If all you want is blue walls on thermal imaging then switch your heating off! And it's cheaper! I assume that people want to heat their homes as effectively and efficiently and economically as possible. That's the point of my previous entries.
Please read them and Tunas entries if you haven't made up your mind yet.

I'm sold on the idea of locating heating under the floor and am trying to understand workaholic's method from earlier in this thread

[quote]James, I take my low thermal mass / fast response goal even to include the UFH. All my UFH is without screed. On the ground floor I lay OSB over 100mm of Kingspan. I fit 50x25 battens to this at 400mm centres and Foil Tec the lot. Two rows of pipe are nailed to this between the battens and floorboards to suit are fitted over. The Foil Tec spreads the heat all over and it is remarkably quick to warm up / cool down. I run with the flow at 40 degrees. I once tried 50 degrees and nearly cooked everyone. I never use spreader plates they are much much too expensive. I use the same basic idea upstairs except that the OSB is fitted between the joists, set down 25mm and no battens used.[/quote]

1. I assume the ground floor construction here is solid.
2. Is the Foiltec laid over the battens and down into the spaces between? How is it fixed in position?
3. How are the pipes nailed to the FoilTec? Are the pipes nailed to the OSB and is that the reason for having it, or does it serve another purpose?
4. UFH suppliers I've spoken to say the problem with laying the pipes like this is the air gap will act as an insulator and reduce heating efficiency by upto 20%. They say that is why they recommend filling this void with a screed. Is there any logic in this?
5. I spoke to the guys at invisibleheating.co.uk, as mentioned in another thread and they say if you leave an air gap it will then be necessary to run the water at temps as high as 60deg! Surely if you put enough pipework in, there should be no need for such high temperatures?

FInally, we have only 4" joists downstairs and up. I'm thinking of installing UFH on both levels. On ground floor (suspended timber floor), by the time I allow for the 25mm gap under floorboards and the OSB (or pos 9mm ply?), that only leaves me 65mm to bottom of joists. How much Kingspan do I need and is there a way around this limitation. I suppose I could raise the floor level on ground floor by 35-40mm, which would then enable me to use 100mm Kingspan.

All help appreciated.
Thanks
Krishna

I guess how your curtains sit, if you have any, is also a consideration -- if you have them down to the floor and the rad ends up behind them you are going to end up heating the window... Perhaps a large internal cill with the curtains sitting on it would be best for the rad under the window situation?

Underfloor heating is increasingly popular in Sweden and seems to be efficient in well-insulated buildings. An important question is is it cost-efficient for ordinary folks/most homes in the UK? How to maximize returns and cost-savings/fuel efficiency on your investment? If your budget is limited then I would recommend most folks to improve wall and window insulation first. Then returning rads to under windows, by external doors and other cold spots of course. (See above)

Good point Chris! You're solution is spot-on. Scandinavians mount a shelf/internal sill behind curtains with a gap between base of window frame and shelf/sill so that some heat rises in front of the window stemming cold and humid penetration of the room (essential) and some heat raises the room temperature. Full-length curtains can be pulled back below the internal sill or preferably shortened.
Heavy lined curtains prove the point that we all want to stop cold air plunges penetrating the room (and giving distant radiators a massive job to do! -which they can't efficiently because their heat rises up the internal wall and across the ceiling instead of stemming the cold air crossing the floor and filling the lower half of the room).

OK, after some extensive googling, there was a research project at the CANMET Energy Technology Centre in Ottawa that used actual test houses with different radiator placements. Simulation algorithms were then developed that modelled the convection and radiation characteristics of the different configurations and used these to derive the annual heating and cooling loads. The test houses are well insulated, airtight and have high performance windows so the results may not be applicable to typical UK construction. Here's the paper for your edification:

http://www.esim.ca/2001/documents/proceedings/Session7-2.pdf

All that said, energy efficiency and perceived comfort are often at odds so the most energy efficient solution may not be the most comfortable - which leads to human factors changing the thermostat for comfort at the expense of efficiency. Air that is at less than blood temperature feels cool when moving over the body which is why a drafty room at 21C feels much cooler than one with perfectly still air at 18C. This is part of the reason UFH systems use less energy than conventional systems - not because they actually use less, but because they give the perception of warmth at lower air temperatures than either forced air or radiator systems.

Paul in Montreal.

I saw the word "algorithm" in the title and gave up...

Chris, spot on. I find a gap of 5 mm works a treat. The better insulated (and less condensed) your window the less the need for warm uprising air to stop penetration of cold damp air from the window. But only in buildings with at least triple glazing and superinsulated walls (I built an inner timber frame, filled with rockwool, clothed in polythene to prevent draughts and condensation of moist air (from inside the room), surfaced with plasterboard (with an adjustable ventilation flue) when I renovated an old house here -very snug and dry) can you begin to place radiators somewhat more freely.

Ian, that's right. Most Scandinavians don't even bother to draw their curtains. But it's not to prevent ice building on the outside. The cold air lowers humidity and condensation doesn't form externally because the outside of the glass is practically the same temp as the air itself, esp with double glazing or more. (On the other hand ice forms on your car windscreen in the morning if your car's colder than the damp air. At stable low temps of -10 or -30 celsius, your car actually ices up less. Excuse the digression!) You're right to bring humidity and condensation into the equation however!
As Paul's link proves the science of this is very complex and not just a matter of simple arithmetic.
I still find this link helpful: http://energysavingnow.com/comfort/ for a Swedish view.

I fully agree with Paul -perceived airflows and humidity certainly make us turn up the themostat whatever the actual temp. That's why ventilation should probably also be discussed here.......at least, where to place it........

A comment about UFH is that its generally reckoned that you need less total heat input into a room with UFH than with any other means of heating as the heat is directed where the occupants get the most benefit/comfort feeling. You can therefore run the room at a lower overall temperature which then reduces heat losses. We have UFH under a tiled kitchen floor and you cannot better a warm ceramic floor in the winter. It uses Hepworths underfloor heating pipe buried in a 100 mm concrete slab on 100mm insulation- no screed and no plasterers just a rough cast slab that had the worse of the tamping marks floated out prior to final setting. Tiled directly onto the "rough" surface. Would have done the whole house had we needed to replace the floors.

Where did you go for your UFH? And what's going on top of the screed please?

My thoughts is that the hotspot issue is a non-issue if the room is adequately insulated. I went to vast expense moving a radiator from under a window in a bedroom because I thought it was dumb to site it underneath the window, yet I have just insulated that wall and will probably do something with the window soon- eg an additional glazing. The cost of moving the thing probably added £500 to the bedroom refurb, and as the room now has insulation that probably loses at least 50% less heat I dont think that the issue of hot and cold spots will be as problematic, the reason is that my flat landlord has done nothing to insulate the (Victorian Terrace) place and over winter the place was terrible - massive Victorian windows with a rad between them - hot and cold all over the place, I had a cold that wouldnt go away for months. Point is that with bad insulation it matters alot in terms of comfort, with good insulation site it anywhere thats convenient for room layout. Radiator reflector panels and a shelf will ensure that relatively little heat is wasted on the window, which could also have curtains and multi glazing.

By the way I would have been better to spend that £500 on something far more worthwhile like additional glazing on the window..

I have serious doubts about underfloor heating - expansion and contraction in the floor - probably a long term maintenance nightmare, imagine if you get a leak too. Furthermore it means the thing has to be on most of the time as it takes longer to get the heat you want.

The great thing about underfloor heating is you can operate a lower temperature,why not have larger wall based rads or maybe an air based heating systems make the most sense - but I dont know much about the nitty gritty - possible complex mechanical issues.

..so that the rising air flows up behind the curtains and is cooled down somewhat by the glass before it had time to heat the room. Any opinions on this?..

If that happened you would probably be living in an older house and so would need the radiators under the windows?

I have an old stone walled cottage and am planning to move a rad from an internal wall to under the window. Would this therefor be wrong or in an old house like has been suggested this would be best?

I agree with hotel/refurber over the value of good insulation.
reduce the number of hotspots with even levels of insulation means fewer cold spots in the room.
then the rads can be sited wherever suits the room layout.
If that is against an internal wall then all the outer walls are still at an even temperature.
I have a client who wanted skirting rads but all I can find online is "discrete heat" any body seen anything of "fin-rad" lately (other than boatbuilders or merchant banks).

craigindav,

Have a look at http://www.hekos.com/UK/index.php and http://www.radgone.co.uk/index.htm and the thread titled "radiators or ufh" in Housing - Renovation.

I am almost certainly going for DiscreteHeat's Thermaskirt - Rapid response times of rads, even heat of ufh, frees wallspace, looks good, does what it says in the blurb, good reports from installers and users, can be fitted by a competent DIYer, can support installation of towel rads. More expensive than wall rads but cheaper and less disruption than ufh.
I am also insulating my walls and solid conc floor.

Graham

The best place to place the radiator is under the window. Not only is it more efficient but you also utilise the space in the room. Your plumber may have a different view on this as you can imagine it means more work for him/her to move all the pipe work to the window.

If you require a bay window radiator visit

www.shivradiators.com


The company custom builds radiators to fit bay windows.