Mod-con boiler: help!
Hi, I have been reading past questions on Mod con sizing and heating system design for months and have learned so much from archived discussions on GBA. THANK YOU. I am now ready to ask a direct question.
I am building a 1500 square foot house in Montana. It is a slab on grade with ICF perimeter and R-10 under slab. 6 loops of pex and I plan on one zone for heating. compact floor plan. I get moderate solar gain and feel the house is performing fairly well not freezing on the interior even with -10 degree days. R-23 walls and R-60 ceiling, so nothing extreme on the insulation for this build. the mechanical room is not huge, 28″ by 5 feet, so that is necessitating the mod-con vs. something like an HTP Phoenix with heat exchanger.
I have a plumber here that I have used in the past and he does a good job but a few red flags came up for me on his bid. I was interested in putting a 55k btu mod con with a reverse indirect water heater for dhw and buffering. When I mentioned the idea to the plumber, I had to explain to him what the reverse part of the water heater was since he had never installed one… first red flag. then when I got the bid it was for a lochinvar whn 85 and a lochinvar squire indirect water heater. l know this boiler is oversized, but I see the squire seems to require a 100k btu boiler minimum, so maybe that was his train of thought. Unfortunately in my region it seems like I cannot find anyone that is savvy on really trying to maximize mod con performance and the plumbers want to just stick to what they have always done and had few callbacks on. I initially wanted to install the heating system myself but i have plenty of other things to do and their would be quite the learning curve for me to get it dialed in. So my questions are:
1. DO you think I am on the right track with a 55k modcon such as the whn 55 paired with a reverse indirect.
2. If yes do you think I will be satisfied with the DHW production of this combo (it will only be about 2gpm) family of 4 but we can take turns running the shower. it seems like DHW production is the downside when paired with a small boiler.
3. should I just ask him to downsize the boiler and go with his direct water heater or trust his sizing. ( I really dont want to do this)
4. It seems the lochinvars are well supported here with navien being second.. I really like the htp UFT-80 but again oversized and no one seems to use them here. I am ok with waiting for parts in the event of a breakdown.. The lochinvar looks great but the pricepoint is double that of htp or navien. Any boiler suggestions?
I know this is a bit scattered starting point and I need to do a more accurate heat loss assessment but I really appreciate any guidance. thanks in advance
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