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Need help with sizing & best brand of combi-boiler for my home

DaveTrade Member Posts: 1
I have a 1945sf 3BR/2.5BA single story home in Placerville, CA. Built in 1983 with open radiant heated floor (solar water) system. The water tank and solar panels ended their useful life 10 years ago. I'm now converting the old system to a closed combi-boiler system with floor set up as a single loop through 7 zones. Roughly 2,442LF of insulated 1/2" Polybutylene piping in concrete slab. All pressure tested with no leaks. The home's calculated heat loss is 36,947 BTU/HR. - I'm thinking of installing a propane fueled Navien NCB-210E. Wondering what you experts out there think of this Navien unit and if you think a smaller model like the NCB-180E or NCB-150E may be adequate for this home. Thank you for any advice you may offer.


  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    edited March 2021
    The problem with a combi -- any combi -- in an application such as yours isn't the building heat load. It's trying to get anything with an even remotely usable match between the building heat load -- especially at off maximum demand times (which is most of the time) and a decent amount of hot water.

    That particular boiler is wildly oversize for your heating application -- but with a maximum domestic hot water heating rating of 4 gpm may be undersize for your domestic hot water.

    Other than that little problem -- Navien makes a good boiler.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England