crawlspace whole-house dehumidifier vibration/noise

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RustyShackleford

RustyShackleford

Minister of Fire
Jan 6, 2009
1,347
NC
I've installed a whole-house dehumidifier in my crawlspace. For various reasons (primarily drainage), I hung it from the floor joists above, using a simple platform made of 2x4s supporting a piece of plywood. Unfortunately, a lot of vibration is being transmitted into the house. I know the hanging is the problem, because it's much louder than when I first tested the thing sitting on the crawlspace floor on some milk crates.

How can I prevent this vibration (and still have the unit hanging) ? I think putting some kind of foam between the plywood and the dehumidifier could work, but the thing has four fairly-small "feet' and I feel they'd quickly crush the foam. I'm wondering if I could put some intermediary material between the floor joists and the hanging 2x4s; something like 4 pieces of heavy rubber (cut from an old tire ?) that are fastened to the joists and the 2x4s hang from the rubber. Maybe there's even a product that does this, like a car muffler hanger (like this, except I can't figure out how big it is: https://www.pelicanparts.com/More_I...nynjbEdhSpu6VPKgI1RVC4lcflwfn1CxoCf-wQAvD_BwE or like Amazon product ASIN B09GK1BZBJ except I dunno if it can handle the weight, 50lbs or so plus the platform).
 
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My installer just set mine on cinder blocks.

Most units have a cable kit available. How about ratchet straps to eye bolts.
 
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EbS-P said:
My installer just set mine on cinder blocks.
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Don't want to potentially damage the crawlspace liner, and probably not high enough.

How about ratchet straps to eye bolts.
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I have a bunch of 1-1/2" webbing. Not sure how to secure it to the joists so it doesn't rip out though, may some good grommets.
 
sneefy said:
There are a lot of options for this, apparently. See link below.
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Yeah, those look like the way to go. Found this outfit that sells all kinds of stuff ...

All Products | Advanced Antivibration Components

AAC carries cylindrical, base, square mounts for damping and reducing vibration and shock protection.
www.vibrationmounts.com www.vibrationmounts.com

... and was thinking the stud mounts (mounted in shear, with the threaded portions horizontal) but the hangers seem better. Their's are way too heavy-duty and expensive, but Amazon has some sets of 4 for a good price that should carry the weight. Not sure how to secure 'em to the bottom of the existing 2x4s though (the ones that come down from the joists).
 
That muffler hanger looks like the same thing that’s on my car. I just replaced the exhaust this spring and without crawling under it, I’d have to say it’s about 1.5” x 5”. It uses a shoulder bolt on each end. And with a muffler and rear pipe which is 20 lbs at the most, it stretches maybe an half inch to an inch. It’s held up all these years under the heat. With the platform, you might have about the same weight spread over 4 hangers. And the movement allowed should really absorb vibration.

Trying to think of easy low cost options for the tray, I think a piece of gym mat might work well. But a plywood tray is an excellent sound board (not good in your case). Having good bracing under the tray would help. But I think the best thing might be to eliminate the tray, and through some thick sponge rubber, attach the dehumidifier to a 2x4 frame instead of its feet, suspended by the rubber hangers.

Another consideration is where is it? If it’s in the middle of a floor span, it’s going to transmit more vibration than if it’s near the edge, or a support column.

3 supports instead of 4 will always make sure there’s weight on each one, otherwise there’s always one that will be slack and can vibrate. But 4 is easier, gives one for safety, and if they’re soft like rubber then at least the slack one won’t make noise.

Just my thoughts, FWIW.
 
Thanks. I went ahead and purchased these: Amazon product ASIN B08RYKRLKJ
Looks they're designed for this. I'll probably just use two pieces of angle or unistrut on the short dimensions, with plywood between them. You're likely right the plywood is bad for vibration, but if the hangers can't dissipate it all, I could maybe put these puppies under the feet:
Amazon product ASIN B01IU6WT5O , or maybe even replace the feet with one that have rubber on the bottom (they're all metal now).

Interesting what you said about the floor span. It's now hanging from joists, underneath the living room, pretty near a girder which separates the living room from the MBR. It's WAY louder in the living room than in the MBR. That girder is stopping the vibration very nicely.
 
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The hanger things worked pretty well. Could be better though.

I can't tell if the remaining noise is being transmitted up through the hangers and the 2x4s, or if it's coming through the air (from the dehumidifier to the plywood subfloor). How can I determine that ? If through the supports, maybe some kind of foam between the dehumidifier and the plywood it sits on. If through the air, maybe some sound-deadening foam underneath the subfloor.
 
Metal dehumidifier feet on a piece of plywood is going to be noisy no matter what. Anything between the two should be an improvement. If you don’t have a piece of heavy sponge rubber laying around, I would try something simple like a towel folded into several layers.
 
Put down a blanket or foam padding to protect the liner and set cinder blocks on top of that, or stack up some 4x4 cribbing to get high enough. You definitely don't want it hanging from the floor joists
 
gthomas785 said:
Put down a blanket or foam padding to protect the liner and set cinder blocks on top of that, or stack up some 4x4 cribbing to get high enough. You definitely don't want it hanging from the floor joists
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I was afraid it would fall off, from the vibration. Anyhow, I'm committed to hanging it. And thanks to those hanger things, it's just about as quiet as it was when I tested it sitting on some milk crates.
 
tlc1976 said:
Metal dehumidifier feet on a piece of plywood is going to be noisy no matter what. Anything between the two should be an improvement. If you don’t have a piece of heavy sponge rubber laying around, I would try something simple like a towel folded into several layers.
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I misspoke before. The feet do have rubber on the bottom.
 
IMO gravity drain is preferred if at all possible. One less thing to fail.

Seems to me if it’s coming through the floor joists, you won’t so much hear it downstairs, as much as upstairs. But if it’s coming through the air, then you should hear it way more downstairs.

To rule things out, I would still try an old towel or blanket under the dehumidifier, to see if it’s vibrating against the plywood. Even if it isn’t, it should provide additional isolation from the floor joists.

You could try pushing against the plywood while it’s running, to see if the plywood itself is acting as a sound board and needs stiffening.

You could check each of the hangers while it’s running and see if there’s any slack that’s causing it to vibrate. It looks like there’s a metal cup against the spring that could potentially vibrate if it’s not firmly weighted down and seated.

If all that’s left is through the air, even the sound of the unit itself running…. I looked into sound deadening through floor sheeting before, when my ex complained about my daughter strumming her acoustic guitar in the basement. Supposedly the best thing to resist sound is mass. So a heavy insulation like rock wool, or compacted old clothes, or whatever. But acoustic tiles might be a good option too. I never did the job, I just defended my daughter because they all made their own noise in the main part of the house.

If it’s still vibrating the floor joists, another option is to spread the load to lessen the actual movement. You’ve already got the girder on one side that does well. You could tie several joists together with a very heavy board, and hang from that instead.
 
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Good suggestions, thanks. I'm actually fairly content now, but might try some of these.

I'm not sure what you mean by "upstairs" and "downstairs" though. It's a one-story house. Does "downstairs" mean crawlspace ?
 
I can hear mine any time it’s on. It’s not obvious. I think it is the AC running now. As they are close by.
 
RustyShackleford said:
Good suggestions, thanks. I'm actually fairly content now, but might try some of these.

I'm not sure what you mean by "upstairs" and "downstairs" though. It's a one-story house. Does "downstairs" mean crawlspace ?
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Yes, crawl space. I have a basement with a dehumidifier running so force of habit.
 
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