Using infrared thermography to see through walls.

When I walk into a home, my eyes always start darting around. It doesn't matter whether its a familiar home or one I've never been in, it's always the same.

First it's all about the home's general construction. Are we in a 1970s "BC Box"? Or a 1950s post-war home? Maybe half the house is the original 1930 bungalow but the 8' basement suggests that the house was raised at some point?

Then we dig deeper. Does the house feel brighter than normal because of an excess of windows? Are there vaulted ceilings? After an hour or so, you can get a pretty good feeling for how a home was put together, where it's "warts" are, and where the likely opportunities for energy efficient improvements lie. That single-pane window might seem like a good candidate to be replaced, but the complete lack of insulation between the garage and the bedroom above is likely why your guest room is cold...

But what about when you can't see what you're looking for? How can we determine whether all the walls in a 1940s home are insulated, and if they are has that insulation settled over time? When the basement of this house was finished, did they put insulation against the concrete foundation walls or just slap some strapping and drywall down? This is where infrared thermography and an infrared camera come in handy.

In this photo: purple = cold; yellow = warm. This is why we insulate basement foundation walls

An infrared (IR) camera lets us see heat rather than what's on the surface. It also lets us see subtle temperature differences that would be next to impossible to sense by feel. Sometimes this can be the first step towards adding insulation or performing air-sealing work that could save a homeowner thousands of dollars of heating costs over the time they live in the home. Sometimes its further confirmation of a known issue.

Practical examples? Sure - here are a few. In these photos, purple and blue areas are cold compared to the warmer yellow and orange areas.

No foundation wall insulation

Stripes = insulated stud wall

Insulation has settled

Door sweep has failed

Might need a foam gasket

Caulking required below trim

Need to air seal attic hatch

Light fixture isn't sealed

Baseboards hate windows

Find the wires before drilling

Might want a tank blanket

Going to need a new door

Armed with these images, we can start putting together a plan to improve things:

• Air leakage around window trim can be sealed up with caulking most of the time, but where the drywall return is really badly done spackle helps.

• Doors and attic hatches should have weatherstripping between the door/hatch and the frame it engages with.

• Electrical outlet and light switch faceplates can be sealed with foam gaskets. This is particularly worthwhile when they're on lath-and-plaster walls (since the bumpy plaster leaves gaps that are best sealed with a gasket)

• A hot water tank is a garage can be blanketed to reduce heat losses if it's not a particularly well insulated tank to begin with. Don't bother with "tinfoil bubblewrap" type blankets - they don't do much. Instead go with something thick and fluffy.

• Vertical stripes on a wall tell us that the studs are cooler than the stud cavities. This usually means the wall is insulated. Discontinuities in insulation can mean a stud cavity was missed or that the insulation inside has settled.

Using an infrared camera is sometimes just a convenient way to quickly identify where a draught is coming from or how the hot-water pipes in a heated floor are configured. But often it can be the best way to determine whether a wall or a portion of a ceiling is insulated or not - beats using a drywall saw...