Underfloor heating - wet system or electric?

[Daisybell1]

I really don't know which to go for

We have an old boiler which I fear is reaching its capacity. Its inefficient but reliable and we're on oil. I'd always planned to have electric underfloor heating to try and reduce our reliance on oil, but now both the builder and plumber are trying to push us towards a wet system.

I realise they're better long term, but oil prices are only going up and the house is likely to be rented out in 6 or 7 years anyway.

The room is 4 x 8m, with a log burner going in the other end, and we'll be hanging on to at least one radiator too.

Can anyone advise? And while I'm here, which thickness under floor insulation do I need?

Thank you!

[Daisybell1]

It's a 4x4m room, plus a bit underneath the removed wall.

The plumber is on the job already plus the floor had already been taken up as the joists were rotten. The plumber saying it was going to be cheaper than the matting was the final decision-maker.

[myron]

Just to be clear, the 'wet' system is the more expensive to install because it's basically more pipework linked to the gas CH but cheaper to run. Electric matting system is much cheaper to install but more expensive to run. If you have been quoted £500, that sounds like a massive bargain to me! - what is the square footage?

[Daisybell1]

Thanks Myron, we're insulating around the external walls, and putting some in the ceiling.

The plumber has said it will only cost £500 to put it in as the floor is having to be redone anyway.

[myron]

We decided to forgo the UFH totally when renovating our entire house due to budget. We originally had specified the wet system together with radiators. Insulating between the floor joists made a huge difference (easy and cheap to do with the ceilings down anyway) - so much that we have to turn off some of the radiators downstairs due to being too hot! If you are over budget, you will save a few thousand by not having it which is another option. No doubt, you will up spending the money elsewhere - such is the case with house renovation. We spent it on landscaping the driveway and patio!

[purplewithred]

I was about to say I put in wet with a gas boiler when we built our house and it was wonderful. We never got round to installing our log burner let alone lighting it, never ended it. (Which was a bit of a shame as I love a real fire).

[Daisybell1]

Quick update, we've decided to go with a wet system. I am still really worried about the impact on our oil bills, and the other works which the plumber say he'll have to do (getting a straight answer out of him exactly what he needs to do is incredibly difficult).

However, he said that installing the wet system would be cheaper than the electric, plus with the running costs being less, it became the obvious choice.

[WhatWillSantaBring]

Could you put the UFH under just the stone part of the floor? It strikes me that the main reason for UFH is to avoid cold stone floors. Wood is much warmer, therefore much less need for UFH.

Having just been talked out of UFH on the grounds of cost, I can see that it is probalby more of a luxury if you're not at home all day. If you had a ground source heat pump then I think it does work out as a sensible solution, especially if you're at home all the time, but otherwise not. I can see that relying on wet UFH when you get in at six and go upstairs at 10 could be a bit of a pain, as you'd need to start running the heating a long time before you got in?

[Daisybell1]

IuThanks all, the maths/physics behind it are interesting and I need to get my calculator out.

We're putting additional insulation in - thermaboarding the walls and we've already got double-glazing.

The idea with the log burner is that we'd like to be able to use it, but not HAVE to use it, if you see what I mean.

[Liara]

I've had both electric and gas ufh.

Electric was stunningly expensive, but faster to heat up. Gas less expensive, but took ages to heat up.

But in the end, I don't like either system. It is just too slow to respond, so you either have it on all the time, which seems to me to be a waste of fuel (whichever fuel that is), or you end up being either chilly or too hot, as you turn the thermostat up and down to try and manage the temperature.

If you have a log burner and a radiator in that room, do you really need any extra heating? I have a room about that size, with a log burner and a radiator and, despite having no floor insulation the room is warm enough usually just with the log burner. Are your windows and doors well insulated?

[MrsTaraPlumbing]

Piglet has explained the physics behind the price.
So - gas powered wet UFH is cheaper to run than electric.

Oil powered will (probably) also be cheaper - especially given that you have an oil boiler anyway.

In my house I do have electric UFH in some rooms and the financial advantages are that it (can be) much cheaper to install with a lifetime warrnaty. I have not found my electric bills too scary! But our UFH does have a thermostat so it so not on constantly it turns off when at temperature. And I have that thermostat low (about 19c). So mostly we do not have toasty toes. When the floor is warm the room gets too hot.
I think UFH is better with well insulated homes and I would always recommend looking at whether you need more insulation.

[PigletJohn]

If you have a room that requires (e.g.) 3kW of heat to maintain it at 20C when the outside temp is 0C, then 3kW is what you have to put in, whatever the source.

Thermal mass of (e.g.) a concrete floor is a bit of a red herring. It takes longer to cool down, but it takes longer to warm up. The amount of energy (heat) out is always equal to the amount in.

Slow heat release e.g. from large hot water radiators or UFH gives a more even and comfortable temperature than, say, an electric convector or fan that switches on and off.

[SidandAndyssextoy]

Yes, I get the simple maths side! But do the two systems provide the same heat, I suppose is what I'm asking. Are they equitable other than in cost?

[PigletJohn]

I can't guarantee it is accurate and up to date, but this chart compares the cost per kWh of various fuels.

You have to compare cost per kWh to get a sensible cost comparison, it's no good saying person A spends £1000 a year more than person B therefore their fuel must be more expensive; they may be using more energy or may even be paying a dd based on inaccurate estimates.

[PigletJohn]

soxtoy

partly depends on how long the system is on each day

'mmmmm, if it takes 3kW to heat a room, heating it with gas will cost about 11p per hour, and heating it with electricity will cost about 34p an hour. So yes, if you heated it with electricity for 15 minutes, it would be cheaper than heating it with gas for an hour.

But heating it for (say) 4 hours a day, electricity would cost you about three times as much as gas.

[beachyhead]

I'm in the same position as you Daisybell, in that we are considering ufh for a kitchen extension and we have an old oil boiler. I'm so worried about fiddling around with the oil source pipe, that I'm more tempted by electric ufh. Also, I'm in the same position in that it's very hard to equate the cost of oil to the cost of gas. As you are paying about £1500 for three deliveries of 1000 litres each (which means you are averaging 50p a litre, which is very good ), then you are running about £125 a month for heating. This sounds cheaper than a similar amount paid on heating through gas.

Could you offset any additional electricity through solar panels? Our proposed extensions points the right way so we are planning to install some to help with the cost.

[SidandAndyssextoy]

Sorry, pressed post too soon. We only have our GCH on for 2/3 hours a day unless it's absolutely bitter. Does heat linger with UFH?

[SidandAndyssextoy]

I will quiz my builder today. Surely it partly depends on how long the system is on each day. Is there any difference between the two? I see the reference to economy 7, but that can't still be a thing?!

[PigletJohn]

Soxtoy

Have a look at the price per kWh on your gas bill and on your electricity bill.

You will find that energy from electricity costs about three times as much as energy from gas.

Electrical heating is cheap to install but expensive to run.

[MrsDavidBowie]

We've had electric ufh for 7 years in a huge kitchen/diner..it's wonderful. We have stone flooring, and it's never been any trouble.

We also have a vertical radiator.

[Daisybell1]

Cataline - do you know what insulation there was around the electric system?

[SidandAndyssextoy]

I'm interested in this thread. We're just getting our kitchen done and will have quarry slate tiles. We've been told by our builder that electric UFH will be cheaper to install and run than GCH. Is this rubbish then? Also that electric is better as it is guaranteed so the cost of a new floor with any problems occurring is covered. Quoted cost to install is £500. This is a very reputable builder by the way.

[PigletJohn]

p.s.

I had an aunt who had electric UFH embedded in her concrete floors when the house was built, and heated overnight on Economy 7. It is slow to respond, but the concrete slab gives out a gentle and continuous heat. The electricity cost will be around half daytime price. I don't know if this installation method is still used as GCH is now ubiquitous.

[PigletJohn]

the pipes are flexible, and very unlikely to leak or burst, unless someone puts a drill or nail into the floor. The electric ones are nearer the surface so more easily damaged.

If there is damage, you can often see where it is with a heat-detecting camera (or by spraying with water, which will evaporate faster where hot)

[Cataline]

Never electric!!! We made this mistake in our old house. Spent a month enjoying toasty toes and the got the electricity bill . Never switched it on again. Cost to run was astronomical!!!

[OldRoan]

Can I ask a question rather than answer one?

If you have a 'solid' floor (eg. poured concrete) and there is a problem with the pipes, do you have to break the floor up to fix it? Is a wet system more likely to have problems (eg. leaking/pipes bursting) than an electric one?

I don't have UFH, but every so often I toy with the idea but the above puts me off and might be something you want to consider.