Loud Heat and AC

[beetlespin]

Upstairs unit is very quiet, you can hardly hear it. The unit is in the attic so all round flexable ductwork is used to the vents and returns.

Downstairs is very loud. Turn up the TV if you are watching it loud. All the ductwork and returns are square/rectangle sheet metal. What makes things worse is the downstairs furnace is in the basement directly below the bedroom so the return in there is exceptionally loud.

Is there anything that can be done to quiet the downstairs short of removing all the ductwork and replacing with the round, insulated stuff?

 

[Milton Shaw]

I had a noisy unit that the air intake was in the side of the unit and then directly into the room with a filter grill. I built a return duct out of hard fiberglass duct with a 90 degree turn in it. This quietened the unit down a lot. You might be able to do something similar just on the return side and get it to acceptable noise levels.

 

[LS6 Tommy]

Is it air noise, or is the unit mechanically noisy?

Tommy

 

[beetlespin]

Is it air noise, or is the unit mechanically noisy?

Tommy

Air

Already have the blower set as low as it will go.

 

[mrpizza]

If its air noise the duct is poorly designed.

 

[Jim greengo]

Have you checked filter?

 

[dcg9381]

When I've seen this, it's a poorly sized return. Is there a "source" of the noise or is it the whole darn thing?

 

[beetlespin]

The returns closer to the furnace are louder of course. There are four returns throughout the house. One bedroom (medium), one family room (medium), one in den (small), one in dining room (small).

The only solution I think would be is to replace with flexable ductwork like what is used in for the upstairs unit.

 

[Jim greengo]

I wouldn't normally consider flex duct work as a cure for anything,other than maybe a lack of sheetmetal working skills.

 

[LS6 Tommy]

If its air noise the duct is poorly designed.

X2. Or the unit is oversized.

Tommy

 

[LS6 Tommy]

The returns closer to the furnace are louder of course. There are four returns throughout the house. One bedroom (medium), one family room (medium), one in den (small), one in dining room (small).

The only solution I think would be is to replace with flexable ductwork like what is used in for the upstairs unit.

I wouldn't normally consider flex duct work as a cure for anything,other than maybe a lack of sheetmetal working skills.

Flex will increase the static pressure and the air noise will increase. Flex is not for runs of more than about 10'. When you see long runs or an "octopus", it's because the installer was unskilled, lazy, gave a low-ball price or any combination out of the three.

Tommy

 

[larry4406]

I’ve had some houses where a black fibrous mat insulation (1/2” thick sheet?”) has been applied to the inner surface of the return for sound deadening.

 

[beetlespin]

I’ve had some houses where a black fibrous mat insulation (1/2” thick sheet?”) has been applied to the inner surface of the return for sound deadening.

Was this just close to ther furnace or the entire run?

 

[larry4406]

Was this just close to ther furnace or the entire run?

The rectangular metal cold air return had sound liner from the return grill box in the room all the way back to the filter box at the furnace. Sound liner on inside of return duct obviously.

Recently had a house where the basement cold air return was direct metal duct connected with a 10" round off the return box to the grille 3' away. Fan noise was hideous and room noise deafening. They removed the metal duct section, connected a flex line off the top of the return box (vs the prior in-line, so 90 degree change), increased the length of the line from 3' to about 10' and the noise was gone.