I have some experience with Grade II listed buildings and heat pumps. 

Three general points:

(1) ASHPs do work OK in listed buildings (buildings are heat source agnostic, a kWh of energy is a kWh wherever it comes from) but they are usually expensive to run because the building typically has poor insulation, and/or has drafts everywhere, and often not much can be done about much of it (making it all the more important to do what can be done). The key point is that compared to a modern well insulated building, a old leaky building is always going to cost more, whatever the fuel, it's a consequence of the building, not the heat source.

(2) Being listed means no PD (permitted development), you will need both Listed Building Consent and Planning Permission. This may or may not be a pleasant experience (mine certainly wasn't).

(3) The nominal kW spec of most heat pumps is usually just a twinkle in the marketing manager's eye. Get the real data, what it puts out when working hard at low temps, the nominal rating is the output from a day when you probably won't need the heating on anyway. 

I'm a bit confused when you say at one point "The property is fairly well insulated..." and then later on "Due to high ceilings and exposed brick in some places it has high heat loss...". Given the ASHP suggested, it seems likely you do have a highish heat loss, but whether that is because of poor insulation, or a large building, is not clear. For a ball park figure, my small three bed cottage has a 'calculated' heat loss of 12.4kW. Many people with more modern houses have heat losses that are much less.

Can you give us more details: age and more general stuff about the building, what the calculated heat losses are etc? Then I am sure we can come up with some comments.

Thanks for the reply, 

so the property is c1780 and was completely renovated in 2021, taken back to basic structure.

it was mostly fibre insulated, stud walled, boarded and plastered, the ceiling was 100mm board insulation in its entirety and again plaster board to finish, this is what I meant when I said fairly well insulated, should have added “given its basic structure” , as apart from the gable ends the exterior walls are just stone, albeit double laid and very deep.

I am waiting for the full report but the engineer was suggesting near 20kW loss.

the two main areas , living room and kitchen are double height and therefore big ‘voids’ to heat so I guess that doesn’t help, it’s on 3 levels as-well which seemed to make the assessor tut a lot!

This is the kitchen to give you an idea.

Our neighbours have a very similar space in a mid 19th century converted barn. They have excellent insulation and the positioning of the house benefits a lot from solar gain on sunny days. The entire area is UFH heating only. They switched to a heat pump last winter, and their house is absolutely roasting. So it can work with decent insulation and a thought through design (and the right size heat pump).

@showi - it looks like a fascinating building, but equally from what I can see in the photo it will be hard (but not impossible) to estimate heat loss. A full heat loss just means working out the areas of all the surfaces, assigning a U value (how much heat goes through that surface per square metre) and then multiplying and summing all the values for a standard set of indoor and outside air temperatures, and adjusting for air changes. The areas/U values are tedious but do-able, the air changes less easy to estimate in an old building - who knows how many air changes a leaky old window frame costs? Lastly, there are things like fire places, which are often forgotten about/ignored, as are things like wind/damp chill (I am sure my house loses more heat in those conditions, but they never appear in the heat loss calculations. The 'calculation' is at best an estimate. Unsurprisingly, potential installers come up with different values, depending on how thorough they are (I had a range from well under 10 (clearly nonsense) to I think it was 14kW, probably a bit OTT, but they did have a 14kW heat pump available, so that might have been a factor).  

There has been some discussion about determining heat loss empirically: given a steady inside and outside air temp, if you know the energy provided (ie consumed and then corrected for efficiency for the heat source) however generated, an old fossil fuel boiler for example, previous electricity use, to maintain that steady indoor air temp, then that is your heat loss in those conditions. In practice , it is hard to get ideal conditions (the steady temps) for long enough, while at the same time accurately measuring energy use, but it can be done, and probably trumps any calculated heat loss figure.

Conventionally, heat loss calculations are done at -2 degrees (or very close too that) outside (heat loss is very dependent on outside air temperature). Even so, your engineer's suggested loss of 20kW is on the high side, unless your building is exceptional in some way. I would ask to see the actual calculations when they have been done. Furthermore, if it is 20kW or thereabouts, then there is no way a 12kW Vaillant or 14kW Samsung heat pump is going to match that heat loss. Even suggesting such ratings if a 20kW heat loss has been mentioned calls into question the competence of the installer.

One common theme that emerges from this forum is that there are many installers who don't really understand heat pumps, and as a result they end up flying by the seat of their pants, often blindfolded, while all the while bullshitting their customer. The antidote is very thorough research before committing to anything. If the installer doesn't like that, then he'll probably be wearing a 10 gallon hat, and will have left his horse outside. Send him packing.     

Must admit I was dubious just speaking to him, really nice guy but we were the 4th he has done since joining Octo and fresh out of training, it was all entering numbers without any consideration for the things even just talked about already on this thread.

no open fire place, small well insulated loft and new double glazed windows throughout.

Have BG coming next week to do the same , they have quoted £9k from the initial info.

I am concerned about the system needed to handle this property, need to get this right first time, once installed it becomes tiresome getting companies back to rectify in my experience of anything these days! 

Posted by: @showi

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really nice guy but we were the 4th he has done since joining Octo and fresh out of training

That might provide a way to move on. I doubt your installation will be an off the peg one, you will need an experienced installer (blame me for saying that!), and if he is fresh out of training he will not yet have gained that necessary experience.

I think it is probably fairly normal if doing 'due diligence' to have to contact a fair number of installers to get to the best one for the job. In my case I contacted well over half a dozen, 50% initial attrition because failed to reply to repeated enquiries, ended up with four quotes (all different in just about any respect you care to look at), second round of 50% attrition to get rid of the obvious tw&ts, and then selected one on the basis his approach (he was willing to listen, rather than just tell me what I needed, without listening, as many do). There was an 'interesting' several month long diversion in that the local authority grant administrators wanted initially to use their preferred installer, a bunch of chancers, gophers and no hopers located well north of Watford which seemed more than a little odd given the LA was on the South Coast. In the end they messed up so badly even before beginning the installation that the grant administrators agreed they had to go, and I was able to use my initial preferred installer.

£9k plus I presume a £5k government grant is probably in the right ball park. £9k without the grant is probably on the low side. Another very important factor to consider is the radiator sizes. As a very general rule of thumb, an AHSP system will need rads with roughly twice the fossil fuel sized rad output eg if the room needs a 1kw rad for a high flow temp fossil fuel system, the ASHP system will need a 2kW rad (at delta T 50, the difference between the mean rad temp and the room temp) to deliver sufficient heat from a lower delta T ASHP system (the room/rad delta t is a mjor driver of how much heat can be delivered). Put another way, as you lower the rad/room delta T from a fossil fuel value of around 50 to an ASHP value of around 30, the rad's output drops by about half, meaning one way another (bigger area, more panels or both) you need a rad with twice the output. Old interesting and small buildings like mine can be challenging - not enough wall space to fit huge rads. I ended up with mostly K3 rads, a bit chunky I've got used to them.

If anyone tells you your current rads will be just fine, ask them to prove that is the case (needs to demonstrate for each room that the AHSP system will deliver enough heat via the rad at ASHP room/rad delta Ts for that room's heat loss). Asking such questions is an excellent way of sorting the wheat from the chaff. If they say 'leave it to the professionals' (my five word equivalent of Ronald Reagan's nine most terrifying words in the English language), then send them packing.   

@showi where in the UK are you based?

Yes it was £9k plus the grant.

on that why am I being quoted £5k and £7.5k grant ? , which is it ? 

Posted by: @editor

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@showi where in the UK are you based?

Marsden, near Huddersfield 

Posted by: @showi

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on that why am I being quoted £5k and £7.5k grant ? , which is it ? 

Looks like it is currently £7.5K for an ASHP (but not as part of a hybrid system), see here. There will probably be other conditions that apply.

Given the grant is £7.5K, that makes the total cost £16.5K, which is on the high side, even if it includes redoing the rads. You can get a ball park figure for parts costs from google, and estimate the number of hours of labour, and come up with the sort of amount you should pay. Getting multiple quotes is useful, if most centre on say £14k, then a £16.5k quote is an outlier and can be sent packing unless there is some compelling reason to chose them. Even so, I'd still want a clear and satisfactory explanation of why the extra money was needed. 

I would recommend you contact @damon - website here.

He’s one of the most respected installers around with a terrific reputation and is based out of Sheffield, so he may just cover your area.