Every July, someone hands us their power bill and asks what's wrong with their AC.
Most of the time, nothing is wrong with their AC.
The AC is doing exactly what it's supposed to do: pulling heat out of the house and dumping it outside. It's just that the house is leaking that heat back in faster than the AC can keep up. So the AC runs and runs and runs, the compressor cycles all day, and the power bill is brutal.
Fixing that bill isn't about buying a bigger or newer AC. It's about figuring out where the heat is getting in.
We've done hundreds of these diagnostic visits in Lehi, Saratoga Springs, and Eagle Mountain. Here's what we usually find.
The attic is almost always the problem.
If your house was built in Utah anytime between 2000 and 2015, there's a very good chance your attic insulation is under-spec for what's actually needed to handle Utah summer heat.
The building code at the time was R-38 for ceilings in this climate zone. That was considered good. It is not good. We now recommend R-49 to R-60 for Utah homes that want real summer efficiency. The difference between R-38 and R-60 in an attic on a 100-degree day is substantial — we're talking 10-15 degrees of temperature difference in the ceiling cavity, which directly translates to how hard your AC has to work.
What we actually check: Go up into your attic (or send us up). Look at the insulation depth with a tape measure. Pink or yellow fiberglass batts at 12 inches deep = roughly R-38. You want closer to 18 inches of blown-in cellulose or fiberglass, which gets you to R-60.
Adding insulation is one of the cheapest ways to lower your summer cooling bill. A typical Lehi home can get from R-38 to R-60 for $1,500-3,000 depending on attic size, and the payback on summer cooling alone is usually 4-6 years. Combined with winter heating savings, it's faster.
Your ducts are probably leaking.
This one shocks people. The ductwork that runs through your attic — the big silver metal or flex duct that carries conditioned air from your furnace/AC to the rooms — is often losing 20-30% of the cooled air through joints, seams, and connections BEFORE it ever reaches a register.
In Utah, where most duct runs are in unconditioned attic space, this is even worse. You're paying to cool air that never actually makes it into your living room. It just leaks into the attic and slowly warms the rest of the house.
We test duct systems with a manometer — a device that measures pressure loss. It's not a guess. In an average Utah home from the mid-2000s, we typically find 15-25% duct leakage. In a well-sealed modern home, it's 5% or less.
What actually fixes it: Mastic sealing (thick gray paint-like stuff applied at every joint) or Aeroseal (a pressurized aerosol sealant that gets applied from the inside). Mastic is cheaper and we can do it in a few hours. Aeroseal is more expensive but gets into places you can't reach by hand.
Either way, the improvement in cooling efficiency is immediate and measurable. We've had customers call us the next week to say their upstairs bedrooms are actually cool for the first time in years.
South-facing windows are doing more than you think.
If your house has large south-facing or west-facing windows — and a lot of Utah homes do because of the mountain views — those windows are passive solar heaters all afternoon.
A single 4x6-foot west-facing window with no coverage can contribute the equivalent of a 1,500-watt space heater worth of heat gain during a hot July afternoon. Multiply that by three or four windows in a great room and you understand why your AC can't keep up at 4pm.
Cheap fix: close the blinds or curtains on the sunny side of the house during peak afternoon hours. Sounds obvious but nobody does it. Just doing this can take 3-5 degrees off the upstairs temperature during the worst part of the day.
Better fix: low-E window film on the hot-side windows. It looks almost invisible from the outside, rejects 60-80% of the solar heat gain, and still lets visible light through. A professional install runs $5-8 per square foot and pays back within a couple summers for houses with big sunny exposures.
Best fix (if you're replacing windows anyway): low-E Argon-filled double-pane windows with a low SHGC rating for the sun-side, higher SHGC for the cold-side. But this is a big-ticket project and only makes sense if you were planning window work anyway.
The thermostat setting game.
There's a lot of conventional wisdom about thermostat settings that actually costs you money.
"Set it higher when you leave the house." Sort of true, but only if you're gone for 4+ hours. Setting the thermostat up 6-8 degrees when you leave for work and back down when you get home saves about 5-10% on cooling. Setting it up 3 degrees when you run to the store doesn't.
"Don't turn it off, it costs more to cool back down." Completely false. This is a myth. It always costs less to let the house warm up while you're gone than to keep cooling it. The energy you save during the coast-up period is more than the energy spent bringing it back down later.
"Close vents in rooms you don't use." Don't. This was true for old gravity systems. It's false for any modern forced-air system. Closing vents raises static pressure in the ducts, stresses the blower, and usually causes more duct leakage, not less.
What actually works: a smart thermostat with a learning schedule (Nest, Ecobee, Honeywell T10, etc.) set to 76-78 during occupied hours, 82-84 during away hours. That's the sweet spot for Utah summer. It's a bit warmer than people feel comfortable with initially, but if you run a ceiling fan in the room you're in, 78 feels like 74.
The ceiling fan trick.
A ceiling fan doesn't cool the air. It cools YOU, by moving air across your skin and increasing evaporative heat loss. This is important because it means:
- A ceiling fan running in an empty room is wasting electricity.
- A ceiling fan running in a room with people in it effectively lowers the "felt" temperature by 4-6 degrees, meaning you can set the thermostat higher without feeling hotter.
- Turn it off when you leave the room. Really.
On a summer evening in Lehi, running ceiling fans with the thermostat at 78 uses dramatically less energy than running no fans with the thermostat at 74. The human comfort is identical.
The stuff that matters most, in order.
If you were going to spend money on summer cooling efficiency in order of impact:
- Add attic insulation if you're at R-38 or below. Biggest single improvement, longest payback. ($1,500-3,000)
- Seal your ducts if they're in an unconditioned attic and you've never had them tested. Almost always saves real money. ($500-1,500)
- Add window film or shade to south/west-facing glass in the rooms you cool most. ($200-1,500 depending on scope)
- Upgrade to a smart thermostat with a real away schedule. ($150-300 including install)
- Run ceiling fans in occupied rooms only. (Free if you have them)
Notice what's NOT on this list: replacing your AC. If your AC is under 10 years old and was sized correctly at install, it's almost never the bottleneck. Fix the house first. Then if it's still struggling, talk about the AC.
The free version
If you want to know what's actually causing your July bills, we do a summer efficiency walkthrough. We look at the attic, the ducts, the windows, the thermostat schedule, the AC itself, and give you an honest ranked list of what would actually move the needle.
No upsell. No pressure. Sometimes the answer is "nothing is wrong, your house is just big and Utah is hot." That's fine too — at least then you know.