Wiring for small water heater and underfloor heating

[Ed-Wood]

Hi, new to the forum so please be gentle with me.

Currently having some renovations made to my kitchen and dining room (wall removed, external door moved, ceiling replaced). A new kitchen is next on the list, and SWMBO also wants electric underfloor heating and a small water heater for instant cuppas… I’m not convinced about either, but that’s a battle for another day (a fairly futile one for me, if truth be told).

After forking out for the building work in the kitchen I’ll be skint again for a good while, so these plans may never happen. However, whilst the ceilings are down there is easy access for wiring virtually all of the way back to the CU in the hallway next door. Makes good sense therefore to run new wiring now for the heater and UFH should it ever be required.

The heater option that the good lady wife fancies is a 1.5kw model.

The UFH would likely cover about 15sqm, so let’s say 2.0 to 2.5kw?

I’ve got one spare slot on the CU.

So my question is, theoretically, could these (and only these) both go onto one new ring of standard 2.5mm twin and earth? Total cable run (CU back to CU) would be c. 22m. In my simple uneducated brain, it sounds OK, but I’d need one of you experts to tell me what I might be missing or what else I might need to take into account (or alternatively how else this should be tackled).

I wouldn’t feel sufficiently knowledgeable to do anything other than route the cables through the ceiling void whilst I have a golden opportunity to do that. I’d have the connections and subsequent testing all completed by a qualified electrician at some point in the future.

Any advice gratefully received.
Cheers.

 

[Fleeting]

The water heater can be connected from the existing ring final circuit assuming there is one.

 

[Ed-Wood]

The water heater can be connected from the existing ring final circuit assuming there is one.

Thanks. I probably should have added that I was trying to avoid using the existing ring that serves the kitchen as it's powering quite a lot of appliances already. Having the opportunity to easily put in an additional circuit seemed too good to miss.

 

[ProDave]

No1, I assume you mean a boiling water tap like a Qooker or similar? Brilliant things. They plug into a 13A socket in the sink unit.

Electric under floor heating. WHY? Direct electric (resistance) heating is the most expensive way to heat anything, then add to that it is then only viable if you have VERY good insulation under the floor. How do you heat the rest of the house?

 

[Murdoch]

When do you plan to fit the floor?

Connecting it later seems a very odd thing to write.

 

[binky]

Thanks. I probably should have added that I was trying to avoid using the existing ring that serves the kitchen as it's powering quite a lot of appliances already. Having the opportunity to easily put in an additional circuit seemed too good to miss.

I was going to say a new circuit would be ideal if the opportunity is there, and it sounds like it is.

UFH wise, what is the floor, solid concrete, suspended wood. UFH is only any good if the floor under it is well insulated, so heat goes 'up' into the room and doesn't soak into the floor underneath.

 

[Ed-Wood]

ProDave: the UFH is my biggest concern (in terms of practicability) for all the reasons you mention. Practicability is not always my wife's first consideration (especially if 'her friend's got one and it's brilliant'...). Rest of the house is gas fired central heating on a reasonably modern condensing combi boiler. Plus a log burner in the lounge. But the kitchen is the coldest room as a big chunk of it is extended out from the main body of the house.

Murdoch: I'll fit the floor when I do up the kitchen - at some mystical point in the future. Even if I don't, the expense of a few metres of cable and 15 minutes drilling out some joists won't seem like much of waste, especially compared to the alternative of ripping up carpets and floorboards above at a later date.

Binky: floor is solid concrete. I'd add as much extra insulation as I could get away with - not too much of concern if the final floor level is raised by a few cm.

 

[ProDave]

ProDave: the UFH is my biggest concern (in terms of practicability) for all the reasons you mention. Practicability is not always my wife's first consideration (especially if 'her friend's got one and it's brilliant'...). Rest of the house is gas fired central heating on a reasonably modern condensing combi boiler. Plus a log burner in the lounge. But the kitchen is the coldest room as a big chunk of it is extended out from the main body of the house.

Murdoch: I'll fit the floor when I do up the kitchen - at some mystical point in the future. Even if I don't, the expense of a few metres of cable and 15 minutes drilling out some joists won't seem like much of waste, especially compared to the alternative of ripping up carpets and floorboards above at a later date.

Binky: floor is solid concrete. I'd add as much extra insulation as I could get away with - not too much of concern if the final floor level is raised by a few cm.

See bits in bold.

With a condensing boiler fit WET under floor heating fed from the boiler.

BUT only if you can get a very minimum of 100mm of kingspan or similar PIR insulation. That will probably nean digging up the existing concrete slab digging down more and re laying. If you hope to just fit a thin insulated panel on top of the screed, forget the idea, you will just waste a lot of money on a very inefficient system that will work badly and cost a fortune.

 

[Ed-Wood]

See bits in bold.

With a condensing boiler fit WET under floor heating fed from the boiler.

BUT only if you can get a very minimum of 100mm of kingspan or similar PIR insulation. That will probably nean digging up the existing concrete slab digging down more and re laying. If you hope to just fit a thin insulated panel on top of the screed, forget the idea, you will just waste a lot of money on a very inefficient system that will work badly and cost a fortune.

Thanks for the advice ProDave. No way we'd go for all the hassle of digging up the floor. I'll gladly use your comments to back up my case (against underfloor heating).

 

[Geoff1946]

My son built an extension and installed wet underfloor heating which is fed from the same boiler as the conventional heating in the rest of the house. It is completely successful, BUT the new floor has six inches of Kingspan under the slab which is then screeded over the heating pipe and finished with wood block. I think the floor slab acts like a big storage heater and I very much doubt if it would work without the thick insulation below.

 

[Ed-Wood]

But... ignoring for now all the pros and (mainly cons) of underfloor heating - in respect of my original question, would a new ring just for the water heater and the UFH be feasible? I seem to recall something about a fixed appliance / installation or whatever over 2kw requiring an independent circuit. Is this a hard and fast rule or a guideline? The 'to-be confirmed-but-highly-unlikely' UFH would probably be around the 2kw mark.

I really don't want to miss the opportunity to sort the wiring now, however unlikely the future potential projects might turn out to be. Ceilings are going back up end of this week and after that my chance is gone.

 

[monkey5]

Fit 2 radials from one MCB if only 1 space in CU and a 20A MCB, or 4mm radial from a 25A (if available for the CU) depending on distance and routes etc

 

[Ed-Wood]

Fit 2 radials from one MCB if only 1 space in CU and a 20A MCB, or 4mm radial from a 25A (if available for the CU) depending on distance and routes etc

Cheers Monkey, if two radials: about 10m from CU to water heater and 8m from CU to UFH. Route would be standard uninsulated 8 inch ceiling void / then (presumably) standard vertical wall chased and plastered. I didn't realise you could run 2 radials from one MCB.

 

[Murdoch]

I didn't realise you could run 2 radials from one MCB.

Er no. One MCB = 1 radial circuit, could be 4 cables , but would still be a radial circuit

 

[Ed-Wood]

OK, for clarity, 2 (or multiple) non-returning cables from one MCB is OK, yes?

 

[Fleeting]

OK, for clarity, 2 (or multiple) non-returning cables from one MCB is OK, yes?

No each final circuit requires separate circuit protection.

 

[Murdoch]

No each final circuit requires separate circuit protection.

Here we go again.

1 x OCPD = 1 circuit

 

[Ed-Wood]

OK, I'm now none the wiser on the 'x2 radials' idea but assume it's a no-go.

So, back to my original scenario: a new ring circuit, 2.5mm t&e, c. 22m end to end, not running through any insulation, feeding only a 1.5kw water heater and a (let's say) 2kw underfloor heating system. Because the ceiling is down and I have the perfect opportunity to run the wires now, at negligible cost/effort (and for now putting aside all the issues regarding efficiency of the UFH etc). Any reason why not, from an electrical regs / safety point of view? What if UFH was 2.5kw?

Did just read in the installation small-print for one make of water heater that it must not be on the same circuit as a fridge-freezer - no explanation given. So why would that be? Seems odd for a piece of kit primarily designed for a kitchen.

 

[ProDave]

Did just read in the installation small-print for one make of water heater that it must not be on the same circuit as a fridge-freezer - no explanation given. So why would that be? Seems odd for a piece of kit primarily designed for a kitchen.

That will be manufacturers arse covering so if their device fails and trips the circuit, they don't get a claim for a lost freezer full of food.

 

[binky]

Thanks for the advice ProDave. No way we'd go for all the hassle of digging up the floor. I'll gladly use your comments to back up my case (against underfloor heating).

Other option is a plinth heater, fits in kick boards under the kitchen cupboards.