On Jan 14, 12:28*pm, "Iowna Uass" wrote:
"Monty" wrote in message

...

I have a home furnace with a lennox control. It's about 30 years old.

The problem is that, when the room temperature is cold, like 55
degrees F, and the control is set to 70 degrees F, the furnace only
runs for about a minute, shuts off for maybe 3 to 6 minutes, then runs
for another 1 minute. I'd rather the furnace ran until the temperature
reached 70, then turned off and turned on again when the temperature
dropped to, say 67.

There seems to be a way of setting things when I take the cover off
the control. But how do I use it? Is it possible to get the controller
to work as I like?

Sounds like a thermostat issue.
Is the thermostat the same age as the furnace?
It could also be the location of the thermostat. If it is in line with a
vent, it may be prematurely warming.

Are you sure it's the entire furnace shutting off, ie the burner and
the blower?
I would bet that what's really going on is that the burner remains
lit, but the
blower is what's going on and off. That is perfectly normal under
those
conditions. My furnace does it too. Here's what's happening:

The house is very cold, 55. You turn up the heat to 70. The
thermostat calls
for heat, the burner lights. When the temp inside the furnace plenum
gets
hot enough, which is a couple mins, it closes a temperature switch
that turns the blower on. Normally, the blower would then continue
to run until the burner shuts off. The blower continues to run,
recovering the remaining heat, until the temp decreases again, at
which point the blower turns off after a couple mins. However, you
have very cold incoming air. So cold that
when the blower starts, the air flow drops the temp in the plenum
below the
shutoff temp for the blower. The blower stops and then the air
begins to heat
again, repeating the cycle. So, you get the blower running for a min
or two, stopping, repeating. That continues until the air in the
house is warm
enough so that it won't drop below the blower turn off temp anymore.

A simple solution to this is to just turn the blower to run
coninuously via the
fan switch on the thermostat. You do that whenever the house is
unusually cold and then turn it off again when it reaches a more
moderate temp, eg 60.

And if the furnace is 30 years old, suggest you look into replacing
it. That furnace was designed to 80% eff, at best, when it was
new. Today it may
be running at 75%. You can get a 95%eff furnace at a reasonable
price and there are substantial rebates available from loca utilities,
state, etc. The best deal was last year when you had that, plus a
30% Fed tax credit too.