Radiant floor with tankless Combi boiler on wood stove

[Adam Farrow]

Before I start calling plumbers I want to know if this is possible and what I need to see if I'm choosing the correct installer. I want a radiant floor heat powered by a wood stove and tankless combiboiler when wood fire dies I want the tankless to pick up the demand. The tankless will be used for dhw. My gas company said they had an issue with navien saying the water into the unit cannot exceed 90 Fahrenheit and the mixing valve was to inconsistent. it sounds like they were using a dhw unit not a combi boiler. But that's also a gas company quoting plumbing. Is there a automatic change over valve controlled by temp? Or a unit I can have both plumbed into and when it drops below desired temp it kicks on?

 

[Michael Young]

If the incoming water to your tankless is already warm, the tankless won't fire.

I modified my wood stove by cutting the back out and installing a coil or 3/4" copper. I circulate water through the pipe and then through an old timey radiator. I have that in-line with a tank-style water heater. The tank style water heater is 50 gallons. The wood stove heats my house and also heats the water in the water heater. The water heater fires ONLY when the water requires a little extra heat (which is pretty much never). In the warmer months, I shut off the valves and drain down the whole system.

like you, my first choice was to use a rinnai tankless. I went with the tank-style and it works great.