Spec ing a rad and UFH question...

once you know how much it costs to run you'll probably turm it off and never use it again.
i have fitted it to some larger rooms under floors i've tiled(when electric was much cheaper) but generally i would say its only for small rooms.

karndean isn't as cold a flooring anyway like tiles.

Re the electric UF.... just because it's there doesn't mean you have to switch it on!
Once the floors down then it's too late so I'd put it in.
Good to have I think but watch the running costs.
I'll have mine turned down to 13c this winter but it will automatically get boosted when the PV production is good and the water is at max temperature.

Take a look at a low profile wet system like Nu-Heat lo-pro. This also has the advantage that the self leveling screed leaves a perfectly flat finish ready for your finished floor covering.

For efficiency, I guess it depends on where you are going with your heat/energy source?

There's other detail needed, e.g. number of exterior walls, etc
I'd start with https://www.myson.co.uk/contact_us.htm and see where you go from there, beware of asking around until you get the answer that you want, which is "one radiator"

Given that eventually we'll all end up on heat pumps regardless of what you might think about them, is there any value in taking steps now to increase emitter size and system volume? I'd be considering wet underfloor and two rads. You can always turn them down or off.

exterior walls are 2, a third is next to an unheated store.

I have looked at wet UFH but the cost was very high and it isn't as low profile as elec do would mess with floor levels. so it's been ruled out

the plan was to have the ufh on very low and just in the mornings like we do with our bathroom. but I am scared of the cost to run now!

and yep I know once the floor is down it's point of no return so trying to decide now! I have approx 2 weeks to make my mind up as the structural work will be complete and we will ne moving on to utilities

thanks for the link to a calc will look later. none of the ones I looked at seem to really account for there being loads of insulation

suggenteny = suggestions

Straight in with the wet UFH on a new build. You don't need radiators in there as well. Kitchen is similar size to yours. No heating under the kitchen units and the floor has two loops back to the manifold.

I have UFH in the kitchen and radiators in the rest of the house. Works as two systems (2 X Nests installed). We run the UFH in the morning only - until it gets really cold and then we have the main whole house heated for an hour or so. Evenings are rest of the house only, UFH is off.

I've got a similar sized high kitchen extension and put in wet ufh only which is great. I skimped on the patio doors and glad I spent the money where I did. Door is much easier to replace. Now I've increased the size of the rads in the rest of the house so the boiler can run with a lower flow temp in condensing mode and will be heat pump compatible in the future. I'd definitely look as t wet ufh again and would have a step into the room if I had to.

I had electric UFH installed in my bathroom a few years ago (back when electricity was fairly cheap...), even back then it was costing £70/month initially until  I ended up only having it on for a couple of hours in the morning to take the cold out of the tiles a bit. I've had it switched off completely now for months and no plans to switch it back on. As you'll have rads in the room (I don't in my bathroom) I'm not sure I'd bother with it - for the next couple of years or so we'll all need to get used to wearing thermal socks inside anyway...

also I was going to put in electric UFH as a secondary heat source / take the edge of the floor temp. (karndean)

given the energy prices is this a really dumb idea? Will cost approx 1k to buy and I’m thinking I shouldn’t bother now.

Don't bother. I recently had a smart meter installed and when I switched off the UFH in the small bathroom we had it running on it saved about £1.00 a day! Electricity has gone up since then. A wet system is a much better idea although you've ruled that out.

the space will be insulated to current building regs.

Can you do better than current regulations?

Insulate, Insulate AND Insulate, I did similar to you 15 years ago current reg's, just not good enough, now so add MORE insulation (if you can), we have wet UFH in new part, but old rads in old part and that's the unbalance, I am currently trying to work out economic solution!! With heating /fuel costs Insulate to reduce the need for heat. C

I'll have a rethink about a wet system I'm sure it was over 5k to buy and install last time I looked versus about 2k for electric and rads.

insulation wise cavities will be filled, slab will have 10cm Kingspan and so will the single story roof section. not sure we can physically fit much more in.

other plans are looking at knocking through the fireplace between kitchen and lounge and have a dual sided log burner. to give more options.

and now thinking of insulating under the floors of the rooms that will be disturbed to run cables and pipes. May as well pull the whole floor rather than just a section....

and we have quite a few old 50s single or dual panel rads. thinking of replacing them too.

this is how project costs escalate....!

Insulate, Insulate AND Insulate, I did similar to you 15 years ago current reg’s, just not good enough, now so add MORE insulation (if you can), we have wet UFH in new part, but old rads in old part and that’s the unbalance, I am currently trying to work out economic solution!! With heating /fuel costs Insulate to reduce the need for heat.

^ that.

Do the maths on more insulation and smaller system vs larger system and energy use.

The low profile UFH by Nu Heat or Uponor is only about 15-20mm thick, but you do need a good level base to fit the trays, so time with a laser is well worth it to establish how level the whole kitchen is. Not too difficult to install if fairly handy.

I’ll have a rethink about a wet system I’m sure it was over 5k to buy and install last time I looked versus about 2k for electric and rads.

That sounds far too much. I did a DIY between-the-joists wet UFH system for about £1k. It doesn't add any height whatsoever as there's no screed, just aluminium trays which hold the pipes, and PIR insulation board between the joists. STS concrete board instead of chipboard flooring, and you can tile straight onto that.

If you have a concrete floor rather than joists you might be forced into a screed system which will add a bit of hieght, but even so it's an obvious choice given where energy costs are going and likely move to ASHPs. You probably will be able to get rid of the radiator(s) too which will free up some space.

Hmmm just been looking at Nu heat as mentioned above. 15mm would fit, we just have the clearance As part of the renovation we will be removing 4 radiators in a poorly insulated part of the house. So I reckon the existing valiant boiler will cope with load.

Sounds a faff to balance it right though

Cost wise it’s 2k to buy which is much less than I expected and actually comparable to a couple of big fancy radiators. Fitting costs would be more though. It will be on a newly laid slab so it should be relatively straight forward

Dumb question. I would presume you don’t install it under the kitchen units and appliances. So those areas would be removed from the calcs and also need to be levelled up.

Also talks of an assumed transition of 70w per m2 which if I compare to the rad I was looking at is about h the same output at 2100w which is around 7.5k btu. So not enough output according to the calcs or does UFH need a different calc to rads?

Complicated!

Take a look at https://www.wundagroup.com/underfloor-heating/ - worth getting a price from them.

Generally much cheaper than Nu-heat etc. We've had it for about 7-8 years now and had no issues at all (that was an aluminium spreader plate system as we were putting it on a suspended timber floor, but screed or the Wundafloor would probably be better).

just had a chat with the builder, his view was the most sensible and cost effective approach is one big rad that hits the btu, and then he suggested a few wet plinth heaters to bring the btu value comfortable in the range.

There will be 100mm of insulation in the floor and LVT he said the floor will not feel cold like it can with tiles.

never heard of plinth heaters till now. they look like they would heat more of the cupboard than anything else! are they any good?

A big rad will be the most cost effective cheapest, but it really won't heat a high room well as the heat will go up before it comes down. You'll end up chasing the thermostat. My ufh doesn't go under the units but I don't think it'd make much difference either way. Balancing is dead easy, 3 valves on a manifold with flow indicators and a thermostat for the manifold, set up as a separate zone. If you need to update single panel rads, you can save up and do this later easily, but you won't be able to do the ufh later. With ufh and bigger rads you'll be able to turn the flow temp down on the boiler and get a much more stable and efficient heating system which is much nicer than rads chucking out loads of heat, then going cold.