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Question DetailsAsked on 6/28/2013

What is a reasonable cost for the installation of a whole house attic fan.

My house is older and has plaster ceiling where the vent will most likely be placed. Only two roof vents and one gable vent for attic ventilation. I understand that additional roof vents will need to be installed.

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OK - to be sure what you are asking about - an attic fan vents the hot air in the attic to the outside world, and can exhaust either through the gable (where a gable vent would normally be) or through a roof exhaust hood. The former is normally preferred, as the fewer roof penetrations the better. This would NOT penetrate to the living space (other than maybe to run electric wire), assuming you have an attic with enough room to move around for installation, although even that is not mandatory, as it could be installed on the outside of the house in a blockout.

A whole house ventilation system is totally different - it is a system that regulates temperature and air exchanges (and sometimes humidity also) by using a whole-house HVAC system that divides the house into many zones, and regulates each individually. Normally found only in newer houses that are built "tight" - i.e. sealed so tight that natural air inflow does not provide enough ventilation and air exchanges per hour, so you have to enforce ventilation in the house and provide regulated outside ventilation air. They have penetrations various places in the house, and part may or may not be installed in the attic, depending on whether you have a convenient and large enough utility room or basement.

The former typically runs $500-800 installed, though can go over $1000 in cases where there is no ready access to electric power in or near the attic, or where multiple fans are needed because of constricted airflow, such as in peaked lofts or chalet- houses with interior finished surfaces also peaked.

A whole-house ventilation system has to be integrated with the HVAC (furnace, air conditioner) system, and can run from $2500+ on a retrofit to $10,000+ on a new installation, and involves cutting a lot of holes in interior surfaces to run ventilation ducts. This type of system would properly be put in only after a complete energy audit and subsequent high-efficiency energy conservation upgrade.

Assuming you meant an attic fan, one other alternative you should consider if you do not already have them is ridge vents, assuming you have a peaked roof. Here is a discussion on that issue -

An attic fan basically moves air from a gable vent at one end to the fan at the opposite end of the attic, mixing incoming outside air from the gable vent with the hot attic air and exhausting it at the fan. It is not very efficient at that for three reasons - it does not remove much of the hot air in the 4-10 inch deep area between the rafters where it is hottest, it moves a lot of outside air in for the amount of hot air it removes and heat removal is uneven, and it uses electricity whenever running. Ridge vents (assuming you have open or accessible eaves) exhausts the air up through the rafter spaces by convection (like a chimney) where it is hottest, and air flow is self-driven by the heat - the hotter it gets in the attic, the better they work, and they are passive - no controls, fans, or power consumption.

You said you understand additional roof vents would be needed - it sounds like someone talked about this with you already. Additional roof vents would give you a bit of local ventilation at each vent, but the area they affect is small, and each added roof penetration increases the risk of water leaks. With flat roofs you cannot get away from that easily, but for peaked roofs I would recommend full-length ridge vents first, with attic fan only if supplemental cooling is needed - as in a desert environment, for instance.

Answered 7 years ago by LCD

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