I am having an ongoing discussion with my plumber about the installation of my ASHP system. Further to previous posts on BuildHub (and very helpful feedback) and a non-committal review by MCS following my complaint I am now looking for someone to review my system and advise where there are issues with installation and non-compliance with MCS or any other relevant standards.

 

I am between Bristol and Swindon.

 

Does anyone have any recommendations of any companies who would cover my area for this sort of review.

 

As always with BuildHub, I very much appreciate input from everyone!

Can't help with a name or company - but what appears to be the issue(s)?

Can't give you a name for your area either, but a few things will make any review quicker and cheaper.

Before anyone visits, pull together the MCS certificate, the room by room heat loss calculation, the design flow temperature, the emitter schedule showing each radiator's output at that flow temperature, the pipe sizes and the commissioning sheet. A lot of compliance problems show up on paper first: emitters too small for the design flow temp, no proper heat loss done, or a unit sized off a rule of thumb. If your system has a monitoring app, a week or two of flow temps, run times and electricity use tells a reviewer more than a one hour visit.

When you ring round, ask for an independent heating engineer or heat pump consultant who does design and commissioning reviews and isn't trying to sell you a replacement system. Ask them to report against MCS MIS 3005 so the findings line up with your complaint.

On the complaint side, if your installer was signed up to RECC or HIES as part of their MCS registration, that consumer code's dispute process can often go further than MCS itself, and an independent report gives it some teeth.

What are you actually seeing, high bills, cold rooms, short cycling or noise? That would help people here point you at the likely cause.

Thanks John and JP for your replies and some very helpful points there JP for finding someone to assess the system.

The issues with the system are partly set out in this thread https://forum.buildhub.org.uk/topic/43959-buffer-tank-hot-when-heating-mode-turned-off/

Potted History

Builder subcontracted local plumber. Local plumber confirmed that Daikin (through their Sustainable Home Centre which is the local plumbers' merchant) would be designing the system and to obtain the BUS an umbrella MCS company would sign the system off and do the BUS paperwork. Daikin SHC provided a design schematic of the system.

Once the system was installed I had some queries (mainly the sizing of the ASHP and why a buffer had been installed when it wasn't on the design) Daikin SHC turned round and said their design drawing was indicative and they weren't the designers (oh great I thought). When pushed further the plumber and Daikin ducked the issue by saying that as the system was signed off by the MCS company then it was all their responsibility and I would have to raise a complaint with MCS. I did that but in the period the complaint was being progressed MCS company has gone into administration and therefore MCS have stopped progressing their investigation.

The builder and plumber have said they will put things right if it is needed but at the moment is it me with my limited knowledge arguing with the plumber with their limited knowledge about what is correct/not correct with the installation. The conversation from their side has largely been that I have hot water and heating... so where is the problem.

Key Issues

No Design - nobody has designed the system so I am not sure what issues there might be in addition to the below.

Oversized ASHP - At the time of install Daikin calculated heat loss at just under 6kw but had no 6kw units available so provided a 9kW unit for the same price. I queried this and was shown their calculation/was assured that the 9kW unit was more efficent than the 6kW unit (which I assume had not allowance for cycling within the calc.). I am not convinced they took account of the MVHR correctly in that calculation either. In the last 12 months the flow temperature has not needed to be higher then the minimum setting of 25 degrees and on the coldest night last winter the unit still had periods where it didn't run due to inside room temperatures meeting the set point.

Buffer Tank - I query the need for it (as did others on the above post) and note that in the MCS3005 is cautions against their use.

Third Party Controls - the only thermostats are third party with no Daikin master, so modulation of the flow temperature isn't possible and cooling mode doesn't work through the thermostats

Isn't it an MCS requirement that the MCS company that's gone bust carried insurance for the situation you're in....flawed design??

22 hours ago, James1234 said:

The issues with the system are partly set out in this thread https://forum.buildhub.org.uk/topic/43959-buffer-tank-hot-when-heating-mode-turned-off/

I've just had a look through this thread to get an idea of the history. I am MCS certified and I'm fully Heat Geek Mastery trained too and actually based not too far from you in Bath.

Rather than go through the unfortunate contractual arrangements between the various parties, which doesn't help anyone right now, we need to pin down the facts.

When was your system actually commissioned and did you receive your installation pack from the MCS Umbrella? You should have had a contract directly with them. As @Dillsue says, in this pack you should have received an insurance backed warranty which must be for a minimum of 2 years for exactly these kinds of situations.

However, to take it forward to obviously need to know the defects and Daikin suggesting the system is okay is very unhelpful, if not entirely misleading.

From what I see in your photos, the installation does not comply with Building Regulations part L as none of the pipe has been insulated around your cylinder etc. That's just the start.

The claim that you have to have thermostatic control in each room to comply with building regulations represents a misunderstanding of the regulation when it comes to heating. Whilst building regs do state this, there are technical reasons why a system designer can design a system without any zones, using weather compensation that fully complies with the regs. The designer simply needs to provide the technical basis of the design decision and how it complies with the aim of the regulations.

The insulation job of your primary pipework from the heat pump to underground ducting is absolutely terrible. I'd want to check that the matt black insulation used beyond the short length of PE coated stuff is actually rated for outdoor use - I can't see what the print says but wonder if it's EPDM which is exterior grade or bog standard class O which isn't. But either way it's a terrible job.

22 hours ago, James1234 said:

No Design - nobody has designed the system so I am not sure what issues there might be in addition to the below.

The MCS design requirements are actually not that comprehensive when it comes to specifying the extent of a design. It only really says that the design has to show the calculated room by room heat loss and that the emitters are sized to counter the heat loss at specified minimum temperatures - indoor and outdoor ones. It doesn't include checking that the heat generator modulates sufficiently for annual average temperature, pipe sizing etc.
If you received a heat loss calculation to relevant standards BS EN 12831 that included an emitter schedule and dhw cylinder sizing calculation together with a MCS performance estimate, it's pretty much there. You also received a schematic from the manufacturer.
All this could be seen by MCS etc. as constituting a design in their eyes.

22 hours ago, James1234 said:

Oversized ASHP - At the time of install Daikin calculated heat loss at just under 6kw but had no 6kw units available so provided a 9kW unit for the same price. I queried this and was shown their calculation/was assured that the 9kW unit was more efficent than the 6kW unit (which I assume had not allowance for cycling within the calc.). I am not convinced they took account of the MVHR correctly in that calculation either. In the last 12 months the flow temperature has not needed to be higher then the minimum setting of 25 degrees and on the coldest night last winter the unit still had periods where it didn't run due to inside room temperatures meeting the set point.

This bit is key here because the 9kW unit is not the same immediate family as the 6kW. Daikin don't seem to publish minimum output data so it's difficult to know with certainty, but the performance measures on open energy monitor show that there is a big difference between the two when it comes to minimum modulation. The 6kW is 1.408kW and the 9kW 4.03kW. Assuming your newbuild is well insulated, a minimum modulation of 4kW if the calculated heat loss of just under 6kW was correct, means you're bouncing off minimum modulation for most of the year. However, if your heat loss was just under 6kW I'd question if the 6kW unit was the right choice in the first place due to potential drop off at your outdoor design temperature.

Do you have the recommendation/advice from Daikin in writing, or from anyone else about the 9kW unit? And do you have anything that states the 6kW unit does actually produce the required heat at your design temperature?

23 hours ago, James1234 said:

Buffer Tank - I query the need for it (as did others on the above post) and note that in the MCS3005 is cautions against their use.

Ironically, this may be your saving grace here, if the 9kW unit is bouncing off minimum modulation, whatever the distortion there might be with the rest of the system.

23 hours ago, James1234 said:

Third Party Controls - the only thermostats are third party with no Daikin master, so modulation of the flow temperature isn't possible and cooling mode doesn't work through the thermostats

For optimisation, yes this is rubbish. There should really be a Daikin master and the system should be running on weather compensation.

What does the usage data look like after a year of use? Do you have you COP/SCOP figures available.

The good thing in all this is that the builder and plumber have said they'll put things right if needed.

Beyond these things, it really depends on what you want in terms of resolution - do you want the existing system refined and optimised or are you looking to go the whole way and try to force a change of heat pump and then a subsequent system modification to suit?

Edited October 20Oct 20 by SimonD

@SimonD thank you for your reply, all very useful. I have sent you a DM.

Attached are the heat loss and sizing calculations from Daikin. At the time Daikin said they didn't have a 6kW unit available, that they would do the 9kW at the same price and their calculations showed that the 9kW was just as efficient.... with the added benefit of the DHW heating up more quickly due to the greater capacity and having the benefit of a back up heater.

[Attachments removed at poster's request]

Edited October 23Oct 23 by jack

16 hours ago, James1234 said:

I have sent you a DM.

Thanks, received and replied.

16 hours ago, James1234 said:

the heat loss and sizing calculations from Daikin.

You may want to remove them as they've got your personal details in them.

But for everyone else, and as I've explained in my DM reply, from just a brief read there are some issues with these heat loss calcs:

1st is the 0.4ACH figure. As you have MVHR, this is a high air change rate (do you have a design calculated leakage rate, or blower test results available?) and assumes a very poor efficiency MVHR and poor airtightness. The building age band is 2005-present which covers lots of changes to Building regulations and thermal performance in buildings. And also, they've input a standard single figure of 0.18 for ground floors which does not appear to follow the industry standard approach to calculating floor u-values using Perimeter/Area ratio, which almost invariably shows variations in floor u-values depending on different room sizes and external exposure. In addition, the reports assume a lack of thermal bridging insulation, so this raises some questions given your recent newbuild.

19 hours ago, James1234 said:

[Attachments removed at poster's request]

@James1234 , it you want these re-uploaded to the post after you've removed your details from them, please let me know. Otherwise, I assume you're happy just leaving them deleted.

@James1234 Agree with SimonD on the heat loss calc. The 0.4 ACH looks high for an MVHR newbuild, and a flat floor U-value often overstates the loss too. That lines up with never needing more than 25 C flow, and a 9 kW unit that barely has to run on the coldest night.

Your own app data is the best check. Pull heat (or electricity) for a few cold days, note the outdoor average, and you can back out a real W/K figure. With MVHR recovery you often land well under the paper calc, which also explains why a unit that bottoms out around 4 kW is cycling.

If you want to see it room by room, tools like heatlosspro.cloud can help you visualise the layout and where the emitters sit against the loss.

1 hour ago, gac said:

If you want to see it room by room, tools like heatlosspro.cloud can help you visualise the layout and where the emitters sit against the loss.

I'd caution against that. The tool doesn't comply with current UK heat loss calculation standards, or MCS requirements. It says in the documentation. So you couldn't use it to assess UK regulatory compliance.

19 hours ago, SimonD said:

I'd caution against that. The tool doesn't comply with current UK heat loss calculation standards, or MCS requirements. It says in the documentation. So you couldn't use it to assess UK regulatory compliance.

Fair point, and worth saying clearly: if you need an MCS / UK standards calc for compliance, use a tool that claims that. I wasn’t suggesting heatlosspro.cloud for a compliance pack.

For the OP’s case I meant it more as a room-by-room sense-check against the paper loss and the cold-day meter data, so you can see which rooms drive flow temperature. Different job from an MCS submission.

4 hours ago, gac said:

Fair point, and worth saying clearly: if you need an MCS / UK standards calc for compliance, use a tool that claims that. I wasn’t suggesting heatlosspro.cloud for a compliance pack.

For the OP’s case I meant it more as a room-by-room sense-check against the paper loss and the cold-day meter data, so you can see which rooms drive flow temperature. Different job from an MCS submission.

Not really. If the tool is using an outdated, non-compliant calculation method, which it is by using the simplified ACH calculation, it's not going to be accurate and most likely going to over-estimate heat loss. The choice of tool and accuracy of heat loss is the fundamental basis of a good heating system design, so using something that isn't appropriate for cross-comparison is a flawed method of even a sense check.

Curious Simon, did you have a bad run with it yourself? For me the room temperature curves matched what I actually measured and confirmed I'd undersized my own heat pump, so as a personal sense-check it earned its keep. For the OP I'd still trust cold-day meter data against the installer's calc over any model argument.

9 minutes ago, gac said:

Curious Simon, did you have a bad run with it yourself? For me the room temperature curves matched what I actually measured and confirmed I'd undersized my own heat pump, so as a personal sense-check it earned its keep. For the OP I'd still trust cold-day meter data against the installer's calc over any model argument.

No, not at all. I'm an MCS certified designer and installer of heat pumps & heating systems. I'm also the developer and host of another tool https://openheatloss.com which due to a lot of problems with black box programming and lack of transparency with a lot of tools, including the use of outdated methods, I developed exactly so anyone who uses it can produce a fully BS En 12831 2017 UK, and MCS compliant calculation. Whether they're doing a design from scratch or need to verify something else.

I know that other tools, like h2x also don't by default provide compliant heat loss calcs and outputs either, but in this day and age, I don't think that's particularly acceptable, especially when charging for it. But this is where the intricacies of BS EN 12831 2017 come into play because although some tools can provide calculations to this standard, they may be using the generic default values in the standard compared to the national annexes. The UK now has a new annex equivalent (because the UK hasn't yet ratified a formal annex) published in the CIBSE Domestic Heating Design Guide 2026.

Users need to know what a tool is delivering and the standards it conforms to to ensure they make an informed decision. It would make it very difficult for a customer to present their report to an installer for discussion/argument or whatever only to find out it doesn't comply with the standards or contains undeclared variations they weren't aware of that undermine the output they're relying on.

It is well known in the industry that the BS EN 12831 simplified method produces inaccurate results based on ACH alone, especially in energy efficient, airtight newbuild, which is why calculation standards have moved on.

I'm not criticising the tool you've linked because I developed one. There are plenty of tools to choose from and people will choose what works best for them. Mine I know is different to all the others I've found: it's totally free, it's open source and anyone can check all the calculations and assumptions from start to finish, but the important thing is that the user knows what they're using and the only way to make a proper comparison is by understanding the standards and basis for calculation.

3 hours ago, SimonD said:

No, not at all. I'm an MCS certified designer and installer of heat pumps & heating systems. I'm also the developer and host of another tool https://openheatloss.com which due to a lot of problems with black box programming and lack of transparency with a lot of tools, including the use of outdated methods, I developed exactly so anyone who uses it can produce a fully BS En 12831 2017 UK, and MCS compliant calculation. Whether they're doing a design from scratch or need to verify something else.

I know that other tools, like h2x also don't by default provide compliant heat loss calcs and outputs either, but in this day and age, I don't think that's particularly acceptable, especially when charging for it. But this is where the intricacies of BS EN 12831 2017 come into play because although some tools can provide calculations to this standard, they may be using the generic default values in the standard compared to the national annexes. The UK now has a new annex equivalent (because the UK hasn't yet ratified a formal annex) published in the CIBSE Domestic Heating Design Guide 2026.

Users need to know what a tool is delivering and the standards it conforms to to ensure they make an informed decision. It would make it very difficult for a customer to present their report to an installer for discussion/argument or whatever only to find out it doesn't comply with the standards or contains undeclared variations they weren't aware of that undermine the output they're relying on.

It is well known in the industry that the BS EN 12831 simplified method produces inaccurate results based on ACH alone, especially in energy efficient, airtight newbuild, which is why calculation standards have moved on.

I'm not criticising the tool you've linked because I developed one. There are plenty of tools to choose from and people will choose what works best for them. Mine I know is different to all the others I've found: it's totally free, it's open source and anyone can check all the calculations and assumptions from start to finish, but the important thing is that the user knows what they're using and the only way to make a proper comparison is by understanding the standards and basis for calculation.

Congrats on openheatloss.com, that looks like serious work. You're clearly the stickler the regs need, and I mean that as a compliment. I'm not a heating engineer at all so I have zero authority, I can only speak from my own experience, but it's helpful to me to have tools that make it super easy to get some sort of indication.

Quick favour if you've got a minute: when you've plugged the same house into both a "black box" tool and openheatloss (or a full BS EN 12831 run), how far off do the black-box numbers usually land, and which bits go wrong most often (ACH, bridges, emitters at low water temp)?

2 hours ago, gac said:

Congrats on openheatloss.com, that looks like serious work. You're clearly the stickler the regs need, and I mean that as a compliment. I'm not a heating engineer at all so I have zero authority, I can only speak from my own experience, but it's helpful to me to have tools that make it super easy to get some sort of indication.

Quick favour if you've got a minute: when you've plugged the same house into both a "black box" tool and openheatloss (or a full BS EN 12831 run), how far off do the black-box numbers usually land, and which bits go wrong most often (ACH, bridges, emitters at low water temp)?

Not speaking for @SimonD but I've used several heat loss programs, Heat engineer, Heat Punk, openheatloss as well as knocking up a spreadsheet myself where I could try and assess the basics

Open Heat loss was closest to actual real world data (I think it still overstated the ventilation losses so an air blower test is on the cards for next year)

13 hours ago, SimonD said:

No, not at all. I'm an MCS certified designer and installer of heat pumps & heating systems. I'm also the developer and host of another tool https://openheatloss.com which due to a lot of problems with black box programming and lack of transparency with a lot of tools, including the use of outdated methods, I developed exactly so anyone who uses it can produce a fully BS En 12831 2017 UK, and MCS compliant calculation. Whether they're doing a design from scratch or need to verify something else.

I know that other tools, like h2x also don't by default provide compliant heat loss calcs and outputs either, but in this day and age, I don't think that's particularly acceptable, especially when charging for it. But this is where the intricacies of BS EN 12831 2017 come into play because although some tools can provide calculations to this standard, they may be using the generic default values in the standard compared to the national annexes. The UK now has a new annex equivalent (because the UK hasn't yet ratified a formal annex) published in the CIBSE Domestic Heating Design Guide 2026.

Users need to know what a tool is delivering and the standards it conforms to to ensure they make an informed decision. It would make it very difficult for a customer to present their report to an installer for discussion/argument or whatever only to find out it doesn't comply with the standards or contains undeclared variations they weren't aware of that undermine the output they're relying on.

It is well known in the industry that the BS EN 12831 simplified method produces inaccurate results based on ACH alone, especially in energy efficient, airtight newbuild, which is why calculation standards have moved on.

I'm not criticising the tool you've linked because I developed one. There are plenty of tools to choose from and people will choose what works best for them. Mine I know is different to all the others I've found: it's totally free, it's open source and anyone can check all the calculations and assumptions from start to finish, but the important thing is that the user knows what they're using and the only way to make a proper comparison is by understanding the standards and basis for calculation.

Would a layman be able to use this tool? I might have a go with it when sorting my building regs but it all goes a bit over my head. Do I need my sap calcs done first to get the losses?

11 hours ago, marshian said:

Not speaking for @SimonD but I've used several heat loss programs, Heat engineer, Heat Punk, openheatloss as well as knocking up a spreadsheet myself where I could try and assess the basics

Open Heat loss was closest to actual real world data (I think it still overstated the ventilation losses so an air blower test is on the cards for next year)

I'm not doubting that and if someone asks me for a recommendation for tools that are the most accurate, I will surely mention openheatloss (though I haven't tested myself)! But for how easy heatloss pro is and i found it to be matching my experience with the install i did 4 years ago, it's pretty amazing. Here is my home (it's an apartment in an old industrial space) https://heatlosspro.cloud/?s=YAzppFumRwF3TzRGRBaV0g

On 03/11/2026 at 07:13, Oz07 said:

Would a layman be able to use this tool? I might have a go with it when sorting my building regs but it all goes a bit over my head. Do I need my sap calcs done first to get the losses?

Yes absolutely, but probably with some effort to get your head around it - it is designed so laypeople can use it to verify heat loss calcs by installers, or do the design themselves. There are instruction videos on the youtube channel to go through the process, step-by-step. And of course, there's direct support available here 😊

On 02/11/2026 at 20:50, gac said:

Congrats on openheatloss.com, that looks like serious work. You're clearly the stickler the regs need, and I mean that as a compliment. I'm not a heating engineer at all so I have zero authority, I can only speak from my own experience, but it's helpful to me to have tools that make it super easy to get some sort of indication.

Quick favour if you've got a minute: when you've plugged the same house into both a "black box" tool and openheatloss (or a full BS EN 12831 run), how far off do the black-box numbers usually land, and which bits go wrong most often (ACH, bridges, emitters at low water temp)?

It really depends on the input of the data. Using default inputs, the industry research suggests nearly 40% land to big and about 11% land too small! But the research also misses some key questions (and answers). In my experience the biggest problem is still the use of ACH. As a very quick comparison, even using a default value of 0.5 is above a well detailed, energy efficient house that still complies with the building regulations natural ventilation requirements. Mine for example has a ventilation loss of 0.38 going by ventilation design. Next is definitely thermal bridges unless the tool is able to do a full BS EN 12831 calc. But there are also other anomalies like the calculation of floor U-values. Several tools just use a blanket value input based on insulation thickness but to do this correctly you need to calculate perimeter/area ratio and also perimeter insulation. Some tools are also flaky in how they calculate internal wall losses between rooms etc.

This is problem, unless you're using explicitly declared variables that are editable like ACH you can't always reverse engineer the assumptions and I've test run tools that give me a 2kW difference on a house of 4.8kW heat loss and not been able to figure out exactly why.

On 03/11/2026 at 07:13, Oz07 said:

Would a layman be able to use this tool? I might have a go with it when sorting my building regs but it all goes a bit over my head. Do I need my sap calcs done first to get the losses?

Just to support what @SimonD said - I regard myself as a layman - if you have an understanding of the fabric of the building/floors/windows etc and can use a tape measure it's perfectly possible to use the tool