Sound deadening

[bobbobwhite]

I have a furnace room that is in the middle of the house and the noise from the motor and fan is pretty loud. What is the best sound deadening material I can use inside the room to reduce this noise?

I have been told to add another layer of drywall inside the room, or use a fiberous sound deadening board . How about foam panels, as this would be a lot easier to install? However, sound deadening is more important than ease of installation to me.

What does the best job of deadening this kind of sound? Thanks.

[jadnashua]

Some of the noise would be telegraphed through the ductwork, so nothing you do short of changes would affect that.

One thing often specified but rarely implemented in the ductwork is a flexible coupling between the furnace itself and the remainder of the ductwork. If the ducts are solid, screwed to the top of the furnace, cutting out a section and inserting a properly designed flexible (special coated cloth) section will stop vibrational transmission of sound through the metal.

A second layer of drywall may be the safest. You shouldn't put just some foam panels up, as this room should be fire resistant (and not give off noxious gasses if it did catch fire).

There are a couple of methods to minimize noise transmission through the walls. If you have enough depth, adding another wall so the studs are independent and can't transmit sound through, then insulating it works. Normally, they'd use a 2x6, then put 2x4 studs set so they alternate at the proper spacing, with normal 16" , and attach the drywall to each side. This breaks the transmission path from one side of the stud to the other since they are now separate. The top and bottom plates are the same, though.

There is some special non-hardening, noise damping caulk that can be used to adhere a second layer of drywall to the first. The second layer helps a lot, and the rubbery caulk decouples both layers.

Another possibilty is to use special clips to separate a second layer of drywall, and then anchor it to that creating a second layer.

Seal all joints well.

First thing I'd do, though, is put in the proper isolator in the output duct and see if that's enough.

[Southern Man]

Definitely the duct connections as suggested. Then insulate the walls with unfaced fiberglass batt, then a layer of drywall screwed directly to the studs, mud and seal the joits and corners. If that's not enough, add a second layer of drywall, but first use a "Z" strip 24" on center horizontally, then fasten the drywall to it. The Z strip is 20 or 22 gage steel, and available at a commercial building supply outlet.

Here's a better explanation (pdf file) http://www.jm.com/insulation/buildin...und_bid002.pdf

[Cass]

Rock Wool, in place of fiberglass insulstion, is one of the best sound deadners you can get.

[bobbobwhite]

... there is not adequate room to work in this noisy furnace room, as the furnace is 6" from the drywall-faced side walls. The furnace is accessed in front by an insulated door but is only about 10" from the door. The furnace is blocked in the rear by a water heater; only about 1' between them. Very tight everywhere. I could slide soundproofing panels used into place and maybe tape them together, or back glue them on to existing drywall. No room to screw or nail.

The outside face of the room wall has new, expensive grasscloth wallpaper on it so my wife won't allow breaking in from that side. Very limiting. Should have insulated after old furnace removal and before this furnace was installed but furnace installer's work schedule didn't allow time. And, we didn't consider that the new furnace would be noisier than the 30 year-old old one even though it has higher capacity. No motor/fan noise comes through supply ducts into the rooms, just from the furnace room itself.

So, does sliding fiberous sound board in from the side and gluing it to drywall appear to be the best solution under such limiting conditions?

[jadnashua]

Code would require a fire resistant wall covering there...make sure whatever you use won't kill you in the end run. The special sound insulation caulk is quite expensive, but good. I think you still have to anchor the panel with some fasteners, but haven't looked for awhile to remember.

[bobbobwhite]

What about expanding insulating foam shot in through holes at the top and/or bottom of the drywall in between the studs? Can I still get that stuff, in spray cans or an application that will still be pretty easy to do?

[Mikey]

What about expanding insulating foam shot in through holes at the top and/or bottom of the drywall in between the studs? Can I still get that stuff, in spray cans or an application that will still be pretty easy to do?

Be real sure you use minimum-expansion foam, or you'll blow the drywall apart.

[Southern Man]

What about expanding insulating foam shot in through holes at the top and/or bottom of the drywall in between the studs? Can I still get that stuff, in spray cans or an application that will still be pretty easy to do?

I'm not sure about the fire rating of that suff, or the sound deadening capacity. It would be safer and cheaper to blow in fiberglass from holes that you cut in the top of the wall. "Rock wool" is better, if you can get it in that form.

[Southern Man]

... I could slide soundproofing panels used into place and maybe tape them together, or back glue them on to existing drywall. No room to screw or nail....

If the fibergalss insulation doesn't provide enough soundproofing by itself you could glue another layer of gypsum drywall on. That will provide a higher STC even without the "Z" channel.