Let us kill the myth first: a thermal camera does not see through walls. It reads the surface temperature of whatever is in front of it, to about a tenth of a degree. Everything useful it does follows from that one capability — because in a building, hidden problems change surface temperatures.
What it reliably finds
Missing and displaced insulation
Insulation gaps show as cold patches on interior ceilings and walls in winter. The camera maps coverage across an entire attic in minutes, showing wind-washed eaves, compressed areas, and the gaps left where someone worked in the attic and never put it back.
Air leakage
Cold air entering at rim joists, top plates, window and door perimeters, attic hatches and service penetrations shows as characteristic plumes and streaks. This is the biggest single driver of Ottawa heating costs and it is invisible to the naked eye.
Active moisture
Wet material is cooler than dry material because of evaporative cooling, and it has different thermal mass. The camera finds moisture behind finishes from a leaking shower pan, an ice-dammed roof, foundation seepage, or a slow supply leak. This is arguably its highest-value use, because water damage is the most expensive thing that hides in a house.
Electrical problems
A loose or corroded connection has higher resistance, and higher resistance under load means heat. Scanning a panel while circuits are loaded finds overheating breakers, loose lugs and unbalanced circuits before they become a fire.
HVAC problems
Disconnected or blocked ducts, radiant floor loops that have failed, and rooms that are simply not getting the air they are supposed to.
Pests
Rodent runs compress insulation into visible thermal channels, and larger nests show as warm masses.
What it cannot do
This matters as much as the list above, and an inspector who does not volunteer it is overselling the tool.
- It cannot see through anything. Only surface temperature.
- It needs a temperature difference. No ΔT across the assembly, no image. This is why envelope scanning is far less useful in mild weather.
- It cannot find a leak that is not currently wet. A pipe that leaks once a month may show nothing on the day.
- It cannot detect mould. It finds the moisture conditions that mould needs. Identifying mould requires sampling.
- It cannot see through insulation. A wall cavity problem with insulation in front of it may not reach the surface.
- It produces false positives. Sun on an exterior wall, a mirror, a heating duct behind drywall, thermal bridging at studs — all read as anomalies. Which is why every finding must be confirmed with a moisture meter, and a report full of unconfirmed thermal images is not an inspection, it is decoration.
Why Ottawa is the best place in Canada to use one
Infrared needs a temperature difference across the building assembly, and a rule of thumb is that you want at least 10 °C. From November through March, Ottawa routinely delivers 30 to 45 °C of difference between indoors and outdoors.
The practical consequence: an infrared scan of an Ottawa home in January is dramatically more informative than the same scan on the west coast in the same month. Envelope defects that would be invisible in a mild climate are unmistakable here. It is genuinely the one technical advantage of inspecting buildings in this city.
In summer the reverse applies — envelope scanning is much less sensitive, though moisture and electrical scanning work year-round. An honest report will state the conditions on the day and what they limited.
How to tell whether it was done properly
A real infrared component of an inspection produces:
- Actual thermal images in the report, paired with a normal photograph of the same area so you can see what you are looking at.
- Temperature scales on the images, and ideally the ΔT for significant findings.
- Moisture meter confirmation of every anomaly that was interpreted as moisture.
- A statement of conditions — indoor and outdoor temperature, and what those conditions allowed or prevented.
- Honest negatives. "Scanned, no anomalies detected" is a real and valuable finding.
What should make you suspicious: a single decorative thermal image with no interpretation, thermal images with no accompanying visible-light photo, or claims of finding things infrared physically cannot find.
Frequently asked
Can thermal imaging see inside walls?
No. It reads surface temperature only. What it detects is the effect of something inside the wall — missing insulation, moisture, or heat — on the surface temperature you can see.
Is thermal imaging worth it in a home inspection?
In Ottawa, yes, particularly in the heating season when the temperature difference across the building envelope makes defects clearly visible. It finds insulation gaps, air leakage, hidden moisture and overheating electrical connections that a visual inspection cannot.
Does thermal imaging detect mould?
No. It detects moisture conditions that can support mould growth. Confirming mould requires surface or air sampling and laboratory analysis.