Anyone used BPC for ASHP? odd statement from them RE: ASHP sizing - Part F?

[Great_scot_selfbuild]

I've been searching around (a lot) for ASHP and who to go with - this is one of the strangest responses. I've attached their quote; I then queried how they came up with the 14kW size. Our timber frame house will be almost passivehaus level of performance and at least 0.6ACH on air tightness. We're expecting (based on a similar house we've visited) to need a 6kW ASHP, UFH downstairs only and bathrooms with electric UFH pads and towel rails.

 

This was their response to me asking why they came up with 14kW. What has Part F (ventilation) got to do with it?

 

Grateful for your thoughts / experience of them (I've not ruled them out yet).

 

"In line with part F regulations for new builds, the minimum heating loads & property floor area have been placed in the manufacturer's selection software.

This is the result.

If your property is not a new build, please provide your SAP report to allow us to verify & calculate a new unit."

[JohnMo]

Do your own heat loss calculation. 14kW is just rubbish and generally not needed unless your house is massive, leaks air and heat like a seize.

 

No need to waste that money on a pre plumbed cylinder, 300L cylinder £3k, should really only be spending £1500 or less.

 

 

[JamesPa]

47 minutes ago, Great_scot_selfbuild said:

I've been searching around (a lot) for ASHP and who to go with - this is one of the strangest responses. I've attached their quote; I then queried how they came up with the 14kW size. Our timber frame house will be almost passivehaus level of performance and at least 0.6ACH on air tightness. We're expecting (based on a similar house we've visited) to need a 6kW ASHP, UFH downstairs only and bathrooms with electric UFH pads and towel rails.

 

This was their response to me asking why they came up with 14kW. What has Part F (ventilation) got to do with it?

 

Grateful for your thoughts / experience of them (I've not ruled them out yet).

 

"In line with part F regulations for new builds, the minimum heating loads & property floor area have been placed in the manufacturer's selection software.

This is the result.

If your property is not a new build, please provide your SAP report to allow us to verify & calculate a new unit."

Probably the same bollox that led two surveyors each spending 3hrs in my house to conclude that my loss is 16kW. 

 

My loss is in fact 7kW confirmed by a proper calculation, gas consumption, the successful replacement of a gas boiler with a 7kW ASHP and subsequent measurements.

 

Be suspicious of the use of assumed high ach values, double counting of room to room losses, and ignoring of any fabric components that are better than building regs at the time your house was first built.

 

Don't believe any survey calculation that isn't somehow sanity checked.  The MCS 'rules' appear, in many cases, massively to oversize and do the public a massive disservice as a result.

 

Also suspect anyone offering a pre plumbed cylinder.  The principal advantage is that they can employ complete rookies to do the onsite work.

 

In case you haven't already been alerted, reject any quote involving a buffer, phe or llh between heat pump and emitters.  The sole purpose of these components, in almost all cases, is to avoid call outs at the expense of a significant increase in running costs and material complication of fault diagnosis for the customer.  A 2 port volumiser either on flow or return (but not between the two) is ok.

 

Also no external controls other than those specifically designed for heat pumps namely homely, adia or havenwise. Under no circumstances fit 'smart' thermostats. I and others can explain why if necessary.

Edited Thursday at 18:31 by JamesPa

[Great_scot_selfbuild]

1 hour ago, JamesPa said:

In case you haven't already been alerted, reject any quote involving a buffer, phe or llh between heat pump and emitters.  The sole purpose of these components, in almost all cases, is to avoid call outs at the expense of a significant increase in running costs and material complication of fault diagnosis for the customer.  A 2 port volumiser either on flow or return (but not between the two) is ok.

 

Also no external controls other than those specifically designed for heat pumps namely homely, adia or havenwise. Under no circumstances fit 'smart' thermostats. I and others can explain why if necessary.

@JamesPa I noted this input on a previous post/response of yours and I've been on the lookout for those aspects in the quotes. There are very few that have come across as honest and accurate (disappointingly).

 

@JohnMo@JamesPa Thank you both! Great input - very much appreciated.

 

 

[Great_scot_selfbuild]

Any recommendations for suppliers of ASHP/ hot water cylinders / components?

[JohnMo]

City Plumbing (ASHP, cylinder), Cool Energy (everything), Cylinders2go (cylinders).

 

Ideal cylinders are rebranded Gledhill. But way cheaper.

 

Panasonic heat pumps appear good. Makes sure ASHP does cooling out the box.

[JamesPa]

13 hours ago, Great_scot_selfbuild said:

I noted this input on a previous post/response of yours and I've been on the lookout for those aspects in the quotes. There are very few that have come across as honest and accurate (disappointingly).

The problem is MCS.  They set some rules about how to calculate heat loss, and if installers follow them then the installer is protected, whereas if installers depart from them then they potentially lose the protection.  So most simply go with the flow, because its safe for them.  Unfortunately the MCS method is quite likely to lead to oversizing in many cases, not least because it uses pretty much worst case values for ACH.  The problem is compounded because many surveyors wont account for fabric upgrades that they cant see (eg wall insulation), on the grounds that if they cant see it it may not be there.  Its all backside covering at the customers expense.

 

I did once have a written exchange with MCS in which they admitted that the current method for calculating heat loss is unsatisfactory but 'unfortunately there is currently no recognised alternative'.  I think this translates to 'we don't want to be responsible for a method, so we are relying on others thus we can blame them if anything goes wrong'.  This, in my mind, is inexcusable and irresponsible.

 

The better installers have sufficient understanding to interpret the 'rules' in a way that gets closer to the right answer.  Sadly many installers are pure grant-harvesters with little understanding, who 'paint by numbers' and thus depend on the near bomb-proof protection that slavish adherence to the MCS rules provides. 

 

Its actually pretty easy to weed out the real dross.  Unless your house is very exceptional, anyone proposing to install a buffer tank or use glycol should be immediately dismissed.  Anyone fitting (or reusing existing) external controls or smart thermostats other than those specifically designed for heat pumps (ie Homely, Havenwise and Adia only) ditto.   Obviously exclude any quotes with silly prices.  These tests alone get rid of the real muppets.

 

Then, as @johnmo says do your own heat loss calculations and/or do some sense checks.  If you have gas/oil consumption that can be used to sense check, alternatively you can make some rough estimates based on house size/construction.  Check that they really did use the right fabric in their calculations, particularly any area which is better than the minimum demanded by building regs for a building of the same age, and ask what ACH they are assuming.  If the sense checks and the claimed building loss (whether calculated by them or you) dont stack up, dig deeper unless you are 6kW or less in which case it doesnt matter because you are going to end up with aa 5-6kW pump anyway.

Edited Friday at 09:14 by JamesPa

[Great_scot_selfbuild]

11 hours ago, JamesPa said:

The problem is MCS.  They set some rules about how to calculate heat loss, and if installers follow them then the installer is protected, whereas if installers depart from them then they potentially lose the protection.  So most simply go with the flow, because its safe for them.  Unfortunately the MCS method is quite likely to lead to oversizing in many cases, not least because it uses pretty much worst case values for ACH.  The problem is compounded because many surveyors wont account for fabric upgrades that they cant see (eg wall insulation), on the grounds that if they cant see it it may not be there.  Its all backside covering at the customers expense.

 

I did once have a written exchange with MCS in which they admitted that the current method for calculating heat loss is unsatisfactory but 'unfortunately there is currently no recognised alternative'.  I think this translates to 'we don't want to be responsible for a method, so we are relying on others thus we can blame them if anything goes wrong'.  This, in my mind, is inexcusable and irresponsible.

 

The better installers have sufficient understanding to interpret the 'rules' in a way that gets closer to the right answer.  Sadly many installers are pure grant-harvesters with little understanding, who 'paint by numbers' and thus depend on the near bomb-proof protection that slavish adherence to the MCS rules provides. 

 

Its actually pretty easy to weed out the real dross.  Unless your house is very exceptional, anyone proposing to install a buffer tank or use glycol should be immediately dismissed.  Anyone fitting (or reusing existing) external controls or smart thermostats other than those specifically designed for heat pumps (ie Homely, Havenwise and Adia only) ditto.   Obviously exclude any quotes with silly prices.  These tests alone get rid of the real muppets.

 

Then, as @johnmo says do your own heat loss calculations and/or do some sense checks.  If you have gas/oil consumption that can be used to sense check, alternatively you can make some rough estimates based on house size/construction.  Check that they really did use the right fabric in their calculations, particularly any area which is better than the minimum demanded by building regs for a building of the same age, and ask what ACH they are assuming.  If the sense checks and the claimed building loss (whether calculated by them or you) dont stack up, dig deeper unless you are 6kW or less in which case it doesnt matter because you are going to end up with aa 5-6kW pump anyway.

@JamesPa thanks - very helpful and clear. I’ve had the same BPC sales rep come back now saying they have checked our SAP report and they have calculated it to be 8.5kW heat loss. I need to do my own check using the spreadsheet tool from Buildhub, but I suspect it should still be lower. TBH they’ve already lost my confidence for a few reasons, but not least defending their method, then running the calcs and suddenly it’s dropped from 14kW to 8.5kW with next to no effort. Then there’s the radio-silence when I asked for clarification about which part of Approved document F he was referencing (yes, F is ventilation - not heating…).

 

As for finding a reliable installer, I’m now taking a different approach by looking at sourcing the parts separate to finding the installer. Everyone I’ve approached so far simply seems to increase their quote/cost by £7500 so they pocket all the grant (combined with the list of tell-tale warning signs you’ve listed).

[JamesPa]

12 hours ago, Great_scot_selfbuild said:

 

As for finding a reliable installer, I’m now taking a different approach by looking at sourcing the parts separate to finding the installer. Everyone I’ve approached so far simply seems to increase their quote/cost by £7500 so they pocket all the grant (combined with the list of tell-tale warning signs you’ve listed).

If you buy the parts yourself you will need to pay the VAT.  May still work out better!

 

FWIW the approach I took in the end was to decide what I wanted (in my case a 7kW Vaillant in a particular location, with no external controls, no buffer tank and 4 rads changed plus a UVC) and then seek quotes based on that, providing them with evidence of the house loss.  Anyone who said 'well I may have to put in a buffer' or 'I will do my own survey (which I do accept they must) and will then determine the loss - it may be more' or suggested using a pre plumbed cylinder were discarded, leaving a small number who would do what I wanted and were, one way or another, going to take into account the measured loss.  Im not saying thats a foolproof recipe, just that it worked for me.

Edited Saturday at 09:20 by JamesPa

[MikeSharp01]

12 hours ago, Great_scot_selfbuild said:

As for finding a reliable installer, I’m now taking a different approach by looking at sourcing the parts separate to finding the installer

Another approach might be to find an installer offering the MCS umbrella scheme. Here the process is that they do the design work, you purchase the bits and install them and they comeback commission it all. I our case they are charging a basically fixed fee, might vary if they have to do more work at the commissioning phase. They apply for the grant take there cut and hand you the rest.

[JohnMo]

2 hours ago, MikeSharp01 said:

They apply for the grant take there cut and hand you the rest.

That's not how it works the grant isn't a fixed value, it's a fixed max value up to £7500. 

[MikeSharp01]

1 hour ago, JohnMo said:

That's not how it works the grant isn't a fixed value, it's a fixed max value up to £7500

That is correct, you need to account for your costs.

 

 

[SimonD]

On 26/09/2025 at 10:13, JamesPa said:

The problem is MCS. 

 

I think it's much wider than that. If you properly read the paperwork for all this, it isn't actually as prescriptive as the majority might have you believe. The current process is defined by EN1283 1 2017 which defines the process for heat loss calculations as well as default values if there are no national appendix figures. This standard has also changed the way in which ventilation losses are calculated. For us, we need to go to the CIBSE Domestic Heating Design Guide which follows this standard and this quite clearly states that while the figures given in the reference tables for things like outdoor design temperature. U-values and ventilation rates can be used when nothing else is available, it permits the use of more accurate figures and that the designer should look for the most accurate data available.

 

The advantage, and problem, with the new standard is that there are now more variables available to use such as differences in ventilation losses due to location and exposure and even cold bridging values, which can have a dramatic effect on the results - e.g. if you know a retrofit or newbuild has used Approved Construction Details you can use appendix K reference values from SAP for cold bridging.

 

But unfortunaly, because the heating industry has been so thoroughly de-skilled over the last 40 years, few seem capable of reading and digesting this stuff properly and using their own initiative. I assume that most designers and umbrellas are probably too lazy to use anything other than the simplified methods. None of the current training even touches this, not even Heat Geek. Nor do many of the software companies make any effort to explain the details and how to modify the settings in the programme for individual projects - and so it defaults to crap.

 

With MCS, if you deviate from default figures, you just need to provide a reasonable justification for the deviation, that's it.

 

As an example, I just went through the process of a design using an umbrella scheme for a design. I'd already completed my own heat loss following a comprehensive survey. The umbrella scheme came back with a result that was almost twice mine. Eventually, we went through 4 iterations until their result was only 300w above mine. It got to the point that I had to tell them that they were inputing the incorrect figures into their design software and that is why we were having the problem. I even had to do some basic calculations on the ventilation design for the property to show that the design was 0.38ACH and not 1.5 just using basic building regs calculations for extract ventilation to show how they were over-estimating these figures.

 

Ideally to deconstruct all of this, you need a copy of EN1283 1 2017 and then navigate your way through a murky world of poorly organised documents to untangle the mess it's all in.

[JamesPa]

26 minutes ago, SimonD said:

With MCS, if you deviate from default figures, you just need to provide a reasonable justification for the deviation, that's it.

I thought that was the case, because there are good installers out there who manage to get things right, but as you say

 

26 minutes ago, SimonD said:

 because the heating industry has been so thoroughly de-skilled over the last 40 years, few seem capable of reading and digesting this stuff properly and using their own initiative.

 

26 minutes ago, SimonD said:

- and so it defaults to crap.

 

 

Surely MCS, if there is any point to it at all (other than for the protection of installers which seems to be its main purpose), should get its mind around this and come up with some way to deal with it.  Instead, it seems to me, it hides behind a load of stuff which can be interpreted to do the right thing but far too often

26 minutes ago, SimonD said:

defaults to crap.

 

I do realise I have played fast and loose with the quotes, but the essential point is that MCS are supposed (I thought) to be the guardians of standards yet it appears from what you say (and what others experience) than unless the installer is somehow exceptionally good, it isn't/doesnt, and of course if the installer is exceptionally good, then MCS isnt needed.

 

Im trying not to be negative, but over on Renewable Heating Hub there is a constant stream of people with poor instals, for identifiable reasons (usually unnecessary buffer tank, oversized or wrong controls) who approach MCS which does nothing other than defend the installer because they have followed the procedure.  I should add that there are also people, including me, with perfectly good installs, but this seems to be in spite of MCS not because of.

 

So where exactly is the added value?

Edited Saturday at 14:07 by JamesPa

[JohnMo]

@JamesPa - it will make you cry, skip the first couple of posts.

 

https://forum.buildhub.org.uk/topic/45364-ssr-query/#comment-633802

[JamesPa]

2 hours ago, JohnMo said:

@JamesPa - it will make you cry, skip the first couple of posts.

 

https://forum.buildhub.org.uk/topic/45364-ssr-query/#comment-633802

 

Thanks for this.

 

There is one just like it at present on RHH, in which the owner has to set two programmers to the same temperature and time to make his ufh work.  Needless to say there is also a buffer involved. Unfortunately owner isn't particularly technical so won't touch the wiring.  Now one of the programmers has failed and he is faced with replacing it as is, perpetuating the nonsensical control system, or a complete rewire of the controls to achieve some sanity.

 

The problem is, as he is non technical, who could he trust to rewire the controls sensibly (and not to make a humongous mess up) and how does he possibly find them? 

 

Sadly, I think his only safe option is to replace the programmer like for like, even though it is clearly a stupidity.  Such is the state of the heating industry it appears.

Edited Saturday at 18:17 by JamesPa

[SimonD]

3 hours ago, JamesPa said:

I do realise I have played fast and loose with the quotes, but the essential point is that MCS are supposed (I thought) to be the guardians of standards yet it appears from what you say (and what others experience) than unless the installer is somehow exceptionally good, it isn't/doesnt, and of course if the installer is exceptionally good, then MCS isnt needed.

 

Im trying not to be negative, but over on Renewable Heating Hub there is a constant stream of people with poor instals, for identifiable reasons (usually unnecessary buffer tank, oversized or wrong controls) who approach MCS which does nothing other than defend the installer because they have followed the procedure.  I should add that there are also people, including me, with perfectly good installs, but this seems to be in spite of MCS not because of.

 

So where exactly is the added value?

 

You're right in your reading of things. The system, although originally set up with the right intentions, has morphed into a mess. The only value added as I can see it nowadays is the benefit of the BUS grant and that the ones on MCS in the first place have had to jump through a few more hoops re training and assessment - just imagine what it could be like if it were a free for all. I suppose there is something in that and it's the one reason I support the existence of MCS.

 

The problems as I see them are:

1. poor training and development - a good training centre for design and installation would typically do it in 5-6 days, but it is delivered and tested in a way to ensure 100% pass rate so you can make your own conclusions about how that works out for the quality of graduates. There are now apprentice schemes for renewables, so we'll see where that goes. Also the content of the training is pretty rubbish and very boring, IMHO, and needs to be updated. It seems as though the training was written in the days of single speed compressors and therefore by default it tells you how to size a buffer as a necessary part of the system and it hasn't moved on since. You don't actually get to play with heat pumps at all, so no fun there.

 

2. It's all too fragmented. So for MCS registration you need to be a member of a competent person scheme, which then registers you with MCS. Then you have to join a consumer code organisation - MCS and RECC, for example have a very cosy commercial relationship by some accounts. When you join the consumer code like recc, you then have to join an insurer to provide deposit insurance and warranty backed guarantee of the installation (with HEIS it's all bundled in). Just joining the insurer can cost about £600-700 ex vat, plus there's a payment for insurance for each job. Then you've also got to become verified with OFGEM for the BUS grant. You may also have to pay to register with Trustmark depending on the work you do. In addition there's then public liability and professional indemnity (if you do the design work). So with the designer/installer, you've got 5 parties involved in the whole thing (not including PL and PI), all of whom can quite easily bounce the poor recipient of a rubbish installation around the houses, with nobody taking ultimate responsibility. If you add in an umbrella scheme, you've got yet another party involved. And with all parties, there's a conflict of interest because it's the installer who pays the fees and is the customer of all these organisations.

 

Dare I say it, but I wonder whether MCS needs to be rolled back to be state owned and run with all the ancillary bits pulled under the same umbrella so that the conflicts of interest can be removed - even if the system were changed in a way that the customer, in order to get the BUS grant, pays a defined fee as part of the installation, which is paid directly to MCS for consumer protection, rather than the installer being the member. And then the MCS vetting and assessing the installers regularly to be on the register. I don't know, I haven't reall thought about it in too much detail.

 

So there needs to be more clarity for the customer. Because MCS has essentially farmed out the assessments to the competent persons schemes, that's probably where the buck should stop and they should be mandated to resolve the situation, or otherwise legislate to force MCS to be accountable. There should also be a redress fund for the rectification of crap installations and that is something that each installer should have to pay into on each installation and where the fund essentially sits in escrow with an independent body, far from profit making organisations. 

 

I know the estimated numbers in terms of crap heat pump installations in my region and how much they think it would cost to rectify them - it's frightening.

[Great_scot_selfbuild]

8 hours ago, MikeSharp01 said:

That is correct, you need to account for your costs.

 

 

I clearly need to bump this up my priority to read up on this in detail.

[Great_scot_selfbuild]

12 hours ago, MikeSharp01 said:

Another approach might be to find an installer offering the MCS umbrella scheme. Here the process is that they do the design work, you purchase the bits and install them and they comeback commission it all. I our case they are charging a basically fixed fee, might vary if they have to do more work at the commissioning phase. They apply for the grant take there cut and hand you the rest.

Any advice on how you identify companies offering this, and then the tricky bit, assessing whether they are any good or not?

[Bramco]

Cool energy do this. See their free heat pump page - https://coolenergyshop.com/pages/free-heat-pump

 

There are a number of members on here that have their heat pumps and I think some used their current scheme for self installers.

 

We had them install ours in the days of the £5000 grant. Cost us all of 200 quid after the grant.

Edited Sunday at 08:22 by Bramco

[JamesPa]

@SimonD

 

If what you say (and I have no reason to doubt it), particularly about training, is true then it explains much of what is (sadly) reported and is horrendous.  Installers should being taught (almost) never to install a buffer not how to size one, and they should also be taught how to avoid the other common problems with installations namely gross oversizing and the use of external controls/poorly set up control systems.  Is there no requirement for CPD in the industry so that trainig remains up to date?

 

15 hours ago, SimonD said:

Dare I say it, but I wonder whether MCS needs to be rolled back to be state owned and run with all the ancillary bits pulled under the same umbrella so that the conflicts of interest can be remove

 

Something needs to be done urgently otherwise the domestic heat pump industry in the UK, and thus the UK attempts to decarbonise its heating system, is toast.  The reputation of heat pumps 'on the street' sucks, so far as I can tell by what I hear in my local pub and elsewhere I encounter 'ordinary' people.  Of course big oil and its supporters in the media are doing their best to ensure that is the case, but the industry is feeding them the material they need.  We shouldn't forget that there is a fair chance that grants will be removed altogether in 3.5 years time if an anti-green government takes over; who will buy a system that their mates down the pub tell them will not work then?

 

Is there any hope that things will change radically and soon?  Is anyone in the industry campaigning?  Government cant be expected to know what the problems are because the industry associations and in particular MCS will be painting a rosy picture of how standards are being raised.  The impetus needs to come for the good guys in the industry who need to call out the problems and propose solutions to Government!

Edited Sunday at 10:24 by JamesPa

[JohnMo]

1 hour ago, JamesPa said:

there any hope that things will change radically and soon

Maybe get worse before it gets better.

 

Don't the better guys just use the system and navigate around it where needed. Do a justification if required to keep a box ticked.

 

If you can acquire the skills yourself - do it yourself.

[JohnMo]

14 hours ago, Great_scot_selfbuild said:

Any advice on how you identify companies offering this, and then the tricky bit, assessing whether they are any good or not?

Do a Google search on MCS umbrella scheme. How good or bad they are, anyone's guess. Suppose you need to try them, see what they output system wise and cost wise, buffers, glycol, stupid large ASHP etc, move on or challenge, see what the response is.

[JamesPa]

16 minutes ago, JohnMo said:

Don't the better guys just use the system and navigate around it where needed. Do a justification if required to keep a box ticked.

 

Based on my experience with installers, exactly that, and they do it rather well. 

 

However the point of the system is not to help the better guys, they don't need help because they already deliver for both the customer and themselves.  The point is to make the mediocre guys better and thus help the customer, and hopefully also eliminate the bad guys altogether.  If the 'system' only works when 'navigated around', its the wrong system!

 

Edited Sunday at 12:04 by JamesPa

[HughF]

“6kW” r290 unit from cool energy is now around £2k, just saying.

 

It’s 3.5kW at -7/45 but that’s probably all you need anyway. Does weather comp.

 

Vaillant cylinder off eBay, bucket of fittings, throw it in yourself.