of your home. You want to seal these as much as possible, as drafts can be one of your biggest sources of home energy loss. You can add caulking around the edges of window frames; replace cracked or missing putty from old-style windows with fresh putty, and paint it to keep it from cracking too; make sure there are no obstructions preventing windows from closing properly. Add weatherstripping to doors. Use wall outlet insulating foam to prevent air from flowing through the outlets.

Your bricks may need tuck pointing if you are seeing inconsistent temperature readings on exterior brick walls. Your insulation may have settled if you see more leakage higher on the wall on a given storey than lower on the same storey. And there may be areas with no insulation at all, for example in corners or upstairs where a lower floor roof (such as for a front porch) juts out.

The key is to try to figure out the cause of each thermal leak, and fix the leaks that are contributing most to heat loss in winter or heat gain in summer.

Getting help from a contractor

It makes a lot of sense to do your own mini-audit with your infrared heat gun first, and call the contractors later. If you know where your thermal leaks are, you’ll be able to ask each contractor what solutions they recommend to your problem. Inviting a contractor over and just telling them the house gets too cold in winter, or too hot in summer, means inviting major repairs that may not do any good.

You can also use your infrared heat gun to gauge the impact of a renovation once it is done, or to assess the amount of installation added to a wall after it is sealed.

Other household energy uses

Use your infrared heat gun to figure out how much heat is escaping from your hot water tank or from hot water pipes. You can measure the tank wall temperature and pipe temperatures – note that for pipes you will need to hold the infrared heat gun very close, because when pointing at narrow objects the gun will pick up the temperatures of things behind it as well if the object does not fill the beam angle.

You can also measure the temperature of air coming out of forced air registers and going into the air return register, if you have central air conditioning. A temperature spread of less than 15F between the registers and cold air return indicates that your air conditioner is probably not very efficient.

Use in the kitchen

An infrared heat gun can be a great tool in the kitchen, whether you’re making candy, deep frying, or striving for the perfect pancake. Just point and shoot at your cooking surface to check whether the temperature is right. The temperature takes a little getting used to for some foods – for example, for making caramel you need to aim for a reading 10F lower than the caramel temperature you’re after, since the surface is generally cooler than the inside.

You can also use an infrared heat gun to measure the temperature of heated water, for example if you’re using a double boiler to heat chocolate, you want the water to approach a boil but not quite reach it. You can measure the temperature in various parts of your refrigerator to see where the coldest spots are (so that jug of milk can keep longer, for instance).

An inrared heat gun doesn’t work particularly well on measuring oven temperature, because you have to open the oven to take a reading, and of course the instant you open the oven the heat escapes. And as with a barbecue, when roasting meat you should be looking at interior temperature, not surface temperature of the meat, but it is helpful to know the grill temperature before yous tart grilling. Many of these devices, however, come with an analog thermometer as a bonus so you can measure interior meat temperatures with that.

Another energy saving use of an infrared heat gun in the kitchen, is for detecting thermal leaks from your cooking appliances. In particular, you can use it to find where heat is leaking into your refrigerator or freezer, and where it is leaking out of your oven. You won’t necessarily know what to do with this information on its own – how much use is it to know what the temperature around your refrigerator gasket is? But if you take readings on both your own appliances and those of a couple of friends or neighbors, you’ll have an idea of whether your appliances are leaking more than the norm, or less. Probably at least one of you or your friends will decide replacing an old appliance with a new, energy efficient one is in order!

Which infrared heat gun should I choose?

There are quite a few of these products on the market. I recommend one with a 1:12 beam angle; some have beam angles as low as 1:2, which means to get a reading of a 1-inch square you have to hold the gun two inches away from the object. For particularly hot surfaces, or for foods that may splatter the gun or burn your hand, a 1:10 or 1:12 beam angle is much better.

You should also look for one that uses inexpensive AAA batteries, rather than the more expensive 9-volt batteries. Many of the newer units use only 2 AAA batteries, which suggests that the designers of these devices have been able to get their energy use down to a minimum. Indeed, in the reviews for two of the three products I feature here, people consistently report that their infrared heat guns last for months on one set of batteries, even when used on a daily basis.

Prices for infrared heat guns have dropped significantly since I first wrote this article. As of 2021, infrared heat gun prices on Amazon are as low as $25.

I personally own a Kintrex infrared heat gun, and while that model is no longer available, I still find it very easy to use both for finding thermal leaks around my home and for cooking. If you’re just planning to use an infrared thermometer around your own home, go for one of the inexpensive models, but if you’re going to take large numbers of measurements on a daily basis, look for one with good accuracy and durability.

Whatever model infrared heat gun you choose, you are sure to get many hours of use out of it, finding the hotspots and cold spots in your walls, floors and ceilings, your garage, your fridge, freezer, your car engine – anywhere that you might want to know the surface temperature. You can even use it to measure the temperature of your compost heap!

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