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Whole House Fans: An Overview

How do they work? How have new designs changed? What are the benefits? Is natural cooling right for your home? These answers and more, from the engineers at AirScape.

Whole house fans can provide effective natural cooling for a fraction of the energy cost of air conditioning. Drawing cool fresh air in through open windows and exhausting hot stale air out through the roof vents, whole house fans create a comfortable, natural living environment while they draw heat out of the structure to reduce air conditioning load for the next day.

In dry desert climates, a whole house fan is a no-brainer – it can eliminate the need for air conditioning completely. What many people don’t realize however, is that even in most other areas of the US, you can use it in conjunction with your A/C to dramatically reduce your energy consumption. Typically, a whole house fan uses just 1/10th the energy of A/C. Plus, you enjoy natural fresh air in your home rather than recycled indoor air.

While traditional whole house fan designs tended to be difficult to install, noisy and not suitable for most climates, AirScape whole house fans use a completely different design philosophy: they’re more efficient, quieter and easier to install than older designs, making this natural and efficient cooling strategy a great “new” option. More on that in a minute.

The cooling challenge

As the temperature outside rises during the day, heat is captured in the walls and interior spaces of your home. In fact, a typical 2000 sq ft house can absorb several hundred thousand BTUs of heat during the day. When evening comes, even though outside air may have cooled nicely, your house is still radiating a lot of heat, making it hotter inside than outside – a frustrating and uncomfortable situation. You can of course use your A/C system to remove all this heat – but that’s expensive and requires you to spend your evenings sealed up indoors. And even then, upstairs bedrooms are the last to cool off, often remaining at uncomfortable temperatures well into the wee hours of the night. There is a better way!

How whole house fans work

A whole house fan is effective whenever the outside temperature is lower than the indoor temperature – typically in the evenings and at night. A whole house fan mounts between your living space and the attic, drawing cool outside air in through open doors and windows while forcing the hottest indoor air into the attic and out through existing roof vents. This cycle quickly creates a fresh, comfortable indoor environment, and, importantly, steadily draws heat out of the structure itself, so you start the next day with a cool house, delaying or eliminating A/C use.

The net result is you enjoy fresh evening air in your home, a wonderfully cool sleeping environment and save a bundle on energy costs.

Traditional units vs AirScape

Traditional designs for whole house fans used 30 inch (or larger) blades to move large quantities of air. They move a lot of air, but they tend to be very noisy, intrusive, difficult to install, and unsuitable for many climates.

AirScape fans use an entirely different approach. Employing multiple smaller high-efficiency fans (designed for computer rooms), housed in a aluminum casing. AirScape fans are designed to work quietly, at lower CFMs, using much less power, to effectively cool your house throughout the night. This approach is much more efficient and better-suited to modern homes and lifestyles. The following paragraphs outline the advantages of modern AirScape fans vs. the old traditional style.

Air flow

While on the surface it may seem like more CFM equals better cooling, it turns out that old-style fans, with their enormous flow rates, were unnecessary overkill. The main function of a whole house fan is not simply to replace hot air with cooler air – it is to cool down the entire structure by drawing off the heat. And this takes time. Even with very high air flow – say 5000 CFM - your house can only shed pent-up heat at a limited rate. So there is a point of diminishing returns that needs to be considered against noise. You reach a point where you could double the airflow, which would quadruple the noise, yet only speed up the cooling process by 20 or 30%. So what’s really effective is slower flow over a longer period with quiet operation.

Operating sound levels

While traditional whole house fans are noisy brutes, AirScape units are quiet and efficient. Even still, there is inevitable noise generated by moving high volumes of air. This is where high/low speeds really help. Sound levels at slower fan RPMs are geometrically lower than at high RPMs, so having a low-speed setting for night-time is important if you are sensitive about noise and/or sleeping in close proximity to the fan. And remember: Cooling your building structure through the night is the key to saving energy and keeping cool with a whole house fan.

Energy efficiency

Old-style whole house fans are big and noisy, so it’s no surprise that they use a fair amount electricity too. A typical traditional fan draws 500 Watts or more. Compare that to the AirScape 1.7, which draws just 140 Watts on high — and about 70 Watts on low (like a single light bulb). Now, compare that to air conditioning — about 3300 watts for a 3 ton AC unit!

Installation

Large old-style units do not fit easily in modern roof rafters, sometimes requiring extensive carpentry to install. AirScape whole house fans fit between standard 16” or 24” framing, and can be installed by the average handyman in an afternoon.

Insulation

AirScape whole house fans have automatic, insulated doors to provide an easy and effective barrier between living space and attic. This is especially important in colder climates, where old-style fans with ineffective barriers often caused problems for their owners. We talk about this more below.

Is a whole house fan right for your climate?

Typically, whole house fans are most dramatically effective and efficient for climates like we have in California – hot days, cool nights with low humidity. If you live in the west, a whole house fan is a no-brainer. However, most US climates can benefit from whole house cooling during at least part of the year. Obviously, the warmer and more humid the evening air, the less effective natural cooling becomes, so your lifestyle and ideas on personal comfort, energy conservation, etc, start to come into play.

While in the west many people use whole house fans year-round instead of air conditioning, in other climates you would use it perhaps in the shoulder seasons, or in complement with A/C. For instance in the US North East, a whole house fan will not be that helpful during those extreme heat waves with high humidity – for those you’ll want your A/C. However, for more moderate summer weather and through the shoulder seasons, a whole house fan can pay off nicely in comfort and energy efficiency. Our experience is that as long as the evening temperature drops below 75 or so, and it isn’t dripping with humidity, you will have a cool, comfortable house. We have many happy customers all over the country, from Seattle and New Orleans to Florida, Indiana and Maine.

Cool climates require leak-free seals for the winter months

This is an important special consideration if you live in a seasonally cold climate. In winter months, when your indoor air is warm and moist compared to outdoors, you do NOT want any air leaking into the cold attic, so the fan unit must provide a positive air seal. Otherwise, not only would you waste energy heating an uninsulated attic, but the moist indoor air could condense on the cold attic surfaces creating potentially serious water, ice and mold problems. AirScape fans have automatic, insulated doors that use heavy-duty actuators on steel doors to provide a reliable seal that protect your home during the heating season.

Limitations of Whole House Fans

The unique AirScape design eliminates many traditional limitations with whole house fans. Problems with difficult installation, loud intrusive operation, attic condensation/heat loss and fussy maintenance are all solved. However, anyone considering a whole house fan needs to understand that they do have inherent limitations as a cooling device.

A whole house fan:

  • is only effective when outdoor air is cooler than indoor air;
  • does not dehumidify — only A/C can save you when night air is 90 deg.F. with 95% humidity!
  • requires at least one open window (more is better).

What AirScape users enjoy most

Thanks to a modern design approach, the increasing importance of energy conservation and a desire for more natural living, whole house fans are enjoying a resurgence. Overwhelmingly, AirScape users are thrilled with their purchase and how it:

  • saves energy with a smart, elegant cooling that is good for the environment
  • solves the problem of excessive heat accumulation in upstairs bedrooms
  • reduces or eliminates dependence on expensive and wasteful AC
  • allows them to enjoy fresh air and more natural, livable home

We hope this page was helpful to you in your exploration of whole house fans. If you decide to go ahead, we look forward to supplying the equipment and expertise you need to join the natural cooling movement.

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