Boiler sizing

Bob L_3

Just want to give myself peace of mind. I'm quoting a house that currently has 260k btu Hot water heat(1 zone) Lots of the radiation in the house has been removed when they put in air. I did a count on the radiators and come up with 367 sq. ft. of radiation * 150 (hot water)= 55,050 * 1.25 = 68,813 + 15% (85% boiler)= 79,135 total btu's I'm putting in a tekmar 260 reset on it with a 40 gall hwt. and have quoted 100,000 btu's and everyone else is way higher on btu's. Am I the dope or am I safe and everyone else just looked at the old boiler rating plate? If I'm off somewhere please correct me before I install a blunder.

Robert O'Brien

And

what does the amount of radiation have to do with sizing a hot water boiler? You size based on the heat loss,under or over radiation is meaningless to the boiler size.

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Big Ed_4

You are sizing a hydronic boiler by the radiation. ???

You size a steam boiler by the size radiation and a hydronic boiler by the heat loss of the house. You need to do a heat loss calulation. You would need to measure the enverlope of the hydronic heated space. Ceilings ,floors windows and walls. Figure the R Factors of each run the numbers and add infiltration. And you would get the BTU loss per ten dergree drop. Figure the coldest day and that is what boiler size you need in net rating. Forty gallon min you need is 85,000 BTU. So if your heating load is under bump it up and if your over you will be fine....