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Need Advice for New Construction Domestic Hot Water + Radiant Floor Heat

Building a 3,000 square foot home in Western Montana, about an hour south of Missoula. We have a basement slab that has about 1,600 feet of 1/2" PEX with 6 zones. The home will have three bathrooms, kitchen, W/D. I'm trying to decide between electric vs. propane water heaters. Our electric is cheap. 6 cents per KWH.

Will I need a separate water heater for the radiant floor heat? If so, how many gallons? As for domestic, would one 50 gallon tank work for the whole house?

Thanks for any advice/brand recommendations you can give. I 've been doing research but still overwhelmed with choices!


  • hot_rod
    hot_rod Member Posts: 22,251
    First off a load calculation to size the heating appliance.

    Next, how much hot water do you have now? Is it adequate? 40- 50 galloons are most common, or a tankless type.

    Plenty of online fuel cost calculators search fuel cost calculators.

    Figure standard electric heat at high 90%. Boilers run mid 80- mid 90%.

    Heat pumps will maximize electric energy use.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream