[vash]

my experience is limited.

i was told by my plumber that the Rinnai i chose needed to be closer to the source of gas. he bought me an outdoor unit that attached to the outside of the home. my job and only job was to keep the shrubs from encroaching on the exhaust.

he said we could put it near the existing water heater, but the double walled stainless exhaust needed per permit was gonna be expensive. (plus IIRC, run a bigger gas line)

in the end, i was happy to have it outside. they are not all that quiet. full roar of a blast furnace when my wife is draining some watershed with her showers.