I’d greatly appreciate feedback on this. I’ve had a pro heat loss done, have attached a pdf
that shows heat loss and gain room by room, zone by zone from OT 0 degrees through 60º, for 68º indoor set temp. Design day is 10ºF. For a mod-con we are hoping we can do an AWT of 130º, meaning SWT of 140º. We’ve insulated about as much as we can with closed cell foam in the attic, dense pack cellulose in the walls, and fiberglass in the basement rim joists. Piping is in series 3/4" copper piping except for the old insulated 1" steel risers. With our current 170Kbtu old oversized boiler, no problem with uneven heating @160º
SWT, 150º AWT.
The two options are the HTP Versa Hydro PHE130-55 or the HTP UFT-80 with a Turbomax 23 Reverse Indirect to act as both indirect HWH and Buffer Tank. The plan is for an ECM circ with three low-energy draw zone valves, outdoor reset.
Total heat loss is about 38.6K btu. (Using the virtual heatloss method of actual usage with our old 75% AFUE boiler, loss shows about 26Kbtu.) The cast iron emitter gain to loss ratio is good for the main and second floors. Basement zone design day loss is about 11,000btu, slantfin baseboard gain only 6,760. I am seriously considering replacing slantfin with CI rads but contractor suggests the buffer in either system choice would handle the emitter btu basement deficit and that I should go through a heating season and see how it works before spending the money on CI rads.Major questions:
1. With either of the above systems, my concern is the ability to work around the low basement emitter gain without short cycling or having to install a valve to mix in a higher SWT for the basement. Can the buffer of the Versa Hydro or Turbomax handle this on design OR shoulder day? Smallest zone loss at 60ºF is 1349btu, with a gain of 3300btu. I’ve read that sometimes you can lower the ∆T SWT/RWT to accommodate this problem.
2. Note that my wife and I have been using a 50 gallon stand-alone gas HWH which fires at 30Kbtu set at 140º mixed down to 120º and we have never run out of hot water even with back to back showers. Our makeup water hardness is 126.67ppm, Chlorides 83.5ppm. Conductivity is 530 mmhos. Ph is 7.28. TDS: 355ppm. If the Turbomax DHW coils corrode over time, then I'm guessing that replacing that unit will be less expensive than replacing the entire Versa if it has the same problem. However the Versa saves more space, and its lowest turndown output would equal the lowest firing rate of 26,000btu/10 = 2,600btu. compared to the UFT-80's 8,000 btu. I think I've just talked myself into the Versa....Thoughts? (Post has been edited/corrected so a few subsequent answers may seem non-sequitur.)