Tankless water heaters and radiant floor heating

Jeffrey Campbell

I have a customer that wants an electric tankless water heater install for his 3000 sf home. The heat load is 67,000. The radiant system will be install in gypsum so the water temps will be low 110 degrees. But I also have to deal with DHW. Can you drive a 50 gallon indirect water heater with 140 degree water form the tankless. I am afraid to install a second tankless for DHW because our incoming water temp is 40 degrees and at that delta T the unit only produces 3.9 gpm.
Finally I have installed 3 Seisco electric tankless units this past year in smaller appications-garages with livng couters above. But they have only been ruuning for a few months. Will these units last?

Radiant Wizard

Question

Why would you use an indirect anyway? Since your spending the money on it why wouldn't you just use another tankless heater.

My other question is that heat load. Seems high for a 3,000 sqft house with radiant. Just by using a simple formula that I have crafted over the years I would say the load is around 48,000 Btu's.

The only thing I worry about with tankless heaters are the heat exchangers. I would be surprised if you got 6-10 years out of the units.

Mark Wolff

Short showers, Dirty Harry

If you like short showers, and are afraid of baths you can have a water heater supplied by 140 degree water. If you want actual hot water and a decent recovery time, you need 170-180 degree water supplying the H2O htr.