underfloor heating

[benpost]

hello again, my flat is ground floor and has concrete floors throughout. it currently has central heating run from a year-old combination boiler. the central heating, i think, was installed some years after the property was built, as there are twin pipes running along the bottom of various walls, linking the radiators. i am planning to replace all the floors in time, and was wondering whether underfloor heating is an option? my kitchen has just been re plastered and has no radiator, so i was going to start in there, using it under ceramic tiles. has anybody any experience of underfloor heating? is it the future? should i use a water system and run it from the combi boiler? or go electric (and use the combi solely for hot water). i'd like to end up with an energy efficient home, and am prepared to spend if it will be worthwhile. it would also mean i can get rid of all the radiators and ugly pipes running along the walls! thanks

[Roger]

The message

from benpost contains these words:

I am currently considering much the same except that I intend to leave the kitchen as it is (it is at a lower level) and only dig up the floor in the main part of the house. If you have gas then I would have thought that gas has much the cheaper operating costs.

Wet underfloor heating operates at a lower temperature than conventional radiators (max 45C IIRC) so it needs to be a separate circuit with a separate control system to any remaining radiators (which might not be a problem in your flat). It also has a much slower response time which means it is better suited to those who are at home more often than not.

But be aware that digging up a concrete floor, particularly a modern one, is a major undertaking and one that would in all probability require some additional excavation to cope with the extra thickness of the floor resulting from the insulation layer and the pipe layer. Even if you have some insulation under the floor it is unlikely to be sufficient for an underfloor heating system.

I don't know whether your property being a flat (and presumably being leasehold) effects the case but you would be wise to explore that issue before you start ripping up your floor.

[The Natural Philosopher]

Currently its very inefficiennt unless used with a lot of underfloor insulation. So yiu have to dig out the whole floor and replace.

Currently water baseed systems are cheaperto run than electric.

Unless you are prepared to do it properly, don't do it at all. You will be disappointed.

[benpost]

i am property thinking bigger than is realisticly possible...

back to the kitchen, which currently has no radiator, and needs a new floor (once i remove the 70% covering of ceramic tiles). could i try installing the electrical underfloor heating before laying new ceramic tiles?

perhaps that would be an easier introduction to underfloor heating...

[The Natural Philosopher]

Unless you insulate under, you will be bleeding about 85% of the heat to warm the planet, not your kitchen.

And the electric costs are about 3 times what oil gas would cost.

If you just want a warm kitchen put in fan blown under unit heaters 'kickspace' and connect them to your wet system.

Add a nice spongy vinyl floor and it will be very nice for your feet.

Use a kitchen stat to control the fans otherwise it will rapidly overheat when cooking.

Fan blown wet heaters are pretty damn efficient at bringing a room up to temperature quickly.

[Dave Plowman (News)]

The big snag with underfloor heating is that it is extremely slow to react to ambient temperature. So not a brilliant idea with the UK climate. Can be very useful for background heating if the energy used is cheap - like say from a heat pump source. But will be extremely costly to run using full price electricity.

[The Natural Philosopher]

The great thing about underfloor heating is that it doesn't HAVE to react to ambient temperatures,. It CONTROLS them by dint of a large slab of concrete floor.

I can some some issues in a kichen, which may get hot and steamy quickly, and need fans to remove this, but thats what happens in kitchens. They tend - when used purely to cook - to be kept cool, and ventilated when being used.

I have never quite understood this trend towards 'kitchen diners'

The last thing I want to do is sit down to eat and gaze at a pile of dirty saucepans and plates etc..kitchens are industrial areas.

[mail]

As usual, I second what the NP has said in this post and agree with the chap who said either do the lot or not

Lot of effort to dig up old concrete and oversite and lay at least 4" of insulation needed ... complete waste of money unless rest of house up to scratch as only about 10% is lost thru floors best spend the money elsewere on insulation chris

[Dave Plowman (News)]

And when the sun streams in through windows?

Hence the need for a system that reacts quickly to avoid wasting energy while making the room comfortable at the start of the day.

No dishwasher to hide them in?

Some consider cooking more of a pleasure than just work.

[whitely525]

AFAIK the wet systems are more efficient but then you have concern of if there are any leaks. The pure electric systems don't have that concern but are more expensive to run

One advantage is it tidies the rooms up as no radiators & pipes... good for new 'minimalist' flats. But I am not sure if it is 'central' heating or metered to individual flats. There is the issue of who is responsible for 'common' parts of a block of flats (which should be spelt out in the lease).

I definitely wouldn't change from what you currently have, it just sounds like a lot of aggravation.

[robgraham]

I think what is interesting is how often we have actually to drive our guests through from our diner/kitchen (living room) away through to the lounge. Unless you, and I mean you NP, have a particularly lounge area which has so much space that people feel comfortable in it, there is a whole lot of us who have a general living space that is in the end the most comfortable area in the house and that's where our guests tend to congregate. Can't remember now quite what the song said about parties in the kitchen, but it was totally accurate.

Rob

[The Natural Philosopher]

Blinds. In pur houyse, in winter, teh sun strems in, and that mens the UFH comes on less. Thats all,. In summer it doesn;lt come on at all, and w draw the curtians by day.

In spring and autimn, instead of cycling between about 15 and 20C sing the UFH on a timer, the UFH simply doesn't come on unless there is a really cold night followed by a dull day.

The massive concrete floors reduce diurnal fluctuatains to 3-5 degrees at the most,and slow down temp rises to at most about 1C per hour from solar - well within a UFH response time.

Well you still have to take them out to wash them. No dishwasher yet can cope with carbonised stew at the bottom of the pan, or porridge, or a roasting tin..or..about 30 other dishes that leave a sticky residue. Scrambled eggs is another one. They don't even get dried coffee out of the cups.

I guess if you microwave pizzas and pot noodles, its fine..

Some consider working at a lathe or milling machine pleasure. I do personally. Doesn't mean I want to eat my luncch off an angle grinder, or look at a swarf covered floor while I do it.

[The Natural Philosopher]

With continuous runs of plastic pipe, there are no leaks.

I would IF you have the balls to do the job properly.

Otherwise the kickspace units are high output per unit area, and use dead space under the units, and produce warm air at tootsie level. Excellent.

[The Natural Philosopher]

Well we have three 30 sq meter spaces..kitchen plus eating, full blown dining room and the 'horizontal' area with the telly.

The dining room gets the lest use, but did sterling service over Xmas,when we actually had three cookers on the go..in two kitchens..ask not why the place is organised this way..history..

We eat in the kitchen mainly, because its quick. Or on trays in front of the TV,. cos we are slobs. I keep intending to part partition te kitchen to increase the separation a bit more.

[AJH]

One of the theories behind having low temperature circulating water in the slab was that if the slab was at 25C and the air temperature in the room rose then as the temperature difference decreased less heat left the slab. Given a large slab area for heat exchange this should be largely self regulating, in theory. In practice I see a number of problems with one multi occupancy building with underfloof heating and a limited heat input.

AJH

[Dave Plowman (News)]

Like all thermal mass systems it also depends on having a fairly constant energy input to it. So ok if only providing background heating to say 55F. If required to provide the more usual 70F or so it simply won't react quickly enough to a change in room temperature for whatever reason.

Nothing new about underfloor heating. It's been round long enough for the disadvantages to be known. As has the conventional water circulation/radiator type - which is why it dominates the market.

[andrew heggie]

I don't see this. I'm not intending to defend underfloor heating as I don't have much experience of it, that I do have is from brief visits to a system that appears to be marginal in longer periods of cold weather, exacerbated by unexpected heat bleeds as the thermal store is depleted. The heat inputs to this can be both unscheduled or on demand for the wood fired back up system (which runs 24/7 except for a forced reboot every 4 hours in weather like now).

I'm not saying you are wrong but you missed the point of my post, which was the power emitted by the slab is subject to negative feedback from the air above.

So if the slab emits 10kW(t) into the room when the slab is at 25C and the room is at 10C it should emit no power when the room is at 25C. Having said that I do know from looking at the circulating temperature in the underfloor pipes that the water circuit return is still ~39C when I was expecting to see only a bit above 25C.

AJH

[andrew heggie]

I advocated these in series with the underfloor heating ( or rather having their return into the underfloor heating circuit injector) to get the air temperatures up whilst still returning low temperature water to the thermal store. to give people a quick warmth after being out for the day without having to anticipate how the underfloor system would be working when they got home.

In practice people were leaving the room stat too high and then finding it hot when they got in, which could only be mitigated by opening windows.

AJH

[Roger]

The message from andrew heggie contains these words:

Was this due to the widespread belief that turning the room stat up increases the heating rate or lack of a predictive controller which I would have thought was essential with a large time constant in the equation.

[andrew heggie]

That may have been a part of it but I'm thinking it's a foible of the ethos of the designers and owners, it's sort of social housing for key workers. There is no provision for monitoring any tenant's heat use and I have no way of knowing if the software has any predictive element to it. In the event it would make no difference because without sunshine there's no way the backup can meet the power demanded of it by the tenants. As I said this leads to this, and another, heat bleed that just makes things worse.

They are so tight that they wouldn't even allow for a link to the internet and a webserver (which could have been by arrangement with a tenant's broadband) so I could monitor what was happening, I am two hours away and some failures are very easy to deal with but I don't get called until the thermal store is depleted.

AJH