Water to water heat exchanger for radiant.

joea99

Wild hair time. Or hare, as befits your mindset.

Thinking about adding a 4 season sun room and heating the slab with radiant. One thought was to plumb a water to water heat exchanger into my potable hot water, heated by a Takagi TK3 and the other side into the slab loop.

Leaving certain details such thermostat, mixing valve, etc. aside for now, how practical, and safe, is such an idea?

Scanning what turns up on search does not really get into potable vs non potable and how safe, they are regarding leakage from one side to the other.

I'm imagining the pressure on the slab side could be maintained near ambient, so "back leakage" might be a non problem?

hot_rod

Sure, size the pump to the pressure drop of the Takagi.  It is similar to connecting a recirc loop and pump
 Components will need to be non ferrous NSF listed on the potable side

The hydronic side will need expansion tank, air removal, etc

joea99

hot_rod said:

Sure, size the pump to the pressure drop of the Takagi.  It is similar to connecting a recirc loop and pump
 Components will need to be non ferrous NSF listed on the potable side

The hydronic side will need expansion tank, air removal, etc

I already have a recirc loop on the Takagi. There is a "kinetic" wireless push button at each hot water sink (except laundry) and a receiver to turn turn the pump on. I'd have to modify it to allow the slab thermostat to override, I guess.

Any thing special to look for on the heat exchanger? Best brands?

hot_rod

The heat exchanger should be sized to the heat load, flow rate and temperature 
how large is the room,?what size tankless

you nay not have enough capacity to heat the radiant and hot water?