"Tim Fischer" wrote in message
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"Eigenvector" wrote in message
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My particular gas furnace is approx 25 years old. It seems to heat just
fine, however its startup behavior seems weird to me.

basically, tick, tick, tick, tick, .......(about 10 seconds later) then
ignition, burners doing their stuff for about 10 seconds, blower comes on
and air starts moving. Burners shut down blower shuts down 10 to 15
seconds later.

That sounds exactly the same as my Lennox of the same era (1980). Upon
startup, it makes about 8 different very loud clicks. On my particular
model, there is no standing pilot -- instead a pilot is lit electrically,
then lights the furnace. One of the clicks is the gas for the pilot
turning on. If you're close and watching, you'll also hear a 'zzzz' sound
of the lighter. Once the unit senses the pilot is on, it fires up the
main burners (click!). There are several other clicks in this sequence
that I have no idea what's going on, but it's been doing that for the 3+
years I've owned the place and seems to be normal (at least it hasn't
broken down yet).

Pretty much all gas furnaces run the burners for awhile, then when it gets
up-to-temp, the blower kicks in. If it didn't, you'd get cold air blowing
out your vents. Conversely, when the thermostat quits calling for heat,
this kills the burners, but the blower keeps going for awhile longer
(either a time delay, or until the internal temp falls below a threshold,
depending on the model).

So yours sounds normal to me. Everntually I want to replace ours due to
effiiciency (it's about 75% efficient internally, probably much worse
overall) and we're in MN where it get's a good amount of hours running
every year so kicking up the efficiency would pay off sooner or later.
But for now I'm making do with the old one...

Like you, the clicks disturbed me when I first moved here. Our old house
had a furnace with a standing pilot and it was all but silent other than
the blower motor...

-Tim
That's certainly reassuring information. It just sounds so ominous, tick,
tick, tick, I keep waiting to hear the KABOOM as the gas builds up to a
critical level. So I guess as long as my furnace isn't venting CO to the
air I should be okay. If it does break down, I think that will be the point
at which I give in and go for an efficient modern one.