I'm in the process of a remodel, though I need to do it in phases. third or 4th phase down the road is to use part of the Master bedroom and make a Laundry room with some of the space. Though I cannot build the laundry room yet, though I need to move the water heater to its new home in the Master bedroom so I don't have to have to roof patched at the old location.

The Laundry room won't be built till the beginning of the year. Its a Direct vent unit and I will have two 3" ABS Pipes (sealed/glued) to a Concentric vent through the roof above the install.

Is there any reason to not have the unit in the bedroom where we sleep? We would have a CO2 detector of course.


  • I can't think of any reason why it could not be in the bedroom where you sleep. – Jim Stewart Sep 4 '19 at 11:06
  • Have you considered using a stainless steel flue instead of a plastic one? There have been some rather nasty flue-gas leakage mishaps with plastic flues (usually DWV PVC) overheating and slow-cooking themselves due to scaling and the likes in the appliance. (Corollary: is your ABS flue piping approved for flue gas service, and if so, up to what temperature, vs the maximum exhaust temperature of the water heater?) – ThreePhaseEel Sep 4 '19 at 11:32
  • Do the PVC flue parts come with the water heater or do the instructions give the specs and you are required to obtain them yourself? I think PVC is specified because this is a "condensing" system to obtain highest efficiency and so liquid is draining through it. Are there stainless steel flue parts that can be made leak free for flowing water? – Jim Stewart Sep 4 '19 at 12:33
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    @JimStewart -- the PVC-for-appliance-venting thing is chintz on the part of appliance manufacturers (it's in the manuals, but violates Code). And yes, there are several manufacturers of stainless steel "special gas vent" (listed to UL 1738 and ULC S636) that is watertight, flue-gas-tight, and rustproof (to the point of having a lifetime warranty, even); note that each manufacturer has its own system though, so you can't "mix and match" parts. – ThreePhaseEel Sep 4 '19 at 22:37
  • @ThreePhaseEel, I often often see the black plastic roof vents for concentric vented tankless water heaters. So this is presumably ABS. I have wondered how hot the condensate is. Is ABS rated for scalding hot water? – Jim Stewart Sep 4 '19 at 23:13

You'll want more than your average CO alarm for this

While everyone should have a UL-listed CO detector to sound the alarm if "imminent hazard" CO concentrations are present, your situation (a combustion appliance mounted in close proximity to inhabited space) merits extra precautions. First, I would get a low level CO monitor in addition to your normal CO alarm if I were in your shoes. This extra unit will tell you if there are issues with your appliance emitting CO before it reaches the imminent hazard point, which is important because chronic low level CO exposure can be a significant threat to vulnerable populations, or simply make you miserable all the time with no idea what's going on.

ABS does not a gas vent make

Furthermore, using DWV materials such as PVC or ABS for venting is wrong, and potentially fatally so. The issue is that while the manufacturers can provide an appliance that keeps flue gas temperatures low enough to avoid deterioration of the flue when it is in new condition, scaling and other efficiency-hampering factors cause the flue gas temperature to rise over the appliance's lifetime, leading to plastic flues deterioriating from overtemperature and eventually failing outright.

Avoiding this is simple, though. All one needs to do is follow the Codes and use a UL 1738 listed Type IV special gas vent system; uniformly, these systems are made of stainless steel instead of plastic, allowing them to withstand the exhaust temperatures of just about any gas appliance made without taking any damage whatsoever. Furthermore, the use of highly corrosion-resistant stainless steel alloys such as AL29-4C allows a properly installed stainless steel vent system to last a long time (lifetime warranties are common), no matter how nasty the condensate gets.

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