Thank you for your response. The lower level of the house (walkout basement) will be finished with a family room, bedroom, studio and work out space. We will have stained concrete floors in these areas. We are hoping to install vents in the ceiling leading to the main level to allow the heat to rise throughout the house. My husband wants to have a few lines run thru the breezeway to the garage to keep things above freezing in those areas.

Is your home finished now? How do you like your stained concrete floors with radiant heating? I am debating about doing that in our new home. Do you find it to be noisy in your walkout basement?

One disadvantage of floor heat in a slab is the incredible mass. Whether that is good or not depends on use. If you plan a dual use room where you set up your exercise equipment and use it, you want relatively cool. If you expect to later lounge with the family and use the same space for home entertainment, I think you will be disappointed.

If your heating needs are low enough, a DHW heater can provide hydronic space heat. To provide both DHW and space heat, you need either a heat exchanger to separate the two systems, or a second DHW heater. I'd suggest either a HTP VersaFlame, or VersaHydro to do both. Westinghouse WGR060NG076 series water heaters use the same design heat exchangers as the HTP and are probably rebadged versions of the HTP Pioneer water heaters. The heat exchangers have a unique design that looks ingenious to me. The Westinghouse heaters are very inexpensive and very efficient. You could install one for each purpose if you are going to be in the house for a long time.

With a lot of boilers, the outdoor loops will require not only antifreeze, but will also require primary -secondary piping to prevent heat exchanger shock with cold water entering and cracking. Some systems will be provided with this anyway just for the rest of the house.

Use an on demand hot water heater with a heat exchanger isolating the radiant heat from the on demand hot water heater. Pull the domestic hot water off the loop between the heater and heat exchanger. I used a Takagi Model T-H3M-DV for my last radiant heat project and could not be happier with the performance. The manual for these units actually shows the layout for just such a dual usage.

The demand HW heater in this appplication is interesting to think about. one would think that they are designed to condense with input water at a psignificantly lower temperature than return water from a heating loop. I guess if they can’t do it, they could be set to max out at less than full output so as to keep the heat exchanger cooler. Would the DHW exchanger be in an indirect tank or a flat plate type? What do you do when there is no demand for heating?

I recently reviewed the Versa-hydro after another question. It made think that for the outdoor loops, you might be able to run a separate circuit for a total of three by using the optional solar thermal input as an output HX, That might be desirable so glycol might be used for only the outdoor zones. Some people use these as an input for wood boilers instead of solar thermal.