Whole House Fans

Posted on: November 27th, 2011 by Glen No Comments

Why install a Whole House Fan?

  • Lower your energy cooling costs by 50-80%.
  • Moving air makes you feel cooler on a hot day or night.
  • Quickly removes excessive heat from the upstairs sleeping areas.
  • Reduces trapped indoor air pollutants including Biological and Chemical contaminants.

Whole house fans (WHF) can save you money by reducing air conditioning energy costs in many parts of the country. As energy prices sky-rocket, the WHF is an investment that saves you money on your electric air conditioning utility bills, year after year. Any time it feels cooler outside your home, you can open a few windows and turn on the WHF to draw that cooler outside air into your home. This soft cooling breeze will help your skin temperature feel cooler and lowers the inside temperature of your home. After the whole house fan(s) draws fresh air into the house it then forces it into the hot attic space. The hot attic air is then pushed out of the attic vents to reduce it's over all temperature.

Whole house fans can also improve your indoor air quality by removing stale and contaminated air in your home. Some studies show that trapped indoor pollutions are a major cause of asthma and may lead to "Sick Home Syndrome".

Note: To improve air quality ASHRAE Standard 62.2 states - whole-house mechanical ventilation system rated at 7.5 cfm per occupant, plus one cfm for every 100 square feet of floor area that can be occupied. Example: a 2000 square foot home with 3 people living there, would require a fan rated at 42.5 cfm to improve the indoor air quality in the house.

The Department Of Energy (DOE) states that, "Whole house ventilation, using a whole house fan, can substitute for an air conditioner most of the year in most climates. Whole house fans combined with ceiling fans and other circulating fans provide acceptable summer comfort for many families, even in hot weather."

Visit the Department of Energy's website for more information.

The old-style whole house fan with 3 blades require a 24 to 36 inch opening in the ceiling. They can be very noisy. Also, these older whole house fans serve as a potential major energy loss because it is basically a large, un-insulated hole in the ceiling. Older style fan louvers may not insulate or seal properly. A fan cover would need to be constructed and installed to seal and insulate this large opening when it's not in use.

Note: In cold climates, warm, humid air from inside the house can travel up into the attic through the fan openings. This warm, moist vapor in the air will condense on the cold surfaces to form water droplets. Excessive water build-up in the attic can result in the growth of mold. Be sure to cover or seal your whole house fan opening if they do not have automatic shutters or dampers built in.

How to size a whole house fan

Fans are rated in Cubic Feet per Minute (CFM).  They should provide about 4 air changes per hour for your home to cool  properly. An example would be a 2,000 square foot home with an 8-foot ceiling which has (2,000 X 8 )= 16,000 cubic feet of air. So, a 1,600 CFM rated fan would give you 6 air changes per hour in a perfect world (Nominal static air pressure, windows screens and small roof vents can greatly reduce the air flow volume). Many homes do not have the required roof/attic vents to handle the release of the large volume of air introduced into the attic space. About 1 square foot of open vent space is required for each 750 CFM of air volume.

Note: Some whole house fans advertise up to 10 – 20 air changes per hour which would require massive ventilation openings in your home's roof, gables and/or soffit. Research the new, modern, quieter compact fans.

Smaller Whole House Fans with insulated dampers/shutters and moderate air CFM rating can be just as effective as the old, big, noisy high-air flow units. The smaller unit fits easily between most roofing rafters. Motorized air shutters/dampers close to prevent air loss into the attic. They offer lower power consumption, quieter operation, ease of installation and smaller roof/soffit vents.

Note: Smaller fans may not create the indoor breeze effect that some people like about the larger fans. Be sure to ask your contractor about advantages and disadvantages of both standard and compact whole house fans.

A quick online search of Whole House fans can produce results like Tamarack Technologies, Quiet Cool Whole House Fan System and Airscape fans just to name a few. After you have picked out your new whole house fan, contact your local licensed electrician or electrical contractor to have them wire the fan properly. Discuss installing timers or remote controls to meet your needs.

General information on Whole House Fans

  • Fans with 4 or more blades tend to be quieter.
  • Look for 2 speed fans to reduce the noise level.
  • Large fans (24- 48 inch) belt drive units tend to be quieter than direct drive fans.
  • Each 750 cfm of air flow requires about one square foot opening to release the pressure from the attic.
  • Roof/gable vents with insect screen reduce the air flow about 50% compared to open vents requiring more vents.

Don't forget to open windows before turning on the whole house fan as it will create a backdraft or suction. When you have a backdraft in the home, the gas water heater or furnace can run out of heat due to the flame being blown out. Backdrafting also affects a fireplace which can result in the ashes being sucked from the fireplace and settling over everything in your home.

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