Having never owned a home before, and certainly never having had to service
a furnace before, what signs should I look for that my furnace is past the
point of serviceability and simply needs replacement? That giant cloud of
gas that forms in the basement shortly before detonation is an obvious one -
Some facts about my situation, but I guess I'm more interested about the
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
All of this seems normal, but I'm wondering why it takes so long for the gas
to ignite (I assume the tick, tick, tick is the sound of the igniter
sparking) and whether or not this is one of those things where you just
close you eyes and walk away.
I keep my filters clean and change it regularly.
At what point would I KNOW that this furnace is DOA and shouldn't be
repaired? At what point should I just call in the HVAC dude and have
him/her/it repair it?
You don't need a new furnace until the heat chamber is cracked and emits
carbon monoxide fumes into the air stream. It sounds like the ignition is
trying several times to fire the gas before it finally does. Maybe you
could take the cover off the ignition chamber and watch it while it is
working. The gas control first turns on the gas valve and ignition. If the
ignitor does not fire the gas, the gas valve will shut down. This is a
safety device. Some systems have a purge fan the starts before all else
does, and this has an air flow switch to insure that there is air flowing
through the firing stream before the gas valve will open and ignition
begins. If you have a purge fan, make sure that this is running when it is
supposed to. Also, check to make sure that whatever is supposed to "see"
the flame does so. Maybe an electric eye needs cleaning, or a thermocouple
needs to be readjusted.
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
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.
It always a good idea to have your furnace serviced for preventive
maintence BEFORE it breaks on a cold nite!
way cheaper and a clean serviced furnace is more efficent and safer.
Waiting till something breaks just isnt a good idea:(
An annual service call to inspect the unit is well worth the money.
You are paying for a recommendation and you should ask any questions
that you have before they leave regarding noises that you are hearing
or life expectancy. Rust in the heat exchanger is something to be
Gas furnaces need ANNUAL inspections to determine when the heat
Heat Exchangers will rust for a number of years. Rust, by itself,is not
bad. The bad part comes when the rust goes all the way thru the heat
exchanger walls and now you are distributing combustion by-products in
the air you breathe
This rust is a common HVAC ploy to get you to replace the furnace LONG
before you need to.
Not true -- use one every time we cook on the stove. My furnace's sound is
much different -- like I said in the post it's a loud click that seems to be
coming from the gas valve (as some of the clicks correspond with the pilot
or burners coming on, etc). Perhaps the OP's sound is different than mine,
if he really means a 'tick'.
Probably great advice, but I don't personally heed it. Spending $100-$150
to have someone vacuum my furnace (I did it once) seems a bit much I do
agree that it's a good idea every few years. I just wish the person who
would be telling me it's time to replace the unit wouldn't be the same
person who has a vested interest in me purchasing one.
We do have multiple CO alarms in the house. Worst-case scenareo -- the unit
goes in the middle of a cold snap in February and I'll be without heat for a
few days and have to make a split-second purchasing decision. But we have
several backup heaters we can use and get buy if this is the case...
I do preventive maintence on machines that arent furnaces. To a
observer it might appear I JUST clean it.
but what you really get for your bucks is a experienced tech who knows
what fails and checks for it.
sometimes that knowledge prevents a much larger and expensive failure
at a later perhaps really inconvenient time.
like 1am on christmas eve, or worse spoot a small gas leak before its a
I dont have my furnace serviced yearly either, but every few years. its
more than looking for a bad heat exchanger
Where they hell do you live that annual servicing costs over $100?
I'm in Chicagland and $80 is the norm.
It's a lot more than vacuuming out the furnace if you've got an outfit
that knows what they're doing.
Not true, I have used one, not mine of course but it certainly didn't do
that. I do apologize, I was mixing in some dry humor in with my comments.
My water heater behaves exactly the same way and I understand that it's
perfectly normal. It does sound ominious to the untrained ears though.
I purchased this house in March, just long enough for it to use the furnce
in the early spring a few times. The real estate agent insisted on an
inspection and cleaning of the unit before the sale, although had I caught
this before sale I would have raised hell. The "maintenance" guy cleaned
the furnace by flipping the filter around so that you couldn't see the dust.
So obviously the seller was a trifle dishonest about the furnace condition.
Judging by the quality of the electrical work in the basement, also totally
inept when it comes to home maintanence.
So I'm gonna have it inspected thoroughly in the coming months, and will
also install the CO detectors as soon as I get some money - dumped
everything I had to pay off card debt.
That's pretty darned old. Well past the age for which you should be
seeking annual cleaning/inspection/servicing. They should check for
CO emission, clean the burners, do a visual inspction of the heat
exchanger, and perhaps other tests on the HX if visual and CO tests
warrant further investigation.
Just ask the question about the long duration of ignitor ticks prior
to turnon during the annual servicing you should already be doing.
And get yourself some Kiddie Nighthawk plug in CO detectors for your
bedrooms if you don't have em already. No way I'd be without em with
a furnace of that age.
Best Regards, --
At 25 years your furnace is probably beyond it's design life but you can
probably get more years with proper maintenance. There are lots of rules of
thumb such as if it will cost more than $600 to repair it then replace, etc.
IMHO, One thing to look at -- if you plan to live there for awhile -- is if
it would make good economic sense to replace your furnace with a high
efficinecy furnace system. With gas and electricity prices going only up
the pay back period is going to be pretty short in most locals and the high
efficiency system will help moderate your future bill totals. Even if you
don't plan to stay in that house for long a high efficiency system will
likely help your resale of the house.
Just my 2 cents -- good luck.
For me, the incremental cost difference between a 60% efficient gas
furnace (likely figure for 25 yr old model) and a 80% efficient model is
With 60% I pay a grand total of $250 for the YEAR. So 80% reduces that
to $220. $30 into $800 is longer than the expected life of the furnace!!!!!
Oh bring back 60% for those of us who almost don't need heat!!!!
10. Your ice cube trays freeze faster on the kitchen counter.
9. The banging noises from the cellar keep you awake.
8. Mice wear sweatters and mittens when they run across your living
7. Your children go outside to warm up.
6. Your utility provider sends you gold plated thank you letters at
5. Your utility meter vibrates so much for use that it falls off the
4. Flocks of migrating birds gather and fly in circles in the warm air
over the top of your chimney.
3. Your house smells like furnace exhaust.
2. Santa Claus leaves a nasty note that he can't drink the frozen milk
next to the rock hard cookies.
1. You wife insists.
Christopher A. Young
You can\'t shout down a troll.
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