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sound reduction in a condo HVAC closet

hmj | Posted in Construction Techniques on April 1, 2007 07:32am

I have been tasked to “soundproof” a utility closet in condo that contains the HVAC equipement. Owner says it is bothersome to the point where she is considering selling. I did some other work there in the past, but not on that room, so I am going sight unseen. 3′ x 10′, I believe it is a hollow door with wall vents to provide air. Steel stud, rocked on the exterior only. Owner says there is some type of sound barrier for the AC/ furnace.

I can’t stop the flow of air, so I am looking at sound absorbing materials. Fire safety is an issue too.

MY thoughts were to hang resiliant channels horizontally, hang homosote off of this, putting vents on toward the bottom to correspond to the vents on the top of the wall. Insulate the ductwork inside the closet. Also replace the hollow door with a solid and put weatherstripping around it. If room allows, hang another door inside the closet in front of the first.

Spray urethane is not really an option for the walls, job is too small for the cost.

Thoughts? Thanks

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  1. GreenEgr | Apr 01, 2007 08:49pm | #1

    I have been very impressed by the sound absorbing qualities of spray cellulose. Your job is too small for that, but maybe you could staple tyvek and then hand pack the wall with cellulose for a similar effect.

  2. DanH | Apr 01, 2007 11:10pm | #2

    Is the sound coming through the walls or through the ductwork? Is some of the sound due to an out-of-balance fan perhaps, or maybe an old belt-driven unit that may need a new belt (or complete replacement)? Can you adjust the fan speed?

    So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
    1. hmj | Apr 01, 2007 11:19pm | #3

      The sound is coming through the walls/door. Condo is 2 years old, the offending sound is the rushing of the air through the AC unit itself - don't think the fan speed is adjustable.

      Edited 4/1/2007 4:20 pm ET by hmj

      1. THETinman | Apr 02, 2007 03:18am | #4

        If the condo is only two years old the fan speed must be adjustable, find out how many tons of cooling it is though so you don't reduce the air too much or you'll risk freezing the coil. (a good rule of thumb is 400-450 CFM/Ton)

        How much room is there between the appliance and the wall?  You might consider ensuring that the appliance is properly isolated and also acoustically insulating the return duct if there is sufficient room.  If there is sufficient room and the duct isn't drastically undersized, it may be as simple as purchasing stick pins and some acoustic insulation and sticking the insulation in the return duct.

      2. DanH | Apr 02, 2007 03:41am | #5

        With our current furnace the loudest noise comes through the return air duct.
        So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin

      3. rpait | Apr 02, 2007 03:32pm | #9

        The sound is coming through the walls/door. Condo is 2 years old, the offending sound is the rushing of the air through the AC unit itself - don't think the fan speed is adjustable.

        The unit is that noisy? I want to know if its the unit fan rotation noise that she hears or the "rush" of the air through the return register.

        if its the mechanical noise you can get dense foam like sound recording studios use to create quiet rooms and you can put that everywhere there isnt heat buildup.

        if its other noise you can build a decorative box or modified hall cabinet with vent holes facing the oposite direction ie front door so as to direct the sound that a ways. So it wont affect the living room for example. You arent cutting off airflow just causing sound waves to bounce a different direction.

  3. ponytl | Apr 02, 2007 03:42am | #6

    get the air handler on some rubber sound pads or springs...

    if it's the air handler itself... you could try the self stick sound deadening material that they use in automotive under the carpet & in the trunk... (self stick ice dam material also works...) apply this to the unit itself... don't block any holes but... you could do the inside of the panels as well as the outside...

    next work on the ducts... wrap any that you can with duct insulation...

    make sure her unit isn't restricted on the return side... it'll make it sound like it suck'n thru a cocktail straw if it is...

    get the best filters you can... they should help some... 

    look for leaks... they make a ton of noise... as do sharp turns in the duct work...

    that should get you going before you ever start on the room walls

    if they are bare studs on the inside...  cut & glue a second layer of drywall to the back of the exsisting drywall... leave it 1/2" shy all the way around... then foam that gap with a can of foam...  make sure there are zero holes (back of outlet boxes ect.. where sound can escape...

    p

  4. semar | Apr 02, 2007 05:42am | #7

    this will be a difficult problem to solve. We ran into the same problem when HO asked to soundproof bathroom adjacent to familyroom.

    Sound will travel thru any opening, whether it is the gap under the door or returnair opening. You can open the wall and insulate between the studs, fill all holes you can find. It still will be "noisy"

    Care has to be taken that you do not cut of any supplyair to the HVAC unit if required.

    For the costs involved and the HO still not satisfied; it is a thankless undertaking

  5. hmj | Apr 02, 2007 02:50pm | #8

    Thanks for all the sugestions. It looks like I will concentrate on the ducts and air handler before the walls. This is a fancy-pants harbour view condo, I can't imagine every unit has ths same problem. I would ask her to talk to some neighbors to see if they had any retrofits done, but this is the kind of building where people don't talk much to their neighbors other than a passing "hello" in the elevator.

    1. THETinman | Apr 06, 2007 09:44pm | #10

      Unfortunately, despite it being a "fancy-pants" building, it was most likely engineered.  That being the case, there a probably only a few floor plans in the building.  If there are only a few floor plans, there will most likely be similar units with similar problems. 

        Is this the original owner?  If so speak to the realtor that sold the unit, possibly the builder.  If the builder was also the seller, they should be able to locate a set of drawings showing how many "different" suite plans there are.  If you can determine how many different suite types, you can then try to see if any are currently foor sale(not sure how the Real Estate market is there).  Then speak to a realtor and ask to see similar suites to see if there are any differences.  The condo board may also have an idea as to suite types.

       

      Best of Luck.

  6. MAsprayfoam | Apr 07, 2007 02:04am | #11

    Check out how those diesel generator units are sound insulated. They still need a lot of air for both the engine combustion and cooling. Some are incredibly quiet in a small package.

    FWIW, anything labled "accustic" is often 2+x price.

    Stu

  7. hmj | Apr 07, 2007 04:04am | #12

    The closet was small and the air handler took up most of the floor space. The noise was from the blower and the compressor. Door was hollow and had a 20"x 20" vent on the bottom - close to the air handler. Fan speed had been turned down as low as possible.

    What I did: Removed the inside grate and covered the whole inside of door (except for the vent cutout) with first a layer or green "Silent Floor" laminate flooring underlayment, then a 1/2" piece of homasote. Added two wood rails that were 1.5" thick to the back of the door. On top of this I put another piece of homasote, cutting a large 15" x 15" hole hole near the top. Over this hole went another set of rails and third smaller piece of homasote. Plenty of air flow. Caulked all joints and gaps. Put foam weatherstripping on the door stops and covered the exposed ductwork and some of the handler (not the warning stickers and vital stats) with foil covered foam duct insulation. Essentially the door was made airtight except for the vent, but since the sound had to bounce around inside the homasote duct before it came out the vent, it was greatly diminished.

    Lady was very happy. Sound was still there, but not enough to drown out, the TV as it had been. All of the middle units in the condo have the same problem. She gave my name to some other middle unit owners.

  8. ktkcad | Dec 26, 2019 07:22pm | #13

    You replaced a 15x15 hole with a 1.5x"24" duct. So you reduced the combustion airflow from a straight 225 square inches (way too big) to at best 36 square inches and you call that 'good airflow'. You have also relocated the lower air supply duct to a higher location. Offset distance from the hemasote to the furnace? All that weight added to a flimsy hollow core door. I can't begin to number the code violations.

    A well-sealed solid core or solid wood replacement door and appropriately sized 50 SI low and 50 SI high combustion air vents somewhere in the utility room would have been the simplest fix. Force the 'sound' to take a couple of '90 degree turns' through the smaller vents by offsetting their openings within the wall cavity they pass through and you quiet it even more. Still, every time that unit runs it's vibrating the floor and that will send noise everywhere just like a base speaker. So the earlier tips to isolate it from the floor with 'rubber feet' and to even hand pack the open wall cavities were some of your best next options. Use them on any additional units you get called to.

  9. MGMaxwell | Jan 04, 2020 10:03am | #14

    Roxul mineral wool. Spun basalt. Fireproof and great sound insulation. Drywall over that [they make dw for soundproofing]. You can run a strip of cork over the studs before attaching the dw. Put cork on the floor. Then add solid core door.

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