Whole house fans use 10–15× less energy than central air conditioning and can cool a home from 85°F to 72°F in under 15 minutes. Here's exactly how they work — and when they're the right choice.
See If It Works For Your Home →Based on a 50–90% reduction in A/C use in hot, dry climates. Actual dollar savings vary by climate, home size, and electricity rate. See the homepage calculator for your home's estimate.
A whole house fan is a ceiling-mounted fan that pulls cool outdoor air in through your open windows and pushes hot air up and out through the attic. Installed between your living space and the attic, it does something your A/C cannot: it replaces the air in your home, cutting A/C use by 50 to 90 percent in suitable climates.
Cool outside air needs a path in. Two or three open windows in different rooms creates circulation. The fan does the rest.
The fan creates negative pressure in your living space. Hot air rises and is forced out through attic vents — along with the radiant heat stored in your walls and ceiling.
Outside air rushes in through the open windows, replacing the hot indoor air. If it's 72°F outside and 88°F inside, your home reaches 72°F in minutes, not hours.
Run the fan at night, then close windows in the morning before outside temp climbs. Your home stays cool all day on thermal mass alone — no A/C needed.
Central air conditioning removes heat from air inside your home. But it doesn't remove the heat stored in your walls, floors, and ceiling — the thermal mass that keeps radiating heat back into your living space all day. So A/C runs continuously, fighting a battle it can never fully win.
A whole house fan does something different: it flushes the entire air volume of your home with cool outside air. That air contacts every surface — walls, floors, furniture — and carries the stored heat out with it. When you close up in the morning, your home stays cool on that thermal mass all day.
On a typical California summer night, outside air drops to 65–68°F while indoor air stays at 82°F. Running a whole house fan for 20 minutes drops indoor temperature to match outside — and that cool thermal mass keeps your home comfortable through the following afternoon without A/C.
After running WHF midnight–6am, home stays 10°F cooler through noon with zero A/C runtime.
Most homeowners use both: whole house fan at night to flush heat and cool the thermal mass, A/C only on the hottest afternoons. A/C runtime drops 60–80%, bills drop accordingly.
The greater the day/night temperature swing, the more effective a whole house fan becomes.
30–40°F day/night swings are common. Summer nights regularly drop to 60–68°F. Whole house fans can reduce A/C use for 80–90% of summer days.
High elevation means cooler nights year-round. Many Mountain West homes can run exclusively on whole house fans with no A/C at all.
High daytime temps but nights still cool significantly. Works well April–June and September–October. A/C still needed for peak July–August afternoons.
Works well in spring and fall. Summer humidity limits effectiveness on humid nights. Still reduces A/C load significantly during shoulder seasons.
Excellent for spring/fall. Summer heat waves with humid nights reduce effectiveness. Works well in homes without A/C during non-peak summer.
High summer humidity means nights stay warm and muggy. Whole house fans can help in spring and fall but are less effective during peak summer humidity.
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