@jords thank you for an informative description of your ASHP investigations.  I've had a Mitsubishi Ecodan installed for just over 2 years now and am generally happy with it, although the MELcloud software leaves a lot to be desired and feels dated.  I wish I had gone for Vaillant.  However I had a good installation experience from a firm in Chelmsford (EPCImprovements) although they installed a 100l buffer.

On replacing rads have a look at the Jaga Strada fan assisted units.  Not cheap but we have them everywhere and they work well and the fans allow higher output at lower flow temps than is the case with regular rads. We also have 2 of their Clima Canal trench rads which are great if you have a suspended floor and want to reclaim the wall space - like this:

Posted by: @jords

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Radiator changes. Heat Geek: 4, Octopus: 8, British Gas: 10 plus a plinth heater for the kitchen.

Anyway just thought I would share my experience with the 3. Maybe I’m being too picky. But if I’m going to spent £10k (after the bus grant) I would like to make sure it’s just right.

I had a fairly similar experience with installers just over 3 years ago.  For various reasons, mostly to do with planning, the project was delayed for 2years (heat pump was finally installed Nov 2024).  During that time I collected information on my gas usage to get a measured heat loss (as opposed to the fabric survey which can be good, but can be way off).  I also read up a lot and decided what I wanted.  I then went out again to get it, which I did.  The outcome was a success.

Had I 'just' gone with the first tranche I would have ended up with a 2x oversized unit, unnecessary pipework upgrades, and as a result more disruption and poorer performance.

I don't think you can be too picky!

PS. I wouldn't worry so much about differences in estimated loss at the room level, unless they are a factor of 2.  However I would worry about differences in total loss.  This can be wildly out (in my case 16kW surveyed, 7kW actual) which can make an enormous difference.  If you have your consumption data you can get an independent measured estimate from this and use it to sense check the surveys.

@jamespa that’s an interesting way to look at it. Given my gas usage the heat loss would be around 4-5kW. But we tend to run our house on the cooler side and like I said some rooms like the kitchen aren’t heated properly. So I imagine their guess of 7-8kW is about right to get the place up to 21 degrees all the time. Octopus is a bit out at 10kW. However would I risk going down to a 7kW heat pump? Probably not. Think the 10kW would be the right one for my house. Anyway I don’t mind upping the exiting rads. As any gains just means I can tweak the flow temp lower.

@downfield it is curious that you are reporting quite positively about EPC Improvements.  @drei has been alleging serious problems with their installation in his home.  It appears to be the same company, so I am wondering how your experiences can be so different.

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/seeking-help-for-in-principle-quote-to-fix-a-botched-heat-pump-installation/paged/7/#post-50504  

@grahamf EPCI subcontracted the installation work out so maybe I got a different team.  Anyway there were 4 of them and they worked hard over 4 days to complete the work.  I was clear where I wanted everything and prepared the loft space to make their job as straightforward as possible and they did a neat job.

Also as we know every install is unique. 

@jords it sounds as though you have been having a frustrating time.  I had some similar experiences.  Here are a few pointers:

1. All installers have strengths and weaknesses.  The most important aspect is that your installer thinks in the same way that you do.  I found a couple of installers who were just pulling in the wrong direction.  I knew that if I employed either of them, we would spend too much time fighting.  My chosen installer was not perfect.  In fact, his supporting heat loss estimator made a mistake that overestimated the heat loss by 60%.  I spotted this and we corrected it.  The contract was a bit vague as well, which made it risky.  However, we agreed on the fundamental approach and got on very well.  I trusted him, so I went with him.  He did a great job and the system is performing brilliantly.
2. Obviously, you live in your house every day.  You know all the subtleties and quirks of your house.  The installer is there for only a few hours and then he will visit another house, and another.   Therefore, it is hardly surprising that he/she may miss things and make mistakes.
3. Despite what people will tell you, heat loss estimation is to some extent an art form.  I reckon +/-30% could be a good result, though others on this forum will disagree with me.  Also, heat loss estimates are usually overestimates.  It is rare to underestimate the heat loss for a whole building.
4. It does not really matter whether you design for -2 or -3C outside.  If your room temperature is 21C, then delta T between the two is 23 or 24C - i.e. a difference of only 4%.
5. I would not accept a design flow temperature of more than 45C, because it makes the system less efficient.  I reckoned that I could not get ours below 42C, but it looks as though the actual flow temperature may be as low as 38C, because the heat loss had been overestimated.  
6. I would tend to believe the installer that recommends more radiator replacements, rather than fewer.  Having said that, you can upgrade more radiators later, if you start with insufficient radiator capacity.  

Posted by: @jords

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@jamespa that’s an interesting way to look at it. Given my gas usage the heat loss would be around 4-5kW. But we tend to run our house on the cooler side and like I said some rooms like the kitchen aren’t heated properly. So I imagine their guess of 7-8kW is about right to get the place up to 21 degrees all the time. Octopus is a bit out at 10kW. However would I risk going down to a 7kW heat pump? Probably not. Think the 10kW would be the right one for my house. Anyway I don’t mind upping the exiting rads. As any gains just means I can tweak the flow temp lower.

Firstly I agree with @grahamf above, very sensible comments IMHO.

There is never any harm in radiators being too big, you can just drop the flow temperature.  Its better if they are in proportion though, ie all oversized by roughly the same amount, but even if they aren't (like mine - for historical reasons) you can deal with it by turning down LSVs on the 'bigger' ones.  However an oversized heat pump is quite likely to be less efficient, is more noisy so more difficult to place, larger and may also lead to unnecessary pipework upgrades.  There are ways to mitigate some of this but its easier if you don't have to.

Also if you want the R290 and/or the Vaillant machine dont be bullied into avoiding either, remember but you are spending a lot of money on your house.  There is a warts and all review of the 7kW Vaillant (written by me) in 'articles' on this forum.  Two 'professional' surveys, each taking 3 hrs, said 16kW but measurements proved them wrong.  Incidentally if you email Vaillant they will give you the names of at least 3 local installers, that's how I found mine and they turned out to be a) very good and b) one of the cheapest.  Obviously this might not be the case with you

Not heating a room generally wont make much difference to the consumption unless the room itself is well insulated from the rest of the house and, as a result, its very significantly cooler than the rest of the house.  The principal barrier to heat loss is (usually) the outside walls not the inside ones, so the heat still gets lost!

From your post above it looks like you may not get this done now until next year.  If that is the case I would encourage you to run your current heating as close to 'heat pump' mode as you can, heat reasonably consistently, and collect data on usage (ideally half hourly smart meter data if that's possible, but daily would do if thats the only realistic option).  You really do not want a 10kW machine if in fact your loss is only 4-5kW, worse still the 10kW Vaillant is actually the 12kW downrated, which reduces the upper limit but not the minimum output, so you risk putting a 12kW heat pump into a 5kW house.

I attach the plot I did, this was from 2 seasons worth of data but one (or less) would have sufficed. 

Obviously you should and must do what's right for you, but if you need to shop around to get what you want then I can only encourage you to do so.

Posted by: @downfield

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@grahamf EPCI subcontracted the installation work out so maybe I got a different team.  Anyway there were 4 of them and they worked hard over 4 days to complete the work.  I was clear where I wanted everything and prepared the loft space to make their job as straightforward as possible and they did a neat job.

Also as we know every install is unique. 

Sounds like you kept an eye on them and maybe that's why they did a decent job.

Did you check their heat-loss and radiator workings, did they use a buffer in your system? They used outdated figures on my rads, and I have a shortfall of around 34% just from the radiators alone? They also used the wrong buffer which is causing distortion and a loss of around 10c. Did they do the design or did you get involved and they followed your design and instructions? I saw in your description you have the Mitsubishi 14kW , they originally wanted to install the Mitsubishi Ecodan R32 14kW in our home, but then opted for the 12kW Samsung. Did they do your solar Installation? I originally had them engaged to do that for us too, after the heat pump, but realised they were robbing us blind, so I got pretty much double the system for the same money.

We pretty much gave them the keys and told them do whatever needs doing to get the system correct the first time around. I didn't know anything about Heat Pumps except that they would only be as good as the installers. Marc was a great sales person, and it is ironic I ended going back to the Heat Geek Elite from Ipswich for remedial assessment, which at the time I thought was too expensive but now wish I selected and had them do the installation (heat-loss cost was £600 VS £300 from EPC back in 2023). Happy to name them, Ali from Smart Heating Solutions. Going forward they will be doing my yearly service.

EPC Improvements subcontracted the heat loss to a company called Regenertec Consulting. If I knew they were using subcontractors for the everything, I honestly would have not engaged with them as I wanted someone that understood what they were doing. It explains my situations and why the managers had no clue how heat pumps operate or how they are supposed to be installed, because the owners are not heat engineers or have any experience or knowledge and rely on 3rd parties. I looked up the owners recently and they had and still have all kind of other business, none related to another, no transferable skills or knowledge. They clearly saw an opportunity with the ECO4 grants and jumped on it. Some people are passionate about their work and what they do, for some it's just a side hustle along many others.

I guess this is one of the question you need to ask installers, "Do you subcontract any of the work?". I cannot recall 100%, unless it is in one of the e-mails, but I swear I asked them if they subcontracted, and was told they do not. Anyhow, Heat Geek removed them from their network if that means anything.

Let us know how it goes with them if you have any problems. That's where my issues started, didn't understand the industry, 0 aftercare and lack of support.

Here is the Solar Quote from EPC Improvements which I went ahead with, but pulled the plug on due to unresolved Heat Pump issues:

I should probably mention that the installers that did my system, somehow provided 12 years GivEnergy warranty as standard, without having to pay the additional £440 EPC Improvements wanted for 10 years extended warranty.

Posted by: @jords

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Anyway just thought I would share my experience with the 3. Maybe I’m being too picky. But if I’m going to spent £10k (after the bus grant) I would like to make sure it’s just right.

It is your right to be picky, and something I wish more homeowners would do. Be meticulous. You are spending a lot of money, and it will impact your comfort and how warm you are.

I find your findings very interesting. I haven't tallied up your columns. They look similar at a glance. Do you have the full final heat loss number from Heat Geek, British Gas and Octopus?

Posted by: @jords

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	Heat Geek	Octopus	British Gas
Kitchen	2280	2223	2233
Playroom	550	667	533
WC	160	185	105
Living Room	1530	2004	1938
Entrance Hall	300		487
Shower Room	650	1167	705
Landing	190	166
Bedroom 3	360	346	473
Bathroom	360	630	408
Bedroom 2	450	371	530
Bedroom 1	660	674	873
Loft Landing	320	565	484
Office / Bedroom 4	640	869	934

Same rooms are very similar. Others very different. They also all chose different outside design temps. Heat Geek: -2, Octopus: -2.4, British Gas: -2.9

Radiator changes. Heat Geek: 4, Octopus: 8, British Gas: 10 plus a plinth heater for the kitchen.

Anyway just thought I would share my experience with the 3. Maybe I’m being too picky. But if I’m going to spent £10k (after the bus grant) I would like to make sure it’s just right.

Go with the highest heat loss per room from the table you provided and you can't go wrong. In contrary, if you get oversized radiators, it only means your SCOP is going to be better and cost less to run:) - win win but will cost a bit more per radiator.

After all no one can guarantee the output of the radiators, not even the manufacturer, it's always guess work, so by selecting the highest heat loss from the table, you are covered.

The question is, do you know the rating of your existing radiators?

I've posted somewhere how to work out your rad output the correct way, but a simplified version would be, if you want your house at 21c, then for every 1000W @ ΔT50 of radiator rated output, you get 344W, which is a factor of 2.9.

For desired room temp of 23c, it will be 295W per 1000W, so a factor of 3.39.

In your case, for your Kitchen heat loss of 2280W you will need 6612 Watts rated radiators (2280 x 2.9 = 6612). Now take in consideration that heat rises, and you may want to oversize the downstairs, but keep the loft bang on, or slightly lower. Will it be all one open zone, keeping all the doors open? If you are containing the heat with doors? then stick to per room heat loss with a +10% to 20% over-sizing on rads.