Underfloor Heating

[siwhitt]

We plan to install Warmup foil heaters in our lounge (under laminate). We need coverage of 19 square metres, so plan to install two 140W heaters: a 12 square metre and a 7 square metre for a total of 11.56 Amps according to page 6 of the manual: http://www.warmup.co.uk/assets/Uploads/Warmup-foil-heater-manual-v2.pdf

I know the system must be protected by a dedicated 30mA RCD, however we live in a relatively small 3 bed flat atop a very old house. There are no spare ways on our existing 8 way consumer unit, and even if there were it would be very difficult for us to run cable directly from there to the lounge. With that in mind I was looking for alternative solutions, one of which appears to be an RCD fused spur, e.g. http://www.fountaindirect.co.uk/warmup-rcd-fused-spur.html

Are there any issues powering the heaters through an RCD fused spur taken from an existing wall socket? Or we could sacrifice the wall socket if needs be if that's a better alternative? Also could anyone clarify where we stand from a Part P perspective?

Appreciate the help. I know the final connections have to be made by a qualified electrician, tested, certified, etc. We had an electrician round this morning, unfortunately he wasn't the most dynamic of individuals. He said the above approach could work after I suggested it to him, but he didn't fill me with confidence! Just want to make sure eveything is being done in the right way.

 

[OwainDIYer]

RCD Fused Spur unit would work, but a 12 amp heating load should really be on its own circuit anyway, and not on the general sockets circuit.

 

[siwhitt]

Understood. What's the reason for that?

 

[ban-all-sheds]

We plan to install Warmup foil heaters in our lounge

Why?

(under laminate).

Will the laminate be OK with that?

Is it the sort of laminate you'll be able to lift easily to get at the UFH when it goes wrong?

And over the top of what, given you're in a top-floor flat?

We need coverage of 19 square metres, so plan to install two 140W heaters: a 12 square metre and a 7 square metre for a total of 11.56 Amps according to page 6 of the manual: http://www.warmup.co.uk/assets/Uploads/Warmup-foil-heater-manual-v2.pdf[/QUOTE]
Would a CH radiator with a 9000 BTU/hr output heat the room adequately? At what surface temperature? Have you worked out how much heat the system will put into the room given the floor temperature you'll be able to tolerate and the emissivity of the surface?

Are there any issues powering the heaters through an RCD fused spur taken from an existing wall socket?

Yes - the guidance is that you do not supply comprehensive electric space heating from a ring final.

Or we could sacrifice the wall socket if needs be if that's a better alternative?

Makes no difference.

Also could anyone clarify where we stand from a Part P perspective?

Part P is a legal requirement to make reasonable provision in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.

So that's what you have to do. One could argue that ignoring guidance in the Wiring Regulations which is aimed at preventing ring finals from being overloaded puts you on the back foot.

Appreciate the help. I know the final connections have to be made by a qualified electrician, tested, certified, etc.

They don't have to be, but it's a good idea.

Also - laminate flooring is noisy - worse than proper wooden floors, and much much worse than carpet.

You should check on the Flooring Forum about soundproofing you can do, or you might (quite reasonably) be on the receiving end of grief from the people downstairs.

 

[siwhitt]

We have one small radiator in the lounge. It's unsightly and doesn't provide us with sufficient heat, so it's going. Yes, the laminate we've chosen is compatible with the foil system, and we're replacing an existing laminate floor so noise will be no more of a concern that it is now. We need around 2,800W to heat the room adequately, and this system will give us 2,660W.

So in a nutshell it sounds like we risk overloading the ring final by not running the heating from a separate circuit. Showing my ignorance now, but how do I determine whether the ring final will be overloaded? How do I determine the current load?

 

[RF Lighting]

I've fitted a few under laminate heaters for customers and they simply do not work.

Your room will *never* get warm. You will regret installing it.


Wood is an insulator. It stops the heat coming through.


Get a bigger rad.



Any fixed load over 2kW should not be supplied by a ring final circuit.

 

[ban-all-sheds]

I lost my original go at this reply, and it's now slightly obsoleted by RFs, but...

We need around 2,800W to heat the room adequately, and this system will give us 2,660W.

The amount of heat which a surface can radiate depends on its properties, and temperature.

Look into the reality of what your floor will do at the sort of temperatures you're likely to be able to tolerate, or reach. Don't be surprised if you only get half that (70W/m²)

Showing my ignorance now, but how do I determine whether the ring final will be overloaded? How do I determine the current load?

The problem is you can't. By their nature socket circuits can have all sorts of things plugged in, or not, at all sorts of places on the circuit, and a ring is wired with cable which is too small to be used on a 32A breaker if it's not a ring. That is only safe if it's not likely that any section of it will be overloaded for any significant time. Hence the guidance that fixed loads > 2kW such as space heating, water heaters etc, not be supplied by a ring.

 

[ericmark]

I was also disappointed when fitting underfloor heating. 27°C is the maximum temperature permitted and this means a 7°C differential compared with 50°C differential on a radiator it will take the chill off a cold floor but will not heat the room.

I did a wet room and the towel rail gives off twice the amount of heat to the underfloor heating.

But to your question, back in 1954 when the housing boom with the new 13A socket and ring final system was started it was designed for heating with one socket in every room my dad,s house had 5 sockets much better than the 2 old 15 amp sockets of my grandfathers house.

With 5 sockets using one for underfloor heating would not be a problem but today most houses have more than 5 in every room and still the same 30/32 amp supply for them all. Also the cables sizes used today is smaller 2.5mm² rather than the old 7/0.029 used in 1954 so today we have changed the guide lines to suit and over 2kW for anything not portable we use a dedicated supply. A 3kW kettle for 3 minutes is OK on the ring but a 3kW immersion heater for 2 hours is not so immersion heaters have a dedicated supply.

There is a risk with a ring final that the draw may be over the rated current for cable on one leg but the experts have decided using only portable appliances over 2kW the risk is low enough to not present a problem.

Although the floor of the wet room was first ripped up and new drains laid then insulation fitted over the drains so no heat should go down into the floor it was useless. My son in spit of what happened in my mothers house still fitted underfloor heating he fitted in in the bed room and it was really some job. Removed the ceiling in room below and all the space between heating pipes and new ceiling were filled with insulation it was duel reason one to stop heat and two stop noise but it is an as well as radiator not an instead. The main reason for fitting is to store the heat. He is also fitting a wood burner which only run economic as a set rate of burn the flue should be maintained at 150°C so it is to be lit once a day and it will heat the floors which will then release the heat over the whole day.

If you look at the original Chester Roman hypocaust

you can see how thick the floors were and lighting a fire once a day kept the floors warm. However if you look at the Romans dress code it was clearly warmer then or they would have frozen so as the country got colder so the hypocaust lost favour. There are always the few who don't seem to mind the cold. Look at the girls waiting to get into a dance hall but I want to be warm.