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new construction in floor radiant boiler sizing with indirect dhw
Searching all over the internet and bouncing back and for, I may have a set-up I am looking to do in my new build that I cannot find an answer to. I am building a 3200 sqft slab on grade with in floor radiant heat and 2x6 R19 walls and in Iowa. I will have a mother in laws area in 1200 of that 3200, on the main. The 1/2" radiant tubing is in place in the slab on 12" spacing with R10 under the slab and 4' of R15 vertically along the stem wall.
Above 2000 sqft of the main level, will be an 1100 2nd story with 3 bedrooms and 2 baths. I will add a 4k btu Buderus style radiator to each bedroom and a 2k btu radiator to each bathroom for heating. Although, I will have an electric furnace for backup/supplemental heat for the entire house, should anything go wrong.
My HVAC guy that is installing the furnace and AC units says my heat load will be around 88k btu.
I am trying to figure out the best size of modulating condensing boiler to accommodate the in floor radiant heat, supply the additional radiators upstairs and support and indirect water heater (60 gallons or so??) for the DHW? I am thinking the average water temperature will be around 150-160 degrees to keep it from short cycling and in condensing mode as much as possible.
I know oversizing a boiler can be bad and am looking at the HTP UFT100 as it may satisfy the radiant as well as the indirect WH with above average daily hot water demands, as the house should be somewhat energy efficient but has 2 kitchens, several showers and laundry daily?
Any thoughts or suggestions would be greatly appreciated!