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calculating hot water boiler size

i recently went on an estimate to replace a hot wter boiler. the boiler was deffin oversized. i measured all the radiation in the house. total footage of all high output baseboard and all 9 copper convector heating elements. whats the easiest way of calculating the size of the boiler based on the info?


  • Paul48Paul48 Member Posts: 4,256

    You need to do a proper heat loss.That determines boiler sizing. You can then compare radiation on a room by room basis against the heat loss.
  • ChrisChris Member Posts: 3,056
    Heat Loss

    Measuring the emitters only allows you to figure their capable btu/hr output at a particular water temperature. It's not a reflection of the heat loss of the structure or building. You'll make the same mistake as the last guy without a heat loss.

    Once you get the heat loss (room by room) you can then do an emitter water temp requirement comparison to find your needed water temperature at design conditions. You'll more then likely find that the system doesn't need 180 degree water.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • heatpro02920heatpro02920 Member Posts: 991
    Chris makes a good point

    I find with a lot of older houses they are over "elemented", so by doing a proper heat loss room by room and then measuring the baseboard and multiplying it by the amount of btus per foot, you can find the minimum temperature you will need, and the result is you can run your high limit at that lower temp...

    I have seen houses with more than twice the baseboard they needed, and you can set the control to run at under 140 and still heat the area fine.. resulting in energy savings and increased comfort. 180* baseboard heat rises to the ceiling much faster than 140* and it takes more energy to heat water to 180 vs -140.... This is common most in older houses, now with the cost of materials new construction seems to have just enough {if that} baseboard...
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