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Underfloor heating with boiler and thermostat

viliusss Member, Email Confirmation Posts: 1
edited September 2021 in Radiant Heating
Hey guys, recently bought a new apartment, and I'm a bit confused with the heating, since it's my first time owning my own place. So I have a gas boiler, which heats the water that heats the floor, obviously. I've read that the optional water temperature is between 95 to 130, something like that. So the main question is, if I have a thermostat in every room that you can control for the room temperature you like, why the water temperature matters? I mean, if I set it to the higher 130, does the rooms just heat faster? Or should I keep the lower 95, how do these things affect my heating and temperatures?


  • Jamie Hall
    Jamie Hall Member Posts: 18,956
    Fundamentally, underfloor -- radiant -- heating is intended to maintain the space temperature, but is not well suited to raising that temperature. Depending on the way it's set up, it can take hours... or longe! -- to respond to a change.

    Ideally the circulating water temperature is set "just right" to do that, so that water circulates all the time and maintains the floor at an even temperature. That's the ideal. In practice, that doesn't always work, so it will usually be set slightly higher than necessary, and a room temperature thermostat can be used to turn off the circulation when the room is warm enough.

    Now it is quite true that a higher circulating water temperature will make the floor hotter, and thus the room will heat up faster. However, there is very much a limit to how hot the floor can be, both in terms of the impact on flooring materials and in terms of comfort. A floor surface temperature of around 80 seems to be about the upper limit in terms of comfort.

    So. Bottom line is that the circulating water temperature going into the floor should be set just high enough to maintain the space temperature, and no higher. In more advanced systems, this temperature is controlled by "outdoor reset", which adjusts that water temperature higher if it is cold outside, and lets it drop if it is warmer. Your system may or may not have that feature. If not, you may find that you need to raise the circulating water temperature in colder weather, but always trying to keep it just warm enough so that the circulator is running almost all the time.

    The boiler will turn on and off to maintain that circulating water temperature where it should be; there are various ways in which this happens and, without knowing more about your particular system, I wouldn't care to speculate on how it is done in your case.

    To reiterate one thing I mentioned above: radiant floors are not intended to raise the space temperature quickly. Thus setbacks are not recommended at all, unless for very long durations (like several days or longer).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England