[Colobill]

I have a carrier gas furnace. When the burners ignite there is rattle type noise. It continues until the blower comes on. What could cause this?

 

[hvac benny]

What model? Mid or high efficient?

 

[Colobill]

Not sure

I'm pretty sure that it's mid efficiency.

 

[Doc Holliday]

I'm pretty sure that it's mid efficiency.

Mid efficiency as in 80%? If you retreive the model number (and brand) from the data plate (possibly a sticker) from the furnace then we can assist you much better than only assuming.

The sticker will most likely be on the inside of the furnace door or in that compartment of the conrol board area when you remove the door. Sometimes the sticker is face down on the underneath of the top of the furnace so you might have to literally look up in there.

Regarldess, if this is an older furnace then something is more than likely loose as rattling is not a common occurance from the factory but one that occurs over time, like a loose muffler on a car that's hit too many bumps in the road over time and use.

I'm guessing your unit is older and not a brand new install...?

 

[Colobill]

Yes it's older

It was installed 11 years ago when the house was built. I'm almost positive it's an 80%. Why would it just rattle when the burners are on and the blower is off. Could it be a flapper in the flue? If it is, how is the best way to check? On the roof?

 

[Doc Holliday]

It was installed 11 years ago when the house was built. I'm almost positive it's an 80%. Why would it just rattle when the burners are on and the blower is off. Could it be a flapper in the flue? If it is, how is the best way to check? On the roof?

The blower is on if the burners are on. In heating mode the blower is set on low speed so you might not hear it but it is on or it should be.

There is a draft inducer motor as well which turns on first to prove that there is negative pressure to be able to pull the flames through the heat exchanger so another moving part that turns before the furnace produces flames. I doubt you have a flap but you do have a cap up on the roof on top of the vent pipe. The exhaust vent pipe might be loose for all I know from behind my computer. It could be a loose metal strap on the vent pipe. Without me being there in front of the furnace or opening up the unit it is hard to say what is going on.

What you can do is remove the service panel of the furnace, go down to your t-stat and put the stat on heat as normal and go back to the furnace and press in and hold the door switch. You can use a piece of tape to hold that switch in. Then listen and locate where this noise is coming from and pay attention to the blower motor and the draft inducer (exhaust) motor coming on BEFORE the burners are given any gas.

 

[Doc Holliday]

My fault, I got that backwards. The blower comes on after the heat exchanger is warmed up and stays on for a short time after the burners are off to push out residual heat.

 

[Doc Holliday]

http://www.youtube.com/watch?v=oIChQ0LtENQ

http://www.youtube.com/watch?v=bPVviJDEB24&feature=related

 

[Colobill]

Thanks

Thanks alot. I'll try to find where the noise is coming from. We hear it in a room above the furnace. I'll check everything you suggested. I appreciate your help "from behind the computer."