A 1,600 CFM Whole House Fan Cools About 500 Square Feet

A whole house fan is the cheapest real cooling most houses can install. It does not make cold air. It throws the hot air in your house out through the attic and pulls whatever is outside in behind it, so on an evening when the outdoor temperature has dropped below the indoor temperature, it swaps one for the other in a few minutes and costs about as much to run as a couple of light bulbs. That is the whole idea, and when the conditions are right it works beautifully.

The trouble starts at the buying stage, because the number printed on the box is airflow, and airflow on its own does not tell you what the fan will cool. Two houses with the same square footage can get completely different results from the same fan depending on how much vent area their attics have. Get that part wrong and the fan pressurizes the attic, the airflow collapses, and hot attic air starts finding its way back down into the house. So there are two numbers to work out before you buy anything, and they have to agree with each other.

What the fan is actually doing

An air conditioner runs refrigerant through a compressor to pull heat out of air it keeps recirculating. A whole house fan does not condition anything. It is an exhaust fan mounted at an opening between the living space and the attic, and when it runs it pushes indoor air up into the attic and out through the attic's existing vents. That outflow drops the pressure inside the house slightly, and that pressure difference pulls outdoor air in through whatever windows you have opened.

Two things follow from that, and both matter more than any spec on the box.

The first is that the fan can only ever deliver the outdoor temperature. If it is 88 degrees outside and 84 inside, running the fan makes your house hotter. This is an evening and early morning appliance in most climates, and a nearly all day appliance in dry places where the outdoor temperature falls hard after sunset. Nothing about a better fan changes that arithmetic.

The second is that the fan is only half of an air path. Air has to get out of the attic as fast as the fan pushes it in, and it has to get into the house through open windows as fast as the fan pulls it out. A fan with nowhere to push is a fan that stalls, gets loud, draws more power for less air, and starts forcing attic air back through ceiling fixtures and gaps. The fan's rated airflow assumes the rest of that path exists. It is not a promise that it does.

The first number: 3 CFM per square foot

The Home Ventilating Institute, the trade body that certifies airflow ratings for residential fans, gives the sizing rule plainly. Take the gross square footage of the house, closets and hallways included, and multiply by three. That is your target CFM, and it produces one complete air change roughly every two minutes.

Run that backwards and you get the honest coverage figure for any given fan.

The 3 CFM column is the uncomfortable one. At the institute's full whole house standard, a 1,604 CFM fan is sized for about 535 square feet. That is an apartment, a finished upstairs, a large open plan room, a garage, a workshop, a sunroom. It is not a 2,000 square foot house.

The 1.5 CFM column is where it gets more forgiving. Three CFM per square foot buys a very aggressive air change rate, and plenty of people are happy at half of it. Drop to 1.5 CFM per square foot and you get one air change every four minutes, which still swaps the air in a room several times an hour and still feels like a breeze moving through the house. At that rate the 12 inch fan covers about 1,070 square feet and the 10 inch covers about 800. That is a realistic small home, a second story, or the part of a larger house you actually want to sleep in.

So the useful way to read a whole house fan spec is not "does this cool my house" but "how fast does this change the air in the space I am trying to cool, and is that fast enough to feel like something." If you want the fan to make a room feel different within a minute or two of switching it on, size to three. If you want a steady cooling flow over the course of an evening, size to one and a half and pick the space you care about rather than the whole floor plan.

The second number: attic vent area, and why it decides everything

The institute's second rule is the one almost nobody checks before buying, and it is the reason whole house fans disappoint people. Divide the fan's rated CFM by 750, and that is the square feet of net free vent area the attic needs to get the air back out.

• 1,201 CFM needs 1.60 square feet
• 1,604 CFM needs 2.14 square feet
• 4,800 CFM needs 6.40 square feet

Some ventilation engineers work to a more conservative one square foot per 500 CFM, which pushes the 12 inch fan to 3.21 square feet and the 10 inch to 2.40. Either way, the point is the same: the attic has to be able to breathe out at least as fast as the fan breathes in.

The words "net free" are doing a lot of work in that sentence. A vent's net free area is the open area left after the louvers, grilles and insect screen take their cut. It is not the size of the hole in the wall. As AirScape lays out, a screened gable, soffit or roof cap vent typically delivers around half its gross opening as net free area, so 2.14 square feet of net free area means roughly 4.3 square feet of actual vent opening. Ridge vents are stingier still: the usual figure is 13 percent of the vent's length in feet, so a 10 foot ridge vent contributes about 1.3 square feet.

Go and add up what your attic actually has before you order a fan. Two gable vents at 16 by 24 inches gross is 5.3 square feet of opening, call it 2.65 square feet net free, which comfortably carries a 1,604 CFM fan and just about carries it at the conservative rule. A single small gable vent and a couple of turbines usually does not. Adding vent area is a far cheaper job than replacing a fan, and it is the single change that makes the biggest difference to how a whole house fan performs.

Ten inch or twelve inch

The CLOUDWAY line splits on duct size first, and that is the decision that sets your airflow and your noise. The 10 inch models move 1,201 CFM at 352 Pa of static pressure and 48 dBA. The 12 inch S12 moves 1,604 CFM at 818 Pa and 62 dBA. Both sizes share the rest of the hardware: an EC motor driven by pulse width modulation, dual ball bearings rated to 67,000 hours, an IP44 rating for dust and moisture, and a gravity fed two door insulated shutter that drops closed when the fan stops.

That static pressure jump is the part worth understanding, because it is not a marketing number. Static pressure is how hard the fan can keep pushing when something resists it, and a whole house fan meets resistance constantly: six feet of flexible duct, a grille, a shutter that has to be pushed open, and an attic that is already under some pressure from the air you are putting into it. A fan with 352 Pa behind it does fine on a short straight run into a well vented attic. A fan with 818 Pa keeps moving air through a longer run, a tighter grille, and an attic that is closer to its venting limit.

Which means the 12 inch is not simply "more air for people with bigger rooms." It is the model that holds its rated airflow in a compromised install. If your duct run is long, your attic venting is marginal, or you are pushing through anything other than a straight shot, the extra static pressure is worth more to you than the extra CFM.

The cost is noise. Forty eight dBA is a quiet room. Sixty two dBA at full speed is closer to normal conversation, and in a bedroom ceiling that is a real difference. Both fans run ten speeds, so the practical answer is to buy the airflow headroom and run it at six or seven, which gives you a quieter fan than a smaller unit working at full tilt, and leaves the top of the range available on the hottest evenings.

Wireless remote or smart controller

Once you have picked a duct size, the S and T models are the same fan with different brains, and the price gap is fifty dollars either way.

The S controller is a ten speed wireless remote with a receiver at the fan and memory that holds your last setting. You walk into the room, pick a speed, and it stays there until you change it. For a fan you switch on at nine in the evening and off when you go to bed, that is genuinely all you need, and the twenty foot cord between fan and receiver gives you room to mount things sensibly.

The T controller is the Controller 69 Pro, with a corded probe that reads temperature and humidity in the room and an LCD that programs trigger points, timers, cycles, schedules and a minimum baseline speed. Set it to start at 78 degrees and ramp with the reading, and the fan handles the evening on its own. WiFi is optional rather than required: every trigger and schedule runs on the controller's own screen with no internet, and connecting the app adds remote control, notifications, historical charts and CSV export.

Worth saying plainly: the automation is the only thing the extra fifty dollars buys. The T models are not stronger fans. If you are going to be in the house, awake, and perfectly capable of pressing a button, the S model puts that fifty dollars toward a bigger duct size instead, and duct size is the upgrade that changes what the fan can do.

What installing one actually involves

This is a ducted fan on a standard 120 volt plug, which puts it in a different category from a traditional joist mounted whole house fan. There is no hard wiring, no new circuit, and no 30 by 30 inch hole in your ceiling. The tradeoff is that you are running duct through an attic rather than dropping a fan into a framed opening.

1. Cut and frame the opening. Ten or twelve inches, between joists or trusses, in a ceiling or an upper wall. Do not cut structure. Check what is above the spot first, because wiring and plumbing runs are the usual surprise.
2. Mount the fan. The dual ball bearings allow horizontal or vertical mounting, so the unit can sit at a ceiling or a wall opening. Use the supplied hardware and, if you are mounting to a ceiling, isolate it from the framing where you can. Structure carries fan noise straight into the room below.
3. Run the duct and fit the shutter and grille. Six feet of four layer insulated ducting comes in the box with stainless clamps. Keep the run as short and as straight as you can and avoid sharp bends, because every bend eats static pressure you paid for. The two door insulated shutter goes at the opening, and it is what stops attic air leaking back into the house when the fan is idle.
4. Place the controller. On an S model, mount the receiver at the fan and keep the remote where you will use it. On a T model, run the 12 foot probe into the room you want the fan to respond to, not into the attic, and mount the controller within its 10 foot cord.
5. Set your speeds. Start lower than you think. Run it up until you can feel air moving through the open windows, then leave it there and see how the room behaves over an hour.

The whole job is a competent weekend for someone comfortable working in an attic, and an hour or two for an installer. The part worth paying attention to is not the fan mounting. It is confirming, before you cut anything, that the attic has the vent area from the section above.

What it costs to run

This is where a whole house fan makes its case. The S10 averages 136 watts, the S12 averages 139, and the T10 averages 150. Peak draw is 250 to 255 watts, and all four models pull 2.5 to 2.7 amps on a standard household outlet.

The arithmetic is watts times hours times days, divided by 1,000, times your electricity rate.

Worth being precise about what that comparison does and does not prove. It tells you what the fan costs to run. It does not tell you what you save, because that depends entirely on how many air conditioning hours the fan actually displaces in your climate, and that is a number only your own summer can produce. In a dry climate where nights drop into the sixties, a whole house fan can replace most evening cooling. In a humid climate where the overnight low is 78 degrees at 85 percent relative humidity, it will replace very little, and it will bring that humidity indoors while it tries.

When a whole house fan is the wrong answer

Three situations where the honest recommendation is not to buy one.

Your overnight low does not drop below your indoor temperature. The fan has no mechanism to deliver air cooler than what is outside. If the night air is not cooler than the house, there is nothing to move in. Check a few weeks of overnight lows for your area against the temperature you actually keep the house at before spending anything.

Your attic cannot vent it. If you have well under the square footage from the venting section and adding vents is not practical, the fan will underperform its rating no matter which model you buy, and it will push attic air back into the house while doing it. Fix the venting first or skip the fan.

You are fighting humidity rather than heat. A whole house fan moves outdoor air in at whatever moisture content it has. If the discomfort in your house is damp rather than hot, a fan that brings in humid night air makes the problem worse, and a dehumidifier or conditioned cooling is the honest answer.

And one situation people talk themselves out of when they should not: a whole house fan does not have to cool the whole house to be worth it. Cooling one floor, or one room, or a garage workshop, at 139 watts, is a perfectly good use of a $499 fan. Size it for the space you care about and it will do that job extremely well.