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Boiler not keeping up...or is it?

drosner Member Posts: 45
I've got a Munchkin 40k BTU boiler with 7 (yes 7) zones of radiators, radiant floor, baseboards, and air handler. I added a zone recently for a 900 sq-ft extension to my house (total of 4000 sq-ft) last winter and haven't had any problems since. However this week we hit single digits and for the first time all of the zones are on at once and struggling to get above 65 (they are all set at 72).

I've been down in the basement all day and it seems like most of the time i'm getting burning hot water to all the pipes leading to the zones. Yet at the radiator/baseboards i'm not feeling that same intense temperature. I have one zone that i can trace in the basement and the very hot water seems to stop along the pathway well before it hits any of the radiators. Every now and then the zones seem to get full heat but then it goes back to warm touch.

Looking at the temp gauge its between 100 and 150 degrees. I would have thought the boiler (its a multi stage condensing unit) would at least be able to keep a boiler out temp of 185 which i think is its default. I'd understand if the incoming temp is low if i'm getting a lot of heat loss in each of the rooms due to the cold.

Is this a classic case of running out of boiler capacity and we just need to wear sweaters the few times a year it gets this low? Or could something be happening with the boiler that isn't obvious to me?

Appreciate any suggestions...


  • Jellis
    Jellis Member Posts: 228
    40K BTU im sure is not enough for a 4,000 sq foot home you need to have a proper heat loss calculation done on your home. to test.
    test your zones 1 at a time. Turning all of your zones off except the one your testing. If your zones come up to temp properly 1 at a time then you know they are all working.

    Here is a VERY ROUGH Heat loss calculator it should give you a VERY ROUGH idea of what to expect, i think you will find you need more than 40K BTU to keep up with your total demand.