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3x Oversized ModCon with Concrete Slab, New Home
I'm designing my new ICF home. 2900 ft2 slab heat 3-zones with master/slave zone synchronization.
I did a ResCheck DOE heat loss estimate with my proposed plans & got UA = 400
Location is Cripple Creek Colorado so my design Temp is about -30*F, thus at 70* indoor, my Delta T is about 100* 400 x 100 = 40,000 BTU/hr.
I have a new in box Buderus GB142-45.
Looks like this boiler is about 3x oversized after being derated for 10,000' altitude.
I did the math on my slab, 40yds concrete x 3,800#/yd (with rebar) = 152,000#
With a Specific heat of .2 it will take 30,400 btus to raise the slab 1*f
So at -30* my boiler duty cycle will be about 33%, at freezing (this is a guess) possibly a 10-15% duty cycle?
So my question is: Should I sell the Buderus & buy smaller ModCon OR will slab act like a large buffer tank & Buderus will perform fine with low duty cycles?