With an infrared gun, you just move about the inside and outside of your house on a hot summer day or a cold winter evening, and take readings at windows, outside doors, walls, and other places where heat may leak through. The detector helps you get a detailed picture of issues with insulation, sealing, or windows in need of replacement.

Professional home energy inspectors often use an infrared camera to show you where you're losing or gaining heat, but thermal imaging devices are expensive and the audit itself can cost you over $200. An infrared point-and-shoot thermometer doesn't provide the same colorful printout, but they sell for about $50, so they put this detailed information within reach of the average homeowner.

Most infrared heat guns come with a beam ratio of 1:12, which means that if you point the gun at a wall 12 feet away, then take a reading, you'll get a reading for a one square foot section of the wall. They also typically come with a laser beam to show exactly what spot the reading was done from.

I recommend beginning your thermal leak audit from the outside. Standing 12 feet back, take repeated measurements with your infrared gun to figure out what the reference temperature is. You are looking for the coolest temperature in cold weather, or the hottest in hot weather when the air conditioner is running.

Don't take readings on a sunlit wall, which can skew your results. Rather, wait for cloud cover, or for the sun to move.

Write out each reading on a sketch of the wall or in note form. Pay extra attention to window readings, because windows are major areas of thermal loss both in hot and cold weather. You might benefit from an inside helper to close blinds and curtains after your first reading so you can then measure the impact of these window coverings on cutting thermal leakage.

Where measurements are much worse than your reference (hotter in cold weather, cooler in summer), take more readings close by, to pinpoint the boundaries of the thermal leak. You might have gaps in, or settled insulation, cracks or even holes in the wall, or a gap in a window or door.

Next do an indoor thermal audit of the outward-facing walls, floor, and ceiling of each room. Choose an inside wall as your reference temperature; exterior wall readings should be cooler than the reference in winter, or hotter in hot weather. Again, you are looking for thermal leaks on window glass, around windows and doors, through light fixtures, in cracks in drywall or plaster, or anywhere that is touching an outside wall. Take close-up measurements of any wall outlets or light switches that are close to the exterior, even if they are on an inside wall.

Check the temperatures of top floor ceilings, as insulation, especially blown in insulation, can get disturbed or matted down in leaky attics. For summer readings, do your ceiling readings twice: once in the early morning before the sun has warmed the attic space, and once in the early evening when the attic is hot, so you can determine how much of that heat is leaking into your living space.

Chances are that windows without their window coverings are your biggest heat leaks, as even the most efficient windows have a much lower thermal barrier capability than most walls or ceilings. You can either replace old windows with new efficient ones, add thermal curtains or shades, or apply thermal barrier window film to the window pane itself.

You will also probably find drafts in walls, particularly at light fixtures or where wires or pipes exit the house. You want to seal these as much as possible, as drafts can be major contributors to home energy costs. Add caulking around the edges of window frames; use wall outlet insulating foam to prevent air from flowing through the outlets. Your bricks may need tuck pointing, or you may have a more serious problem: settled cellulose insulation between wall studs, in which case the only solution is to gut the room from within and put in new insulation and drywall. If the walls have no insulation whatsoever you may just be able to inject foam insulation, which is a cheaper option.

It makes a lot of sense to do your own mini-audit with your infrared point-and-shoot thermometer first, and ask for contractor estimates later. If you have identified your big thermal leaks, you'll be able to ask each contractor what solutions they recommend to your problem. Asking a contractor over and just telling them the house is freezing in winter, or too hot in hot weather, means inviting major repairs that might not do any good.

You can use an infrared point-and-shoot thermometer for countless other measurements around the home, such as reading hot water pipe temperature before and after adding pipe wrap; reading the air coming out of forced air registers and going into the air return register, if you have central air conditioning, to gauge air conditioner efficiency; measuring cooking temperatures on your stove; or finding the best location in your basement for a wine cellar.

Whatever model infrared gun you choose, you will doubtless 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 you need to know the surface temperature. You can even use it to measure the temperature of your compost bin - without getting your hands dirty!