First of all I'd like to give a huge THANK YOU to all of the contributors on this forum (and to the Holohans for founding and hosting it) for all of the many insights that you've given me in the lead-up to this post, and hopefully have gotten me 99% of the way to my answers from all of the content that I've read through here in the past couple of months.
I have a failed Burnham V73 105 MBH with a 1993 date code on it (big crack in the center section of the heat exchanger) in a 1977 single family gambrel located in Groton, MA. The house has 1,992 total square feet of heated space with 768 square feet of finished (but unheated) basement. There are three heating zones with standard 3/4" copper fin tube loops in the home, with the following measurements:
- 301" of finned tubing, 1479" total tubing length (including elbows/45's equivalent lengths), 16,120 BTUs/Hr
- 408" of finned tubing, 1700" total tubing length (including elbows/45's equivalent lengths), 35,762 BTUs/Hr
- 472" of finned tubing, 1773" total tubing length (including elbows/45's equivalent lengths), 14,778 BTUs/Hr
All BTU's per hour are based on the SlantFin Heat Loss Calculator web tool, using U-Factor of .07 for the exterior walls, .15 for the unconditioned basement ceiling / first floor floor and .65 for the double-paned windows, and .05 for the top floor ceiling. 70 degree / 1 degree based on location.
The current heating system is set up badly, really poor piping layout and set up to "pump towards" on the return on all three loops, with dedicated circulators on each. Chimney was lined with stainless 3 years ago when I first moved in. I am looking at the Burnham MPO-IQ84, the Burnham V8H3W, and the Weil-McLain WGO-2 as replacements, given that I've seen / heard significant short cycling with the V73 in my time here and with a total BTU/Hr of 66,660 max I really don't need much boiler even if I end up adding a zone for hot water or the basement (or both) in the future. Plus, we supplement with wood heat throughout most of the really cold heating season.
Attached is my current system replacement design. I'm moving from three circulators to one Delta P unit controlled with zone valves and incorporating a boiler protection bypass controlled by a Caleffi ThermoProtec valve. Interested to hear the community's feedback in terms of whether this is a reasonable design given the above scenario.
Thanks in advance!