Electric UFH - Do I *really* need thermal insulation boards?

[powerbook]

Hi

I am not being stingy (a glove box stuffed full of selco/screwfix/tool station receipts can prove that) however I don't like buying things that are a bit of con (e.g. those reflective panels behind radiators!) and I have always been curious about these thermal tiles so I would like someone do give me a definitive answer about these things please.

I am about to lay an electric UFH cable mat (ground floor lounge) and wondered if I really need thermal insulation boards. Are there any physicists/engineers here who understand heat conductivity etc to the level of maths equations?! My gut feeling tells me these thermal boards would probably have a positive effect but by how much is the question? Negligible amount? I know lots of people sell them but then snake oil also used to be popular years ago!

I have had the timber floor up and installed RW6 Rockwool slab (the highest density one they do) between the floor joists which was left over from another project. I friction fitted them and used expanding foam here and there to get a very good seal. Underneath that I laid loads of loft insulation on a roll while leaving enough room for air to circulate around the joists.

On top of the joists in 28mm quietboard T&G chipboard (which has the foam backing). On top of the this I will lay 5mm SLC and bed in the electric cable mat. And top of this will be 20mm engineered oak planks.

Sorry for all the detail but I though I might as well write it all.

So, I don't have a massive concrete slab of un-insulated floor, so would it be worth me fitting 10mm of thermal insulated boards?

Cheers for any advice

 

[RF Lighting]

Have you got a radiator in this room?

If you're planning on using the UFH to heat the room, then forget it. It does not work, especially when you cover it with 20mm of engineered insulation planks.

Sorry to be so negative, but I've done for too many jobs where people have spent a fortune on electric UFH for it to just not work.

 

[powerbook]

Hi

the room has a HW radiator in it. The UFH will hopefully give the room a lift. It has always been pretty cold in there during winter, so much so that we don't use the room. However now we have insulated under the floor (was just a massive empty void).

So fingers crossed this December it will feel better in there..

Cheers

 

[SimonH2]

From your description I can't see that insulation board will do anything for you. But, you will need something resilient to bed the wire into and I'm not sure SLC will do it unless you can 100% guarantee that the wire won't be proud of it's surface anywhere (which would mean it getting damaged by the board sat on top).

 

[ban-all-sheds]

the room has a HW radiator in it.

Would you consider lagging it with 20mm of reasonably high u-value material, or would you think that was a pretty stupid idea?

 

[SimonH2]

Given the relative surface areas, it would have to be a much, much thinner section. UFH under floor boards does work (if designed correctly) - and in this case I get the impression the OP is looking to use it to improve the comfort of "cold floor", not as the primary heat source.

That does bring to mind something else the OP may need to consider. He's got a not very thermally conductive base, and not very thermally conductive overlay. I'm no expert, but I suspect he ought to have heat spreader plates somewhere in the equation or he'll just have hot lines where the wires are and cold in between. I know when they were doing my brother's house, the UFH water pipes were clipped into metal pates sat across the joists to spread the heat away from the pipes. IIRC one proposal included casting screed slabs in-situ between the joists for the same reason.

 

[bernardgreen]

Oak is not a good conductor of heat so the heat from the wire will take a long while to reach the top surface of the oak. For a warm surface the wire and the screed will have to be hot. The hotter the mat the more heat will be lost downwards.... even though there is insulation under the mat some heat will be lost that way.

Ensure the temperature sensor in the screed is in a sleeve which will allow it to be replaced when it fails.

Also remember exactly where the wires are so you avoid putting a screw through the wires when fixing the oak down. ( easy done. I put a screw through a pipe when laying my oak on marine ply wood floor in the bath room )

 

[ericmark]

Only fitted one electric underfloor heating and total failure and this was with tiles fitted over the electric mat. Time was a big thing takes at least an hour to warm up tile so to warm room a few hours and we found without the towel rail the room never got warm.

As a addition well maybe but for most people they don't want to wait the time required for warm up. Only an option where used 24/7.

My son has fitted water underfloor heating up-stairs which as yet untested. But still has radiators as well and even if it does not work not really a problem.

 

[powerbook]

Thanks for the reply. I have decided to go ahead and buy the insulation boards, polystyrene type with no cement backing. They were cheap anyway...

Does anyone know the best way to fix them down on to chipboard? Can i use an adhesive rather than waste time with screws and penny washers?

Yes I will def use a conduit for the cold tail. We have UFH in our bathrooms and one failed last year. Simple job to replace the sensor. By the way we have 12mm floor tiles and I seem to remember an inch of SLC going down and the tiles are still warm in 15mins. So if anyone is thinking of installing UFH as a secondary heat source I can def recommend it.

Thanks