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In floor heatload sizing

icy78 Member Posts: 404
So we've been asked to install a combi boiler for a residence which already has the pex in the concrete. 1 zone is 6- 250ft loops, the other, a garage is 2-250ft loops.
How do you size for this? Not asking that it's done for me, but a point in the right direction for some good literature. The bigger zone is approx 30 x 60. The smaller is about 30 x 25.


  • Ironman
    Ironman Member Posts: 7,399
    The proper way is to do a heat loss calc like an ACCA manual J.

    Realistically, a slab will probably have an output of 25 btus per sq. ft. on average, but there are a lot of variables. Your tube spacing looks too wide to achieve that number. Do the load calc and avoid a lot of problems.

    I would NOT recommend a combi as it would be well over-sized for space heating. Use a properly sized boiler + an indirect.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.