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how it works:
Cool outside air is pulled in through open windows while hot air out is forced out through existing roof vents, drawing out building heat.
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energy use - cfm/watt |
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3 ton AC unit:
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0.4 (bad)
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Tamarack HV1600:
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6
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Tamarack Ghost:
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6.2
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AirScape 1.7:
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12
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AirScape 1.0:
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14 (best)
(cfm/watt)
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How much can you save?
The answer to this depends on your climate and your sense of
personal comfort zone. If you live in a hot, dry southwest climate
and don't mind a little heat buildup in the late afternoons, you can
often live without AC totally, saving up to 90% on your cooling
bill. If you live in a 4-season climate with more humidity, you'll
need to supplement your whole house fan with AC when the weather
gets more extreme.
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summary of pros & cons |
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advantages
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requires as little as 1/10th the energy of air conditioning
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your home is cooled naturally with fresh outdoor air rather than recycled indoor air
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creates a cooler second story sleeping environment more effectively than typical AC
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many electric utilities offer incentive rebates for installing whole house fans (PG&E is one)
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new smart models install easily and operate quietly with none of the disadvantages of traditional whole house fans
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limitations
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only effective when outdoor air is cooler than indoor air
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does not dehumidify (only AC can save you when night air is 90 deg.F. with 90% humidity!)
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requires at least one open window (more is better)
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traditional designs have some drawbacks: difficult to install, noisy, and require maintenance. Also, unless properly sealed,
they provide a "hole" in attic insulation, causing massive heat loss and condensation damage. These issues are eliminated
with "smart" whole house fans that we sell.
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sound level samples |
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We recorded the sound of both AirScape and Tamarack units for comparison - keep in mind we recorded 3 feet from the units so
they might sound different in your home!
try it here
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How To's: Our Do-It-Yourself Help Section
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Whole House Fans.
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A whole house fan is a quiet, energy-efficient and pleasant way to keep your home cool and comfortable. Here's everything you need to know about whole house fans from the engineers at hvacquick.com.
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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 fresh and comfortable 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 AC to dramatically reduce your
energy consumption. Typically, a whole house fan uses just 1/10th the energy of AC. Plus, you enjoy natural fresh air in your home rather
than recycled indoor air.
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While traditional whole house fan designs tended to be difficult to install, noisy and not suitable for most climates,
the last few years have seen innovative new "smart" designs that are more practical, efficient, quieter and easier to
install, making this natural and efficient cooling strategy a great option for a much broader market. This web page is
designed to give you all the information you need to decide if a whole house fan is right for your home.
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 AC system to remove all this heat - but that's expensive
and requires you to spend your evenings sealed up indoors breathing stale air. 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 is mounted in the attic drawing cool outside air in through open doors and windows
while forcing the hottest indoor air out the 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 AC 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.
suitable climates
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, thanks to new smart designs with,
among other features, their automatic insulating doors, most US climates can benefit from whole house cooling. 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 instead of air conditioning, in most
other climates you would use it in complement with AC. 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 AC. 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. Again
though, whether you would agree with us on this does depend on personal taste and lifestyle. We have many happy customers in most areas of the US.
UNIT SELECTION CONSIDERATIONS
traditional units vs new "smart" units
Traditional designs for whole house fans used 30 inch (or larger) blades to move large quantities of air. However these large units do not fit easily
in modern roof rafters, sometimes requiring extensive carpentry to install. Also, they tended to be very noisy. So the benefits of whole house
fans were not easily enjoyed.
In recent years, a range of new "smart" fans has emerged - employing multiple smaller high-efficiency fans (designed for computer rooms) inside
a casing that fits between standard 16" or 24" framing. This design breakthrough makes it much easier to take advantage of whole house fan cooling.
Our view is that the new compact designs are far superior in almost every application.
calculating required air flow
While on the surface it may seem like more cfm equals better cooling, it's not quite that simple. 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 3000 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.
As a rule of thumb, 1000 cfm will work nicely in a 1500 sq ft house. The other rule of thumb is 400-500 cfm per bedroom being ventilated.
For larger homes, multiple units can be installed.
energy efficiency
The whole house fan is inherently an energy-efficient device, so most brands are extremely efficient compared to air conditioning. For
instance, the AirScape 1.7 uses just 140 watts to push 1700 cfm - compare this with the 3300 watts for a 3 ton AC unit!
operating sound levels
While traditional whole house fans can be very noisy, the computer room fans used in modern designs are quiet and efficient. However
there is inevitable noise generated by moving high volumes of air. Again, this is where a dual-speed unit can 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. Remember: Cooling your house through the night is the key to saving energy and
keeping cool with a whole house fan. There is no fan on the market that will do this more effectively than the AirScape 1.7.
To help you relate to this, we have produced sound samples of our units for you
to compare. Keep in mind these cannot replicate how the unit may sound in your installation and are meant as a relative guide only.
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 would condense on the cold attic surfaces creating
potentially serious water, ice and mold problems. AirScape units provide reliable positive seals to protect your home during the heating season.
durability/reliability/warranty
A whole house fan is one of those things in life that you just want to work - no maintenance, no breakdowns, no hassles. AirScape units
come with a 3-year warranty. As well, the modular design means a faulty component can be swapped on site rather than having to ship the unit
out for repairs.
does it need maintenance?
Most traditional whole house fan designs require periodic maintenance, which can be challenging depending on your attic access. All of the
fans we sell are maintenance-free - the fans are sealed and permanently lubricated.
controls/switches
Some models required hard-wired switches mounted on the wall; others come with remote controls which, besides being convenient, can make
installation simpler. On the other hand, you can't lose a wall switch!
INSTALLATION CONSIDERATIONS
physical requirements
The new compact multi-fan units are designed to fit into standard rafter configurations. Here is a picture of an AirScape 1.7 as it would
sit in the framing of a typical attic.
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make sure you have adequate roof venting
A whole house fan depends on existing roof vents to exhaust air. If there is not enough venting a positive pressure build-up forces hot,
dusty attic air back into the house through light fixtures and other cracks. How much venting do you need? Provide one square foot of
unobstructed venting for every 450 cfm. Double that if the venting is obstructed by insect screening, louvers, etc. So a 1700 cfm fan would require
approximately 4 square feet of unobstructed roof venting. Typically, a roof vent in new construction provides a X sq ft opening, so you can
guesstimate your existing capacity simply by counting the vents and inspecting one to see if it is screened. If your house does not have enough,
extra roof vents can be added for relatively little expense in most cases.
tips for using a whole house fan effectively
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Only use it when the outdoor air is cooler than your indoor air.
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Make sure your AC is off when you run the fan or you'll be blowing expensive AC air right out of your house!
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We recommend running your whole house fan all night long. Here's why: The goal is to cool your entire house down, not just the air. It takes time to pull the heat out of the sheetrock, structure and contents of a house. By ventilating all through the night, the house starts the next day thoroughly cooled so you can delay or eliminate running energy consuming air conditioning the next day.
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With two-speed units, use high to quickly cool down the house and low setting to run quietly through the night.
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Never operate the unit without opening a window - this can create negative pressure in the house and cause dangerous backdrafting with gas appliances.
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Still have questions about whole house fans? Call us at 877-711-4822 or e-mail sales@hvacquick.com. We're in the office Mon-Fri, 8am to 5pm Pacific time.
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