Vibration Isolation Mounting for Tankless Water Heater

[Wayne Whitney]

Hello,

I'm about to move my exterior wall-mounted tankless gas water heater. It is currently lag-screwed into the wall studs, and I get a fair amount of nuisance fan noise inside, so I'd like to use some vibration isolation mounts when I remount it.

Now the unit weights 48 pounds, is 10" deep, and it is supported via two rear brackets 24" apart vertically, each bracket with two bolts. So I get a load on each of the top bolts of 12 lbs in shear and 5 lbs in tension, and a load on the each of bottom bolts of 12 lbs in shear and 5 lbs in compression. [This assume the center of gravity is in the middle of the unit, which may or may not be true.]

Based on this, I chose some bonded tube mounts, Barry Control 22001.

They are designed to attach to a 3/8" plate through a 3/4" hole. Since the loads are so low, I'm wondering if I could use 3/8" thick redwood? Or if not, 3/8" plywood?

Also, with the unit on flexible mounts, I'll need to use flexible supply connections for gas, water and electricity, right?

Thanks, Wayne

[Bobk207]

Wayne-

The loads are pretty small so the r/w will probably suffice plus it will handle hte weather better than the plywood.

Yes you will need flexible connections for your utilities otherwise they will become the new "hard mounts" through which to transmit the noise.

The "mechanical path" of the each utility must me less stiff than the overall mounting system......a loop of moderate diameter comes to mind.

cheers Bob

[rlaggren]

3/8" any-kind-of-wood is pretty marginal. Consider error and the ravages of time or somebody/thing falling against the applianace. Plywood might hold, but it's not that hard to install the isolaters as designed.

"Surface" mount 3/8" x 2" wide metal plate(s) on (say) 1/2" spacers on the finish wall. Predrill the plate, make the spacers thick enough to allow installation of the isolators easily. Unless you're _really_ hurting for space, adding 2" or less to the depth of the appliance won't matter much; but if so, when the wall is open install vertical

2x2 (or whatever) blocks back 3/8" (or so) back from the stud surface and attach the plate to that (or make the block proud to put the plate flush w/the finish wall).

If you use aluminum plate (available from recycle joints - eg. Alco in San Leandro) you can cut and drill yourself; use a regular holesaw for

3/4" holes. Just be careful to separate the different metals (thin rubber gaskets work well) and use SS fastners if the assembly will be in a moist place (like outside in the weather). You could probably drill mild steel youself also, but figure on wasting a couple hole saws and an hour or so on 3/8" plate. 3/4" water flex are available at the plumbing supplier. I suggest you use the female/female type for easy replacement later.

How have you liked the tankless heater?

Rufus

[Wayne Whitney]

Hey, thanks for the response. I agree with basically everything you said, although it took me a couple days of figuring it out to come to the same conclusions, with the help of BobK207.

I decided to use the isolators to mount the plate to the house, and then mount the tankless rigidly to the plate. Seems a little simpler.

Right, I decided on aluminum for ease of machining, and I was planning to use something to separate the aluminum plate from the steel water heater bracket. If I decide to have a gap between the two plates, would an 1/8" be enough? I'm thinking a really small gap would still trap water.

I like it great with the caveat that under two conditions it doesn't provide as even a temperature as a tank water heater. One is when starting and stopping the flow (e.g. between showers), the "cold water sandwich". The other is a very small effect when the total demand changes, as the burner adjustment slightly lags the flow. Of course, a tank water heater also doesn't provide even temperature under some circumstances, e.g. when it runs out!

So I am going to try adding a very small (2.5 gallon) electric tank heater just after the tankless heater to even out the temperature fluctuations. I calculated it will cost about $30/year in standby losses, hopefully it will do the trick.

Cheers, Wayne

[rlaggren]

If it's going to get wet regularly, 3/16" or so might be better - allow more air flow. Alternatively, you might consider just using a gasket w/some "bedding" goop on both sides. It's a simpler solution and squeeze-out along the top would reduce the water pocket along the top edge. The bedding is intended to completely coat and fill the surfaces and leave no opening or space for water to enter. SOP for deck hardware on boats and I've pulled hardware that's been installed for 20 years and found the bedding still "live" and not evidence of water. There are also "shoulder" washers available to keep a fastner from touching just about anything, but I'm not sure that's warrented here. IAC, the thing that's going to "die" is the mild steel bracket first, the aluminum 2nd, the SS fastners last. The SS and the aluminum is no problem because the aluminum is such a large area compared with the fastener; not sure if the same applies to the SS and mild steel. Plain old rust may be more the issue than galvanic stuff, though.

That sounds like an excellent idea to try. You could probably insulate the life out of the tank (since It's electric) and cut your losses further; I guess the limiting factor would be convection currents in the pipes from the WH tank, so mount it above the tankless. Could put an insulating pad under it too (closed cell camping foam?).. Electric WH's are pretty reliable so once you got the setting right, you can probably forget it for 10 years; do install earthquake straps. But please leave easy access and clearance for maintenance - this is the plumber speaking. A light and an electrical outlet near the appliance is always greatly appreciated also!

Rufus

[Wayne Whitney]

Hmm, after considering these issues it will be simplest to go with your original suggestion. That is, mount the aluminum plate to the house rigidly with some wood stand-off blocks, and then use the rubber isolators to mount the steel water heater brackets to the aluminum plate. This avoids the contact of dissimilar metals and provides a

1/2" air gap between the bracket and plate.

I was planning to put it in the crawl space, so mounting it above is not really an option. I guess I should put some upside down U-bends in the piping to the tank water heater? Perhaps I'll just use flexible water heater connectors and bend them into a U-shape.

Cheers, Wayne

[rlaggren]

With 24" flex connectors, you can put a full loop in them provided the piping is located properly. We do this when possible to reduce convection flow. The only problem with flex connectors, it's hard to get the usual pipe insulation to work; the readily available stuff is pretty stiff and doesn't want to conform to the bend and gaps and pops off if you have slit it for the install - the usual circumstance. There is a soft insulation that works fine, but you probably need to visit an air conditioning or hydronic heating supplier to get it and it costs more.

Good luck on your project.

Rufus

[LightsAREon]

Try an air hammer arrestor instead. The loop thing works but most inspectors aren't too happy about anything that has more than 270 degrees of bend in them. If this is just a DIY job, go for it. There are insulation tapes that will do the job but you have to go to a tru plumbing supply outlet (not Lowes or Home Depot).

[ChicagoDreamer]

replying to Wayne Whitney, ChicagoDreamer wrote: Very old post I know! But how did the isolators turned out? From high school, I thought I remember, it doesn't matter if there is soft material in between. The issue is what the screws are connected to. That's what transfer the vibrations which must be minimized. Right?