Gas and Oil Home Heating Furnaces - Unusual noise /thermal expansion?

Hello,

This fall I had my forced air gas furnace cleaned. The fellow who did it increased the blower motor speed (he said two steps) to improve air flow through our the house. So far great, however now when the furnace runs it produces a very annoying clanging / rattling sound which seems to come from the top of the furnace body (sorry for my lack of a technical term here). I's the part above the burners if that helps! It did not produce this sound before the cleaning / speed adjustment. When I questioned the furnace repairman, he indicated that the sound was due to thermal expansion of the metal in the body of the furnace itself. To prove his point he had me run the furnace fan with the heat off. The clanging / rattling sound did not appear. Is there anything I can do myself to stop the sound while keeping the blower fan speed as it is now? I do think the higher speed is helping with more effective heating of the house.

The furnace model is: HEIL Ultimate II installed Oct. 97.

Thank you.

Chris

To determine at what speed the fan should run, one needs to know how much temperature difference there is between the supply & return also the amount of temperature rise the manufacturer specifies. Incorrectly set fan speeds (too high or low) can cause furnace damage.

Grady,

Thank you for the reply. Will an incorrect fan speed cause the noise?

Chris

Without hearing the noise first hand, I can't really say what causes it. I can tell your that having the fan speed set to yeild the proper temperature rise can make a big difference in how long the furnace will last & how well it will perform during it's lifetime.

Grady,

Thank you for your insight. I'm going to call a professional to come and have a look / listen.

Chris