I need a sound barrier around my furnace.

Freds · Apr 22, 2005

Good replies so far. A lot of better hotels use fiberglass insulation on inside walls for sound deadoning.

Is it the actual motor that's noisy or is it an air type sound, such as the air entering from the RA grill that's on the plenum? That air can put up quite a racket and is very common from some furnace installers not having enough RAs located throughout the house. It's good to have a grill on the RA plenum and pull a little basement air, but it may have been put there to compensate for not having enough upstairs. Completely cover it and see if the noise goes away, then either add more RA for the furnace or you and your buddy can put some 1/2" duct liner in the RA drop and plenum. A lot of commercial jobs have the RA lined to quiet the system down.

If it's a vibration type noise, see if the furnace is on isolation pads (usually cork and rubber today) and if there is a canvas connection on the RA and supply plenum.

You may have to do several things.

edit: I meant to add... You said your furnace was electric forced air, right, not gas? It uses electric coils (so basically it's an air handler)?

If it were gas, and NOT a high efficiency with its own combustion air inlet pipe, that would be another reason you need to keep the louver in your door/wall.

heehaw · Apr 22, 2005

we recently bought a new "super quiet" dish washer...the difference between it an the others we looked at, was some rubber looking mats glued on the outside of the unit..it almost looks like that rubbery stuff they put on roofs to preventice damming...but it makes a heck of a difference..you might try putting that sort of stuff all over the outside of the fan housing?
heehaw

BubbaJr · Apr 22, 2005

I have a geothermal furnace/ac in my basement that is really noisy (it has the compressor in it instead of outside like a regular heat pump setup). A friend in the HVAC business said I need to isolate the metal ductwork from the ceiling joists and that will cut down on the vibrations transmitted through the wood in the structure. He suggested taking out the metal ductwork next to the furnace (in both the intake and exhaust sides) and replace it with a section of fiberglass duct. Or you could replace a section in both with rubber or canvas boots. I'm going to try and quiet mine down this summer by building a room around it and unsulating the walls with fiber glass bats, then isolate the ductwork.
Good luck with yours. /forums/images/graemlins/grin.gif

thcri · Apr 23, 2005

( Unfortunately (for me), I need a louvered area in the bottom of the wall because there is a cold air return right at the bottom of the plenum where it enters the furnace.

Brian )

If you have an opening right next to the blower there isn't much you can do to get rid of the noise. If it was me and if you could I would get the return opening ducted away from the blower some. If the blower compartment is open there isn't much you can do other than slow the motor down, but be careful especially if you have air conditioning. All the other insulation may help some but not enough for anyone to notice.

murph

Junkman · Apr 23, 2005

Don't know if you can still buy Homosote, but it was great for noise remediation. It came in 4'x8'x1/2" and worked well. Two sheet, one over the other worked even better. Just put that up on the studs and then cover with sheet rock.

tawilson · Apr 23, 2005

Me tinknocker! Duct liner and flexible connections are great for quieting furnaces. As for the r/a opening, put a lined elbow on it with section of lined duct and that will suck up noise too.

BubbaJr · Apr 23, 2005

Don't know if you can still buy Homosote 

Homosote is still available at our local lumberyard. It's a pressed paper product that will absorb sound and vibrations (and also moisture), for those that are unfamiliar with it.

bczoom · Apr 24, 2005

Fred,

Yes, my furnace is ele. and basically an air handler.

The noise (when standing next to the furnace) is probably 60% motor and 40% air movement. There are no vibrations or otherwise. The motor sounds as it should and is only about 2 years old.

As for the RA at the bottom of the plenum, it does have a grill.
We (neighbor and I) put it on the bottom of the plenum when he put some hot air ducts in the basement. In general, I would say yes, there's probably an inadquate amount of RA's in the house. If I close the basement door most of the way (leave it about 1" open) the door will pull itself closed. I did remove the grill and cover the hole. There was no noticable difference in volume.

The framing around the furnace is complete. Unfortunately, I screwed up and put a door too close to this framing so I can't put homosote or otherwise on the outside of the framing. Actually, I don't know if I can get much on the inside either. The solution for around the furnace compartment is pretty much reduced to something between the studs.

When I put a ceiling in, that will hopefully reduce the air movement sound in the plenum.

Since the area is just a kids play room, I wasn't going to try very hard (read - spend lots of time/money) to get this real quiet. I can just turn off the fan.

Like Murph and others have mentioned, with that louvered door, there's probably not much I can do since it'll come out through there.

Today, I'm going to pull the polyisocyanurate and replace with fiberglass, hang the door and drywall everything. I'll let you know how it comes out.

Thanks everyone for the thoughts and information. I should have asked this a long time ago, prior to having the whole area framed, and the rest of the room finished (so I could move doors or whatever to get more space for insulation material).

Brian

bebster · Apr 24, 2005

Maybe put the fan on a timer -- like they have for things like saunas. Turn it up to 60 minutes, and the fan will stay off for that amount of time. If the kids don't like the noise they can shut it off for up to an hour. But when they leave you'll know it will come back on within the hour. Most timer switches turn things on, so this might require some special (inverted) wiring of some kind.

Freds · Apr 24, 2005

When you covered the grill opening it probably started pulling air through the cabinet, but it sounds like you know it's a RA problem anyway, especially if it's pulling doors closed. /forums/images/graemlins/shocked.gif
I'd get your friend to give you a hand and add a couple returns into the existing joist panning in the same rooms as the heat ducts. If you have a drop ceiling it will be just a little harder to frame them in, but it can be done, or you could cheat and replace a tile with a piece of egg crate and then cut a hole in a larger sized RA duct that you have access to and that air can find its way to. Technically any electrical wires should be in conduit if you do this, but no one checks a house and offices used to be done this way for years. If you have a plaster ceiling... I hope you remember exactly where the ducts are above it /forums/images/graemlins/blush.gif
Depending on the size of the RA drop and elbow I would also line these with 1/2" duct liner. You don't want to choke them down too much, but if you can get rid of close to 40% of the air noise, it will be noticably quieter.