# Radiators vs Underfloor heating



## Madra Rua (14 Jan 2013)

Morning all,

Will be commencing ground floor extension in April...the question of heating has just come up with the builder. We currently have oil central heating with radiators. Apparently the laying of underfloor would work out the same as if we just went with radiators in the new extension. 

Would love to hear some advice re both in terms of pros and cons and running costs.

Many thanks.


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## dub_nerd (14 Jan 2013)

Pros: very even, comfortable and controllable. (I find it stays within half a degree of the set temperature). Easier to plan room layout without rads.

Cons: Extremely slow start from cold (12-24 hours or even more when floor slab is very cold). You need to be running it 24 hrs/day in winter and it's not much use for switching on/off in spring/autumn when days are warm and evenings chilly. There's a setback setting to combat this so you can have it on but automatically drop temp by 2-6 degrees at time of low usage. It's a more complicated arrangement than rads (manifold with mixer and thermostat wiring from zones), so you may find it more difficult or expensive to find help if anything goes wrong.


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## Madra Rua (14 Jan 2013)

Thanks so much for your reply dub nerd - very helpful


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## burmo (14 Jan 2013)

dub_nerd said:


> Pros: very even, comfortable and controllable. (I find it stays within half a degree of the set temperature). Easier to plan room layout without rads.



Room planning is true, but it is definitely possible to control room temperature accurately as I have built heating controllers to do this. This is keeping in mind that you have similar zone control for radiator / underfloor heating.


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## lowCO2design (14 Jan 2013)

please please please do not install underfloor heating unless you have someone preparing details for your builder, as it needs lots of insulation to avoid heat loss, that means thermal bridge free/ or as close as and preferably attention to air-tightness . if you have oil central heating its not really the best heat source for running UFH in an existing home. where on the system would the UFH be on the boiler hot water feed/loop?

talk to shej a poster on here, who has an mid 00's house (gas & UFH) with crazy heating bills, mainly because the house is poor insulated with little attention paid by his builders to air-tightness. 

at least with rads in a bog standard home (no offence meant, I mean a home where min retro-fit regs are used) the heat is relatively instant, matches your existing set-up and can be controlled/ curtailed easily.


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## dub_nerd (15 Jan 2013)

lowCO2design said:


> please please please do not install underfloor heating unless you have someone preparing details for your builder, as it needs lots of insulation to avoid heat loss, that means thermal bridge free/ or as close as and preferably attention to air-tightness . if you have oil central heating its not really the best heat source for running UFH in an existing home. where on the system would the UFH be on the boiler hot water feed/loop?
> 
> talk to shej a poster on here, who has an mid 00's house (gas & UFH) with crazy heating bills, mainly because the house is poor insulated with little attention paid by his builders to air-tightness.
> 
> at least with rads in a bog standard home (no offence meant, I mean a home where min retro-fit regs are used) the heat is relatively instant, matches your existing set-up and can be controlled/ curtailed easily.


 
I'm think the OP is talking about a new extension, so I'm assuming the correct attention will be paid to insulation under the floor and elsewhere. Of course, this is vitally important -- your underfloor slab needs to be massively insulated at the bottom and sides, using foam and reflective materials. (I'm no expert, but I watched my own being put down).

As regards how the boiler hot water flow is matched to the low-temperatures for the underfloor, this is completely standard -- the boiler water is mixed with the returning cold flow from the underfloor zones; a mixer valve with a temperature probe controls a thermostatic valve on the boiler feed, so that the right amount of hot water is mixed with the cold water returns.

However, there is no doubt that the slow response of underfloor heating can be a major drawback.


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## quadrangle (16 Jan 2013)

What is the difference in energy consumption between Underfloor and Rads. 

My understanding is that if you have rads you set them to turn off and on at specific times, and obviously have the freedom to heat as you please. It seems that underfloor is dictated to by the thermostats in the zones. So if you set your room temperature at 19 degrees, and allow a set back temperature of 5 degrees below that, then the heat source will kick in at 14 degrees and cut out at 19 degrees. This could happen several times a day in cold weather. I plan on building a bungalow that is about 1500 square feet ground floor plus a conservatory plus a converted attic. 

Assuming top spec insulation, 300mm pumped cavity, ground insulation and spray insulation under roof what source of heat for me? I would hope that underfloor would not need to cut in as often with a high spec of insulation but I would also think that rads might be sufficient.


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## ang1170 (18 Jan 2013)

dub_nerd said:


> Cons: Extremely slow start from cold (12-24 hours or even more when floor slab is very cold). You need to be running it 24 hrs/day in winter and it's not much use for switching on/off in spring/autumn when days are warm and evenings chilly.


 
Note sure what you mean by "running it 24 hrs/day": do you mean the boiler is on for that time, or just that it can come on?

We've had under-floor heating for about five years now. It's "on" all the time, winter and summer, controlled by thermostats (we've quite a few separate zones). However, for about half the year, the boiler never actually comes on. Even during the winter, it's typically on for a couple of hours in the morning (to bring it from the night-time setback temperature to the daytime one).

I'd agree it is slow to heat from absolute cold (the boiler failed during the really cold spell a couple of years ago and it was nearly a day before it was back to temperature). However, provided your insulation is good, it never gets that cold: you’re effectively just topping it back up for a couple of hours a day.

It takes a couple of months to settle down in the sense of getting the thormostat settings correct, but once that's done we literally almost never touch it, unlike previous rad-based systems I've had where I had to constantly turn them on/off, turn the bolier on/off, change thermostats etc.

In short, we’re very happy with it.


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## quadrangle (19 Jan 2013)

What heat source are you using for the Underfloor?


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## ang1170 (21 Jan 2013)

quadrangle said:


> What heat source are you using for the Underfloor?


 
Gas boiler.


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## quadrangle (22 Jan 2013)

For a 1500 square foot house, rads are probably most efficient with oil given that natural gas is not available to me. Geothermal is probably most efficient with underfloor.


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