Hi,

I have a Rinnai R85 in a townhouse that I purchased about a year ago. It's being used to heat two zones of water for a baseboard heating system (of course when I purchased the home, I did not realize it should not be used for this). It actually does a good job and despite it being on the first floor, it is pretty quiet and heats the place up fast. My problem is on the second floor. I have a bedroom directly above the unit. When the upstairs zone is on, in this one bedroom I often hear a low pitch humming noise and if I walk in different parts of the room it can get louder or even completely go away kind of like the floorboards are vibrating a little.. Or some insulation maybe? This only seems to be the case when the (air intake?) motor spin at a low speed for several minutes after it gets going. It is very annoying and sometime I end up having to either sleep with a fan or shut the upstairs zone off and crank the downstairs zone up a bit instead. Is there anything I can do about this, short of having someone come down and get to the pipe causing the problem? I think there is a little air in the pipes because I hear a flushing noise when the unit turns on and shuts down. As for the pipes coming out of the unit and heading towards the ceiling, I can feel just a small amount of vibration when the unit is causing the noise, but it is almost so small that you have to be looking for it to feel it. Thanks for any help!