Radiant Floor, temp control, outdoor reset, condensing boiler

Floyd_16

Your water temps. are not going to be that radically different....pick the highest temp. that you need, and setup the boiler to do that on a design degree day..... the lower temp zones will not be significatly different most of the time. Definetly not enough to justify the extra expense of mixing to different temps.
Also the Ultra already has the reset built into it, so it will do everything that you need... stand alone..... just make sure that you pipe it P/S according to the directions that come with the boiler.
If you have any questions... all the info is on the WM website and can easily be downloaded by anyone.....

Floyd

BC_2

radiant floor, temp control, outdoor reset, condensing boiler

I am considering putting radiant floor heating into a new construction project using 1/2 PEX in a 1.5" thin slab of portland cement mixed with sand on top of the subfloor.

If I use a condensing boiler such as a Weil-Mclain Ultra and thermostatic mixing valves to control each zone's water temp, will I lose the benefit / efficiency of the condensing boiler & outdoor reset? If so how should I control the water temp to each zone? I would think that variable speed mixing pumps would be prohibitively expensive because wouldn't I need one for each different water temperature that is required? Thanks

Unknown

First, forget the sand mix. Bad way to do radiant.

Second, why would you try to use a thermostatic mixing valve to control zone temp? Balance your water temperature requirements, and let the condensing/modulating boiler do the "mixing" with its own modulating and outdoor reset. use good thermostats on the zone (like tekmar's 500 series), and you have varying water temps with outdoor reset and the simplest of piping jobs, just basic primary-secondary.

BC_2

I need different temps for each zone. The basement is a thick slab that requires lower temp water than the thin slabs on the first and second floors. I would probably keep the basement at about 60 to 65 degrees F, while keeping the other floors at a higher temperature. I would think that different areas may also require different temps based on the floor coverings. What would you recommend for the thin slab mix instead of the sand / portland mix? I am trying to keep the weight to a minimum while still piping on top of the subfloor and using a thin slab rather than staple up. Thanks

Unknown

You're better off with extruded plates under the floor than a sand mix; sand mixes are extremely difficult to do with any kind of precision. Water temp might be a bit higher, but at least you know it will be consistent. Otherwise a gypcrete or lightweight concrete will be needed... or over-floor dry system like a sandwich method or prefab panels..

It is very rare that a basement needs its own water temperature. By nature, they do not change temperature quickly, and with decent thermostats they should be able to maintain good temperature. At most, we would consider a "high limit" tempering valve to cut off the temperature to a certain maximum, but we wouldn't bother mixing a completely seperate reset curve there... especially not with a condensing boiler providing nice, outdoor reset water there... compress the tubing in the thinslab (you don't want to be over 9" o.c. anyway in most cases to avoid heat striping) and get the water temperatures to a similar range as much as possible and call it good.

Of course it's your system and you see the actual water temps needed, so take my advice with a grain of salt, but that's how I'd tackle it.