Splitting supply to 2 underfloor heat zones

[Custom45]

Hi,
Installing some electric underfloor heating in 2 rooms, both will total approx 3kw each (20m² with 150w/m² mats), each on a 16a thermostat with 2.5mm² running to CU on 16a breaker each.

However as there is limited space available in CU can they be connected to a single 32a breaker, then using 4mm² out to a junction box which then splits to 2.5mm² to each thermostat?

Cables will be clipped direct to surface in loft (roof timbers & raised off insulation), dropped down into room and buried in wall surface in suitable conduit. Heating in each room may be in use at same time.

Thanks very much,

 

[ericmark]

You need to read the instructions, if the mats are under 13 amp each, then you can use a fused connection unit to each mat, and a larger supply to the fused connection unit, however it seems an odd question, as to create a new circuit is notifiable, and if you are a scheme member your unlikely to be asking the question, and if not then you are likely to have problems with the LABC inspector, I know I did when fitting UFH in late mothers house.

He wanted to see calibration certificates for the test equipment etc, and my qualifications, at first he refused to let me DIY, but then relented as I produced my degree, so I think your question may not be the problem, but the problem is how to notify the work.

 

[Custom45]

Thanks for the answer, so as long as I'm under 13a for each one then that's a yes, as long as it's via an FCU?

Sorry, I forgot to mention, I'll be doing the work but an electrician will check and make final connections before signing off, I was led to believe that's allowed? I'll run all this through with him before I do anything obviously, but he's away for a while (I'm not doing work til new year anyway), but I just want to get it planned now, hence asking here first. Cheers

 

[EFLImpudence]

There are various options.

Do you not think it would be better to ask your electrician what he will accept?

What does "planned now" mean? Drawing that diagram?

 

[EFLImpudence]

Also - is 6kW (or any amount) of underfloor electric heating in two rooms a good idea?

 

[Custom45]

Also - is 6kW (or any amount) of underfloor electric heating in two rooms a good idea?

Why wouldn't it be a good idea?

 

[EFLImpudence]

Well, it's six units of electricity every hour for just two rooms - plus, presumably, heating for the rest of the house.

What are you paying per unit at the moment?

How hot do you think it will get?

 

[Custom45]

On economy 7 around 15p night, 30p day. The place is all electric and we prefer to keep it that way (has oil fired boiler which has died), so electric heating is only option, having rads with electric combi would be same running cost surely? Place is very well insulated though, so although it'll never be cheap to heat, I don't think it'll be astronomical. Plus we have a good sized solar installation helping with hot water cylinder and some air heat pumps.

Do you think 150w/m² mats would struggle to heat a room then?

 

[ebee]

at first he refused to let me DIY

In what sense would he/could he not let you?

 

[ebee]

As a generalisation paying in KW for heating by electric is not a good idea if gas is a reasonable option but if is mitigated by solar etc then it could be worthwhile

 

[Custom45]

As a generalisation paying in KW for heating by electric is not a good idea if gas is a reasonable option but if is mitigated by solar etc then it could be worthwhile

We're in a remote location, so no mains gas. It's a big house, but outside space is a premium so don't want oil or LPG tanks. We've only just moved in but I've seen previous readings of what the solar generated and it's quite good, and as I said it's a well insulated property (400mm rockwool in roof, 100mm pir in walls).

I appreciate it's going to be expensive to run, but we accept that.

 

[ericmark]

In what sense would he/could he not let you?

The inspector wanted me to pay for a third party inspector which was going to cost more than the cost of the whole job. And would mean no EIC only a completion certificate, and the power would need to be left off until it had been inspected.

He would not accept a C&G 2391, but my son asked if the inspector they select does not pass it, what then, would they not have to take the word of the most qualified, if so then any third party inspector would need to be the same or higher than me, and then the LABC inspector backed down, together with my pointing out that I was hardly likely to put my own mother in danger.

I don't think he knew what a C&G 2391 was, but he wanted to be sure we knew what we were doing. But my point is the work will require notifying and if asking the question asked, not sure how much the LABC inspector will allow to be DIY.

In Wales the fee is £100 plus vat for first £2000 worth of work, and any third party inspection is on top, so looking at around £250 to be allowed to DIY, so hardly worth doing DIY.

 

[ebee]

"I'll be doing the work but an electrician will check and make final connections before signing off, I was led to believe that's allowed?"

No it`s not really allowed, however I am not suggesting that it does not happen that way though.

 

[Murdochcat]

As a generalisation paying in KW for heating by electric is not a good idea if gas is a reasonable option but if is mitigated by solar etc then it could be worthwhile

Problem with this is the distinct lack of PV energy when you need heat in the winter. 1.2kw today, 0.3 kw yesterday.

 

[ebee]

Agreed (By Solar etc -I actually was thinking inclusive of wind, waves and heat source pumps too, the whole lot of things we might add into the mix - or might not either)