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Heat loss

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cm6230
cm6230 Member Posts: 18
in THE MAIN WALL

stumbled upon US boilers free heat loss calculator online. Has anyone used this to get you close ?

Seems pretty good, what are your opinions?

Comments

  • hot_rod
    hot_rod Member Posts: 26,355

    better than guessing. The more data you can enter into a program the more accurate the results.

    But a number of assumptions need to be made regardless, unless you do a blower door to nail down infiltration, maybe an infrared scan to check insulation quality.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    cm6230
  • pecmsg
    pecmsg Member Posts: 6,708

    Historical Fuel Usage

    HVAC Load Calculation - Maunualj - Whole House Loadcalc

    cm6230Hot_water_fan
  • Kaos
    Kaos Member Posts: 833
    edited November 19

    For existing structure, the quickest and most accurate heat load is from fuel use. Older houses have too many unknows for any Man J type of calculation to be accurate. In case of fuel use about the only error is boiler efficiency, DHW loads and passive solar gains.

    The math is pretty straight forward:

    https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

    If you want even quicker, in zone 5,6, winter fuel use in Therms X 42 is about your heat loss. So if you burn 1000Therms of gas, your heat loss is around 42000BTU.

    Hot_water_fancm6230
  • hot_rod
    hot_rod Member Posts: 26,355

    If the home uses gas or LP for cooking, DHW the numbers will be skewed. Solar gain, wood stove, indoor gains also.

    Screenshot 2025-11-20 at 8.05.05 AM.png

    The online load calcs are quick and easy for a double check.

    usboiler.net has one

    hydronicpros.com has a free trial version

    Screenshot 2025-11-20 at 8.12.06 AM.png

    If you are old school and have a tape measure.

    https://www.scribd.com/document/553217971/Heat-Loss-Table2011

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    cm6230

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