Sorry if this has already been answered elsewhere on this forum, did a search and tried wading through, but didn't see anything related. We're constructing a new house in SW Wisconsin. I already have an outdoor boiler and in my current house we're using using a water to air exchanger for forced air and water to water for the domestic hot water. I plan on using the boiler for the new house and want to use radiant in-floor for the basement and garage slabs and continue using forced air for the main floor of the house. In discussions with a heating contractor, he's advising that my water temp from the boiler is too hot (180 F) for the concrete and that we'll have to temper it down before it gets there. I can't find info anywhere to indicate if he is correct or just blowing smoke. What say some of you? Thanks in advance for any input.

yes, that's too hot. you'll need to mix down with the radiant return water, preferably either through a heat exchanger doing injection or with a mixing valve.

You will need 2 closely spaced T's of primary loop, a pump sized to the pipe load, and a 3 way mix valve to bring it down to 110 or so. Pump is between the mix valve and supply side of the pex manifold.
Dan
or... you could use the 180 degree slab to cook eggs on....

With my naive mind I had thought that I'd have a zone thermostat controlling the pump and that 180 degree water would heat the slab faster but would not increase the slab temp that fast that it would be uncomfortable.

I recently finished a radiant floor, wood boiler with automatic propane backup in Genoa, WI and we will use outdoor reset to control water temperature delivered to the slab. A fixed mixing valve will work, but has to be set to "design" temperature - the coldest day of the year. This will not save fuel or give you optimum comfort like outdoor reset.

We always isolate the expensive radiant floor components from the generally nasty open outdoor wood boiler water.

I plan on running a water-to-water exchanger from wood boiler to electric boiler with the e boiler supplying the water to the in-floor and the water-to-air for the forced air. E boiler would only heat when the wood boiler water drops enough in temp or I have to take it off line for repair/maint. I guess I'll have to trust the heating contractor to know what he's doing as I don't really understand how the temp will drop that much by mixing radiant return water. With two closed systems (wood and electric) I don't see adding water from outside to either system as viable.

What about a three way valve, controlled by a thermostat on the electric boiler that would only allow the wood boiler water run through the water-to-water exchanger only when the temp drops below about 130 or so? Set the electric boiler to heat with the elements at 110?

The best electric boilers (like the one in my house) have built-in outdoor reset.

Sounds like you have a good plan,
Badgers right, Thermolec boilers have out door reset, also a Taco 3 way valve with out door reset will work well also.
Keep in mind you will need some kind of switch to keep the wood boiler pump off when it is not hot so you do not heat the wood boiler and supply return lines up with your electric boiler.
Dan

Unless you want the back up to keep the wood boiler from freezing up.

glycol, back to the heat exchanger loop.

Has anyone tried using glycerin instead of glycol? It is about half the cost and is considered a greener chemical. Any insist or data? Glycerin use to be preferred many years ago.... Thoughts?

Always reinventing the wheel, for one project?

Propylene glycol made for space heating by companies with real engineers and experience with heat transfer, boilers etc. More environmentally friendly? Who's environment?

http://www.epa.gov/iris/subst/0543.htm

If you are going to use the outdoor boiler, I would get a 4 way mixing valve with an outdoor reset such as the Viessmann Dekamatic HK1. Totally self contained and the 4 way will protect the boiler from cold return temps which are a killer for wood systems..