What a thermal camera can find in a house inspection

You're reading through an inspection report and stop at a purple-and-yellow picture of a ceiling with a dark patch circled in red. The caption says "thermal anomaly." Is it a leak, a gap in the insulation, or nothing at all? A thermal camera can point to possible moisture, missing insulation, air leaks, overheating wiring and worn window and door seals. It can't confirm any of them by itself. Here is what the scan can show, why fall is a good time to do one, what it costs and how to read the findings.

01What a thermal camera can and can't find

A thermal (infrared) camera measures surface temperature and shows it as color. That's all it measures. It can't see water, wires or rot behind drywall. It shows that one patch of wall is cooler or warmer than the wall around it, and a trained person works out why.

That makes it a screening tool. InterNACHI, the inspector trade group, says infrared has limits and should not replace other inspection tools. HomeAdvisor and InterNACHI both list the same main targets:

• Possible moisture, such as a ceiling stain that hasn't shown up yet or a wet wall cavity (InterNACHI notes this works when paired with a moisture meter)
• Missing or shifted insulation in walls and ceilings
• Air leaks around doors, windows, outlets and ducts
• Overloaded or overheating electrical parts
• Roof leaks and HVAC problems
• Worn weather stripping and aging window and door seals

Treat every colored blob as a clue. A moisture meter, a closer look or a licensed tradesperson turns the clue into a finding. Moisture shows this most clearly, because it causes the most expensive mistakes.

02Moisture and leaks

Wet materials change temperature differently from dry ones. FLIR, a major camera maker, explains that water shows up through evaporation (which cools a surface), capacitance (wet material holds heat longer) or conduction (it moves heat faster). On camera, a damp spot on drywall usually looks cooler than the dry wall around it, often in an irregular shape that spreads out from the source.

These differences are small, so the camera matters. FLIR says entry-level cameras pick up about a 1.5°C difference on a painted wall, while expert models go as low as 0.02°C. For moisture work it recommends a sensitivity of about 30 mK (0.03°C) and says the job "will require a higher-performance camera." A cheap phone attachment can miss a slow leak completely.

A moisture-like pattern still doesn't prove water is there. Drafts, recessed lights, ductwork and a framing member can all leave a cool patch. FLIR's advice is direct: "always use a moisture meter to confirm." Weather and indoor humidity can also change how a wet area looks on the day of the scan.

Common places a scan flags possible moisture:

• Ceilings under bathrooms, attic spaces and roof penetrations
• Exterior walls below windows, where flashing fails
• Walls next to tubs, showers and laundry hookups

If the report shows a cool spot here but lists no meter reading, ask for one before you call it a leak or rule it out.

03Insulation and air leaks

This is where thermal cameras earn their place, and fall is a good season for it. The camera needs a temperature difference between inside and outside to show where heat escapes. FLIR recommends at least 10°C (18°F) between indoors and outdoors. A heated house on a cold October or November morning usually has that. A mild afternoon often doesn't.

Timing within the day matters too. FLIR suggests starting in the morning, before the sun warms the outside walls and hides the pattern.

What shows up:

• Missing or settled insulation: dark rectangles between studs, or a cold band along the top of a wall where insulation has slumped
• Shifted insulation: FLIR notes rodents sometimes move it to build nests, leaving cold spots
• Air leaks: streaks around door frames, window trim, exterior outlets and duct boots

The U.S. Department of Energy's guide to home energy assessments names infrared scans and blower door tests as the most common ways to find air leaks. The two work well together. A blower door depressurizes the house, which pulls outside air through every gap and makes leaks show up much more clearly on camera. If you're sealing drafts before Thanksgiving guests arrive, an energy audit that pairs the two gives you a short, specific to-do list.

04Electrical hot spots and HVAC

The camera reads heat in both directions. A breaker, wire connection or outlet that shows up much warmer than its neighbors can point to a loose connection or an overloaded circuit. FLIR says scanning the breaker box, outlets and other equipment can help find loose power connections. On the heating and cooling side, it can show leaking ducts, uneven radiant floor loops or registers that never warm up.

A hot spot doesn't always mean a fault. FLIR warns that loaded electrical equipment runs warm, so "just noticing a hot spot might not indicate a problem." The person reading the image has to know what normal operating temperatures look like.

Scanning a panel safely means removing the cover while the circuits are live, so leave it to a qualified inspector or a licensed electrician. Don't take the cover off yourself to get a better picture. If a report flags a hot breaker or connection, have a licensed electrician check it before closing or before the heating season loads the circuits up.

05When the scan works badly

The same image can mean different things depending on the conditions when it was taken. Scans are least reliable when:

• The temperature difference is weak. With less than about 10°C (18°F) between inside and outside, insulation and air-leak patterns fade.
• Surfaces are shiny. FLIR notes that polished metal and other low-emissivity surfaces aren't measured accurately. They reflect heat from around them, so the camera may be showing a reflection of the inspector.
• The target is far away or small. Wide-angle cameras suit close objects. Small or distant targets need a narrower view.
• Weather changes the surfaces. Sun, rain and wind on exterior walls change readings, and indoor humidity affects moisture patterns.
• Furniture blocks walls. A bookcase against an exterior wall keeps that section warm, and a sofa removed just before the scan leaves a "ghost" behind.

Home inspection cameras are typically accurate to about ±2%, according to FLIR, which also warns that misreading an image can lead to costly demolition that turns out to be unnecessary. Before anyone opens a wall, make sure a meter or a second method backs up the image.

06Cost and who to hire

HomeAdvisor puts the average cost of a thermal imaging inspection at about $400. Most people pay $200 to $500, with a full range of $100 to $700. Angi's estimates are similar. Local prices vary.

How it's billed:

• Included: many home inspectors include it in their standard fee.
• Add-on: others charge $50 to $200 extra, often for moisture, mold or energy-audit scans.
• Stand-alone: a separate scan adds about $100 to $300 to the inspector's base rate.

A typical scan takes 30 minutes to 1.5 hours. Homes over 4,000 square feet can take more than two hours and cost more.

Before you book, ask:

• Is the inspector trained in thermography? InterNACHI offers an Infrared Certified® credential, for example.
• Will the scan be done with enough indoor-outdoor temperature difference? A cold morning beats a warm afternoon.
• Will the report show each thermal image next to a regular photo of the same spot, with moisture meter readings for any suspected wet area?

A good report labels each finding as "possible" or "confirmed" and says how it was confirmed. If a scan points to a real problem, the next call goes to the right trade: a roofer for a ceiling leak below the roof, a plumber for a wet wall by a bathroom, a licensed electrician for a hot breaker. If repeated moisture has damaged framing, call a structural engineer.

Sources (9)

• FLIR: How to Detect a Water Leak with Thermal Imaging
• FLIR: Ensuring Energy Efficiency for Homes or Buildings with Thermal Imaging
• FLIR: Thermal Camera Tips to Avoid Common Home Inspection Mistakes
• FLIR: Tracking Down Hidden Problems During Home Inspections with Thermal Imaging
• InterNACHI: Infrared Thermography Overview
• InterNACHI: Infrared Certified Requirements
• HomeAdvisor: Thermal Imaging Cost
• Angi: Thermal Imaging Home Inspection Cost
• U.S. Department of Energy: Home Energy Assessments