We've just installed a new Condensing Combi boiler last week, Lochinvar NKC199N. I've noticed the installer set the outlet temperature to 180F/82C and the return temperature to inlet is somewhere around 169F/76C. To me, this temperature set point is way to high but with the fact that it was cold out side last week 5F/-15C, we are in Massachusetts.

We have 4 zones, 3 zones control forced hot water baseboard and the other zone controls radiant floor (concrete slab for our greenhouse, we use a mixing valve to reduce water temp to 130F/54C for floor). So while the other 3 zones satisfied the room temperature, the 4th zone for the radiant floor seems to keep running most of the time to keep the slab warm with this cold temperature outside, but since the outlet set point is 180F/82C, I feel that we are wasting the energy.

So my question is should I change the outlet set point to 130F/54C? so we can just send 130F/54C straight to radiant floor, ignoring the mixing valve, and I expect the return temperature to drop to somewhere 110F/43C, so it can be condensing. Is "130F/54C" good enough for baseboard heater?

  • The biggest issue here is a condensing boiler doesn't do a lot of condensing at 180F. That wastes energy. I would lower the boiler setpoint by about 10 degrees (F), every few days and see if your house maintains tstat setpoint. if it does, great, if not just turn it back up. but 180F is pretty high for a condensing boiler. Obviously a lot depends upon outdoor temps and the insulation of your home. Feb 8, 2022 at 17:59

1 Answer 1


The baseboard is what requires the high temperatures, if all was UFH 40°C flow would have been more than enough, baseboard require quite high temperatures to be able to heat decently.

UFH is great if kept running 24/7 with the lowest temperature possible (usually there are automatic mixing valves, or boiler directly, that set the temperature according to outside probe), fixed setpoint systems are really old-school.

I think you could use dual-setpoint: bring consensus contacts to the boiler where if any of the baseboard zone is calling the setpoint is set to 80°C and fallback to 40°C if only UFH is running. Many boilers require an additional "zone control board" to allow this.

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