Furnace is making a whistling/humming sound

JayBird

Greetings all,

I have a filter installed at the bottom of my furnace where the blower fan is located in addition to the normal return filter upstairs.

I've been noticing a whistling sound when the blower is on and when I slide the filter thats near the fan out, the sounds stops. I slide the filter back and the sound returns.

Does this sound indicate my fan may be starving for air? I've been told its just filter noise but I'm not sure. Any thoughts?

Thanks.

hvac122

It sounds like you are starving for return air. Why the 2 filters? What type of filters? Some filters will restrict air more than others. Some restrict way to much.

JayBird

Yes I am starving for return air, My burner was short cycling and the HVAC company closed the hole near the furnace and added it down bottom near the fan. The burner was reaching high limit (too hot) from too small of a return duct. Former homeowner added a second return but wasn't helping. Since the one was added down bottom near the fan the short cycling has stopped. It was a cheap fix, but maybe not the best thing to do. The hole is about 14 x 16 roughly, maybe a tad larger. I wonder if it needs to be bigger??

I use the "mid grade" filters. A little better than the fiberglass but not like the expensive 3M ones

hvac122

If I am understanding right the return air was added very near the furnace? If it was added to close it could cause your furnace or water heater to backdraft which is very dangerous. It sounds like you need a pro to size things properly and to do some duct changes so you don't starve the furnace. This will cause premature failure of your furnace and A/C. It is critical to get enough return to the furnace and many are way undersized.

JayBird

A pro did come out and determined the duct is a little too small. Hot air was having trouble escaping causing the burner to reach high limit and cycle on and off. So yes, an intake was added at the base of the furnace next to the fan and that helped it get the proper air flow and the burner stopped short cycling. Whether it was the best thing to do? I'm not sure but the pros recommended it and they installed it. All he did was cut a square hole in the base of the furnace on the other side, opposite where the main return comes in and I added a filter to it.

Any comment on the slight whistling/humming sound I'm hearing? Is it something I should be worried about? Some say its just filter noise.

hvac122

If this is a gas furnace then that is a really bad place to add a return. It would be against code here. If its electric it would be OK. The whistling more than likely means that you are still short on return air and this needs to be fixed. You don't what your furnace to be running at the top of the temperature rise as it will shorten the life. I would call someone that understands ductwork to evaulate your system and give you some options for repair. If its whistling in heating its really going to have problems in cooling as the fan sill be in high speed, if not already.

JayBird

Its an oil furnace...... The company that came out is a well known company thats been in business for years. I would hope the tech would know better then to install something wrong but then again I'm sure it happens daily. It appears the furnace is getting better air flow because its not short cycling anymore.......thats s plus.

bigMikeB

A return close to the furnace (oil or gas) can pull in flue gas as well as make the burneer fire imporperly. And is against code many places as H122 stated. Have it piped to another location by another contractor.
A/C operation will just compound the situation and freeeze the coil.