How to Detect Drafts with an Infrared Thermometer (4 Steps)

TL;DR: Point an infrared thermometer at baseboards, window frames, and outlets on cold days. Surfaces 10–15°F colder than your interior walls signal air leaks. Map the cold spots, seal them with weatherstripping or caulk, then re-scan to confirm. A $25 tool can cut heating bills 10–20% in a single winter.

_Last reviewed: July 2026 · 6 min read_

Drafts hide behind trim, under doors, and inside outlet boxes—places your hand misses but your heating bill doesn't. An infrared thermometer turns invisible air leaks into readable numbers in seconds, no fog machine or incense required.

Okoniq Property Hub logs every scan, photo, and fix in one maintenance timeline, so you remember which windows you've sealed and which rooms still need work.

Where should you aim an infrared thermometer to find drafts?

Start on a cold day when the temperature difference between inside and outside is at least 20°F—the bigger the delta, the easier cold spots appear. Set your thermostat to your normal winter temperature and let the house stabilize for an hour.

Aim the thermometer at these high-risk zones from 12–18 inches away:

• Baseboards and floor edges, especially along exterior walls
• Window and door trim, both the frame and the wall 2 inches around it
• Electrical outlets and switch plates on exterior walls
• Recessed can lights in top-floor ceilings
• Attic hatches and pull-down stair perimeters
• Plumbing penetrations under sinks where pipes enter the wall

Your interior wall surfaces should read within 2–3°F of room temperature. A spot that reads 10°F colder is leaking air. A 15°F drop means you've found a major gap. Write down each reading and mark the location with painter's tape so you don't lose the spot when you grab the caulk gun.

Many landlords pair this scan with an attic insulation check—cold ceilings often signal missing insulation above, not just a draft below.

What temperature difference signals a real draft?

A 5°F drop is normal near single-pane windows on very cold days—thermal bridging through the glass itself. You're looking for 10°F+ differences on surfaces that should be room temperature: drywall, trim, outlet covers.

For example, if your living room wall reads 68°F and the baseboard 2 feet away reads 54°F, air is moving through that joint. If an outlet cover on an exterior wall reads 48°F when the adjacent drywall is 70°F, you've found a direct path to the outdoors.

Use a consistent scan pattern: measure one baseline interior wall, then compare every suspect surface to that number. Keep a notepad or use your phone's voice recorder to log each reading with the location—you'll forget which window was 58°F and which was 62°F after the third room.

Drafts often cluster. If one outlet is cold, check the others on the same wall; if one window leaks, the rest in that room probably do too. Scan methodically rather than chasing random hunches.

How do you seal the leaks you've detected?

Match the fix to the gap size. Cracks under ⅛ inch take acrylic latex caulk; gaps ⅛–¼ inch need foam backer rod first, then caulk on top; anything wider than ¼ inch requires spray foam.

For cold baseboards, pull off the trim, stuff fiberglass insulation or foam into the cavity behind it, then caulk the seam where the baseboard meets the drywall before re-nailing. For outlets, install foam gaskets behind the cover plates—$8 for a 12-pack at any hardware store. For window and door frames, add weatherstripping if the sash moves; use caulk if the frame itself is leaking where it meets the wall.

After sealing, wait 24 hours for caulk to cure, then re-scan. The temperature should rise to within 3–5°F of your interior baseline. If it's still 10°F cold, you missed a secondary leak nearby—check above and below the spot you sealed.

Track every fix with a photo and date. When you sell or prepare a seasonal property for winter, you'll have proof that the weatherization is complete.

Can an infrared thermometer replace a blower door test?

No, but it's a faster first pass. A blower door test (where a contractor depressurizes your house and measures total air leakage) costs $300–$600 and gives you a whole-house leakage number in air changes per hour (ACH). An infrared thermometer costs $20–$50 and shows you exactly where the cold air enters, one surface at a time.

Use the thermometer to find and fix the obvious leaks yourself—windows, doors, outlets, baseboards. If your heating bills stay high after sealing those, then schedule a blower door test to catch hidden leaks in the rim joist, ductwork, or attic ventilation paths.

Professional energy auditors use both tools together: the blower door creates a pressure difference that makes leaks easier to spot with thermal imaging. You're doing a budget version of that workflow—wait for a windy day or turn on bathroom exhaust fans to pull outside air through cracks while you scan.

Some models have a laser pointer to mark the exact measurement spot; others show the last reading on a backlit screen. Either works. Emissivity settings matter for shiny metal surfaces (set to 0.95 for drywall, wood, and painted trim), but most units ship with that default.

FAQ

How cold does it need to be outside to detect drafts with an infrared thermometer?

At least 20°F colder than your indoor temperature—ideally 30°F+ difference. If it's 68°F inside and 40°F outside, cold spots are harder to distinguish from normal thermal bridging. Wait for a day in the 20s or lower to make leaks obvious on the screen.

Can you use an infrared thermometer in summer to find air conditioning leaks?

Yes, but reverse the logic: on a hot day with the AC running, scan for warm spots on interior surfaces. A wall or ceiling that reads 10°F+ warmer than surrounding drywall is leaking hot outdoor air or lacks insulation. The technique works year-round; you just flip the target temperature direction.

Do infrared thermometers work through glass or plastic?

No—they measure surface temperature only. If you aim at a window, you're reading the glass temperature, not the air behind it. To check for leaks around a window, aim at the frame, the wall beside the frame, and the trim; skip the glass itself unless you're diagnosing condensation issues.

What's the difference between an infrared thermometer and a thermal imaging camera?

An infrared thermometer gives you a single-point temperature reading wherever you aim the laser. A thermal camera ($200–$3000) shows a heat map of an entire wall at once, color-coded by temperature. The camera is faster for whole-house audits; the thermometer is cheaper and fine for targeted leak-hunting after you've narrowed down suspect areas.

Should you seal every cold spot you find?

Not always. A cold floor over an unheated crawlspace is normal if the crawlspace is vented; sealing the floor won't help unless you also insulate it or close the vents. Focus on spots where conditioned indoor air is escaping to the outdoors—window frames, outlet boxes, attic hatches—before tackling cold surfaces that are cold by design.

This is educational information, not energy-audit or construction advice. For whole-house air-sealing or insulation work that involves structural changes, consult a licensed contractor or certified energy auditor.