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Radiant Floor Heating on/off at night?

3 replies [Last post]
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Joined: Jan 15 2005

Should I leave the radiant floor heating on all the time in the winter or should I have it, via the thermostat, turn off at night and back off in the morning? I have been told that it takes so long to heat the cement slab up that it should be left on but this takes up so much energy. Any thoughts/advice would be appreciated. Thanks.

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Joined: Jul 28 2004

I'm far from an expert, but my understanding has always been that it takes 6 hours for a radiant system to get up to speed.
We have lived in an Eichler for over 30 years and we never turn the heat down at night.

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Joined: Jan 18 2005

I have been specifying radiant heat in high-end homes for years.

Radiant heat should not be turned off at night. Harris is correct, the lag time is too great for this to do any real good. The amount of time that a radiant heat system lags varies depending on the thermal mass that the heating tubes are in, but could be anywhere from a few hours to a few days. In this case the thermal mass is the entire slab of the house, a fairly significant amount. By turning off the heat at night you may not even feel a change in temperature until the following morning or beyond.

The energy that it takes to get the system including the slab back up to operating temperature may even be more than the energy needed to maintain that temperature consistently.

The exceptions to this rule are thin electric systems or possibly water systems used in very low thermal mass siuations such as metal plates in the joist space of floors over basements.

Joined: Mar 2 2004

This might depend on what you are using to heat your Eichler. Some of the original boilers took forever to heat a house. Today's boilers are much more efficient than anything built in the 80's. (Don't even ask about the 50's and 60's). In fact, one of our Stanford customers tells us that he got money from Eichler for his heating system, when he proved in court that it could not heat the house.
My Eichler had a better boiler that was installed in 1980. It seemed to make a difference pretty fast. The set-back thermostat worked great. I had it shut down at 6 or 7PM, come on at 5AM and run til 7:30AM to give the house a boost for the 'morning hustle', then back on at 1:30PM. I programmed it differently for weekends, when we were more likely to be at home during the day.
I think you will find differing practices and results, depending on the many variables in today's Eichlers. To me, it makes sense to let the system idle at night so the house cools off a little when it is not noticed.

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