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
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.
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.
Thanks. I didn't mention in my OP that I also have a wood stove
ducted into my furnace hot air plenum. The wood stove has a blower
that pushes hot air into the plenum. The delema I've had with this is
that when the furnace fan runs, it nearly overpowers the wood stove
blower such that I need to really maintain a pretty hot wood fire to
keep the air warm coming out of the registers. I have tried to power
up the wood stove fan but then it seems to take the heat away from the
wood stove too much and it becomes more of a cycling problem. Either
I end up having to run the furnace fan continuously or shut it off
completely. If I run the furnace fan continuously, usually in the
coldest weather (below zero degrees F.), The house will stay fairly
warm but in warmer weather above zero degrees F the house will get way
too warm and I have to shut off the furnace fan completely. Thus its
a continuous on or off cycle with the furnace fan switch. I was
wondering if I could adjust the furnace fan limit switches so I
wouldn't have to be shutting the furnace fan off/on so much. The oil
furnace is a late 1970's model so I don't think the hotter plenum
temps adversely affect the plenum when the furnace fan isn't running.
Also, I wouldn't want to make any drastic changes to the oil furnace
controls so it will run properly when we are not at home and no fire
in the wood stove. Any ideas on what I could do to make this system
work better would be helpful. Thanks again!
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