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Heating & Air Conditioning

Noisy cold air return

16 years ago

It is a whistler - not terrible but slightly annoying. When we moved in, we never fired up the old furnace because of manifold cracks, so I don't know if it was also noisy. Before installing the new furnace, the HVAC guy said the ducting should be fine. A lower fan speed works, but it takes forever to heat the house.

The duct opens from below into a larger box. For some reason, extra drywall was removed from the top of the hole, which is roughly 22-1/2" x 4-3/4", and an extra 4 or 5 inches from the sides of the hole exposing some 2x4s framing the box. The vent cover (31-1/4" x 7-1/4") is about 3/4" deep and mounted against the drywall.

Because the vent is much larger than the hole, I suspect the whistling is caused by air coming through the louvers at the sides that are doing nothing more than covering exposed 2x4s. This air has to turn 90 degrees and travel 4 or 5 inches through a space only about 1-1/2" deep before entering the duct box. I can easily open the hole maybe another 3/4" at one side (probably not much help?), but more than this in either dimension would involve cutting into some 2x4s.

Would it help to get a smaller vent, closer to the size of the hole - replacing some of the missing drywall? Would a wooden vent help the noise? Maybe an egg crate vent with bigger holes? Or all of these? Or none of these?

Any and all suggestions are greatly appreciated.

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You don't mention where the furnace and duct is located but being in a cold basement or especially an attic where cold air naturally falls, you could have some migration. In addition you may have a fresh air make up duct that is letting even colder outdoor air into the return duct from the outside. This you should check, some are wide open to the outdoor intake duct and can have a manual damper while some have a motorized damper that should be controlled with blower operation. Make sure the return duct doesn't have any leaks and check connections and cabinet for leaks and cracks for air to infiltrate. Most furnaces have lousy gaskets on the blower doors and do not seal well. You might try taping the seams with a good aluminum duct tape. The problem with covering the return is having the furnace turn on without removing the cover could result in unit control and/or blower damage, including overheating and fire.
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An HRV is required by code on all new homes in the US. This is for ventilation air. I have one, works great. See link. Costs less than solar. An ERV will recover moisture too as well as heat. If you do not have a sealed combustion furnace (2 pipes, intake & exhaust) and have a gravity furnace, a combustion air duct is required to supply air for the furnace burner. You can create a "cold air trap" by placing a box on the floor and dropping the combustion air duct into the box (No top). You may also be able to connect the Combustion air duct to the return duct to the furnace (Check code). Attach duct at least 10'0" away from the furnace soas not to crack the heat exchanger with the cold air. Connecting to the return also creates a slight positive pressure in the house reducing infiltration/drafts. Stay Warm! Dan Martyn Here is a link that might be useful: Broan HRV
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It would appear that somehow your fireplace insert is tied in with you regular heating system. You will have to go do a little crawling around and tracing of the duct work and block it off where it needs to be. You have to be careful though to make sure it doesn't affect the rest of your system. If you're not comfortable doing it or not sure you're probably better off hiring someone who will understand what they're looking at in your house. It's pretty difficult to see into your basement from here.
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Thank you for your thoughts renovator and sombeuil! As far as winter and summer settings I see no way to adjust the vents--they are apparently always open,both of them from the room's vantage points at least! Poor man's A/C sounds like something that might be of benefit to keep but---if I had to choose, at least for that room, I'd gladly give it up to have the new passageway from the living room to the new dining room (former master bedroom and powder room). The other issue is that in the 50's it was no big deal (apparently) to get up off the sofa, in front of company etc. and walk into a hallway into the bathroom--a straight view of that doorway from the living room. If we could open up the new way, we'd build in a corner cabinet in the present opening which is on an angle with 3 bedrooms (and living room) converging in front of the bathroom! Some more food for thought I guess--thank you again!! janice
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