connect on demand water heater to an indirect tank?

jrv8984

Is it possible, advisable. I would prefer to use my 70 gallon indirect tank year round instead of having a tank for the summer and using the coal fired indirect for the winter? So if I could just hook up an on demand to my indirect tank it would make things simpler.

JohnNY

I've done it. You don't have to go through the indirect tank's heat exchanger/coil. Just connect the gas-fired tankless water heater to the domestic side of the indirect as if it were a domestic hot water source and a storage tank, which is exactly what it is.

JohnNY

You'll need changeover valves and someone to run the tankless heater through a cycle or two once a month or when it's not in constant use. This is how we address hot water in buildings where they want to take advantage of "waste heat" left in the boiler in winter and run a smaller appliance in warmer months.

jrv8984

How would I size the on demand unit to feed the 70 gallon indirect tank?
It would only be used 4-5 months a year over the summer, otherwise it would be turned off.

jrv8984

anybody?

Larry Weingarten

Hi, You could probably use the smallest tankless unit you can find, as long as your draw is something less than 70 gallons.
Yours, Larry

Poppasmurf

You would size it according to the expected demand. If you have one bathroom and one kitchen- it would be quite different from say 3 bathrooms 4 bedrooms with 3 teenage girls.

mikeg2015

Rather than a tankless, why not a “summer boiler”? Get the smallest condensing boiler you can find and connect it to the primary loop. It also will be a backup in case the main boiler fails and can carry the building in shoulder season.