Wiring Electric Underfloor Heating

[Kadi]

Hi All, I’m doing a DIY project but needed some advice before I comitted and would really appreciate any help/advice you can offer.

I have recently moved in to a new house and wanted to put in electric underfloor heating in the hallway. The property is a bungalow and all the wiring goes in to the loft and then back in to the rooms, its been re-wired recently (from what I can tell) and has channels within the walls to use in order to drop the wiring down in to the rooms. The property already has underfloor heating in the kitchen and the main bathroom. It’s wired on its own circuit from the mains (consumer unit) through the use of a junction box.

I’ve checked all the wire ratings and RCD ratings and all seems to be fine – the wattage rating for both of these mats/loose wires adds up to 1.3kW. I'm looking to add another mat/loose wire in to the circuit of 750w.

My question is can I tap in to the existing junction box and make use of the RCD/mains and drop the wire in to the hallway to power the mat/loose wire? I appreciate I will need an electrician however wanted to size up the costs and whether or not I’ll need a new circuit as at current I have no free slots in the consumer unit.

Thanks in advance or your replies and apologies if my wording/terminology isn’t spot on – I’ve also done you a little diagram (of my madness)!!! Also if you could go easy on the abuse that would be great

 

[ban-all-sheds]

I have recently moved in to a new house and wanted to put in electric underfloor heating in the hallway.

Why?

Seriously - what are you expecting it to do?

 

[Kadi]

Hi BAS, i've read all about you

The hallway is quite large and an access point to all rooms (its a old style layout), it gets cold very quickly - as its in a bungalow i wanted to make it as comfortable as possible.

 

[ban-all-sheds]

Do you not have gas heating?

The output of that UFH you are proposing is about the same as a 1m x 40cm single-panel radiator. Would one of those be big enough to heat the hall? If not, neither will this mat.

And why does the hall get cold quickly? Where does it lose heat? Through the walls? The ceiling? The floor?

Does your existing UFH actually heat the rooms, or just take the chill off the floors?

Just banging in a bit of heating mat in the hall without considering any insulation problems (particularly in the floor - do you know what its construction is?) might not be the best approach.

 

[Kadi]

There is gas heated radiator and the idea is to take the chill off the floor - enough to make it comfortable to walk on. There aren't any insulation problems, it's just that there is always people coming and going for visits and it gets cold quickly.

 

[winston1]

There is gas heated radiator and the idea is to take the chill off the floor - enough to make it comfortable to walk on.

Wear slippers.

 

[ban-all-sheds]

There is gas heated radiator and the idea is to take the chill off the floor - enough to make it comfortable to walk on.

Footwear.
Rug.

There aren't any insulation problems, it's just that there is always people coming and going for visits and it gets cold quickly.

If there are no insulation problems then the floor will not be getting cold quickly, once the space is up to temperature.

If you mean the space gets cold quickly then UFH won't help.

 

[ericmark]

We also wanted to get the hall warmer, as you say conventional layout, after a lot of experiments and thought I realized the problem was control, if I opened up the lock shield valve, hall would heat fast, but other rooms did not get time to heat up. I will not at this point go into how I cured the problem, but with any boiler unless some really expensive system like EvoHome is used, you need to have the thermostat in a room with no other form of heating, no doors to outside, and set to be coolest room in the house.

Often this room is the hall, not ideal as it has a door to outside, but if you put in extra heating it will really mess up the gas heating.

I have just got my father-in-law to fit a radiator into his living room, it only had a gas fire, now not only is the living room more controlled, so is every other room, because that gas fire would heat the thermostat and so all other rooms became cold.

I would shelve the under floor heating for the moment, and ask your self why the hall is so cold, it may be all you need to do is adjust some lock shield valves, if for example nearest radiator to boiler has the valve wide open, this can stop other radiators heating up.

 

[JohnW2]

... you need to have the thermostat in a room with no other form of heating, no doors to outside, and set to be coolest room in the house.

I don't really understand that, since it sounds rather like a contradiction in terms. If one has a single thermostat set so as to make the room it's in 'the coolest room in the house', how can the temperature in other rooms be higher?

Kind Regards, John

 

[Iggifer]

I don't really understand that, since it sounds rather like a contradiction in terms. If one has a single thermostat set so as to make the room it's in 'the coolest room in the house', how can the temperature in other rooms be higher?

Kind Regards, John

The idea behind that is nowadays you set the temperature in rooms individually with TRVs.

The stat will then only open when that central, non-heated room reaches temp - ie never.

You’re better off having the stat in a room with a rad with no TRV and set the temperature and TRVs accordingly

 

[JohnW2]

The idea behind that is nowadays you set the temperature in rooms individually with TRVs.

Indeed, and not just 'nowadays' - I've been doing that for a very long time (at least the 30 years I've been in my present house.

The stat will then only open when that central, non-heated room reaches temp - ie never.

If what eric meant was "rely on TRVs and position/set the room stat such that it will never 'go off' ", then fair enough, but one might just as well not have the room stat in that case (or, wherever it is, turn it up so high that the temperature will never reach it's set temp).

Kind Regards, John

 

[Iggifer]

If what eric meant was "rely on TRVs and position/set the room stat such that it will never 'go off' ", then fair enough, but one might just as well not have the room stat in that case (or, wherever it is, turn it up so high that the temperature will never reach it's set temp)

Yea you may as well just link out the stat.

In my flat it’s in the lounge, which has two rads (only a couple of TRVs in some other rooms) and it sucks. The room you want the warmest is always trying to close the stat

 

[ericmark]

If the radiators a balanced with simple lock shield valves then each room in theory should heat up in unison with each other as long as the only heat going into the rooms is from the central heating boiler and no heat can escape, i.e. it does not have a door to the outside. The main idea of the wall thermostat is it turns off the whole central heating on a warm day, so if put in what has been set to be the coolest room, then it can be set low enough to switch off heating on what is potentially a warm day. By adding TRV to the system then the TRV stops a room getting too hot, and the wall thermostat stops the boiler cycling on a warm day.

However this room which is kept at say 12°C spot on for keeping the wine, is not found in most houses. So we have to find other ways around the problem, one could put a wall thermostat in every room and a TRV in every room, the main difference between the TRV and wall thermostat is the TRV controls the flow, it is not simple on/off so it will modulate the boiler meaning little or no hysteresis, but you still need the wall thermostat to stop the boiler cycling.

Systems like EvoHome have a "thermostat" which gets the temperatures from all the TRV heads not the air temperature around the "thermostat" and alters the voltage with opentherm so it controls the modulation of the boiler. The "thermostat" is really a hub which collects all the info and works out how hot the circulating water needs to be to maintain an even temperature.

Cheap skates like me, have to cheat, I have two wall thermostats and there is a TRV on the radiator of the room with the thermostat in, this being the hall, theory is when front door is opened then the TRV will open wide and reheat the hall quickly, however before it gets to the wall thermostat temperature the TRV will start to close, so the last degree or two takes a lot longer to attain giving the other rooms chance to warm up.

The wax and fluid filled TRV heads are only approximate, however the electronic heads are spot on, so you select which rooms to fit cheap TRV heads and which to use expensive electronic types in.

However any other heating where the wall thermostat is will result in it turning off too soon, so if I fitted under floor heating in my hall the net result would be rest of house gets cold.

 

[JohnW2]

The wax and fluid filled TRV heads are only approximate, however the electronic heads are spot on ....

Do the electronic ones have remote sensors (I didn't think they did)?

I have no experience of electronic ones, but I've often looked at all my non-electronic ones and wondered how on earth they even vaguely do what they are meant to do, since their heat sensor is usually sitting just a couple of inches away from a radiator which, when 'working' is virtually too hot to touch and, indeed, whose bodies are often pretty warm (probably warmer than the desired room temp) after the CH has been running for a while.

Kind Regards, John

 

[Seb101]

Hi All, I’m doing a DIY project but needed some advice before I comitted and would really appreciate any help/advice you can offer.

I have recently moved in to a new house and wanted to put in electric underfloor heating in the hallway. The property is a bungalow and all the wiring goes in to the loft and then back in to the rooms, its been re-wired recently (from what I can tell) and has channels within the walls to use in order to drop the wiring down in to the rooms. The property already has underfloor heating in the kitchen and the main bathroom. It’s wired on its own circuit from the mains (consumer unit) through the use of a junction box.

I’ve checked all the wire ratings and RCD ratings and all seems to be fine – the wattage rating for both of these mats/loose wires adds up to 1.3kW. I'm looking to add another mat/loose wire in to the circuit of 750w.

My question is can I tap in to the existing junction box and make use of the RCD/mains and drop the wire in to the hallway to power the mat/loose wire? I appreciate I will need an electrician however wanted to size up the costs and whether or not I’ll need a new circuit as at current I have no free slots in the consumer unit.

Thanks in advance or your replies and apologies if my wording/terminology isn’t spot on – I’ve also done you a little diagram (of my madness)!!! Also if you could go easy on the abuse that would be great

Hi Kadi, while the elders argue about the merits of old money versus new money, let me answer your question.

You say you have checked the ratings on the RCD, usually the there is an MCB (breaker) for the circuit and an RCD for multiple circuits (if it's a combined one it's called an RCBO). Either way, it's the breaker current you need to be sure you are not exceeding (technically the RCD max current and the total current for the incomer as well, but the chances of going over that with 1.3kw are slim). Whats the rating on the UFH breaker?

In general, yes, you can do as you suggest. If you are wiring it into an existing circuit (and not directly into the Consumer Unit) and the UFH is not in a special location (bathroom etc) then you could do all the work yourself without requiring Part P.

You could also likely safely wire 1.3kW as a fused spur off any ring-main socket in your house.