Are you heating a house or your shop? In a warehouse I would use
Co-Ray-Vac or Space Ray. Rinnai is supposed to be good stuff but is
high tech. Many contractors who put it in can't fix it. Kind of
expensive too. Defininately NOT DIY job! Worked on a Rinnai in a
commercial laundry, had to be reset after a power failure, for the
model they had.

Stretch