What does it mean when Rinnai says that the R94LSi fires from 15,000 to 199,000 btus / hour?
Unlike old style tank water heaters which fire at only one rate, most modern tankless water heaters will use only the amount of gas necessary to heat the hot water being used at any given time. To do this they measure the incoming water temperature and the flow rate, compare that to the desired output temperature, and fire at the rate necessary to meet this need. If you change any of these variables, the tankless unit re-calculates and adjusts its firing rate accordingly. The tankless unit will therefore fire anywhere between its minimum and maximum firing rate. Rinnai units offer the lowest minimum flow rates available. As with minimum flow rates, the lower the minimum firing rate the more flexibility you will have when you only want a small amount of hot water.
