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How do I run my underfloor heating system efficiency?

Posted by Cathy Debenham on 27 October 2014 at 9:19 am

See: Air Source Heat Pump: Is it right for your home?

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.

Find out why heat pumps are the perfect partner to underfloor heating.

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.

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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6 comments - read them below or add one

Sandra Hayes

Sandra Hayes from Comment left on: 13 March 2017 at 1:52 pm

Hi Dennis,

A flow temperature of 75 degrees sounds very high for an underfloor heating system.  A flow temperature of 35 to 60 degrees would be more usual, depending on the fabric of your home, the type of underfloor heating and the floor finish. 

It is very hard to advise on how long you should have the heating on for and what flow temperature you should use.  So much will depend on how well your home is insulated, when you are at home and what temperature you feel comfortable with.  As it says in the blog above on way of dealing with this efficiently is to leave the heating on all the time, but to control the temperature using the thermostat.  As you have room thermostats in all your rooms, this may well be the best option for you.  Try it and see wehther it works for you.

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DennisMComment left on: 15 February 2017 at 12:08 pm

I also have moved into our new home which has an extensive wet underfloor heating system. The house is a single story with three separate areas (with their own separate manifold) and has 12 different zones in total, each controlled by a room thermostat. The one gas boiler also controls the hot water which is a very modern separate storage cylinder

We've never used ufh before and am a little confused in how to operate it and how it differs from a radiator/trv system. It's easy to set both the heating controls and the individual thermostats and the separate heating system for the hot water. We've already noticed that it takes rooms in the house much much longer to reach an adequate temp in the main living rooms - lounge, kitchen, dining room) than we were used to with radiators at our previoius house

My questions are fairly simple ones ..

1 What temperature should the heat output for the ufh be set at the boiler (It is currently at 75 degrees which is close to its max)

2. How often should we switch the boiler on and off? Currently it is one for about 2.5 hrs in the morning (7.00 to 9.30) and about twice as long in the evening (4.00 to 9.30).

3 As an alternative to the current arrangment, should we simply leave the boiler on from say 6.00 til 9.00 and run the boiler at a much lower temp, say 60 degrees

Thanks in anticipation


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Boilerdoctor247Comment left on: 9 November 2014 at 6:18 pm

Hi guys im a udfh expert and give you some advice 

*underfloor heating if set up correctly will run independant of your heating (radiators) 

*You should be able to control each area via thermostat , i always set up my installation via wireless sytem various manafacturers availible Uponor have great systems and John Geust speed fit but depending on your current manafold manafacturer 

Regarding rehau udfh system sounds like boiler time or temperature control is not working correctly the boiler should respond to a signal from programmer and switch of ethier by temprature or time.

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Cathy Debenham

Cathy DebenhamComment left on: 6 November 2014 at 5:15 pm

Hi David 

I did put a call out on Twitter this morning for ufh experts who might be able to answer your question, which I'm afraid is too specific and technical for me. But so far, no response.

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David Newton

David NewtonComment left on: 6 November 2014 at 5:11 am

I have a question and apologies if it has already been answered somewhere else. I moved into a property in the spring and have a Rehau wet underfloor heating system which has been turned off until now as it wasnt required. I have now turned it on and set the time/temperature parameters via the thermostat, but in the 24 hours since I turned it on, the boiler has been on constantly regardless of the time of day. On the Rahau control panel I still have five red lights on (against the full 7). This doesnt seem right to me - the property is nice and warm but my gas bill is going to be ridiculous at this rate.....any ideas? Is the system just warming up or do I have a problem?

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ADODDSComment left on: 27 October 2014 at 9:40 am

I would say that you need to find out how the system has been piped up.It should be on a separate circuit with a separate pump and mixing valve to control the temperature into the underfloor system. This should be set at no more than 50 degrees for a screed floor .The thermostat in the room of the underfloor should open the valves on a manifold for that zone , switch on the underfloor pump and switch on the boiler though there can be different configurations.If you have more details of the install I may be able to help.In the first instance though I would check that you can operate the underfloor independently of the rest of the heating system otherwise you may find inefficiencies.Rgds Alex

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