5 Ways to Reduce AC Costs This Tucson Summer

Five things, ranked by impact: attic insulation, a solar attic fan, sealing attic air leaks, thermostat discipline, and an AC tune-up, and the first one alone is worth about 25 percent on a summer cooling bill. That is where the money is: customers who bring their attic up to R-38 to R-49 report about 25 percent average savings on summer cooling, and an under-insulated Tucson home typically spends $150 to $300 more per month than it needs to from May through September.

Here is the list, ranked by how much difference each one makes in a Tucson home:

• Upgrade attic insulation to R-38 to R-49

• Add a 30W solar attic fan

• Seal air leaks between the house and the attic

• Set the thermostat at 78 to 80 and leave it alone

• Get the AC tuned up before June

We do the first three. The last two are on you and your HVAC company, and they still matter. The rest of this post gives numbers for each.

The attic is the largest source of heat gain in a Tucson home. It sits at 140 to 180 degrees on a summer afternoon, and every square foot of ceiling is a path for that heat to reach the rooms below. Most homes built before 2000 have R-11 to R-19 up there. The target for our climate zone is R-38 to R-49, which cuts heat flow through the ceiling by roughly half to two thirds compared to R-19.

We blow CertainTeed InsulSafe fiberglass directly over the existing insulation, no tear-out needed, at about R-2.5 per inch. Blown-in insulation runs $1.25 to $2.00 per square foot of attic installed to R-38, so a 1,500 square foot attic is roughly $1,875 to $3,000, done in 2 to 3 hours in one visit. With about 25 percent average summer savings, typical payback is 2 to 4 years, and the fiberglass is rated to last 20 to 30 years without settling.

Insulation resists heat. A 30W solar attic fan removes it. The fan moves about 1,550 CFM, covers attics up to about 2,000 square feet, and typically drops attic temperature 10 to 25 degrees on a summer afternoon. It runs only on sunlight, so it costs nothing to operate and works hardest between noon and 4 PM when the attic is hottest. A thermostat is included and it shuts off at night.

The fan needs intake to work: about 1 square foot of net free soffit vent per 300 CFM, or roughly 5 square feet for our unit. We check that during the free evaluation and quote the fan afterward, since the price depends on the roof and any intake work. On a home that is already at R-38 or better, the fan is the next upgrade. On a home at R-15, do the insulation first and the fan second, or both in one visit.

Every hole in the ceiling is a chimney. Plumbing stacks, wiring penetrations, recessed lights, bath fans, the gap around the attic hatch, and the top plates of interior walls all let 78 degree conditioned air escape upward and 160 degree attic air drift down. On an older Tucson home the total area of those gaps can add up to the equivalent of a window left open a few inches all summer.

Sealing is inexpensive relative to the other items on this list. Foam and caulk at the penetrations, weatherstripping and a rigid insulated cover at the hatch, and gaskets on the recessed lights. We look for the common leaks during every free inspection and point out the ones worth closing before new insulation goes over them, since it is far easier to seal a penetration before it is buried under 15 to 20 inches of fiberglass.

Holding the thermostat at 78 to 80 while you are home and letting it drift higher when you are out can trim cooling cost by 10 to 15 percent over a summer. Each degree of setpoint is worth roughly 2 to 3 percent on the cooling bill in a Tucson summer. A programmable or smart thermostat does the remembering for you.

The mistake we see is big swings. Dropping the house from 85 to 74 at 5 PM makes the AC run flat out through the hottest part of the day and into the evening, and on a home with thin insulation it may never get there. A steady 78 to 80 with good insulation above it is cheaper and more comfortable than chasing a low number with a hot attic. If the house cannot hold 78 without the system running 50 minutes of every hour, that is an attic problem, not a thermostat problem.

A tuned system moves more cold air per dollar of electricity. Correct refrigerant charge, a clean condenser coil, a fresh filter and a checked blower motor are all things a spring tune-up covers, and a system that is low on charge or choked with a dirty coil can use 10 to 20 percent more power to do the same job. Book it in April or May, before the HVAC companies are buried in July emergencies.

The tune-up and the attic work reinforce each other. A tuned AC pushing into a house with an R-49 attic and a 140 degree attic instead of a 170 degree one reaches setpoint faster, cycles off, and rests. Shorter run time is where the savings on the bill come from, and it is also why systems in well insulated homes tend to last longer.

Start with your worst summer bill. If your attic is below R-38 and the home is spending $150 to $300 more per month than it should from May through September, that is $750 to $1,500 a summer. A 25 percent reduction on a typical Tucson cooling season covers a $1,875 to $3,000 insulation job in 2 to 4 years, and every summer after that is money kept. Our savings calculator lets you plug in your own square footage and bill.

Arizona Attic Pros is family owned and run by Mike, Arizona ROC #365778, insured and bonded, with 4.9 stars from 55 Google reviews. We serve the Tucson metro same day on most jobs, and Casa Grande, Sierra Vista and the Phoenix East Valley on scheduled service days. Schedule a free inspection or call or text (520) 261-3001, Monday through Saturday, 7 AM to 6 PM.