Max supply water temperatures for radiant.

mburg

What would be the highest water supply temperature for radiant in a concrete slab, or gypcrete? 

Alan (California Radiant) Forbes

On a well designed system, 130°F.

hot_rod

maxxon states that its gyp products resists breakdown up to 150F

Why do you ask?  That would be a very high temperature on a floor, even with a covering over it

mburg

I understand that you should never design a system that requires that high of a supply temperature, but could there be any damage to the tubing, or concrete if higher water temperatures are used? 

Is there any concern if 180 degree water goes into a gypcrete or concrete system at startup for a bit. 

I am replacing a condensing boiler that feeds 14 space heating zones and a 120 gallon indirect. There is currently mixing valves for all 14 space heating zones. I was considering removing all of them and allowing outdoor reset to set a supply temperature for all zones. (Except garage and basement. I will leave mixing valves on those zones) Some of the valves are leaking and it seems like a good way to get a bit more efficiency out of the system. 

My concern is after a domestic hot water call the boilers, near boiler piping, low loss header, etc will be up to 180 degrees. Depending on how many zones are calling after a domestic call it could take several minutes or more to cool the water to a more appropriate temperature. 

Would this be a bad idea? 

hot_rod

A small, short slug of 180F water into the radiant will not be a problem. I doubt it would last a few minutes and would dissipate quickly.
Does your system control have a post purge setting? You could dump that higher temperature into the indirect. Most relay boxes and boilers have post purge for one circulator.

mburg

That’s a good idea. 

Thanks for the input.