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RE: Furnace Settings

To: <shop-talk@autox.team.net>
Subject: RE: Furnace Settings
From: "Randall" <tr3driver@comcast.net>
Date: Wed, 14 Dec 2005 08:54:48 -0800
> Have you ever checked or adjusted the fan and limit switches in
> it?  I was about 14 years old when I saw some discussion on Bob
> Villa's show about it.  My parents about s**t when the gas bill
> dropped by $600 in one year  ;)  That was like 1980ish, also.
>
> Basically, the thermostat controls the burner and the limit switches
> control the blower based on the internal temperature.  You want about
> 90dF low and 110 high.  It lets the burner pre-heat so you don't get
> a cold blast, and runs the fan after the burner has shut off so you
> don't waste heat up the chimney.

I've not checked it with a thermometer, but feeling the air from a register
seems to confirm that the fan switch is pretty close.  When the fan starts,
after the cool air in the ducts is forced out, the first air is only a little
warm.  It gets much warmer over the next 20 or 30 seconds as the bonnet reaches
full operating temperature.  Then when the burner shuts down, the fan continues
to run until the air coming out is only slightly warm.

Note that there should also be a limit switch that kills the burner if the
bonnet overheats (eg if the fan fails).  Mine is fixed at 170F.

Randall




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