Author Topic: Energy saving - thermostat, boiler temperature and radiator valves  (Read 1330 times)


  • Walrus Stache
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  • Posts: 6809
  • Location: London, UK
Our heating setup is that we have a combi boiler where you can set the water temperature that runs through the pipes separately for tap and heating, one single thermostat in the hall (right by the front door so it freaks out every time we open it. Thanks, installer) for the whole house, and radiator valves on most but not all of the radiators. Were a two-storey Victorian red brick semi-detached with a high, open stairwell so a lot of the heat from downstairs rushes straight upstairs.

I have already set the radiator valves to max downstairs and much lower upstairs, as so much downstairs heat comes upstairs and the thermostat is downstairs.

What is the most efficient balance between water temperature and thermostat? I usually set the thermostat at 17-18 degrees C but do whack it up for an hour or so if Im really feeling cold. Is it better to have the water temperature set high so that the house comes up to temperature quicker (but then the boiler works harder) or to have it set low so the boiler works longer but less hard and the heating stays on for longer?


  • 5 O'Clock Shadow
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  • Posts: 16
Re: Energy saving - thermostat, boiler temperature and radiator valves
« Reply #1 on: December 13, 2017, 05:23:51 PM »
The most efficient boiler temperature is "as low as possible". Whether that's the best temperature for your house depends a lot on your boiler. If it's an older model you can have return water temperatures that are too low and damage the heat exchanger, possibly cracking it and ruining the unit.

I STRONGLY recommend reading the manual for your boiler to see what it is capable of.

The best effeciency will come if you have a condensing type boiler and can turn the water temperature down enough to allow condensing to happen. This will let you harvest the heat of formation of the steam in your exhaust gas.

If you are really lucky your unit will have a feature called "outdoor reset". This lets you attach an outdoor thermometer to your boiler, and it will adjust your water temperature based on the outdoor temperature. Then you can run effecient, low temp water when it's mild out but still get the high temps you need when it's really frigid outside.

There are also seperate outdoor reset units available to refit older boilers, but unless your really handy I wouldn't consider it a DIY job.


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