Last August our power bill hit $387 for one month in a 1,400-square-foot house. The AC ran nearly nonstop, the windows were old, the thermostat was a manual one we’d been meaning to replace for two years, and the bill arrived with a note that said “high usage alert” like we hadn’t already noticed.
Cooling a house in summer is one of the highest single-line items most households face, and it’s also one of the most fixable. Not all AC-saving advice is equal. Some of it makes a real difference, some of it sounds smart but barely moves the needle, and some of it (like “just open the windows at night”) is the kind of advice you give when you don’t know what else to say.
We’ve spent the last couple of summers actively trying to lower our cooling costs, both through behavior changes and small upgrades. Here’s what’s actually worked, ranked roughly by impact.
Get a Programmable or Smart Thermostat
This is the single highest-leverage move you can make, and most people put it off because it feels intimidating. It isn’t. A modern smart thermostat is a 30-minute install, costs $130-250, and pays for itself within one cooling season for most homes.
The savings come from a simple insight: there’s no reason to cool an empty house to 72°F all day. A programmable thermostat lets you set a schedule (warmer when you’re at work, cooler when you’re home), and a smart thermostat goes further by detecting whether anyone’s actually home, learning your routines, and adjusting on the fly.
A few options worth knowing:
- Google Nest Learning Thermostat ($249 for the premium version, $129 for the Nest Thermostat). Learns your routines automatically, which is convenient if you don’t want to bother programming a schedule. The motion sensor knows when the house is empty.
- Ecobee Premium ($249) or Ecobee Enhanced ($189). Comes with a remote sensor that solves a real problem in multi-floor homes: temperature averaging across rooms instead of just the hallway where the thermostat lives. We use one of these and the room sensors made a real difference in our upstairs comfort.
- Honeywell Home T9 ($199). The budget option that does most of what Ecobee does, with included sensors and a clean app.
The Department of Energy estimates a properly programmed smart thermostat can cut cooling costs by 10-15%, and our experience matches that. Going from 72°F all day to 78°F when we’re at work and 74°F when we’re home shaved roughly $40-55 off our peak summer months without making the house actually uncomfortable.
The key is actually programming it (or letting it learn). A smart thermostat that’s set to one temperature 24/7 isn’t doing anything a $25 manual one can’t.
Replace the Air Filter (Yes, Seriously, Right Now)
This is the cheapest, most-skipped, most-impactful maintenance step in the entire HVAC world. A clogged air filter forces your AC to work harder to push air through, which means longer run times, higher energy use, and faster wear on the system.
Most filters need to be replaced every 1-3 months during heavy use. The exact interval depends on:
- Whether you have pets (shorter)
- Whether anyone in the household has allergies (shorter)
- The MERV rating of the filter (higher MERV = clogs faster)
- How dusty your home runs (older homes, construction nearby, etc.)
If you can’t remember the last time you changed it, that’s your answer. A new filter from a hardware store is $10-20, takes 90 seconds to install, and can improve airflow noticeably within hours. We set a recurring calendar reminder for the first of every month during cooling season and just do it.
A few things to watch:
- Buying filters in a 6-pack from Amazon or Costco is dramatically cheaper than buying them one at a time at Home Depot. A 6-pack of decent filters runs $45-65, where individual filters at the hardware store are often $15-25 each.
- Don’t oversize the MERV rating. Most home systems are designed for MERV 8-11. A MERV 13+ filter (like the heavy-duty allergy filters) restricts airflow on systems that aren’t designed for them, making the AC work harder.
- Reusable washable filters sound good but generally aren’t. They’re noisier, less effective, and a hassle.
This is genuinely the highest dollar-per-effort move in this entire article. Five minutes of work, $15 in materials, real bill impact.
Seal the Leaks That Are Costing You Most
Cool air leaving your house through gaps and old weatherstripping is the same as running the AC with the windows open. It just doesn’t feel that obvious because the leaks are small.
The places that leak most in a typical house:
- Under exterior doors. A weatherstripping replacement kit is $10-20 and takes 15 minutes. Hold a piece of paper to the bottom of your door at night with the AC running. If it flutters, you’ve got a leak.
- Around old windows. Caulking gaps around the frame, replacing brittle weatherstripping in the sash, or adding plastic film during peak summer (yes, even in summer) seals up older windows substantially. A roll of caulk and a tube of replacement weatherstripping is $20-40 total.
- Attic hatches. Most attic access doors have terrible insulation around them. An attic hatch insulator kit ($30-50) cuts a real source of heat infiltration from above.
- Outlets and switches on exterior walls. Foam gaskets that go under the cover plates ($5 for a pack) reduce micro-leaks. Not huge, but very cheap to do.
A blower door test (offered by many utilities for free or low cost) will identify your worst leaks in an hour. If you can’t get one, just feel around the edges of doors and windows on a windy day with the AC on. The leaks announce themselves.
We did a one-Saturday weatherstripping pass three summers ago. Total cost: about $65. Estimated impact: roughly 8-10% lower cooling costs. Best dollar-per-hour project we’ve done on the house.
Use Fans Strategically
Ceiling fans don’t actually cool a room. They cool the people in the room by moving air across skin. The implication: there’s no reason to run a ceiling fan in an empty room (just wastes electricity), and there’s also no reason not to run one when you’re in there.
The benefit: a ceiling fan running at moderate speed can make a room feel 3-4°F cooler without changing the actual temperature. That means you can set your thermostat 3-4°F higher and feel the same. Each degree higher on the thermostat saves roughly 3% on cooling costs, so a 3°F bump is around 9% savings.
Some specifics that actually matter:
- Ceiling fans should rotate counter-clockwise in summer (looking up at them). Most have a small toggle switch on the body. This pushes air down. Clockwise is the winter setting that pulls cool air up to mix with warm air.
- Box fans in windows at night can flush hot air out and pull cool air in if you live somewhere that genuinely cools off after dark. This is region-specific. In Phoenix or Houston in August, your nighttime air is still 85°F, and this trick is useless. In the Northeast or Pacific Northwest, it works great.
- Tower fans are quieter than box fans and decent for bedrooms. Lasko makes a few good ones in the $40-70 range.
The combination of “thermostat 3-4°F higher” plus “ceiling fan running in the room you’re in” is the easiest behavior change with the largest comfort-to-savings ratio in the entire article.
Block the Sun From Hitting the Windows
Direct sunlight through a south- or west-facing window is the same as having a small space heater running in your living room. The amount of heat that comes through unshaded glass on a sunny afternoon is genuinely large, and it’s the AC’s job to remove it.
Solutions in order of cost:
| Solution | Cost | Effectiveness |
|---|---|---|
| Close blinds/curtains during peak sun | $0 | Moderate |
| Add cellular (honeycomb) shades | $40-150/window | High |
| Install exterior solar shades | $150-400/window | Very high |
| Apply window film (reflective) | $20-60/window DIY | High |
| Plant deciduous trees on south/west sides | $50-300 + years | Very high (long term) |
The dirt-cheap version: just close the blinds in rooms that get direct afternoon sun, every day during summer. It looks ugly, you lose the view for a few hours, but the temperature difference in those rooms is meaningful.
The DIY upgrade: reflective window film. 3M and Gila brand films cost about $30-60 for a roll that covers a few windows, take an hour to install per window, and reject 50-70% of solar heat. The view is mostly preserved (it looks slightly tinted from inside, more reflective from outside). We did three west-facing windows two summers ago for about $90 total. The afternoon temperature in those rooms dropped by 4-6°F.
The longer-term play: cellular (honeycomb) shades. They have a small air pocket built in that insulates against both heat and cold. Levolor and Bali make decent budget options at $50-100 per window, custom sizes, and you install them yourself.
Don’t Cool the Whole House if You Don’t Use the Whole House
If you have a multi-zone HVAC system, use it. If you don’t, just close the vents in rooms you’re not using, especially guest rooms, formal dining rooms, and unused offices. You’re paying to cool every cubic foot of conditioned air. If half your house sits empty 10 hours a day, you’re paying to cool nothing.
For unused upstairs rooms in summer, you can also close the door, which keeps cool air from escaping into rooms that don’t need it. The same logic in reverse applies in winter.
The DIY version of zoning: window AC units or portable ACs in the rooms you actually use during peak heat, plus the central AC set to a higher temperature for the rest of the house. A modern window unit ($200-400) can cool a single bedroom for the cost of a few cents per hour. If you spend most of your time in one or two rooms, this can dramatically reduce the load on the central system.
The exception: if your central system is already doing fine and isn’t oversized, mucking with vents and zones can actually create back-pressure problems that make the system less efficient. Modern variable-speed systems in particular don’t love having vents closed. If you have a recent high-end system, talk to an HVAC tech before going aggressive on zoning.
When to Just Replace the Unit
If your AC is 15+ years old, you’re paying a tax to keep it running. SEER ratings (the efficiency rating for AC units) have improved enormously in the past decade. A 1995 unit might be running at SEER 8-10. Modern units are SEER 16-22. The energy difference is roughly 40-60%.
A new central AC system runs $5,000-12,000 installed depending on size and brand. That’s a real chunk of money, but if your old unit is costing you an extra $80-150/month in electricity during summer, the math starts working out faster than people expect. Add the federal Energy Efficient Home Improvement Credit (up to $2,000 for qualifying heat pumps and other equipment as of 2025) and the timeline shrinks further.
The honest version: most people don’t replace until their existing unit dies. That’s fine. But if your unit is on its last legs and you’re already nervous about the next failure, planning the replacement is usually cheaper than emergency replacement during a heat wave when contractors are slammed.
What Actually Doesn’t Save Much
A few popular tips that don’t really move the needle:
Closing curtains in unoccupied rooms. Marginal. The sun heats the curtain, which heats the room slightly more slowly, but the room is still warming. Real solution is window film or shades.
Setting the AC really cold for a quick blast. AC doesn’t work that way. It cools at a fixed rate. Setting the thermostat to 60°F when you walk in just makes it run longer to overshoot the target. Set it to your actual desired temperature.
“Cooling the body” with cold drinks and cold showers. Real, but barely measurable in terms of system savings. Drink the cold water because it feels good, not because it’ll lower your bill.
Smart vents that close automatically. Marketed heavily, mixed reviews on actual savings, often more expensive than they’re worth. Skip unless you have a very specific zoning problem.
The Realistic Plan
If you want to lower your AC costs noticeably without spending a fortune, here’s the order:
- Replace the air filter today ($15)
- Install a smart thermostat this weekend ($150-250)
- Weatherstrip doors and caulk windows this month ($60-100)
- Add window film to the worst sun-facing windows this month ($60-100)
- Set the thermostat 2-3°F higher and run ceiling fans in occupied rooms
That’s a few hours of work, $300-450 total in materials, and a realistic expectation of 15-25% lower cooling costs for the rest of the season. The smart thermostat alone usually pays for itself within 4-6 weeks of summer use, and the rest of the upgrades pay back over 2-3 cooling seasons.
The temptation is to either do nothing and complain about the bill, or to call an HVAC tech and start spending thousands. Most of the savings live in the middle: small, incremental, mostly DIY changes that add up fast. Your house doesn’t need to be cold to be comfortable. It just needs to be cool enough, in the rooms you’re actually using, without the system running flat-out from June through September.