Electric underfloor heating layout

[JT101]

Hi all

I have installed a couple of those foil backed Pro-Therm electric underfloor heating matts, and am about to install another, each under engineered floating floor.

To be honest, the layout has been a complete nightmare. Thought I had it planned out with a nice border round the edge, but ended up having to slice the matt up into loads of pieces (not cutting through the wire obviously), and running it all over the place where I could find a slither of space. I'm sure you get the picture (see attached images).

I contacted Pro-Therm directly but they said that they were suppliers only, and so could give no advice on installation. Nice! Watching this video (

) gives you an indication that you go off in 2 directions and zig zag, but they way they do it, meeting in the middle is very risky. If you get it wrong, you have a lot of spare matt with nowhere to go!

Obviously if you have one matt, life is simple, but starting with the main cables near the entry point into the wall, and working outwards back and forth.

I'm sure space is lost, as you cut the matt and rotate it 180 degrees, but it still ends up covering a much bigger area than I intended.

So, the question is, is there a trick to doing this, or some sort of software that can map it out for you, or do you suffer the same problem?

 

[SimonH2]

I've only done electric UFH once at a mates house - we used a roll of wire for that. Having the wire pre-fixed to a mesh saves time laying it out, but as you've found, loses you a lot of flexibility.

 

[ericmark]

With Rayochem the heater is designed to self compensate the hotter is gets the higher the resistance goes, it is not a simple resistance wire but a chemical impregnated special so the maximum temperature is limited by the heating element it's self, as far as I know it is the odd one out, all the others need pockets laying with the elements which have sensors in to stop the temperature of the floor exceeding 27°C and if there is going to be furniture in the room the mat is not laid where the furniture is to go. In my case it was a wet room so there was no furniture.

I was a major job to fit it, in our case the drains needed moving so the floor was coming up anyway, but 6 inches of polystyrene and then plywood went in before the heating mat as other wise all you do is heat the ground below the house, the builder destroyed the first one, and it had to be lifted and relaid with new heating mat and it was a case of taping in position while the special tile cement was used to hold tiles into position. Plus of course the pocket (bit of pipe) with the sensor in.

In our case we also had a towel rail and idea was to fast dry the wet room floor so my mothers wheel chair and her would not slip on wet tiles. We also used sculptured tiles which was a mistake, as they held the water. In fact the whole system was a waste of money, once the insulation was fitted the floor stayed reasonably warm without the heating on, and the floor took that long to heat up, time to dry without UFH was around 60 minutes, with UFH it was around 50 minutes. It also would not heat the room on its own, the bathroom extractor removed more heat than the floor put in, hall which it came off kept at 18°C wanted wetroom at 22°C but best the UFH on it's own could do was 19°C it needed the towel rail on to get room warm. OK it was a small room but the towel rail was putting in over twice the heat gained from the UFH, so when the sensor stuck in the pocket, we never repaired it, even left on 24/7 the tiles only hit around 30°C so it was never fixed.

However most people have furniture in rooms so the mats are laid with at least a 2 foot boarder so edges are not heated, I suppose furniture on legs would be OK, so this

is OK but most people have a book case like this

which you can't use if the heating element goes to edges of the room. Under floor heating as we found is slow to both heat and cool, the modern idea is to make heating times as fast as you can, so you can use geofencing and the like so home not heated when not in use, so for an old peoples home where you want nothing likely to burn residents, and all rooms always heated UFH works well, but I like rooms at different temperatures through the day, so night around 17°C morning raises to 20°C and evening around 21°C while sitting watching TV, I also select when each room is to be heated, so don't heat rooms not used. There is so little heat from UFH you don't have that option, so in the main UFH is set to heat the floor where you stand, it is not used to heat the room, it is nice to have your feet on a warm floor, but you will not be standing around the edges of the room, at 27°C it can never heat most rooms unless on 24/7 which is expensive, so you don't try to heat room with it, it just heats the floor where you will have your feet on it.

I would say from using the wet room, it needs to switch on at least an hour before using the room just to warm the floor, and to warm a room assuming no ventilation, you will need it on 5 hours before using room, and it would take another few hours to get to a comfortable temperature, so it is either left on 24/7 or you have some other form of heating as well.

Since it is known that people don't fit the insulation under the floors, making it very expensive to use, when buying a house we avoided any with UFH unless they could show us that insulation had been fitted, so make sure you take photos of the insulation, we looked at a very nice house and the lady showing us around was so keen to tell us how her late husband had laid the UFH, it was not a selling point, we rejected that house because of the UFH we were not prepared to take the chance. In the main if laid well then it will be wet, electric is seen as cheap and nasty even if it's not. Unless of course there is no option for central heating.

 

[Diver Fred]

>>Snip<<

So, the question is, is there a trick to doing this, or some sort of software that can map it out for you, or do you suffer the same problem?

Afraid so - but you are to late to employ it. I'll post my thoughts based on my experience of laying EUFH mat in my bathroom.

When you measure up the room you need to subtract 250-300mm (10-12 inches) off the major dimensions so if your room is 2.6x3.5m (8'8"x11') (9mSq) then you need a mat to cover 2.3x3.2m (8'x10'6") (7.35mSq - in practice 7.5mSq).
When I did my bathroom I measured the room up, made a plan with exact measurements and took that to the suppliers, they rounded down and said I should have 4mSq. I really struggled to to use all; laying out all the mat and heating cord and that was after I'd removed a dividing wall which I hadn't decided to do before buying the mat. I'd have been better to buy 3.5mSq. As I'd cut the mat I could not take it back to exchange for a smaller one.

You could ask if it's possible to shorten the electric heating element; the manufacturer, not the supplier. Sorry I'm unable to offer any better advice.