From: grande@cbnewsd.cb.att.com (brad.l.grande)
Newsgroups: misc.consumers.house
Subject: Re: Whole-House Fan Choice is Not a Breeze
Date: 8 Sep 92 18:08:18 GMT
Distribution: na
Organization: AT&T

In article <f_nn=+b.greg@netcom.com>, greg@netcom.com (Greg Bullough) writes:
> In article <Bu2tCK.DyC.2@cs.cmu.edu> goddard+@cs.cmu.edu (Nigel Goddard) writes:
> >
> >The function of the fan in terms of cooling are:
> >	1. To replace hot internal air with cool external air.
> >	2. To provide a breeze which is cooling in itself (skin chill).
>  
>   3. To pump air which is cooler than the ambient attic temperature
>      into the attic, thus improving house cooling.
>  
> In my experience (3) is very important. My whole house fan has
> cut the time the gable fan runs by a great deal.

An article in Consumer Reports on house cooling a couple of years ago discussed
item 3 above and suggested that if you had sufficient insulation (don't remember
the exact amount but I do recall that it was what you would find in any post
1970's energy crisis built home) that heat infiltration through the ceiling
was minimal and the whole house fan would not have an effect on this aspect.
The article went on to suggest that if you did not have sufficient insulation
that it would be cheaper to add insulation than to add a whole house fan.  It
also said that power attic ventilators were not effective if the insullation
was adequate and therefore they were not an effective investment.
> 
> >
> >Your CFM requirements depend on how fast you want to do 1 and how
> >much of the house you want 2 to be operative in.  

Other posts have discussed the CFM trade offs.  The issues boil down to how
fast you want to exchange the air and how fast you want the air to move past
you.  Once you exchange the hotter inside air for the cooler external air,
on the order of a minute or more in real time from the time you first turn
the fan on, the house won't cool any faster than the outside air will during
the night, which is on the order of hours.  Therefore, a smaller fan will not
have a noticable effect on the rate at which the house cools and tracks the
external temperature.  As far as velocity of air and how that feels, that is
very easily controlled by opening and or closing windows and doors of the
rooms that you want/don't want to cool.  After a few minutes of exchanging
all the air, just close the doors to the rooms that you aren't going to use
that night.  When we retire for the night, we only leave the two occupied
bedrooms and the kitchen windows open and get a tremendous breeze through them.

A downside of a whole house fan is that your house will become more dusty
as the fan pulls dust with the air into the house.  Keeping unused rooms
closed after initial air exchange will help minimize this, but you will find
more dust in the house and stuck to the screens.

You have to be careful with a whole house fan in that if you do not have
sufficient air input, it could suck air in the furance and water heater
flues risking either extingquishing pilots or sucking CO into the house.  We
have experienced fire place oders in the house when we don't have enough
windows and doors open.

We have a 30" Emerson dirct drive (Reg $230 we got on sale for $129) and
use it to cool 2100sq.ft.  The manufacturer recommends a 36incher, but we
get all of the benefits and saved over $200.  It takes less than 2 minutes to
exhange all the air and you can definitly feel the air movement.

As far as using the fan to exhaust new construction chemical odors, that is
a very good idea.  Remember that the temp inside the house lags the outside
by several hours.  So turning on the fan during the day may just make your
house hotter sooner.  You will need to wait until sundown to effectively
use it anyway, so you will get the benefit of chemical exchange anyway.

Good Luck!


Brad Grande	WB0OYX
Another bike riding beer brewing kite flying amateur radio operator who
	still likes CD's!

AT&T Bell Labs
Naperville Illinausea
PLEASE SEND RESPONSES TO:	grande@iwtil.att.com
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(708)-979-7853
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