Find Air Leaks in Your Home and Save Big on AC This Summer. Here's How I Do It

CNET

05-06-2025

Air conditioning can send your summer energy bills soaring, but there are smart ways to keep costs in check. Setting your thermostat to a steady, reasonable temperature helps -- but just as important is making sure all that hard-earned cool air isn't sneaking out through cracks, gaps, or poorly sealed windows and doors.
It's not easy to maintain comfortable temperatures during extreme weather, but I developed a DIY ventilation system that brings in cool air at night and schedule smart blinds to block direct sunlight as much as possible. And never underestimate the power of fans.
More recently, I found a new tool to find leaks where cool air is escaping causing the house to warm more and the AC to be less efficient: a thermal camera. I used the HSFTools Finder S2 thermal camera and conducted a DIY home energy audit to look for air leaks that were costing me precious dollars spent on energy..
These same leaks cause heat to escape during winter, so the strategy has year-round applications for lowering energy costs.
A rundown of the HSFTools Finder S2
The Finder S2 thermal camera's USB-C connection means it doesn't need a bulky battery pack, instead relying on your phone for power.
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I'll hold off on an in-depth review of the HSFTools Finder S2, as I have limited experience with thermal cameras, but I'll mention a few features that helped with my energy audit. First, this thermal imager connects to the USB-C port on Android smartphones but doesn't support iPhones. (Apple users should consider checking out the Topdon TC002C instead.) I love the option to launch the app automatically when plugging in the camera.
However, the Finder S2 requires a lot of power -- draining my phone's battery by about 4% after 10 minutes. While this won't affect short inspections of smaller homes, you'll need to recharge your phone after extended use. (For better battery life, I suggest getting a standalone handheld model if you use a thermal camera often.)
I played around with the Finder S2 to get comfortable with its features, mostly taking pictures of my cat.
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Even if you turn on the Finder S2's Super Resolution mode, the overall resolution maxes out at 512x384 pixels, which is lower than standard 480p quality. It's more than enough to see temperature differences around windows during an energy audit but you may need to play around with the settings if you plan to use it for creative work.
Enabling the Digital Camera setting shows a view from your phone's camera on the screen with the option to save images -- but not videos -- from both cameras simultaneously. As for videos, I couldn't get the Finder S2 to work unless I rotated the image 90 degrees in the app.
You can adjust the Finder S2's colors, measurement tools and sensitivity in the HSFTools app.
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I appreciate the wide selection of color palettes in the HSFTools app. My favorite color setting is "white hot" because of the high contrast image compared to other modes. The app's outstanding measurement tools tell you the temperature of the hottest and coldest objects on the screen or of a specific point you select. I love taking the guesswork out of home improvement.
You can get the Finder S2 for about $250 -- although it's often available for $170 -- which is typical among smartphone thermal camera accessories like the Flir One Gen 3 and Seek Thermal Compact. While the price is good for a midrange infrared camera, remember that you might only use it a handful of times -- it's often better to pay for a professional home energy audit. (Don't forget to check if your area has a free energy audit program.) Still, the HSFTools Finder S2 was more than adequate for my DIY home energy audit.
How I used a thermal camera in my home energy audit
My energy audit uncovered an uninsulated ceiling corner that might explain why my home gets so hot in the summer -- time to tell the landlord.
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After familiarizing myself with the thermal imager, I took a structured approach to finding problem areas. I followed this thermal imaging inspection guide from the International Association of Certified Home Inspectors.
Read more: Stop Installing Your Thermostat Here. It's Costing You Money
I started by turning off my HVAC system before shutting my windows and front door. InterNACHI's guide recommends testing on a day where the outdoor temperature difference is 15 to 20 F warmer (or cooler) than inside so I chose a rainy spring day for my audit. I was happy to see my window seals were in good condition. However, I discovered a small, drafty gap under my front door that I filled with foam backer rod from the hardware store.
Fixing the air leak under my front door probably won't save much on my energy bills but it was an effortless DIY project.
John Carlsen/CNET
The actionable part of my home energy audit ends at doors and windows for now but there's plenty more for homeowners to look at. The Department of Energy suggests checking wherever you suspect air leaks or poor insulation, particularly fixtures, along the edges of rooms and between different building materials.
While recaulking seals and replacing weatherstripping around windows are simple DIY projects, you'll need more money and time to upgrade insulation inside walls. You can check out Energy Star's Home Improvement Savings tool to see incentives, rebates and tax credits in your area. If you're a renter, consider telling your landlord about these resources.