# Underfloor heating in extension, rads elsewhere: best practise?



## David_Dublin (29 Aug 2012)

I have a 4 year old (i.e. new!!) Baxi mega flo gas powered condensation  boiler. We have rads only now, but are planning building on a new  kitchen. Could we use the current boiler to power the current rads,  and also power underfloor heating? 

My concern is that underfloor heating might take longer to heat up, so  we might end up needing to have the heating on for longer. Is this a  valid concern? Is there anything else to consider when deciding to put  in underfloor? I presume the thermostats look after heat temperatures,  i.e. the water in the underfloor is not required to be as hot as the  water in the rads. We have some sort of siemens clock that allows for  separate hot water & heating, as these are on separate circuits.  Would the best practise to be to have a third circuit for the  underfloor, and have that times to come on earlier?

Sorry if all these are silly questions.


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## jpd (29 Aug 2012)

it would be good to have a separate circuit for the u/floor heating with separate controls. 

The most important thing to to make sure that the extension is very well insulated - floor, walls, windows and ceiling/roof.


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## David_Dublin (29 Aug 2012)

Thanks JPD. Would my current boiler support additional controls? I think the answer is yes. So effectively it means having three circuits, and a controller that supports three circuits - is that the sort of thing? With the thermostats on the underfloor being set to a much cooler temp than those on the HW & CH? Thanks...


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## jpd (29 Aug 2012)

U/floor runs around 40C

As for your boiler, you need to talk to someone you is expert in the matter


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## Shane007 (31 Aug 2012)

Design flow temperature for radiators is 73C whilst for UFH is 45C. There is absolutely no issues in having a combined system as long as certain measures are taken. All decent installed UFH systems have mixing valves that mixed flow and return temperatures at the manifold and circulate within the UFH loop until the temperature drops below the design temperature and hotter flow water is mixed in to maintain. A delta T of 11C is crucial.

Where it becomes trickier is to balance the system at the boiler. Radiators also require a delta T of 11C so no problem there. Condensing boilers need a delta T of 20C so a second mixing valve maybe required at the boiler or better still a modulating circulating pump with a mixing valve at the boiler. If you want to go the whole hog, install a buffer tank and this will maintain the "system efficiency" at its maximum.


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## David_Dublin (3 Sep 2012)

Shane007 said:


> Design flow temperature for radiators is 73C whilst for UFH is 45C. There is absolutely no issues in having a combined system as long as certain measures are taken. All decent installed UFH systems have mixing valves that mixed flow and return temperatures at the manifold and circulate within the UFH loop until the temperature drops below the design temperature and hotter flow water is mixed in to maintain. A delta T of 11C is crucial.
> 
> Where it becomes trickier is to balance the system at the boiler. Radiators also require a delta T of 11C so no problem there. Condensing boilers need a delta T of 20C so a second mixing valve maybe required at the boiler or better still a modulating circulating pump with a mixing valve at the boiler. If you want to go the whole hog, install a buffer tank and this will maintain the "system efficiency" at its maximum.



Thanks a million for all the info, great to know the optimum set up, and talk to the plumber/builder about how they plan to work it.


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## lowCO2design (3 Sep 2012)

david, note that your insulation levels should up around the 200 PIR/PUR mark with underfloor heating and thermal bridging - especially at floor/wall junctions and the dreaded threshold must be carefully addressed.


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## David_Dublin (4 Sep 2012)

lowCO2design said:


> david, note that your insulation levels should up around the 200 PIR/PUR mark with underfloor heating and thermal bridging - especially at floor/wall junctions and the dreaded threshold must be carefully addressed.



Thanks for the post, but there appears to be a significant undercurrent of warning. Dreaded threshold....am I walking into years of misery with misfiring/failing systems? Is this something that I should not do?


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## lowCO2design (5 Sep 2012)

David_Dublin said:


> Thanks for the post, but there appears to be a significant undercurrent of warning. Dreaded threshold....am I walking into years of misery with misfiring/failing systems? Is this something that I should not do?


not at all, its just i see lots of poorly constructed houses with problems with underfloor, but that's because the system once in, is hard to improve on. so my warning is get the building fabric right first. UFH is great. the reason I raise the issues is many of us focus on the system and not the bigger picture, its like the guy installing windows but not insulating between them and the wall.

ask your underfloor contractor how much insulation should be installed around the UFH system, then ask your architect. then comeback and tell us what they have to say


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## David_Dublin (5 Sep 2012)

Ok, thanks for the input, much appreciated.


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## Shane007 (5 Sep 2012)

Absolutely nothing wrong with UFH. The problem is UFH controls and installers. Get both those right and you will have an excellent system, toasty feet when you get out of the shower and if your hall is wide enough, somewhere to dry the bed clothes!


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## David_Dublin (5 Sep 2012)

One last Q on this. Primarily itd be in the kitchen, h=the wife wants wood, I'd tiles or some sort of screed type floor. What types of wood should I be looking out for/voiding for underfloor?


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## Shane007 (5 Sep 2012)

Timber is a natural insulator and tiles (ceramic) is a natural condutctor, therefore tiles is always the preferable choice for UfH.


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## David_Dublin (6 Sep 2012)

Shane007 said:


> Timber is a natural insulator and tiles (ceramic) is a natural condutctor, therefore tiles is always the preferable choice for UfH.



Thanks, yeah that was the jist of what I had read alright. Wife wants wood though, and I dont want radiators - something has gotta give!


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## Shane007 (6 Sep 2012)

I have 22mm solid oak in most of the house and tiles in kitchen, bathrooms and hall. Mine works fine but I am not a lover of a lot of heat. I have UFH in all rooms. Buy if you are maximising the system, then you would have to go with tiles or change the wife, but no guarantee that the new one would be happy either! Lol


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## David_Dublin (6 Sep 2012)

Do QS's do costing for changing the wife 

I think there will be many stand-offs, with negotiation and give & take, I'll just have to dig the heels in on the tiles, and let her have the eh.....homebase light above the mirror in the bathroom. I can be flexible, you see!


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## lowCO2design (7 Sep 2012)

David_Dublin said:


> One last Q on this. Primarily itd be in the kitchen, h=the wife wants wood, I'd tiles or some sort of screed type floor. What types of wood should I be looking out for/voiding for underfloor?


will there be UFH under the units, is there an island? will the ufh be heating up your food cupboards as well as your feet?


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## David_Dublin (7 Sep 2012)

No, it would be laid once the layout of the units is decided


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