Air intake tankless heater heater
Want to install a Rheem performance platinum 9.5 gpm natural gas tankless hot water heater. The mechanical room it would be in has a 6 inch conduit for fresh air that comes direct from the outside, plus a grate through the wall connecting it to the surrounding basement, around 1500 sq ft total taking into account both rooms. I have a 2” vent pipe from my current hot water heater. This Rheem states you need to have an intake direct from outside. However, it would seem it would get plenty of combustible air from the room, and I would likely never get a negative pressure situation because of the fresh air intake they put when the house was built. Do I have to run an intake pipe direct to outside (would require ripping out ceiling).
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Check the installation manual, most can use fresh air from the room. It is always better to pull fresh air from the outside, less chance of back drafting the unit.
2" sounds too small for all the ones I've seen, most need 3" piping.
It seems even if I used 3”, I would imagine there is still more resistance to combustible air through that than a 6 inch conduit into the room.
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