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Posted by Twayne on January 17, 2008, 8:50 pm
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>>>> I have a oil forced air furnace and am wondering if the fan
>>>> control is set properly to go on and off with the best heat
>>>> recovery efficiency?? ?What do others recommend to set the limits
>>>> at. Currently I am at about 70 / 120 degrees for stop / start
>>>> limits. Also wondering what the average furnace fan uses for kw in
>>>> a day if on continuously. ?Thanks!
>>>> Steve
>>
>>> Consider any responses you get as WAGS because there are too many
>>> unknown variables in your post. ?It varies widely by brand, type,
>>> location of sensor, and several other things.
>>
>>> Right or wrong, here's how I did it. ?Feel the air coming from the
>>> registers. ?It should be warm when it comes on and still slightly
>>> warm when it goes off.
>>
>>> Check our furnace specs.
>>
>> the coller on and off the more efficent it is BUT, who wants a icey
>> draft?- Hide quoted text -
>>
>> - Show quoted text -
>
> My understanding (which could very well be way off base) is that the
> newer high-efficiency furnaces have heat exchangers that can not
> handle as much heat as the huge old clunkers could. Therefore the
> blower comes on way before the heat exchanger is at full temp to
> prevent damage. This results in an output of cooler air at the
> beginning and end of the heat cycle, with the blast at the beginning
> being the worst. Yes, the new models heat up faster and produce heat
> faster and therefore are more efficient, but you have to put up with
> that initial blast of cooler air.
>
> Is this just an urban myth?
IME, yes it is but I'm also far from any kind of expert on these
matters. What does occur to me is, there is more than one heat sensor
(actually if there's one, there's two) and sometimes 3 or more for the
newer systems to keep all the factors in balance. There can be several
stages to some of these systems. Any furnace designed to blow
noticeably cold air wouldn't gain much of a reputation. Cool for a few
seconds, as in evacuating the cool air from the ductwork is one thing
but purposely blowing cold air is quite another one.
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