Underfloor heating water v electric

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  • Underfloor heating water v electric
  • hammerite
    Member

    We’re going to have some renovations done on the house where our kitchen, dining room and part of our lounge will be knocked in to one. We’d like underfloor heating. The builder has suggested going for electric as it’ll save on install cost – they won’t have to dig any of the floor out for a start. I’m concerned, however, with the cost of electric heating over gas – our fuel bills are already pretty hefty.

    Any experts able to give me an idea about install and running costs for both? I’ve looked online for some calculators but not seen any. We’ve not measured up actually what area would need covering.

    TheBrick
    Member

    FYI you can have wet under floor heating powered by electric but I guess you are referring to resistive heating mats.

    Electric is about 1.5 the price of gas per kWh so your bill will be 1.5 as much. If you want to work out the required energy usage you will have to measure the floor area and work out your insulation values.

    hammerite
    Member

    Yes resistive mats v wet system.

    Premier Icon Smudger666
    Subscriber

    Erm, electric is approx 3 or 4 times the price of gas.

    Eg my gas price is 3.96p/kWh, leccy is 14.5.

    Premier Icon FuzzyWuzzy
    Subscriber

    I think my bathroom (approx 6m2 heating area) cost me £30-40 a month over winter, it’s probably a worst-case scenario in terms of insulation though (100mm in loft, 2m2 of it is on an internal wall with just plaster board behind and the floor although it had insulation backing board put down is above a very cold garage which I doubt helps). I’ll certainly think twice about installing it when I get around to renovating my kitchen.

    I think the main problem is just how long is takes to heat a room, some (supplier) web-sites state it’s cheap to run as it heats a room much quicker than central heating but I call bullshit on that. It’s basically always on but you schedule it either to be on normal or eco mode. Eco mode I think I have set to 10c, the tiles feel cool but not cold like that however the room temp drops to chilly overnight (winter at least). So I have normal mode set to 35c and initially had it set to come on about 2 hours before I use the bathroom in the morning but although that made the tiles warmer it wasn’t really heating the room noticeably. I currently have it come on 4 hours before now and the bathroom (after a cold night) is just about warmish. Bearing in mind it’s a fairly small bathroom (4m2 heating on the floor) and one wall also has electric under-tile heating (the remaining 2m2) so more heating than a pure floor-only bathroom would have my experience is it heats much more slowly than it would with a decent sized radiator.

    Since it’s got milder though I have noticed it being fairly hot some mornings so do need to experiment a bit more and I’m sure over summer I’ll probably only have the wall panel coming on regularly (to dry the towels that are on hooks on it) so should get a lot cheaper.

    Also it does slightly raise the level of the floor in most situations (although in my bathroom it’s just got an asymmetric door threshold and you don’t notice the 0.9mm step up.

    I guess it would depend how much extra a water-based system would cost to install in your case but I’d certainly favour that sort of system unless it was thousands more to install.

    trail_rat
    Member

    after seeing my mates electric system that never gets used because if you dont keep it on eco mode (always on using leccy) its useless at even warming its self up.

    We went with a wet system laid on gypsum mats on our suspended concrete floor and just straight off the heating through a set temp mixer manifold.

    It heats up with the Central heating and the floor gets toasty quickly.

    There is a very very small uprise – but as above we just used an asymetric threshold and you dont notice it.

    bamboo
    Member

    You can get low rise underfloor heating kits that run off your central heating. My colleague has it installed, I can’t recall the brand name now. The whole system only raises the floor height by 15mm, and you can lay your flooring on too (no screed etc)

    sharkbait
    Member

    You can get low rise underfloor heating kits that run off your central heating

    I believe they are very spendy though (according to my builder).

    Generally, if you want a wet system you’ll most likely have to dig the kitchen floor up and lay a new one [unless you can cope with the height increase] which will take time and obs cost money. Take into account the cost of skips for the old floor @ £220/skip, insulation (prob £200) plus labour, new concrete (2 cubic meters just cost me £250) and the cost of the pipework . Wet systems are pretty complicated and require a manifold to control the flow of water – they can be quite spendy to run also according to my BIL – but he’s on oil.

    An electric system will be cheaper to install but will raise the floor level by about 5mm or more if you put add thermal board underneath. Although electricity is more expensive it is also 100% efficient which helps.

    We’re just doing our kitchen and I’m putting down 10sqm of electric on top of 10mm thermal boards – but this is purely to take the chill off the tiles and not to actually heat the room. We also have PV which will help in the shoulder months but not during the winter. You can also easily control electric and ‘if’ it goes wrong you can just leave it while a wet system ‘could’ leak meaning that you have to pull up the floor to fix it.

    Premier Icon bikebouy
    Subscriber

    Don’t forget to future proof your house because this government are going to Ban Gas boilers soon..

    And that’s not that far off..

    🤷‍♂️

    I know a few people who’ve had electric installed…and don’t use it as the costs are prohibitive. You might save money on the installation but if you’re not going to use it then it’s just money down the drain. Better off spending on the install for wet and actually getting the use of it.

    Banning of gas boilers…I just don’t see it? well for new build maybe but homes that already have it will always have it. The cost of converting an existing home to electric is expensive and imposing that cost onto millions of people overnight just wont happen. I can see new build homes being electric, but not the continuation of homes that already have gas systems installed. They wouldn’t ban fossil fuel cars overnight and wont do the same with CH systems. And it is not clear that currently and for the foreseeable, it is any better for emissions and the environment. Modern boilers are extremely efficient and new technologies, like smart thermostats, are minimising their use and reducing emissions significantly, so putting all that additional load on a national grid, which isn’t so green, will be shooting yourself in the foot. Renewables cannot do it alone (been proved so many times in so many countries so not even worth arguing against no matter how we might want it not to be true), they can only be used as top up to a base load generation system – which at the moment is still predominantly gas or coal…we need to make the switch to nuclear if we’re really serious.

    And besides…who are they going to sell all that shale gas to?

    Premier Icon lesgrandepotato
    Subscriber

    Do you have an insulated slab? If not you’ll be wanting to dig out either way. If you do then I guess electric could work. We’ve gone fully zoned wet and it’s great. 2500sqft and we’ve used about 600l of oil since the start of December.

    trail_rat
    Member

    ou can get low rise underfloor heating kits that run off your central heating. My colleague has it installed, I can’t recall the brand name now. The whole system only raises the floor height by 15mm, and you can lay your flooring on too (no screed etc

    this is what we have.

    installed last week so i can confirm

    I believe they are very spendy though (according to my builder).

    is not the case – it sounds like your builder just doesnt want to do it.

    Premier Icon bikebouy
    Subscriber

    Banning of gas boilers…I just don’t see it? well for new build maybe but homes that already have it will always have it.

    I listened to an R4 programme last week on the subject, should still be available on iplayer.

    Apparently all new home from 2025 will be banned from having Gas Boilers (individual single use) and developers are looking to replace them with one communal boiler for 6-10 homes.

    And banning of replacement Gas Boilers in homes sometime thereafter.

    Just sayin 🤷‍♂️

    trail_rat
    Member

    Just sayin 🤷‍♂️

    yeah but we were supposed to leave the EU 3 weeks ago….and again last week ….

    – and that hasnt happened yet either.

    sharkbait
    Member

    it sounds like your builder just doesnt want to do it.

    OK, I must have been thinking of some other system then.
    It’s me that doesn’t want a wet system – we already have a heating system in the kitchen and a stove in the snug which is now being knocked into the kitchen so a wet system would have been overkill in our case, plus any rise in the floor level would have been fairly unacceptable – we just want to take the chill off the tiles so electric will be fine.

    We have a house by the beach (no gas anywhere in the village) where the bathroom is heated by electric underfloor and I only switch it on when we’re there for a week or longer (but that’s usually in the summer and the PV offsets pretty much all of the running cost.)

    nicko74
    Member

    We’ve gone electric in our house; couldn’t tell you what it costs as it was part of a full renovation and we haven’t turned them off…

    But since this seems to be a thread for knowledgeable people: one of our underfloor electric mats seems kaput – it’s not heating, the thermostat claims it’s on, but nowt is happening. Any suggestions as to what it might be and how easy (or otherwise) it might be to fix?

    Whatever sort of UFH you have it’s slow to respond – it takes a while to heat up, and some time to cool down after you switch it off. Even fairly high temp UFH runs a LOT cooler than radiators so it takes longer to warm the room.

    It works best left on for long periods in a well insulated house. My BIL had electric put down in their extension and the room is always cold – he’s too tight to run it as intended (and it does cost a lot to run).

    Hefty fuel bills implies your insulation is poor. You’d be better off sticking with radiators IMO

    Premier Icon jimdubleyou
    Subscriber

    We have electric mats in our new extension, which is insulated up the yin yang.

    We have it on for an hour in the morning before we get up and for about 4-5 hours in the evening. Can’t say our bills have been massive over the last year – we’ve had a lot of work done, so increased insulation may well have hidden the increased cost.

    Have had to switch it on a weekends a couple of times, but it seems to heat up quickly. We have a wood floor finish rather than tiles.

    sharkbait
    Member

    Any suggestions as to what it might be and how easy (or otherwise) it might be to fix?

    I’d put a multimeter on the output of the thermostat if possible. If power is being output then possibly a broken wire for some reason – fix would involve pulling up the tiles!
    (that said at least it’s not pissing water out!)

    Are you sure you’ve got more than one mat as they tend to be a single mat?

    hammerite
    Member

    Thanks all.

    I think the hefty fuel bills might well be down to a 25 year old boiler. We can’t insulate the walls any further, loft insulation is up to 300m, it’s unlikely we have any floor insulation. We’re replacing most of one of the walls with bi-folding doors with the renovation.

    My main concern with not having a gas/wet system is that the rest of the house will still use gas to heat the rads. So we’d end up working the boiler to heat the rads and using electric at the same time to heat the ufh. We may as well just use the boiler to do both.

    I’m fine with the idea of leaving ufh on during the winter and keeping the heat at a lower constant temp.

    Bear
    Member

    Electric underfloor is very expensive to use as a primary heat source in comparison to a wet system run off a natural gas or oil boiler.
    Both systems can be fitted over an existing floor with electric being a slimmer profile, but wet systems can be as low as 15mm I believe. I’ve not any experience of that overlay type but I’ve fitted many wet systems with no problems apart from other trades being clumsy.
    Wet underfloor should be cheaper to run than radiators due to the low temperature of the water that circulates through it. Combine this with a modern condensing boiler and it can be cheap to run.
    You do need to try to learn how quickly your building heats up and cools down as you need to think of when you want the room to be hot and turn it on early enough to achieve that. Likewise as you most likely have some thermal mass you can turn it off far sooner, so the on period for the heating doesn’t necessarily match the time that you use the room. Also the use of a setback thermostat or programmable type is prudent to ensure you aren’t letting the building cool too much and leading to long warm up times.
    Message me directly if you want a contact for a good underfloor company that I’ve used for many years.

    I think the hefty fuel bills might well be down to a 25 year old boiler.

    probably not as much as you think. New boilers are over 90% efficient, old ones 60%+ so you might know 25% off your bills but they’re not going to halve.

    It’s all energy at the end of the day – doesn’t matter whether you’re using both gas and electric at the same time. however, a kw of heat from electric costs you 3x one from gas (so even with an old, inefficient, boiler gas will be cheaper)

    nicko74
    Member

    Thanks sharkbait, will try that

    Are you sure you’ve got more than one mat as they tend to be a single mat?

    Sorry – I meant in different rooms (kitchen and bathrooms). One in each 🙂

    Premier Icon cynic-al
    Subscriber

    As above elec is 4x gas per kWh, you will soon lose the discount of the installation costs.

    A mate has 1 room with electric underfloor and gas elsewhere, they don’t use it as it’s too expensive.

    trail_rat
    Member

    So apart from one guy and his fear of drowning in the leak from underfloor heating we are all in agreement that electric is pretty darn expensive.

    Premier Icon leffeboy
    Subscriber

    and even with electric I think you need to dig the floor out to fit insulation underneath.  I had one installer that said it was ok to fit on top of a concrete floor because ‘heat went up’ so there wouldn’t be any worry about having to heat up a huge lump of concrete.  They didn’t get the job.  It might be there is slim insulation but I seem to remember we but a good few cm of insulation under our wet system before the screed went on top

    Rickos
    Member

    I know a few people who’ve had electric installed…and don’t use it as the costs are prohibitive.

    Exactly my experience. In a large kitchen, tiles, resistive mats, 6mm of insulation underneath. Graphing our power costs was quite an eye opener, so it was only ever used on the very coldest days.

    Premier Icon jam bo
    Subscriber

    I looked at all the options when we were renovating our house last year. I opted to wear socks instead…

    sharkbait
    Member

    OVO Energy comparison

    I think there are pros and cons to both and it really depends on three main factors:
    – whether you’re doing a new build/big renovation (i.e. floor out) or just a bit of an overhaul
    – what your fuel source is, gas or oil/lpg/electric, etc.
    – whether the underfloor is your primary heating or just background

    In each case the former would indicate its probably better to go with a wet system while the latter situation might be better with electric.

    (My sister’s got wet ufh and the other day the manifold decided to start leaking which caused a load of damage and expense)

    and even with electric I think you need to dig the floor out to fit insulation underneath. I had one installer that said it was ok to fit on top of a concrete floor because ‘heat went up’ so there wouldn’t be any worry about having to heat up a huge lump of concrete. They didn’t get the job. It might be there is slim insulation but I seem to remember we but a good few cm of insulation under our wet system before the screed went on top

    tiles, resistive mats, 6mm of insulation underneath.

    That’s your problem right there.

    From Celotex site –
    In line with the latest Building Regulations, it is required that all new builds have insulation positioned below the concrete slab. However, underfloor heating should also implement insulation above the slab and directly below the pipes to reduce the effects of downward heat loss. We commonly see floor build-ups on new builds with insulation only above the slab.

    6) How much insulation is required?
    As an industry, the general consensus is that 100mm of PIR insulation is used for underfloor heating applications.

    From BuildIt magazine
    The position of the insulation within the floor structure is important, too. After changes to Building Regulations in 2002, all new builds need to have insulation below the concrete slab. But with UFH, more insulation needs to be added above the slab, directly below the pipes, to reduce the mass of material to be heated, improve response times, and reduce downward heat losses
    How much more insulation is added depends on how much, if any, insulation is in the slab, and the height allowance of the floor. A rule of thumb is to just use as much as possible.
    .

    We had restricted height on our newbuild so our ground floor only has 25mm under the screed (but the ground floor slab forms the ceiling of the basement which is also a heated space). Theres a few hundred mm under the basement slab and in the basement walls

    Premier Icon cynic-al
    Subscriber

    OVO Energy comparison

    Contains no energy comparison and lots of untruths.

    philholmes
    Member

    I had this company come and fit UFH into my new build house. As the kitchen was already in i didn’t want to lose any height. took them 2 days to put in 200m of pipe in our 6m x 3m room, but would have been much quicker if it was a screed slab rather than concrete.

    Should add, our ground floor construction is 300mm concrete FND, 140mm Jablight insulation then 150mm RC35 concrete on top, so was set up OK to take the ufh cut into the top slab.

    Really happy with the install and their professionalism, very little dust created and nice lads doing the work.

    not cheap, but since installing we have it running for 3 hours each morning and no other radiators kick in throughout the house for the rest of the day.

    https://www.jk-gb.com/

    Also get the bonus of having a cool looking tron floor before its covered

    klaus
    Member

    We have both electric and wet systems on our house, I cant comment on installation costs, as it was already there when we moved in.

    The electric system is installed in the upstairs bathroom, but its always turned off as it takes ages heat up, and loses heat very quickly.

    We have a wet system in the living room, this is set to a thermostat but is always on. Again it does take a while to heat up, but generally it retains the heat for hours on end. I’ve quite often gone into the room at 3/4am, and thought it was still on as its still warm, but this is partly due to it being very well insulated.

    It seems to be very cheap to run, and other than a log burner, is our only heat source in the room, and its very easy to cook yourself!

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