This isn't home improvement, per se, so please feel free to let me know if there is a better forum for this.

I have been told by two people, one of whom is a boiler repair technician, that it's not a good idea to set my nighttime thermostat temperature too far below what I have it set at when I'm awake. Neither gave me a satisfactory explanation - just vague "it shouldn't be done" sort of stuff.

My question is why? Will it cause damage to the boiler (~3-4 years old, natural gas) if it's set, say, 10 degrees F different? Will it cause damage to anything else in the house?

I have three zones (basement, first, and second floor). Basement is always at 60. First floor is 70ish while we're home during the day, and presently only 66 at night. I'd like to set it to 60 at night but have been nervous to do so. Second floor is where we sleep, so 66-68 at night is fine.

1 Answer 1


The advice is for the purpose of avoiding frozen pipes.

  • The larger the difference in thermostat settings, the longer the heat will be off.
  • The longer the heat is off, the bigger the temperature differences between the cold parts of the room and the warm parts of the room.
  • Your thermostat is likely to be in a warmer part of the room (inside wall, at eye level) and your pipes are likely to be in the cold parts of the room (in the walls or on the baseboards, often down low).

I had frozen pipes when I was using a room the night before and had the heat up around 70. Then the night time setting of 45 degrees took effect. The baseboard radiators froze before the heat at the thermostat reached 45 degrees and kicked the heat on. This was on a night when the temperature was below zero. I also had some cold air coming in directly behind that radiator. (I have since installed additional insulation there.)

My plumber offered to install a special controller on my boiler that circulates some hot water through the radiators every half hour or so even when the thermostat doesn't call for it. This type of setup will allow wider temperature swings with less risk of frozen pipes. I opted not to do so because the controller itself was expensive. Adding some insulation and having a slightly higher night time temperature were easier.

To avoid frozen pipes:

  • Keep the night time setting well above freezing. At least 50 degrees. My plumber recommends at least 55.
  • Avoid large temperature swings so that the corners of the room don't cool down to below freezing. I wouldn't worry about the 10 degree difference that you are proposing, but a 20 degree difference is more worrying.
  • Put the heat on "hold" if the temperature outside is going to particularly cold that night.
  • Must have been an expensive house to heat. Properly insulated houses don't really have this issue.
    – Ecnerwal
    Nov 14, 2013 at 18:51
  • This particular room is over the unheated garage, on its own zone, and leakier than the rest of the house. Pretty much the worst possible combination for this type of problem. The additional insulation I added directly behind the radiator helped a lot. Nov 14, 2013 at 18:56
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    @Ecnerwal I hope you never suffer a frozen pipe due to your confidence in 'properly insulated houses.' Set the thermostat low enough for long enough when its real cold outside, and you can have problems in just about any structure, especially where pipes are near exterior walls. I've seen a few new construction, well-built houses suffer burst pipes when the occupants went away for the winter. Not pretty.
    – mac
    Nov 14, 2013 at 21:01
  • @mac - I've seen the problem - in a nice old New England house where the drafty, uninsulated rock-walled crawl space was used to run heating pipes. The house I'm in now is no paragon of good insulation practices, and it handles a 10 degree setback just fine, right through the winter. Worse yet I run a woodstove in the room where the thermostat is, so the heat doesn't come on for many hours at a time. A building which is a paragon of good insulation practices will go days without a problem. If the occupants leave for the season and the furnace fails to light, that's a different issue.
    – Ecnerwal
    Nov 14, 2013 at 21:22
  • A properly built house should never have frozen pipes as long as the thermostat is not set to 40 degrees. Alas, LOTS of houses aren't properly built and have inadequate insulation in spots so this is an issue.
    – DA01
    Nov 14, 2013 at 21:58

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