When I bought a house bedecked with floor-to-ceiling French doors, I got sunshine and an odd fixation on heat loss. Full of charm and quirks, the building had been built in 1922, when electricity was scarcer than it is today. I don’t say “we” because my husband never thought about the cold.
And the unlikely hero of this winter’s energy experiment wasn’t some expensive thermal camera or a rackful of smart sensors. It was the thermometer inside my Pixel Pro, which lurked quietly in Thermometer and was tailor-made to answer the question every new homeowner asks: where is my heat going?
Turning a Pocket Sensor Into a House Audit
Wondering about those good-looking but suspect panes, I opened the Thermometer app, tapped Walls and windows, and began sweeping. Reading across the glass and out to the aluminum frame (a.k.a., the stile) and then putting my hand on the fabric blind, this pattern emerged when we did a bunch of sweeps in different rooms at different air temperatures, on different floors: the blind was near room temperature; the glass about 1–1.5°C colder; and it felt like back-of-your-hand cold—why not use or buy an IR thermometer?—a darned cool touch on that aluminum stile, especially near joints.
That gradient makes sense. Aluminum is a well-known thermal bridge, and even the best double glazing won’t keep up with the air temperature of the room. Windows can represent about 25–30% of the thermal losses and gains in your home, according to the U.S. Department of Energy, so those tiny deltas really do matter. More significant, though: I wasn’t observing erratic cold points, or big differences between the location and any of its nearby neighbours—none nearer than a 2°C difference—so I could safely eliminate obvious drafts for now.
The conversation changes when you can see numbers instead of guessing by touch. It allowed me to distinguish between “this feels cold because of tissue” and “this is losing heat.” That’s the distinction between living with big windows without feeling them and throwing money at problems you may not have.
So, Do Shutters and Blinds Help at Night?
I ran a simple A/B test. There are two sets of matching doors in the same room, same exposure, with the same blinds. During daylight hours, with sun on the glass, readings were essentially equivalent whether the exterior aluminum roller shutter was up or down. The break came after the sun had set: with the shutter closed, both stile and curtain read warmer. Nothing dramatic, but consistent—exactly what you’re looking for when trying to determine an attachment’s value.
Building science backs this up. A study by Lawrence Berkeley National Laboratory and the Attachments Energy Rating Council indicates that a well-fitted window attachment establishes a still-air layer, which reduces conductive and convective losses. Cellular shades can cut heat loss by double-digit percentages; simple roller styles do less but provide some help. Outside shutters are usually better than inside shields, in most cases, when well closed up, especially at night. I had an immediate, room-by-room confirmation from the Pixel readings without having to wire in sensors or export graphs.
How Accurate Is a Phone’s Built-In Thermometer?
Previous generations of the feature were criticized for accuracy and compared poorly against dedicated IR tools. Since then, Google’s thermometer feature has gotten FDA clearance for body-temperature readings in the U.S., which theoretically should mean better calibration and consistency. For consumer diagnostics, all that matters is consistency across measurements: if it reads the same surface in the same way every time, then even if your airtight tolerance needs are not quite met, you can still compare relative differences.
Technique matters. Keep a consistent separation distance and aim as perpendicular to the surface as possible. Avoid any reflective or direct sun; shiny metal under-reports due to emissivity. Instead, stick a small piece of matte tape (household masking tape) to the frame and measure there for reliable comparisons. Measure after the room has settled for 20 to 30 minutes, and also take readings at night for worst-case conditions.
A Ten-Minute Technique That Every Homeowner Should Do
- Pick one room. Mark the room’s air temperature on a thermostat.
- Three brief points for each window or door: the glass center, the frame close to a corner or joint, and the surface of any shade or curtain.
- Compare deltas, not absolutes. We’d expect 0.5–1.5°C cooler than room air from double glazing, while the frames should feel colder, particularly if they are metal. One last tip: look for anomalies—one section of frame might be lower by 3–4°C, or readings may vary around the perimeter by more than 2°C, either of which can indicate leaks or substandard sealing.
- Validate suspicions. Keep a smoke pencil or an incense stick near questionable joints to observe whether smoke flutters. Recheck after closing a shutter or drawing the blind; small changes that build over nights add up to real savings in a season.
- If you discover a problem, escalate: a pro energy audit using a blower door and thermal imaging can identify infiltration and insulation holes, and many utilities or local energy agencies will help underwrite such visits.
What the Numbers Told Me About Heat and Windows
My doors are performing their functions: no sudden temperature cliffs, no obvious drafts, and definitely some benefit from closing the exterior shutters when it gets dark outside. Because heating systems are sluggish and energy prices wobbly, it’s a real-world victory to shave a few degrees of surface loss out from under nighttime cover. And it solves a daily conundrum—go big on daylight, seal up at night—without leaving you guessing.
A Feature That Actually Paid for Its Existence
I used to forget about the Pixel’s thermometer. Now it’s a first-line diagnostic tool that I can take from room to room, season to season. Not as thorough as an audit, but a quick and easy method to test hypotheses, prioritize fixes, and determine whether attachments like blinds or shutters are doing their job. For new homes and first-time homeowners, that’s not a gimmick—it’s tangible information in your pocket.