Tank size?

johnraymond

I was just asked to hook up the radiant floor heat in a partially finished home. Apparently towards the front left area of this house it has concrete slab floor covering a 16 x 20 room with a 12’ ceiling. In the crawler two 1/2” pex lines stub into it. A supply and return.

He has a 50 gallon electric HWT and an electric tankless (that I don’t have the make, model etc on) in the laundry room about 15’ away from the room with the slab. The load on the hot is two full baths, clothes wash., kitchen sink w/dishwasher. Can I use the 50 gallon tank for the heat too?

STEAM DOCTOR

If I am understanding the question correctly, you would like to use the same tank for domestic hot water and for radiant heating. If that is the question, then I think you seriously need to step back and ask yourself if you are qualified for this job. Using the same tank is close to a guarantee to give the occupants of the house legionnaire's disease. Besides for the other host of problems that make this just about impossible.

GroundUp

You can do whatever you want, but it's a terrible idea to connect the radiant and domestic to the same appliance unless using a heat exchanger to separate the two systems. Not to discredit you or your skill level, but it may be in your better interest to recommend a professional for something like this. STEAM DOCTOR was a little extreme with his comment as the chance of Legionnaire's is very minimal, but it's still a chance and nobody who values their business or their client's health would consider such a thing. If anything, suggest a separate 6-20 gallon water heater (2500-3000W) to do the radiant only.

Mad Dog_2

Legionnaires thrives up in the radiant heat range and is only 100% killed at 165 F. I have seen some gas hot water heaters using the same water at 125-130...scary. That being said, for smaller radiant jobs I have had great success with the Bradford White Combi-Cor which keep the two mediums seperate & using a mixing valve to keep Legionella down.

As always, shoot us some pictures & a sketch & we will guide you the best we can. Mad Dog

hot_rod

Do a heat load on the space first. Assume 5,000 btu/ hr as a guess, 320 sq ft X 15 btu = 4800 btu/hr.

So you want enough HW tank capacity to still provide DHW.

I would throw a plate HX on the side of the WH and separate the radiant .

There are pre-made HX modules, or build one with HX air purger, pump,expansion tank relief and two fill purge ball valves.

mattmia2

note that this will likely cost more than a small mod con boiler and trim.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1853792#Comment_1853792

A HX module can be built for a WH for under a grand, less if you shop E-bay

GroundUp

https://forum.heatinghelp.com/discussion/comment/1853792#Comment_1853792

Where are you buying a mod con boiler for less than the cost of a $100 heat exchanger?

mattmia2

i was referring to the packaged thing. the hx itself is more than $100 then the second circulator, the fittings and essentially all the boiler trim

GroundUp

Ah, yes the packaged thing. But in reality an exchanger for that purpose could be had for well under $100. The circs and all other components would be necessary with a boiler too, so the only difference really is the HX.