From: John De Armond
Subject: Re: Removing excess heat from house
Date: Sat, 25 Aug 2007 05:49:48 -0400
On Sat, 25 Aug 2007 02:52:28 GMT, "JERD" <jedunk@REMOVEbigpond.net.au> wrote:
>With summer fast approaching down-under I am thinking of installing a large
>blower to remove excess heat from my house.
>Is it better to remove this heat (via a large fan ducted to the outside)
>from the house living area or from the roof cavity?
If the outside temperature is tolerable/comfortable then a whole-house attic fan is
da cherries. This large low speed fan installs in the ceiling and pulls air from the
house and into the attic. It thus ventilates both the house and the attic. I'd not
have a house without one of these. The volume of air moved is large enough that a
cool breeze can be felt in any room.
I prefer the belt-driven kind over the direct drive. The belt drive is generally
quieter, the motor more rugged and it opens the option of a DC variable speed motor.
That's what I have on mine. A more modern but more expensive option is a small three
phase AC motor and an electronic variable speed drive. Hard to beat a good permanent
magnet DC motor and inexpensive SCR speed control.
If AC is necessary, venting the attic alone will help. Self-powered turbine vents -
those round rotating balls you see on many building roofs - work amazingly well and
require no power. If you don't like the look of those things then eave vents and one
or more intake fans located low on the eave wall will do the same job at the expense
of some power.
I strongly recommend against electric roof vents. A few years ago when I was
researching a magazine article on house fire, I interviewed several senior fire
officials in and around the Atlanta area. They all said the same thing, that powered
roof vents were perhaps the major source of non-accident house fires. Seems that the
extreme summer heat bakes out the bearing grease, the motor seizes, the thermal
protection doesn't and the motor catches fire. If you require a powered fan, put it
low down where the air is cooler and have it sucking in cool air rather than blowing
Another thing that is very effective is aluminum foil infrared reflective barriers in
the attic. This is usually paper-backed foil that is tacked either over the roof
rafters or over the ceiling joists or both. It reflects back the radiant heat coming
from the roof. Some folks try to do it the easy way and just stuff the foil between
the roof rafters. This causes the reflected heat to become trapped and roof damage
results. Tacked across the rafters, it leaves convection spaces between the roof and
foil for cooling air to circulate. This works best when the house has apex vents
that let the hot cooling air flow directly outside.