Rinnai: converting from a storage tank to tankless: what changes, and what it costs to change it

A conversion is a tankless installation plus everything the old tank was quietly relying on. The atmospheric tank used a chimney, a 1/2" gas connection at 40,000 BTU/h and no electricity; the tankless unit needs sealed PVC venting to an exterior wall, a 3/4" gas connection on a supply sized for up to 199,000 BTU/h, a condensate drain and a 120 V receptacle. An electric tank had none of the gas or venting at all. Those four items, plus removing the tank and capping the old flue, are the conversion allowance the estimator shows as its own line.

The other half of the conversion is expectations. Tankless delivers continuous hot water at a limited flow, not unlimited flow, and not instantly at a distant tap. CANRO's assessment checks your peak simultaneous use against the unit's flow at the winter temperature rise and tells you if a single unit will fall short.