Are whole-house fans loud?

Two adjacent categories are rated for noise and one is not, which is worth seeing side by side.

• Bathroom and ventilating fans are certified in sones in the ENERGY STAR dataset, model by model. The quietest in our catalog are filed at 0.1 sones.
• Ceiling fans are certified for airflow efficiency, not noise, but the CFM-per-watt figure at least correlates with how hard the blade is working.
• Whole-house fans have no certification program at all. Every airflow figure is a manufacturer claim, and the noise field is simply blank — the specification sheets we work from state no sones and no dBA.

So anyone quoting a decibel figure for a whole-house fan is quoting marketing copy. What can be compared is the design and the speed data, and those turn out to predict the experience reasonably well.

The whole-house fan people remember as deafening was a large blade bolted directly into the ceiling behind a louvered grille. Three things made it loud, and all three have been designed out of current units.

1. The motor was in the room. It sat immediately above the grille, so motor noise arrived unattenuated. Ducted fans put the motor several feet away in the attic, with flexible duct between it and the ceiling — duct absorbs sound as well as carrying air.
2. The blade was working hard. A single-speed fan running flat out makes tip noise and turbulence. Modern ECM motors offer real speed control, and noise falls steeply with speed.
3. The louvers rattled. Gravity-operated shutters clattered on start-up and buzzed while running. Insulated, gasketed dampers do neither, and they seal the opening in winter as well.

Published figures for a 4,280 CFM unit:

Power is a good proxy for noise in a fan, because both track how hard the blade is working. Low speed uses 18% of the power for 55% of the airflow — and a motor drawing 73.9 W is not making the noise of one drawing 408.

That gives a buying rule the airflow tables do not: buy a fan large enough that its low speed does the job. A small fan on high is the loud combination; a bigger fan on low moves the same air more quietly and for less electricity. It is the same principle as making any fan quieter, with a larger machine.

• Distance from the grille to the fan. More duct is quieter. Keep the housing as far from the grille as the supplied duct sensibly allows.
• No kinks or tight bends. Restricted duct makes turbulence, which is broadband hiss at the grille and lost airflow at the same time.
• Isolate the housing. Hang it on the supplied straps rather than resting it on joists, so vibration does not enter the structure and get radiated by the ceiling.
• Grille position. A central hallway rather than directly outside a bedroom door. The fan pulls air through the whole house; it does not need to be over anyone’s head.
• Window opening. An under-opened window makes its own whistle as air squeezes past. Open more window than feels necessary and both the noise and the airflow improve — see the operating rules.

There is no honest way to give you a number, so here is the useful version: a correctly installed ducted fan on low is a broad rush of air rather than a motor, comparable to a bathroom fan two rooms away, and it is accompanied by air movement through every open window in the house. On high, it is unmistakably audible in the hallway below the grille and it is not a setting anyone sleeps under.

Most owners run high for twenty minutes to flush the day’s heat after sunset, then drop to low overnight. That pattern is also the cheapest way to run one, which is worked through in what a whole-house fan costs to run.