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heating a new extension: underfloor or rads?

15 replies

Elibean · 21/01/2010 13:50

Its going to be 3m out from the entire back of the house (34ft wide) and is almost north facing, so although light won't be a problem (glass doors, velux windows) heat could be.

We were going for underfloor, in the extension part (its rads in exisiting kitchen and family room) but a heating engineer has just told dh that he sees loads of problems with cold extensions, people asking him to add rads, etc.

We only have two end walls (both of which we want furniture against) and two smallish bits of wall in the middle, between the glass doors at the front and between the kitchen and family room at the back: we could put vertical rads here.

Would that be enough? Should we go for both?!? I'm worried its still going to be cold as one vertical rad in the middle of the room isn't much when its that wide a

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mumtooneson · 22/01/2010 23:17

We've recently had a 3m north facing extension and have had a water based underfloor heating system installed in both the new and old part of the kitchen. It's lovely and warm. Haven't had the first bill yet though!

Elibean · 23/01/2010 08:32

Thanks! Keep hearing horror stories, so this is very reassuring. I guess the crucial factor is a strong enough boiler.

I'm glad you're enjoying yours, and don't think the bill should be too shocking with a non-electric one

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ilikeyoursleeves · 23/01/2010 14:11

not sure if this helps but we are planning on putting a wood burning stove in our new extension which will be about a 8m x 6m L shaped kitchen diner thing, also north facing. Would that be an option?

Elibean · 23/01/2010 19:20

How lovely

I suppose it could be, but every inch is accounted for atm...that said, we have just had half a poplar cut down, so there is more than enough wood to use for a few weeks!

Is the stove your only source of heat, or an additional one? I don't know much about them really..

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BecauseImWorthIt · 23/01/2010 19:23

Friends of ours had an extension that sounds very similar - they went for a wood burning stove and under floor heating. But their first quarter's bill was over £600! So they're having radiators installed as well.

nicky1968 · 23/01/2010 19:30

We have a south facing conservatory opening out from our kitchen and have electric underfloor heating. It added about £200 to our annual electric bill (although we also bought a small chest freezer too so that would be adding a chunk to the elec bill too so altogether the added cost would be less than £200). I don't think that if we had radiators that the conservatory would be warm enough to use all year round but as it is we turn it on in November and off again March/April and it's great. We're in there all the time.

neolara · 23/01/2010 19:32

We had underfloor heating put into our kitchen and it's bloody fantastic. The kitchen is never cold. However, it is a lot more expensive than radiators.

Elibean · 23/01/2010 20:53

Isn't it the electric one thats expensive to run, though? We're definitely thinking plumbed, rather than electric.

The concern has been because its a very wide room, 34ft by 9ft, more or less. Two rooms open out onto it, and its going to run the full width of the back of the house.

We do have a brand new, big boiler but I'm worried the underfloor heating will simply not provide much heat....we have two bits of wall we can add vertical radiators onto, so I hope that the two together would be enough, even if its expensive to heat in mid-winter.

The heating engineer spooked us though, saying he'd just had to fit a woodburner into an extension because both underfloor and rads together were insufficient

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cece · 23/01/2010 20:56

We have a new large extension. Very well insulated and three vertical rads in it. It is lovely and warm.

However, where the rad pipes go under the floor it feels lovely and warm. In hindsight I think we should have gone for the underfloor heating. BTW we put Amtico on the floor and it is lovely with the heating pipes underneath it. Fine without but lovely with.

TheRedQueen · 23/01/2010 21:38

Elibean: We have underfloor heating in the whole of our ground floor. It's water-based, with the water being heated by gas. I don't think the plumbed variety is too pricey: our annual gas bill is around GBP 900, which is for a four-storey house with five bedrooms. (Note: House is around 5 years old and in Germany so insulation probably generally better than in UK, but winters are also - usually! - colder.)

The amount of heat you get from underfloor heating depends not only on the boiler, but also on what the floor consists of. In some of our ground floor, e.g. the kitchen and guest bathroom, we have tiles, which are always toasty warm, as are those rooms as a whole. In the lounge/diner we have hard wood flooring. Here the temperature is not quite so high as the wood tends to absorb more of the heat so the air temperature is cooler, but it's still warm enough. We do also have a log-burner in the lounge, but this is more for effect than warmth. The only time we ever really use it for warmth is when the temperatures get really low (e.g. we used it a couple of weeks ago for warmth when we had temps of around minus 10C).

One thing you do have to be aware of with water-based underfloor heating is that it takes longer to get warm when you first switch it on. Whereas a radiator starts blasting out heat fairly quickly, it takes a couple of hours longer for underfloor to really kick in. Some people therefore go for a mix - underfloor, but with the odd radiator to take the chill off the air while waiting for the underfloor to warm up. If you're really not sure which way to go, you could always have the basic, essential plumbing for radiators put in when the underfloor is done (i.e. the bits that you would otherwise subsequently have to start ripping up flooring and destroying plaster for), but otherwise just wait and see how the underfloor performs.

Elibean · 24/01/2010 13:16

Wow, thanks Cece and RedQueen - thats exactly the sort of experience I was hoping to hear about.

We have oak flooring throughout the ground floor, so were going to use engineered wood to match in the extension part - and I think we'll definitely add in at least a couple of vertical rads if we can, based on what you've told me!

Thanks again.

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nappyzonecantrunfortoffee · 24/01/2010 13:31

We have an extension mid progress - downstairs room will be width of house and 3 m out like yours 2 useful walls and 2 big window/ door thingys with small bit of wall between them, plumber is putting a rad at each end of ours despite it being south facing. I wish id thought on tbh and put in a vertical in the middle. hmmmmmmmm

RedLentil · 24/01/2010 13:35

We're just planning our north-facing extension and we will have two vertical rads on the walls that support the RSJ for the room above.

You can use a BTU calculator to figure out how powerful your rads need to be.

We'll have a stove too, but we want the room to be warm when the house is in use without running two forms of heating and so we won't use it as the main heat source.

The length of time for heating up has put us off the underfloor options.

Sorry that's a bit incoherent.

ilikeyoursleeves · 24/01/2010 16:37

Hi Elibean, the stove will be secondary to radiators. Not sure how many radiators we will have in the extension, not even thought about that yet!

TheRedQueen · 24/01/2010 21:42

Eli: a point about wood flooring over underfloor: we were advised not to have very long planks of wood, but to have have a pattern using shorter pieces. The heat causes the wood to "work" and longer planks can warp. Also, be prepared for the gaps between the pieces of wood to open and close depending on the time of year and how much you are using the underfloor. (Alternatively, you might consider wood-effect tiles. There are now some great designs in these, and you can then have your cake and eat it, i.e. get the "look" of wood, but benefit from the extra bit of heat you get from ceramic on underfloor heating).

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