Which heating system to use in this kind of extension?

[vexation]

We're building a single storey, 5m x 4m flat-roofed extension to our kitchen (rather than a typical bolt-on conservatory) as we want to be able to use it all year round. It has floor to ceiling glazing on three elevations to make the most of the central garden setting. The otherwise well-insulated ceiling has a flat skylight. I haven't got the U values for the glazing to hand but it's noticeably chunky compared to what we already have. The floor is beam and block to be finished with 100 cellotex and a 50mm screed. Wet or dry UFH are the options we're considering.

When it comes to specifying the heating Ideally we would go with underfloor as there is only one masonry wall for a radiator (provided by the house it's built against) and what remains of this after the existing french window opening is earmarked for furniture.

A lot of the discussion steering people away from electric UFH is in relation to conservatories due to their enormous heat losses. If we had masonry walls with cavity insulation I don't think there'd be much objection to electric. However, we're a little bit unusual in having fully glazed external elevations which I've not seen in discussions regarding heating.

Electric would be extremely handy as we'd otherwise have to destroy a tiled kitchen floor to get to the existing CH pipes. Another awkward issue would be where to locate the pump/valve gear for a wet system. On the other hand there's an unused 13A Fused outlet on the back of the outside wall. Lastly, I can see gas prices closing-up on electric in the not-too-distant future as the UK energy mix changes to lower carbon sources. Any thoughts would be greatly appreciated.

 

[flameport]

A lot of the discussion steering people away from electric UFH is in relation to conservatories due to their enormous heat losses

Electric heating is not recommended because it costs 4x more to operate - electricity being far more expensive than gas, oil or most anything else.
Heating a conservatory is usually futile regardless of how it's heated.

destroy a tiled kitchen floor to get to the existing CH pipes.

there's an unused 13A Fused outlet on the back of the outside wall.

In the scheme of spending £1000s on an extension and having major building works done over a period of weeks/months, the presence of a fused spur is totally irrelevant. If extending the kitchen, surely you will want new flooring throughout the kitchen, rather than just shoving a box on the back of the house with different flooring, and forever highlighting that fact?
In any case, a floor is a one time cost. Heating with electricity is a lifetime of unnecessary expense.

I can see gas prices closing-up on electric in the not-too-distant future as the UK energy mix changes to lower carbon sources.

Not going to happen for decades, or ever.
50% and more of UK electricity is obtained by burning gas.
That can only change if baseline generation is increased - meaning more nuclear power stations, and those are decades away.
Even if/when that happens, substantial additional generation which can be switched in quickly will still be required to cover those times when the sun doesn't shine and the wind doesn't blow.
Currently, gas is the only realistic option for that. If gas prices increase, then so will the price of electricity.

 

[^woody^]

Use whatever is in the main house

 

[vexation]

Hi flameport.

Electric heating is not recommended because it costs 4x more to operate - electricity being far more expensive than gas, oil or most anything else.
Heating a conservatory is usually futile regardless of how it's heated.

Yes, I suppose that's really what I'm getting at. Is what we're constructing only a little bit better than a conservatory? It will certainly have fewer losses but that would need quantifying. I think the biggest difference will be in the roof. Regardless, the price differential per KWh between gas and electric is hard to ignore when looking at standard tariffs.

In the scheme of spending £1000s on an extension and having major building works done over a period of weeks/months, the presence of a fused spur is totally irrelevant. If extending the kitchen, surely you will want new flooring throughout the kitchen, rather than just shoving a box on the back of the house with different flooring, and forever highlighting that fact?
In any case, a floor is a one time cost. Heating with electricity is a lifetime of unnecessary expense.

I take your point however the Architect deliberately wanted to retain a degree of separation between the kitchen and extension. The kitchen and rest of the house is of a period style whereas the extension is decidedly modern with a level threshold out to a patio with ceramic tiling linking the inside and out.

I only wish the energy market would remain as stable and predictable as you say but things are already changing quite rapidly. Dynamic electricity pricing is now a thing; Octopus was charging nothing for Electricity for a few hours on Christmas day. They claim that very occasionally they actually pay customers to use energy. With the ability to store heat in a thermal mass and control it using their software API there's a chance such non-standard electricity tariffs might even beat gas with the right setup.

 

[vexation]

Hi Woody.

Use whatever is in the main house

I'm sure that's a very sound strategy. If it was electric in the main house it would be crazy to fit a boiler just for the extension! But I somehow feel it doesn't address the lingering questions I still have about switching to electric (!)

 

[^woody^]

You can't pipe it from the first floor? Vertical radiator to use less wall space?

Anything but electric, unless you own your own substation, and have doubled the insulation and tripled the glazing.

 

[vexation]

You can't pipe it from the first floor? Vertical radiator to use less wall space?

Interesting suggestion woody. I had't thought of using a vertical radiator. I always looked at those and thought they were style over substance as 'radiators' are partly convective. If I could be convinced that it would be as effective as a horizontal rad and not just send heat out the roof, I might give it some serious consideration.

However, wet UFH would still seem like the best choice given that it's spread out evenly over most of the area, providing heating to the far corners. Finding somewhere for the pump gear is going to be a challenge.

 

[^woody^]

You can get some very high output vertical rads - single or double, which equal or exceed a traditonal radiator that would otherwise be used. Review the specifications, as whether the tubes are flat or oval or even the colour makes a difference to output.

The perception of them not being as good as horizontal rads, or heating only the ceiling because they are taller is common, but wrong.

Underfloor heating needs to be used in a completely different way - on for longer and switched on much earlier, and the perception of the warmth is often different too.

 

[motorbiking]

I have a couple of vertical rads that are approx 450 wide and put out 2KW each. the other option is a trench radiator.

 

[Ian H]

We have a narrow vertical radiator in the corner of our big ish kitchen. I worried that the heat wouldn’t spread but it works a treat.

We have electric underfloor heating in there too which very rarely gets used.

 

[tomfe]

My suggestion would be to listen to the others and either use wet uf or rads.

However it's your house, you sound like you've made your mind up, so go for electric under floor. Then in a year put some radiators in.

 

[scbk]

Speaking as someone with no experience of mains gas (and the electricity costs more up here). I saw someone who had a small air source heat pump in their conservatory/sun room, which is cheaper to run than normal electric heating (but more to install)

 

[flameport]

Dynamic electricity pricing is now a thing; Octopus was charging nothing for Electricity for a few hours on Christmas day. They claim that very occasionally they actually pay customers to use energy. With the ability to store heat in a thermal mass and control it using their software API there's a chance such non-standard electricity tariffs might even beat gas with the right setup.

Novelty pricing and sales gimmicks do not change how the electricity is generated, and unless that company is intent on operating at a huge loss, there is absolutely no way that electricity can be cheaper than gas, or even comparable in price.

 

[vexation]

I was already convinced to forget electric by post#6. It's a toss-up between wet ufh and a 4kW vertical radiator in the center of the masonry wall. The rad gets around the problem with finding a place for the ufh pump. I will take a good look at those trench rads motorbiking pointed out though.

 

[motorbiking]

Your other option is to install a log burning stove - or perhaps even a hot/cold aircon unit.
If any of the windows are fixed, these could work:
https://www.theradiatorcentre.com/floor-standing