Boiler sizing for new home?

Discussion in 'Boiler Forum' started by farm2u, Feb 16, 2018.

  1. farm2u

    farm2u New Member

    Joined:
    Jul 2, 2014
    Location:
    Washington
    I have a new 4500 sq ft home with all electric radiant floor heating in Dungeness. The heat loss calc came in at 41,000btu/hr. What size boiler should I buy? The installer recommends a 58,000 btu unit.
     
    Last edited by a moderator: Feb 16, 2018
  2. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The load numbers seem a bit high for your ~27F 99% outdoor design temperature. Was it calculated by the HVAC installer, or an engineer/architect? I'd expect a new code-min house to come in at about 7-8 BTU/hr per square foot for a radiant house that size, rather than ~9 BTU per foot.

    ASHRAE recommends ~ 1.4x oversizing for fossil burner boilers, and that's probably where the (41K x 1.4x = ) ~58K number come from. But that's to deal with trading off efficiency vs. comfort a the 25 year low temp, etc. From an efficiency point of view oversizing doesn't really matter much with electric boilers, but there's really no need to oversize by more than 1.2x.

    In your location controlling the room air temps with modulating ductless air source heat pumps and the floor temps with with an electric boiler operating off a floor thermostat usually makes economic sense, cutting the heating power used typically by more than half. It would offer high efficiency air conditioning for the 2o minute per year you might actually NEED it. :)
     
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  4. farm2u

    farm2u New Member

    Joined:
    Jul 2, 2014
    Location:
    Washington
    Was done by PacWest Sales in Port Angeles. Component load 21K, infiltration load 14K, downward 5K, radiant into rooms 36K total 42K. Figured 17'F and 23 mph wind as we on the straights(temps sounds too low but thats another issue as we are at sea level) . Lots of windows and 9' ceiling but otherwise typical 1 story raised foundation with 2" concrete floor 1/2" PEX system. Right now it is maintaining a steady 64' f without a hitch and with well insulation and thin floors I just want to make sure recovery time is in hours not days or weeks.
     
    Last edited by a moderator: Feb 16, 2018
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