Underfloor heating in new Extension
Discussion
I have tried the search but, as it is still broken, I cannot find any reasonably similar threads so here goes.
I am in the process of buying my first house, should exchange this week, and it came with planning permission for a side and rear extension. The additional space is open plan and adds just over 26 m2 to each floor. On the ground floor this forms a new kitchen with a “den” area and is open plan to the dining room, another 15 m2 or so. I have contracted an Architect to do the Buildings Regs submission and all is progressing well.
My question relates to heating, and how to provide the water for it. As it is all open plan, and mainly kitchen, I was thinking that an under-floor water heating system would be the best bet. I cannot retrofit this throughout the house as it is 1950’s construction and the floor is one single cast block of concrete! Would this be a good idea? Also if I do go down this route would some form of ground heat pump be economic to install into the garden to provide the water or am I best of fitting a regulator to the existing combi-boiler and using that?
Many thanks,
Jon
I am in the process of buying my first house, should exchange this week, and it came with planning permission for a side and rear extension. The additional space is open plan and adds just over 26 m2 to each floor. On the ground floor this forms a new kitchen with a “den” area and is open plan to the dining room, another 15 m2 or so. I have contracted an Architect to do the Buildings Regs submission and all is progressing well.
My question relates to heating, and how to provide the water for it. As it is all open plan, and mainly kitchen, I was thinking that an under-floor water heating system would be the best bet. I cannot retrofit this throughout the house as it is 1950’s construction and the floor is one single cast block of concrete! Would this be a good idea? Also if I do go down this route would some form of ground heat pump be economic to install into the garden to provide the water or am I best of fitting a regulator to the existing combi-boiler and using that?
Many thanks,
Jon
You can add an ufh system onto your existing boiler - it uses it's own pump and a blending valve to mix the temp down to ufh levels.
There's even a fairly cheap conservatory kit available that doesn't even need it's own pump - it just works as an extra rad circuit would - only does a small floor area tho'.
For the sake of 26m2 a ground source heat pump may be overkill
There's even a fairly cheap conservatory kit available that doesn't even need it's own pump - it just works as an extra rad circuit would - only does a small floor area tho'.
For the sake of 26m2 a ground source heat pump may be overkill
If you want to use a hot water heat pump for this, and air sourced would be the way to go even in the UK, then you would be far better with a deep slab of concrete rather than thin to give plenty of energy storage.
As far as I know UK uses just something like a 2 inch slab, which is fine for a quick response fossil fuel fired system. A heat pump is much better run during the day (as it's warmer) and the energy stored in a thick slab - NZ uses 4 inch. The energy then comes out in the evening and night - it's like a giant storage heater using a quarter (or less) of the energy normally required.
This part of the system would be totally separate from the rest of the house heating.
Important thing is to have pipes fitted, I would suggest a deep slab in any case - a gas fired system will work fine just with slower response times - so as Ferg says this part should have it's own separate time clocks regardless of anything else
As far as I know UK uses just something like a 2 inch slab, which is fine for a quick response fossil fuel fired system. A heat pump is much better run during the day (as it's warmer) and the energy stored in a thick slab - NZ uses 4 inch. The energy then comes out in the evening and night - it's like a giant storage heater using a quarter (or less) of the energy normally required.
This part of the system would be totally separate from the rest of the house heating.
Important thing is to have pipes fitted, I would suggest a deep slab in any case - a gas fired system will work fine just with slower response times - so as Ferg says this part should have it's own separate time clocks regardless of anything else
The advice I have seen says that the under-floor system should be fitted with a minimum of a 400mm slab underneath, then the DPC, then 200mm of insulation followed by the pipes and then a 50mm screed to finish. The water is fed by a mixer pump that takes hot water from the boiler and reduces the temperature, using a mixture of the return waters and the cold water supply, before passing this through the pipes. This can be controlled by either a stand alone thermostat and timer or using some fancy system that has an additional external temperature sensor so it anticipates the changes outside and compensates inside. This was explained as necessary due to the long lead time for the system to heat the internal space. The cost of this was not listed, so I am assuming that it is very expensive! The heat pump would supply the water at the correct temp for the under-floor system so no mixing is required, but I do not need much (it is a small system) and I am not sure if the expense would be worth it. Probably not once you read the previous responses, although I am anticipating keeping the house for 14-15 years for the kids schools if that makes any difference.
I was planning to fit some form of wood floor over the screed and I am guessing that it does not want to be too thick as this would act as another layer of insulation over the heat source.
I was planning to fit some form of wood floor over the screed and I am guessing that it does not want to be too thick as this would act as another layer of insulation over the heat source.
As the extension hasn't been built the important bit will be to decide what system you want before building and ensure you get it built accordingly. Don't get the shell up and then try and adapt a system to fit.
ETA: Why is your Architect not advising you about this?????
ETA: Why is your Architect not advising you about this?????
Edited by mk1fan on Thursday 2nd September 10:19
Ferg's right about connecting it as a new zone. It's unlikely to be worth installing a heat pump for a (relatively) small area - if you're on mains gas you certainly won't save any money on fuel even if you ignore the cost of the machinery.
We think UFH is wonderful (so far, haven't done a full winter yet) - no draughts and a comfortable even heat. It is relatively slow to respond, so it's better suited to a house that's used through the day rather than brief morning/evening spells. Because of the slow response time, it's much better suited to well insulated houses than draughty ones as it can't quickly adjust to the natural daily fluctuations in outside temperature.
It helps to have enough foundation depth - our wet UFH is in 60mm screed on 150mm of insulation, and that's on a 200mm slab - it all adds up to a deep hole. A decent amount of insulation under the screed allows the floor to stay warmer even when unheated - if your house is 1950's with a concrete slab, you're probably aware that the floor can suck heat out of your feet.
We think UFH is wonderful (so far, haven't done a full winter yet) - no draughts and a comfortable even heat. It is relatively slow to respond, so it's better suited to a house that's used through the day rather than brief morning/evening spells. Because of the slow response time, it's much better suited to well insulated houses than draughty ones as it can't quickly adjust to the natural daily fluctuations in outside temperature.
It helps to have enough foundation depth - our wet UFH is in 60mm screed on 150mm of insulation, and that's on a 200mm slab - it all adds up to a deep hole. A decent amount of insulation under the screed allows the floor to stay warmer even when unheated - if your house is 1950's with a concrete slab, you're probably aware that the floor can suck heat out of your feet.
Tuna said:
Ferg's right about connecting it as a new zone. It's unlikely to be worth installing a heat pump for a (relatively) small area - if you're on mains gas you certainly won't save any money on fuel even if you ignore the cost of the machinery.
We think UFH is wonderful (so far, haven't done a full winter yet) - no draughts and a comfortable even heat. It is relatively slow to respond, so it's better suited to a house that's used through the day rather than brief morning/evening spells. Because of the slow response time, it's much better suited to well insulated houses than draughty ones as it can't quickly adjust to the natural daily fluctuations in outside temperature.
It helps to have enough foundation depth - our wet UFH is in 60mm screed on 150mm of insulation, and that's on a 200mm slab - it all adds up to a deep hole. A decent amount of insulation under the screed allows the floor to stay warmer even when unheated - if your house is 1950's with a concrete slab, you're probably aware that the floor can suck heat out of your feet.
The new extension will be very well insulated, the 2010 building Regs see to that, and so should retain the heat well. The old part of the house is a different matter and I will have to look how I can try to improve the thermal performance. Ideally I would install UFH throughout but it is just not possible. I will, probably, just have to invest in a very good quality underlay and flooring. I was going to try and use the same style of wood floor throughout the entire ground floor but needed a high thermal co-efficient in the old part of the house and a low one in the new may rule this out. It is all more things to consider before the actual building takes place.We think UFH is wonderful (so far, haven't done a full winter yet) - no draughts and a comfortable even heat. It is relatively slow to respond, so it's better suited to a house that's used through the day rather than brief morning/evening spells. Because of the slow response time, it's much better suited to well insulated houses than draughty ones as it can't quickly adjust to the natural daily fluctuations in outside temperature.
It helps to have enough foundation depth - our wet UFH is in 60mm screed on 150mm of insulation, and that's on a 200mm slab - it all adds up to a deep hole. A decent amount of insulation under the screed allows the floor to stay warmer even when unheated - if your house is 1950's with a concrete slab, you're probably aware that the floor can suck heat out of your feet.
I’ve been looking at wood floor underlay’s and there seems to be a potential problem here. For the UFH’ed area I need a low tog underlay and these appear to be about 3 mm thick whilst the high tog rated ones are at least 5 mm thick. As the floor flows between the two areas am I going to need to raise the new extension floor by 2 mm to ensure a flat floor or is there an easier option that I am missing?
I don't want to sound harsh but you need to speak to the installer, manufacturer and/or your Architect. This forum isn't intended to provide definative advice on the detail design of building projects. Nor should it be relied upon to do so.
You have a Professional on board, use them. It's worth the money to get the job done 'right' and as you want it.
You have a Professional on board, use them. It's worth the money to get the job done 'right' and as you want it.
mk1fan said:
I don't want to sound harsh but you need to speak to the installer, manufacturer and/or your Architect. This forum isn't intended to provide definative advice on the detail design of building projects. Nor should it be relied upon to do so.
You have a Professional on board, use them. It's worth the money to get the job done 'right' and as you want it.
I am, my bank manager will attest to that, but it is always useful to get another opinion, even if it is one from an internet forum that you have to take with caution. I don’t expect detailed advice but generic “this is a good idea, this is a bad idea” is useful as is “I did this and it works”. If you don’t have any background knowledge then when the Architect starts talking about 4 inch Celcon blocks how do you know he is not under or over specifying? I am not expecting detailed building structural calculations or drawings just a flavour of what is possible and realistic.You have a Professional on board, use them. It's worth the money to get the job done 'right' and as you want it.
Well you haven't given enough details for anyone to do that.
I could tell you about hardwood floors but any informal remarks may not be relvant to your application.
I'm not trolling. I have spent a lot of time with Clients who don't have a clue about buildings/materials/detailing/regulations that have asked vague questions to other parties and then taken the responses as formal advice. Advice that is irrelevant to the application.
If you are wanting a second opinion on advice that you have been given then you need to provide exactly the same information for people to consider. I can tell you right now that there will definately be at least two different ways of building your extension.
I could tell you about hardwood floors but any informal remarks may not be relvant to your application.
I'm not trolling. I have spent a lot of time with Clients who don't have a clue about buildings/materials/detailing/regulations that have asked vague questions to other parties and then taken the responses as formal advice. Advice that is irrelevant to the application.
If you are wanting a second opinion on advice that you have been given then you need to provide exactly the same information for people to consider. I can tell you right now that there will definately be at least two different ways of building your extension.
Jonleeper said:
The advice I have seen says that the under-floor system should be fitted with a minimum of a 400mm slab underneath, then the DPC, then 200mm of insulation followed by the pipes and then a 50mm screed to finish...
That's from scratch - google polypipe overlay ufh, 40mm onto the slab - ours covers 52m2 and is the best thing we did with our extension. As we were refurbing the whole house the 40mm raise in the floor was taken through to the front as well rather than have a step at the kitchen door.mk1fan said:
Well you haven't given enough details for anyone to do that.
I could tell you about hardwood floors but any informal remarks may not be relvant to your application.
I'm not trolling. I have spent a lot of time with Clients who don't have a clue about buildings/materials/detailing/regulations that have asked vague questions to other parties and then taken the responses as formal advice. Advice that is irrelevant to the application.
If you are wanting a second opinion on advice that you have been given then you need to provide exactly the same information for people to consider. I can tell you right now that there will definately be at least two different ways of building your extension.
It’s always interesting how these sort of threads grow! I have looked back and my original question was about the viability of using a ground source heat pump for such a small run of UFH. In replying to a response the subject of the flooring arises and then I get a free 5 mins in the office and the subject of underlay is introduced. I have the full specification here on the Building Regulation Submission and it lists things that I have no idea about – Celotex T-Break TB3000 boards or Catnic Stronghold Wall Connector (in the context of BS 5628) – but will, I’m sure, mean a lot to both the Council Inspector and my builder. I was only wondering if there was an obvious solution I have overlooked when connecting a new floor with an existing one and getting the levels correct, other than raising the new floor by the difference. I have often found that if one asks a large audience, especially one as diverse and surprisingly knowledgeable as PH, you often find examples of “best practice” or novel solutions.I could tell you about hardwood floors but any informal remarks may not be relvant to your application.
I'm not trolling. I have spent a lot of time with Clients who don't have a clue about buildings/materials/detailing/regulations that have asked vague questions to other parties and then taken the responses as formal advice. Advice that is irrelevant to the application.
If you are wanting a second opinion on advice that you have been given then you need to provide exactly the same information for people to consider. I can tell you right now that there will definately be at least two different ways of building your extension.
quote=Ranger 6]
Interesting site, their Overlay™ Lite looks to be 18mm thick and might work across the rest of the ground floor. I wonder if it would be best to blend the two systems or just go with overlay across the lot? 40mm is a bit much but 18 would not make too much of a difference. Did you go for some form of heat pump or are you running of a standard boiler?Jonleeper said:
The advice I have seen says that the under-floor system should be fitted with a minimum of a 400mm slab underneath, then the DPC, then 200mm of insulation followed by the pipes and then a 50mm screed to finish...
That's from scratch - google polypipe overlay ufh, 40mm onto the slab - ours covers 52m2 and is the best thing we did with our extension. As we were refurbing the whole house the 40mm raise in the floor was taken through to the front as well rather than have a step at the kitchen door.If they've got it down to 18mm that's great. I'll dig out some pics of ours being installed.
Ours wasn't 'just' an extension, we refurbed the whole house from top to bottom so the heating/hot water was a changed to a whole brand new unvented system. The original boiler was deemed just capable of running the whole place but a circuit board fault meant it was changed after a year.
The kitchen is the only room with UFH and the system is run from a manifold and pump seperate to the rest. I don't know enough about the technicalities to add much more I'm afraid. You can come and have a look if you're near enough?
Oh, BTW good advice we were given was about floor covering - use a thermal mat (Ditra Mat in our case) if you've got any form of stone or tile floor.
ETA: Jon, you're not that far from me so the offer of a look is there PM for contact details.
Here's the manifold during the build;
Water pipes being laid in the insulated former;
Ours wasn't 'just' an extension, we refurbed the whole house from top to bottom so the heating/hot water was a changed to a whole brand new unvented system. The original boiler was deemed just capable of running the whole place but a circuit board fault meant it was changed after a year.
The kitchen is the only room with UFH and the system is run from a manifold and pump seperate to the rest. I don't know enough about the technicalities to add much more I'm afraid. You can come and have a look if you're near enough?
Oh, BTW good advice we were given was about floor covering - use a thermal mat (Ditra Mat in our case) if you've got any form of stone or tile floor.
ETA: Jon, you're not that far from me so the offer of a look is there PM for contact details.
Here's the manifold during the build;
Water pipes being laid in the insulated former;
Edited by Ranger 6 on Thursday 2nd September 20:55
Jonleeper said:
I’m sure, mean a lot to both the Council Inspector and my builder. I was only wondering if there was an obvious solution I have overlooked when connecting a new floor with an existing one and getting the levels correct, other than raising the new floor by the difference.
It's good that you have a specification to present to your builder. It means they can concentrate on building rather than designing, finding and resolving issues.As with all things though it doesn't matter how good the design is if the guy building it doesn't care! Your right to query how the new is going to connect into the old - especially as it's going to be open plan and the joint 'visible'. However, this depends on what the existing conditions and the proposed are.
Ask your Architect to explain how the new and old are going to interact and how they've designed the joint/connection so that the finished floor / floor finish isn't going to be affected. Then post up their answer.
I actually like my Clients to ask questions.
Ranger 6 said:
If they've got it down to 18mm that's great. I'll dig out some pics of ours being installed.
Ours wasn't 'just' an extension, we refurbed the whole house from top to bottom so the heating/hot water was a changed to a whole brand new unvented system. The original boiler was deemed just capable of running the whole place but a circuit board fault meant it was changed after a year.
The kitchen is the only room with UFH and the system is run from a manifold and pump seperate to the rest. I don't know enough about the technicalities to add much more I'm afraid. You can come and have a look if you're near enough?
Oh, BTW good advice we were given was about floor covering - use a thermal mat (Ditra Mat in our case) if you've got any form of stone or tile floor.
ETA: Jon, you're not that far from me so the offer of a look is there PM for contact details.
Here's the manifold during the build;
Water pipes being laid in the insulated former;
Hi Ranger the kitchen looks great.Ours wasn't 'just' an extension, we refurbed the whole house from top to bottom so the heating/hot water was a changed to a whole brand new unvented system. The original boiler was deemed just capable of running the whole place but a circuit board fault meant it was changed after a year.
The kitchen is the only room with UFH and the system is run from a manifold and pump seperate to the rest. I don't know enough about the technicalities to add much more I'm afraid. You can come and have a look if you're near enough?
Oh, BTW good advice we were given was about floor covering - use a thermal mat (Ditra Mat in our case) if you've got any form of stone or tile floor.
ETA: Jon, you're not that far from me so the offer of a look is there PM for contact details.
Here's the manifold during the build;
Water pipes being laid in the insulated former;
Edited by Ranger 6 on Thursday 2nd September 20:55
You say that the only room with UFH is the kitchen.
Have you separated in 5 different zones? Or I am looking the wrong thing on the manifold?
We are having an extension build right now and I am looking to install one to ours. But I am looking to have 3 zones on mine.
Blooming minefield ha?
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