Jadnashua
Retired Defense Industry Engineer xxx
The unit I have is 80K BTU, but can fire down to 16K. It's almost 95% efficient at full output, but approaches 100% at the low end. It was a fairly complicated install, and I had a big indirect WH installed, and it was over $9K. You may not recoup the increased costs, but who knows where the energy costs will go. Took a two-person team nearly 3-days to tear out and install new. There are other units that would be less, and you have to account for the indirect, and multiple systems, and zones that were installed and the large indirect wasn't cheap, either.