Cooling a house costs more than heating it in most of the US south, and the gap is closing in the north as summers warm. The good news is that summer cooling response is much more controllable than winter heating. Heat loss happens through walls, floors, ceilings, and infiltration all at once. Heat gain in summer is dominated by two paths: solar radiation through windows and conduction through the attic. Address those two paths and the AC system runs less, lives longer, and costs less.
Start with the AC system
1. Schedule a professional AC tune-up. The technician should check refrigerant charge with gauges, test the capacitor with a multimeter, clean the condenser coil, clear the condensate drain, and check airflow at registers. A complete tune-up takes 45 to 90 minutes. Reject 15-minute “tune-ups” that consist only of replacing the filter and checking outdoor power. Those are upsell visits, not service.
2. Replace the filter and set a reminder. Standard 1-inch filters need replacement every 30 to 60 days during peak cooling season. Pleated 4-inch filters last 6 to 12 months. A dirty filter reduces airflow 20 to 40% and can freeze the evaporator coil, which dumps water through the ceiling and shuts the system down on the hottest day of the year.
3. Clear the outdoor unit. Cut back any vegetation within 2 feet. Remove leaves, grass clippings, and debris from the fins. Rinse the coils gently with a garden hose from inside the unit outward. Never use a pressure washer because it bends the aluminum fins permanently. Bent fins reduce heat transfer 10 to 25%.
4. Check and clean the condensate drain. Locate the drain line (usually a 3/4-inch PVC pipe near the indoor air handler). Pour a cup of distilled white vinegar into the drain access. The vinegar kills algae and slime that can clog the line. A clogged condensate drain triggers the safety switch and shuts off cooling.
Address the attic
5. Check attic insulation depth. Most US homes need R-49 to R-60 insulation (14 to 20 inches of blown cellulose or fiberglass depending on type). Houses built before 2000 commonly have R-19 to R-30. Topping up insulation from R-30 to R-49 costs $1,200 to $2,800 for a typical 1,500 sq ft attic and cuts cooling and heating costs 15 to 25%. The payback is 4 to 7 years.
6. Verify attic ventilation. Soffit vents at the eaves and ridge vent at the peak should allow continuous airflow that exits hot attic air. Blocked soffit vents from blown insulation are common. If your roof shingles are aging fast or summer attic temperatures exceed 140°F, ventilation needs work. Baffles at the soffits keep insulation from blocking airflow.
7. Seal attic air leaks. Recessed lights, plumbing chases, attic hatches, and HVAC penetrations leak conditioned air upward into the attic. Spray foam around penetrations and weatherstrip the attic hatch. Air sealing the attic before adding insulation produces 2 to 3x the energy savings of insulation alone.
Manage solar heat gain
8. Install window film on south and west exposures. Quality solar control film cuts solar heat gain 40 to 70%. For climates with summer peaks over 90°F, this is one of the highest-ROI cooling improvements available. Skip north and east-facing windows where the payback is poor.
9. Use cellular shades or exterior shades on the hottest windows. Cellular shades reduce heat gain 30 to 50% when fully lowered. Exterior solar shades and awnings reduce heat gain 60 to 80% because they stop the sun before it hits the glass. Awnings on south-facing windows are particularly effective because they shade in summer but allow winter sun under the lower sun angle.
10. Plant deciduous trees for west-facing windows. Long-term project, but a mature deciduous tree shading west-facing windows reduces afternoon cooling load 20 to 40%. Pick fast-growing species like red maple or tulip poplar and plant 15 to 20 feet from the wall.
Cool with less AC
11. Set ceiling fans counterclockwise. Look up at the running fan. Air should be pushed downward, creating a breeze felt below. The breeze evaporative-cools skin and makes the room feel 3 to 4°F cooler at the same thermostat setting. Turn fans off in empty rooms. Fans cool people, not rooms.
12. Set the thermostat strategically. 78°F when home, 82°F when away, programmed to start cooling 30 to 60 minutes before you arrive home. Modern smart thermostats learn your schedule and pre-cool efficiently. Avoid setting back more than 7°F because the recovery period uses as much energy as steady-state cooling at the lower temperature.
Two more worth considering
Whole-house fan. In climates where night temperatures drop below 70°F, a whole-house fan installed in the attic pulls cool night air through open windows and exhausts hot attic air. Operating cost is 1/10 of central AC. Effective only when nights cool below 70°F, which rules out the Gulf coast and southwest deserts.
Attic fan or ridge vent upgrade. Powered attic fans are controversial because they can pull conditioned air out of the house through ceiling air leaks. Skip the powered fan and verify ridge and soffit vents are clear. Passive ventilation is more reliable and free to operate.
Final notes
Cooling load is dominated by sun and attic. Address those two paths first. The AC system runs better with less work, which extends its life from 12 to 15 years to 18 to 25 years and pays for the prep work several times over.
See the HVAC filter replacement schedule and spring maintenance checklist for related tasks. The methodology page covers how we evaluate cooling products at The Tested Hub.
Frequently asked questions
When should I schedule the AC tune-up?+
Late March through early May, before HVAC companies hit peak season. A tune-up booked in April runs $90 to $180. The same service booked in July as an emergency call costs $200 to $400 and you wait 3 to 7 days during a heat wave. Spring tune-ups also catch failing capacitors and low refrigerant before they cause a midsummer compressor failure, which is the single most expensive AC repair at $1,500 to $3,500 for a new compressor or $5,000 to $9,000 for full system replacement.
Does closing vents in unused rooms save money?+
No. Closing vents in unused rooms increases static pressure in the duct system, which strains the blower, reduces overall airflow, and often causes the evaporator coil to freeze. Modern HVAC systems are designed for full-house airflow with all vents open. Close the door instead, or install a smart room sensor that adjusts central temperature based on occupancy. Whole-house zoning systems are the right answer if you really want different temperatures in different areas, but partial vent closure is a myth that increases energy bills.
What is the cheapest single change that reduces cooling costs?+
Setting the thermostat to 78°F when home and 82°F when away saves 6 to 10% on cooling for each degree above 72°F. A house held at 72°F costs roughly twice as much to cool as one held at 78°F in most US climates. Adding ceiling fans (running counterclockwise in summer) makes 78°F feel like 75°F at no incremental energy cost. The combination saves the average household $150 to $400 per cooling season versus a 72°F set point with no fans.
Should I cover or shade my AC condenser unit?+
Partial shade from a tree planted 8 to 12 feet from the unit reduces operating costs 5 to 10%. Avoid covers, tarps, fences, and lattice that block airflow. The condenser needs 2 feet of clearance on all sides and unrestricted air movement above. A unit shaded by morning sun is ideal because the highest cooling demand happens during afternoon peak temperatures. Never put a structure directly over the unit because the discharged hot air will recirculate and reduce efficiency 20 to 30%.
How much can window film actually save?+
Quality solar control window film on south and west-facing windows reduces solar heat gain 40 to 70% and cuts cooling costs 5 to 15% in sunny climates. Professional installation runs $8 to $15 per square foot. DIY film runs $1 to $4 per square foot but is much harder to install bubble-free. Payback period is 4 to 8 years for professional installation and 1 to 3 years for DIY. Film is most cost-effective in southern climates with extensive west-facing glass. Northern homes get less benefit.
Morgan Davis
Morgan Davis writes for The Tested Hub.