I’ll start out by saying my furnace works fine, and this noise is not new. I am more just curious than worried. Here are the symptoms and what I know:
The noise happens just prior to the burners being lit.
It sounds metallic, like metal hitting metal maybe?
It is not a noise from gas exploding, you can clearly hear the gas light normally about 1 second or so after the noise.
It’s also not the fan, after the burners go for about 30 seconds to a minute, the fan kicks on, and then the house heats like normal.
Because the fan isn’t going yet, I can verify it is not the ducting making the noise, from a pressure difference.
So, my theory is that maybe it’s the solenoid or whatever component turns on the gas flow to the burners prior to lighting. What would make it bang like that though? The furnace is original to the house from '87. You can hear it upstairs, and when you are downstairs and it does this, it straight up startles me!
Let me know your thoughts, and if it’s anything that I should look to fix/replace.
Do non-HE heaters have these draft blowers? And if so, would it sound like a hammer hitting an anvil once, and then stop until next time the furnace kicks on?
Yes some old furnaces have the motors, my furnace does and it’s only an 80%er from the late 80’s. All high efficient furnaces have induced draft motors/combustion motors.
They can make a grinding noise usually when they have bad bearing or are getting old, but I don’t think it should sound like an hammer hitting an anvil.
why don’t you take a picture or even better post a vid and I can see what I think.
Here are a few photos of the furnace. Like I said above, it’s from '87, and has a traditional flue, non-power vent.
And here is a link to a short video of the noise. I had my wife turn the furnace on upstairs so that I could record it. Don’t mind me jumping when it makes the noise, it still startled me…
Sounds like its the ignition module, it has spark ignition, that sound is it zapping while sparking to ignite the pilot. Once it senses pilot it stops sparking and then opens the main gas valve.
The ignition module is probably getting old and buzzing loud, but again this is just from watching the video, i could be wrong since I’m not standing in front of the furnace.
pull off the top panel and watch it again, watch it light te pilot first and then the noise stops, then it opens the main gas valve and burners are lit.
His furnace is working though, but you’re right there are cheap 80% furnaces. Once I do mine I’ll go with a 95% one though.
its probably just a relay in the ignition module that’s old and buzzing. I wouldn’t replace it unless it broke and was an expensive repair or unless they upgrade to a 95% furnace. Going too big of a furnace can cause air flow issues if the duct work isn’t changed, everything needs to match. I know you said going smaller, which usually is done when they go to a higher efficient furnace because the BTU output increases when efficencey is improved.
That is correct. We did have trouble with the duct work when we put in the 80 percent furnace, we had to build a larger cold air return.
I did not go with a 95 percent furnace, because we were using the chimney to vent, and didn’t want to install the PVC outside of the house, plus it was a rental property and I wanted it done as cheap as possible.
