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?
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
The "mechanical path" of the each utility must me less stiff than the
overall mounting system......a loop of moderate diameter comes to
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
"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?
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
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.
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. <G> A light and an electrical outlet near the
appliance is always greatly appreciated also!
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.
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.
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).
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?
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