I was wrong with my comment about the 2 wires. When I read 2 cables I was looking at the diagram for 'single core heat mat'. I did not see the heat film model further into the instruction manual.
Under floor heating system problem
- Thread starter North
- Start date
I have never crimped a cable under a tiled floor. I've got a feeling that the RCD may not like the tile adhesive seeping into the cable joint.
There's not normally any need to crimp wires under the floor! What a strange design this is. I can't really see doing that being an acceptable way of installing mains wiring. If the cold tails were several meters long it would be straightforward to run them all to a low level box in the wall with a blank plate over the top. The photo appears to show the wires being extended with insulated and sheathed flexible singles. Who carries that on their van and what wholesalers have it in stock? I can't see it listed for sale on the website either.
That's normal.
They'll have a number of standard sized mats, and for a large room it's really a lot easier to supply 3 smaller mats than one very large one - and easier to fit as well. Because of the way the system works, there's a maximum length of the element wire, so even if they did make one big mat for your room, it would have more than one element on it.
That's a horrible arrangement - for reasons others have given.First off, the element arrangement isn't balanced. Any conductor carrying a current will produce a magnetic field - but if you arrange for the return conductor carrying the current back to it's source to follow the same route then the magnetic fields will cancel out. The UFH my mate put in his bathroom was a twin core cable with earthed braid - so none of those problems and a 3 core cold tail on it. But as I read the diagram, there's going to be a "loop" that will create a magnetic field which is far from ideal. I've seen an office full of computer screens wobble to the point of unusable due to this effect, but even though CRT TVs and monitors are now rare, it can still create hum in audio systems.
Secondly, the last thing I'd want to do is bury crimp connections like that in the tile cement. I'd want to bring the cold tails up to a box (or boxes since there's 3 mats and the tails will be spaced apart) set in the wall and wire them back from there.
I'm not sure why anybody is surprised that a company whose entire existence is based on selling something useless is supplying cheap'n'nasty products.
Thanks for advice so far. returning the units is not an option at the moment. the underfloor heating is going to be under wooden laminate floor and in the kitchen so i agree that crimping may not be necessary. i just looked at the junction box and there are 6 connectors; two for the sensor and two L/N connectors. Would it make sense connect the bigest mat to one L/N and join the wires of the two other small mats and connect them to the other L/N connector?
Those numbers don't add up.
When you say junction box do you mean thermostat controller? if so, no you need to connect all the mats to the Load L and N terminals and the mains to the Supply L and N terminals. The floor thermistor to the sensor terminals. Otherwise one set of mats will be on permanently and your floor will get burning hot in that area.
I'm guessing you don't have much (any ?) first hand experience of a good UFH system ? There are most definitely a large number of situations where they are far from useless. But I will not deny that there are many that are badly specced, badly installed, incorrectly operated, or just the wrong solution to the problem.
Tell me how well they work under wooden or laminate flooring.
Include in your explanation details of the thermal conductivity and surface emissivity of such materials.
For all flooring types show how much heat they will put into the room per unit of area, assuming a comfortable surface temperature, and whether that will be enough to maintain a desirable air temperature.
For stone and tiled floors, please explain what sort of control system will manage the effects of the thermal hysteresis of those materials to give an effective way to control the air temperature in the room.
Include in your explanation details of the thermal conductivity and surface emissivity of such materials.
For all flooring types show how much heat they will put into the room per unit of area, assuming a comfortable surface temperature, and whether that will be enough to maintain a desirable air temperature.
For stone and tiled floors, please explain what sort of control system will manage the effects of the thermal hysteresis of those materials to give an effective way to control the air temperature in the room.
In practice, quite well in my experience. The conductivity may be low, but the surface area is large. That assumes a properly designed and installed system.
Are you offering to pay for my time doing those detailed calcs ? No ? Thought not. Besides, you haven't provided nearly enough detail - or are you after some random figures for some random hypothetical property ?
There's no thermal hysteresis in the materials, but there may be in the control system. In practice, it's not much different to radiators - especially where there's a room stat involved. You know, that "traditional" control system that lets the whole house cool off, then fires up and heats it quite rapidly by several degrees before repeating the cycle. Even most thermostatically controlled radiators cycle like that because people believe that balancing isn't needed with TRVs resulting in "on-off" operation with temperature overshoots. I've certainly experienced places where the temperature cycles noticeably.
What I can tell you from first hand practical experience is that there are properties* where it works, and works very nicely. That's practical experience, not theoretical, which is why I have a feeling you've never experienced a system that works properly - you wouldn't be quite so negative about them otherwise.
I also have first hand experience of systems that didn't work very well** (think floor slab used as storage heater with off-peak heating), and I suspect it's that reputation that colours your opinion.
Note that I did not say that UFH is a panacea for all situations. Clearly there are many where it's not suitable - for example I'd not use it as the sole form of heating for a high-loss space with thick carpets.
* I know a few people who are very happy with their UFH. I'll describe one specific one - a relative's house. It got completely gutted and rebuilt internally, and most of it is heated only by UFH. There's a thermal store for mains pressure hot water and heating, with inputs from wood burner and solar panels, with a gas boiler (hardly used) for backup. Nearly all the property is heated with UFH, some of it with engineered floorboards over (low conductivity and low thermal mass, and metal heat spreader plates holding the UFH pipes), part of it stone (slate) flags (high conductivity and high thermal mass). Zones are controlled by wall mounted stats (could be sensors but I'm not that familiar with the system) controlling the valves on the UFH manifold. They are very happy with it, and when I've been there I've found it a very comfortable house to be in. It's comfortable underfoot - and a big issue is that psychologically, if your feet are cold then you tend to feel cold, if your feet are warm then the room itself can be cooler and you don't feel cold. Even my mum who really feels the cold feels comfortable when we visit.
What is really noticeable are the areas without UFH (heated by rads), and the flagged bits really need thick socks and slippers even though the room itself can be as warm (or even warmer) than the UFH heated zones.
One factor that probably helps with this house is that it has thick stone walls which themselves are a significant thermal mass, and the UFH is a wet system so does not push a fixed power into any zone - the water temperature is thermostatically controlled (thermostatic mixing valve), and if it's been reasonably well setup, will reduce power input (reduces delta-T between water and slab) as the temperature of the floor increases.
** I had another relative who lived in a sheltered housing flat years ago. The UFH was electric and run off Economy 7 to heat up at night. Mornings were toasty, evenings were cool, unless the sun came out and heated the whole place up (it had a large south facing window). And of course, as you correctly point out, a thin carpet with no underlay.
If you really wanted to, you could design a UFH system with individual zone heat input control, slab temperature sensors (note that these are normal - required ? - with electric systems), and adaptive twin (nested) loop PID control. But that would probably be somewhat overkill.
The right hand ones (marked AC230V) are the ones from the supply, the middle two are to L&N to the mats and the left hand two are the sensor.
Just as is already writen in the instructions.
Just as is already writen in the instructions.
What's the combined load of all 3 mats?
It sounds as though your elements do not contain an internal earth. Have you got an earthed metallic mesh to install over the elements as required by BS7671?
It sounds as though your elements do not contain an internal earth. Have you got an earthed metallic mesh to install over the elements as required by BS7671?
No - just general "laws of physics" type stuff about just how much typical floor surfaces can radiate into the room at what temperatures, and whether those are reasonable.
Well - maybe I used an unusual term, but "hysteresis is the time-based dependence of a system's output on present and past inputs". If you were to plot how the temperature of the floor varied over time as heat was turned on, and then off, you'd get this sort of shape:
so IMO "hysteresis" is an understandable term.
I'm pretty sure that a stone floor has a much higher thermal mass than a radiator.
And regarding the example you cite, how typical, and to-be-expected-by-the-sellers-of-electric-UFH-mats, is that application?
What colours my opinion is the extraordinarily poor response to an acute need for heating, or an acute disappearance of the need for heating.
I also have concerns about the efficiency of it when an insulator is interposed between the heat source and the room to be heated. And about the ability of it to deliver enough heat in real life situations where people have furniture.
According to the people who sold the product to the OP, the resolution of the carpet issue is to have more powerful UFH.
Not interested - if a thermometer does not say that the air in the room is at 20° then it is not at 20°, no matter how toasty your toes are.
To be expected with stone floors.
The sensible, responsible solution to that is footwear and mats/rugs, not UFH.
Does he want it because he wants to go barefoot, or is he expecting it to heat the room?
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