How do I run my underfloor heating system efficiency?
Posted by Cathy Debenham on 27 October 2014 at 9:19 am
Q: I have just had a wet underfloor heating system installed in my new extension activated from my boiler. My builder has set it and sent me a link for the instructions on how to use it but he did not answer my basic question. With ordinary radiators you have to have your heating switched on and then the radiators come on - for most of us twice a day. The rest of my house works on that basis.
However, my builder says the new underfloor heating is better left on and controlled using the thermostat. At the moment I don't have any heating on so I am not sure whether the underfloor is on or not - it is showing a consistent temperature but the weather is mild anyway. So the question is do I need to switch my heating on all the time to get the underfloor to work and how do I balance that with my radiator situation? I like a cool bedroom at night and frankly don't want heat at night. Please explain for a complete novice.
A: Let's start with the basics. Your boiler is always on - by which I mean it's ready for use. However, it's not active until your programmer (or timer) calls for heat. How and when it does that will depend on how it's been programmed. Generally you can select on (on all the time), off (ditto - you'll probably want this setting in summer) or timed (which is where the twice a day you mention in your letter is set up).
Ideally, as well as the programmer you will also have a thermostat. Once the temperature in the room with the thermostat reaches the right temperature the boiler turns off again. When it falls below - and the timer is at an active period - it comes back on again.
My guess is that with your two separate heating systems you will have two heating circuits, controlled by separate programmers. These are usually positioned on the wall near the boiler. Your builder should have explained how to use the new one and given you a booklet with the instructions in case you forget. I suggest you get him back to give you a demonstration.
Underfloor heating runs at a lower temperature than radiators, so your builder's suggestion to run the underfloor heating all the time, controlled by the thermostat makes sense. You use your thermostat to set the temperature you want. It is an efficient way of running the system. To understand why, imagine that your underfloor system is just like a very large radiator. The larger the radiator, the lower the temperature of the water within it (known as the flow temperature) needs to be in order to keep a room warm. Now imagine that that radiator is set in concrete, screed or some other solid material. In order for the heat to penetrate into the room, not only does the water need to warm the pipes it runs through, as with a regular radiator, it now also needs to warm that screed.
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To get the pipes and the screed up to temperature takes a lot of energy. Repeatedly turning the system on and off, as you would with regular radiators, will waste energy. However, once both pipes and screed are warm, they will hold the heat efficiently. Keeping your heating on constantly and your thermostat set low, means your room will stay nicely and consistently warm without having those very energy intensive peaks and troughs in temperature or long periods of cold while you wait for the system to heat up.
However, if you like your bedroom to be cold at night you should be able to programme the underfloor heating system to turn off at bedtime and come on again in time to warm the room before you get up. Your builder should tell you how.
Photo credit: Bryn Pinzgauer, Flickr CC
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Need help with any Jargon?By Cathy Debenham
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