The exhaust pipe on Rinnai R75LS.

by Lyda
(Riverdale, Georgia)

We are currently finishing up a new construction of our ranch home. Within our home we had a R75LS Rinnai water heater installed in our master bedroom closet. My question is that on the outside of the home the exhaust pipe is sticking out, which I understand we have to have. However what I would like to know is can this pipe be cut to where it is not so long sticking out?? Thank you

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Dec 19, 2011
Proper venting on Rinnai R75LS
by: Anonymous

I will assume that you had installed Rinnai R75LS water heater with the separate air intake and exhaust pipe with the horizontal terminations.

According to Rinnai and other manufacturers, the vent system is certified and listed together with the water heater so should be used from the manufacturer and installed per codes.

So, any alteration in its design or intent might void the warranty, affect the proper water heater operation and make the environment unsafe, especially with the unit installed in the bedroom.

Rinnai R75LS is the direct unit with the sealed combustion that uses the fresh air from the outside for the proper and safe work. This is how it should be. At the same time the exhaust gases are send out.

I am guessing that the reason for cutting the vent pipe is the visual appearance, but safety is more important. If it is impractical to have the exhaust pipe sticking out, the best will be to have the vertical termination, through the roof, but might be more expensive.

Rinnai R75LS water heater, when using the separate vent pipes, should have the air intake pipe shorter than the exhaust pipe. The distance from the end of the air intake pipe to the wall should be 4” while for the exhaust pipe 12”. The pipes should be minimum 12” above the ground or snow level. Both intake and exhaust should slope toward the outside with the minimum ¼” per foot angle, to be in the same pressure zone and face the same direction.

The exhaust vent pipe is longer as you don’t want the air intake pipe to get the products of combustion back into the system and since there is condensation you don’t want this acidic condensate dripping on the wall. The length should be based on the recommendation so the water heater can have the unobstructed air flow and the transfer of the flue gases.

So my answer to your question will be to keep the venting pipe as is and without modifications.

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