Radiant floor setpoint

zepfan

We have a job that has in floor radiant heat system, and fan coil units. There are separate pumps for the fan coils and for the radiant floor. The building has a condensing boiler, so we can run a very low return water temperature without damaging the boiler. The boiler has the option for three different priorities, Currently the fan coils have a setpoint of 180 degrees, and my question is what should the setpoint be for the radiant system? 90 degrees? It is a concrete floor, with four different zones. We do not have a lot of radiant systems here.
Thanks to all

Big Ed_4

Depends on design , but without knowing start at 120*.

EdTheHeaterMan

I had a radiant heat in the Concrete Slab Addition system in my previous home, I also used a condensing boiler. I got plenty of heat using a 110°F water temperature with a 10°∆T so the average water temperature was about 105°F. The remainder of the home was a staple up using aluminum transfer plates. That 110° water was about the highest I wanted to put on those Hardwood Floors.

If you do not have Hardwood floors to worry about, then I would start at 120° and go down from there. If you get the temperature to over run the thermostat setting by more that 3°F then lower the boiler temperature by 5° and see how that works for a few days. You need to let it operate for at least 3 days before you try another temperature change. It can take that long for the Slab to change temperature and see if it is any better.

It may take 24 hours for the 120° boiler water temperature to show up as a room temperature change when you have a large mass like a concrete slab.

GroundUp

I run all of mine at 100* to start, and adjust from there if necessary. Most end up being just fine with 100* on a design day, but some are lower and some higher. My shop at home runs about 85* at design of -30F outdoor but I only keep it 65 inside

hot_rod

you might run the unit heaters lower also. The lower the swt the more  efficiency you get from the boiler