Hi,
I am by no means an expert but the first two things I would be considering are the noise generated by the heat pump and whether it will be a nuisance to the flat below or the occupant in the bedroom.
They can run with radiators but because they run at a lower temperature you would need larger rads. Would you have space for that? Could you consider underfloor heating? It might be worth getting a company to come and quote for you (even if you plan to fit much of it yourself).

+1

Also consider an air-to-air heatpump? Ideal for smaller spaces and heat loads, more efficient and much cheaper than a wet system. Looks like an aircon system and can also be used for cooling in Summer.

I am a bit confused if you are taking the ceilings down to open up to the "apex" then how will you avoid the sound from one room travelling over the dividing walls to another? If you are going to open up to the roof then underfloor heating is best any radiator heating will not be effective where you want it. You could do electric UFH and run at night on cheap tariff. A heat pump may not be cost effective for such a small area whatever the size the installation cost is a sizeable chunk and as previously mentioned they can be noisy.

The whole flat will have most walls taken down as currently stud, and rebuilt to go much higher as i am extending ceiling height. The new ceiling will be clad in birch ply hopefully and the extra height will improve the sense of space.

If the air source pumps are noisy then this has to be an issue. Affecting my flat and the one below. I have a feeling this will rule it out.

If i really insulate well, what do folk think about these small electric wall heaters you find in many flats ? Would they be ok to heat the space? I am thinking it will not need that much heating because it is going to be well insulated. I am doing new D/G. The roof should get 120mm overall kingspan insulation (or what ever the minimum is now), plus i will reline the walls with 50mm insulation as well.

The floor will be insulated with 170mm approx loft type insulation. This is really for sound deadening as there is no sound barriers between these flats as they were done in 1965 (old victorian house split into 3 flats).

Posted By: marsadayIf i really insulate well, what do folk think about these small electric wall heaters you find in many flats ? Would they be ok to heat the space?

If by 'really insulate well' you mean to passivhaus level and assuming you include an MVHR system then yes, electric wall heaters will be fine.

The floor will be insulated with 170mm approx loft type insulation. This is really for sound deadening as there is no sound barriers between these flats

Doesn't do much for impact noise though. That needs specific treatment.

Think at end of day what is it you want? an OK job or a quality job. We are all different in our expectations. I agree with DJH floors need specific treatment to prevent noise, guess you do not want you neighbours complaining maybe they will be ok with it but they could change and new ones might complain so might as well do a proper job whilst at it.
What I should have mentioned was that insulation boards shrink a lot when exposed to heat which they will between rafters have seen evidence of it big gaps. The rockwool above it cushions the effect.

As WillinAberdeen suggested, consider Air to Air.

If after conversion you still have loft space available, then the indoor distribution could all be housed up there, with supply registers in each room. Return registers are easily built into new stud walls, or also in the ceiling, if pushed; and no radiators required, freeing up all that wall space in a smallish area.

Installing the outdoor unit on cantilever arms on a wall is no problem, and rubber dampers cushion against vibration, IMO noise isn't really an issue with quality modern equipment.

Although you'll need F gas final connection, filling, and commissioning much of the other tedious legwork you can do yourself with your gas engineers approval.

As for DHW cylinder with a couple of immersions is the simplest route. For the bathroom an electric towel rad would be useful.

If ducted Air to Air is impractical also look at wall hung units, or low level units.

For hot water you could consider point of use supply. I once met someone who had installed these wherever he needed hot water. Logic was he never wasted electricity in keeping water hot in a tank. Would be ideal I think in a small dwelling as less conflict possible from multiple outlets calling for power at same time. He had no baths just showers.

I am doing everything on this flat so new electrics, new plumbing. So the install cost is not an issues.

Reading more about the topic, it does seem gas is the best option. I will have hot water on demand and so not wasted hot water being stored for x weeks with no use. The unit will take up less space than HW storage and say heaters.

Gas will be moving to full hydrogen in the next 15 yrs as well. So i think a move to all electric is not needed.

Still plenty to weight up though.

How about calculating and costing the options?

I don't think anyone on here will be able to give you a conclusive answer without you identifying the variables and calculating the heat loss.

First thing I would pick up on is your statement that it ''is going to be a holiday home and so used mostly in the summer time''.

What will the season be - 6 months? Look at some historical weather data for lowest temps and you can probably work out the likely input required. I would imagine you could use Degree Days but my head refuses to get itself around them.

Who pays the bills? Is it your (and your family's) holiday home, or is it let out?

''If i really insulate well, what do folk think about these small electric wall heaters you find in many flats ? Would they be ok to heat the space? I am thinking it will not need that much heating because it is going to be well insulated. I am doing new D/G. The roof should get 120mm overall kingspan insulation (or what ever the minimum is now), plus i will reline the walls with 50mm insulation as well.''

djh said: ''If by 'really insulate well' you mean to passivhaus level and assuming you include an MVHR system then yes, electric wall heaters will be fine.''

He's right, but you may do the calcs to work out the heat requirement and the likely annual bill and feel that, even with your proposed levels of insulation elec heating would be 'affordable'. At least you would be heating with a fuel whose carbon intensity is falling, rather than with gas, where this is not the case.

Just a final point on your roof plans. You said:

''I will need to baton out the rafters anyway to accommodate the new insulation. Currently only a 75mm deep rafter and i will need to leave 50mm gap.''

If you batten out the rafters to the full insulation depth you add a further 'timber fraction' (bits where there's timber where there should be insulation). If you have 25mm between rafters after the 50 air gap then just go across the whole lot with 75mm PIR, tape at all joints and perimeters as VCL, fix 25 x 50 battens horizontally to match your plasterboard sizes and then friction-fit a final 25mm between the battens. It is reasonable to have the VCL 25mm back in a 125mm 'sandwich', or if you want to be 100% then use a sheet VCL over (under!) the whole lot, taped at all joints and perimeters. I would advise air-tightness tape, not foil tape, particularly at the perimeters - foil tape rips over time.

I hope this helps.

Posted By: philedgeThe report above suggests that hydrogen infrastructure roll out will commence from 2030 onwards yet Northern Gas Networks have just raised finance through Abundance to upgrade much of the north of englands gas network for completion by 2026.

Do you have a link? My quick search indicated that Northern Gas were inviting the public to subscribe funds to replace metal gas mains with polyethylene, with the funding organized by Abundance. Which would be a completely different scenario if that's the one you're referring to.

Replacing mains is a regular maintenance task that the gas supplier would have to fund in any case, so why the public should be asked to stump up for it is questionable, rather than normal commercial funding. Perhaps commercial funding sources are aware that investing in a new gas main when the long-term prospects are somewhat doubtful might not be the best investment they make this year, whilst the great unwashed can be relied upon to buy Blackpool Tower again and again?

If Hynet ever produces any 'green' hydrogen at scale instead of 'blue' hydrogen, I shall be overcome with emotion.

Commerce is as usual trying to make a dollar in whatever circumstances it finds itself, and exploiting public and government confusion and ignorance remains an excellent source of an edge, as ever.

The cash raised through Abundance was only part of what NGN wanted. Ive no idea how much they wanted but likely significantly more than the £1m Abundance investors stumped up. Heres a public summary https://www.abundanceinvestment.com/our-impact/investments/northern-gas-networks

I appreciate that national infrastructure is significantly more than the 2 projects Ive stumbled across but it seems that hydrogen infrastructure is starting well ahead of the dates stated in the gov doc. Domestic roll out may well be a long way down the road but the gov forecasting a start in early 2030s and NGN seemingly starting in early 2020s is a worringly big difference. Maybe NGN are out on their own getting started and the gov are only looking at whats happening in the south??

<blockquote><cite>Posted By: Nick Parsons</cite>How about calculating and costing the options?

I don't think anyone on here will be able to give you a conclusive answer without you identifying the variables and calculating the heat loss.

First thing I would pick up on is your statement that it ''is going to be a holiday home and so used mostly in the summer time''.

What will the season be - 6 months? Look at some historical weather data for lowest temps and you can probably work out the likely input required. I would imagine you could use Degree Days but my head refuses to get itself around them.

Who pays the bills? Is it your (and your family's) holiday home, or is it let out?

''If i really insulate well, what do folk think about these small electric wall heaters you find in many flats ? Would they be ok to heat the space? I am thinking it will not need that much heating because it is going to be well insulated. I am doing new D/G. The roof should get 120mm overall kingspan insulation (or what ever the minimum is now), plus i will reline the walls with 50mm insulation as well.''

djh said: ''If by 'really insulate well' you mean to passivhaus level and assuming you include an MVHR system then yes, electric wall heaters will be fine.''

He's right, but you may do the calcs to work out the heat requirement and the likely annual bill and feel that, even with your proposed levels of insulation elec heating would be 'affordable'. At least you would be heating with a fuel whose carbon intensity is falling, rather than with gas, where this is not the case.

Just a final point on your roof plans. You said:

''I will need to baton out the rafters anyway to accommodate the new insulation. Currently only a 75mm deep rafter and i will need to leave 50mm gap.''

If you batten out the rafters to the full insulation depth you add a further 'timber fraction' (bits where there's timber where there should be insulation). If you have 25mm between rafters after the 50 air gap then just go across the whole lot with 75mm PIR, tape at all joints and perimeters as VCL, fix 25 x 50 battens horizontally to match your plasterboard sizes and then friction-fit a final 25mm between the battens. It is reasonable to have the VCL 25mm back in a 125mm 'sandwich', or if you want to be 100% then use a sheet VCL over (under!) the whole lot, taped at all joints and perimeters. I would advise air-tightness tape, not foil tape, particularly at the perimeters - foil tape rips over time.

I hope this helps.</blockquote>

I will think about the way i insulate the roof. It sounds a potential better idea. The jointing sounds a good idea.

I will work out the requirements, but super busy with the renovation.

I will be paying the fuel bill and i do think all electric will be ok going forwards.

I am going for basic electric wall heaters with WiFi control, electric shower and two small under the counter HW heaters for the 2 x sink HW demand.

I will save on the gas meter standing charge, plus the annual check and the meter would need moving anyway as currently sat where the shower room will be. So the install cost will be more compared to going for a combi and normal shower, but overall the price difference is going to be an extra £500.