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I am planning to replace my hot water tank with a Noritz NRC98-DV tankless hot water heater. The best location to mount the new heater is in the basement on an outside concrete wall. The heater will be at a height that puts it half above grade and half below. The climate here includes severe winter weather.

The instructions with the heater assume I'm mounting it via screws to a wooden wall (e.g. "...be sure to hit a stud..."). Rather than building a full wall with studs, it would be more convenient for me to mount either directly to the concrete wall or perhaps to, say, a piece of plywood that is mounted directly to the concrete wall.

Will the plywood method or the direct mount method work for me? Is one or the other preferred? Are there moisture/condensation considerations with either method? Are masonry screws (e.g. Tapcons) the preferred method for attaching?

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I think you should mount a plywood backer plate with tapcons or ramset nails. The advantage of having the heater mounted to the plywood is that it will be easier to place and screw on once you have the plywood secured well to the wall. If for some reason you need to remove the heater for service, you won't have to deal with removing tapcons which rarely go back in again. They always strip out the concrete and won't grip properly when you try to reinstall them.

  • Yup, yup, yup, yup! – Harper Jul 31 '16 at 21:18
  • Excellent point regarding ease of mounting and removal for service or replacement. One thing I worry about is condensation between the plywood and the wall. To mitigate I can think of some sort of barrier under the plywood (maybe shingle underlayment?) or furring strips that create an air gap -- not sure which is better. – Travelling Man Jul 31 '16 at 23:02
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    I ended up borrowing a hammer drill to drill six 5/32" holes for 3/16" x 3-1/4" hex head tapcons. The tapcons + washers were slightly countersunk (which was probably not necessary) into two treated 2x4 furring strips, . Finally, a 2'x4' piece of 3/4" plywood was screwed to the furring strips. – Travelling Man Aug 7 '16 at 15:08

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