Can I just add to the above that there are many on here who have successful installs. 

There are also quite a few who are willing to try to provide simple advice to help sort the wheat from the chaff, if potential purchasers post a summary of a few simple details of their house and the system proposed.  Of course without seeing it and doing an independent design there is no guarantee, but the majority of problems we see here are down to a very few simple things which are easily spotted before committing. 

@jamespa, excellent point.

And it's also worth sharing what you said or asked an installer that was the moment when you decided "you're hired" or "see you later".

Posted by: @editor

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And it's also worth sharing what you said or asked an installer that was the moment when you decided "you're hired" or "see you later".

For reasons to do with how things panned out I went through two 'phases '.  In the first phase I was fairly 'open minded' (ie I didnt discard installers particularly quickly), but didn't proceed.  By the time I had got to the second phase I knew what I wanted and told each installer contacted  as part of the brief.  The following were immediate 'see you later' signals in this second phase

• Wants to fit a buffer, LLH, PHE between emitters and heat pump, or pre-plumbed cylinder
• Gives some flimsy reason to ignore my soundly (IMHO) measured loss based on gas consumption
• Wants to fit external controls

It really came down to the basics!

I have a feeling that designing a retrofit heat pump system for a most typical, tolerably insulated, reasonably normally constructed houses of perhaps 250sq m or less (ie the vast majority of our housing stock) is actually quite simple* namely:

1. Calculate the loss AND sense check it by some independent means.  Once you have reconciled the calculation and the sense check (not before) proceed.  If you cant reconcile, assess the effect of the uncertainty and if necessary take some more measurements. 
2. Look at the existing pipework and make an intelligent guess whether it will be sufficient.  Note that this is not going to be fool proof unless all floorboards are taken up, so be aware later in the process at step 4
3. Change any necessary radiators for the desired design temp (preferably 45 or less).  Be a bit pragmatic about this
4. Fit a heat pump, two antifreeze valves, a UVC, three port diverter, a couple of filters, air release valve, manufacturers controls.  Fill with either pure water or water plus inhibitor.  Under no circumstances (for a house of the kind described) fit a 3 port buffer, glycol or external controls other than Homely, Adia or Havenwise, volumiser if needed.  If you want fit TRVs but set them all (or almost all) to max and instruct householder to leave at least the vast majority them there.  Disable any existing external controls or otherwise take them out of the main control loop
5. Check flow and radiator heating after crude balancing, if insufficient rethink water pump
6. Once that is sorted fully commission.  Set WC according to design calculations, balance radiators.  Either instruct homeowner how to adjust WC and tweak radiator  or plan a return visit.  Tell and leave homeowner with leaflet on how to run heat pumps
7. Do the work diligently

Unfortunately (based on what is reported here) some installers:

• fail on (1) omitting the sense check and blindly taking the loss calculations as gospel,
• either obsess about or don't even think about (2) and (5) when they have no way of knowing for absolute certain other than by experiment, thus either ignoring the potential problem or replacing pipework unnecessarily
• fail on (4) fitting unnecessary or counterproductive components such as a buffer or external controls
• omit most of (6), slinging in 'safe' (ie over high) parameters to avoid call outs due to 'not hot enough'.

Thus we end up with (some) oversized systems with buffers and controls that are either unsuitable or not properly set up.  Throw in a bit of failure on (7), and its a recipe for disaster.

*in principle - I concede that there are onsite challenges to solve, but the basics, which is what seems to go wrong, is really quite simple.

Unfortunately your post is too accurate and the product is gaining a poor reputation. I often say to people if Panasonic, Mitsubishi & Samsung etc make them surely they work, and they do its completely as you say Mars, the installer being the issue.  Its a multitrade product and has many transfering across into fitting HPs and with grants it draws in crowds of 'fitters' who often work to a price or bonus with the system being sold to the customer through a call centre. I say never entertain those calls, do your own research and get a few quotes, never buy from the typical old school salesperson, we give the info required and answer questions and even take a demo unit or show them a working system, you then make your own decision and we never follow up quotes.

Posted by: @dgclimatecontrol

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the product is gaining a poor reputation.

wrong tense I fear, judging by what I hear at my local pub (which is, after all, important as it affects people's choices). 

Of course the oil industry and a section of the media are amplifying the bad and attenuating the good to assist.

Posted by: @dgclimatecontrol

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I often say to people if Panasonic, Mitsubishi & Samsung etc make them surely they work, and they do

Excellent point.

Its perhaps surprising that the manufacturers haven't stepped in, fed up with their product being abused.

Posted by: @dgclimatecontrol

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it draws in crowds of 'fitters'

and 'grant chasers' who have no intention of staying in the business once they have completed the harvest.  Solar panels were the same in the early days, but more difficult to mess up.

These systems are not as complicated as it all appears, James always hits the nail on the head and Mars just has a way of telling it like it is. I am not sure why but this all shocks me and then makes me wonder if we "my teams" are doing anything wrong, after all we are just engineers.

I was approached today about a new set of UFH controls and even after I said 3 or 4 times that all ASHP have the amount of controls they need to run everything on a home heating system the UFH control company sales chap kept telling me but their new controls are better, all wifi, all app related and the best in the business at zone controlling will defiantly add more efficiency to the heating system, when I defended the poor ASHP the response was, well a correctly set up boiler that is running at over 100% efficient is cheaper to run than an ASHP anyways, our controls create that. As you may imagine I smiled and made my excuses with my busy day and left. I did not have the heart to argue the 100% thing, its just about money and selling me something thats never going to be needed, companies are actually making this stuff and saying this stuff???

Anyway this made me think after and its something thats not often covered in all of the listed incompetencies, this is all about money, making money, making more money, job and knock, I see it all the time with our rescue jobs. Now don't get me wrong we are here to make a living but the only reason to not calculate heat loss correctly is (cutting the corner to make more money) to not change a pipe (cutting the corner to make more money) to skip a rad (cutting the corner to make more money), to commission the system in 2hrs (cutting the corner to make more money). If it is not cutting corners to make more money, be the cheapest and win the most work then its all of the items listed by Mars and James.

I don't know how to explain to a customer the best way to spot a good company or not I assume the customers we get is because our teams say or show the right stuff, what I do know as I ask every client that I quote, why we did not get the work? Nearly all of them tell me that all the quotes we did not win is just down to price and they went with the cheapest, many customers want the cheapest, what is nice is that most of the time we are 2nd as they confirm so that says something maybe, good price but not cutting something out maybe, obviously we win some of them in 2nd place, perhaps the cheapest worried them. 

Advice on top of the other advice here:

Compare apples for apples ASHP for ASHP, don't be afraid to ask questions or ask why 1 company wants to change 4 rads and the 2nd company want to change 5, it may be that you need that extra rad or the 2nd in the end design it back out upon the question

Have an opinion on your own design, we ask what temperature would you like the system to run at and explain the differences with changing rads V cost of running at a higher temp.

Don't get hung up on the days it takes to complete the works, a 2 day install completed by a team of 6 is not better than a 5 day install by a team of 2, often time taken and thought placed into the job on site allows for a better installation, a company trying to smash your system in 2/3 days is loosing 6x the money for a single days delay, if like we do sometimes notice the route thats was supposed to be taken is restricted for some reason, taking time to explore and plan on the job is required. When the survey is initially done, that engineer or sales person is not cutting through your walls or extensively exploring your loft, these things get established on the job, if there is an issue on site and loosing 6 days money is an issue it could be tempting to say cut a small corner. 

Ask to see the system in their home or their offices, if it is good enough for them it is good enough for you, if you like what you see take a picture and compare it to yours at the end.

Try to find a company thats an expert in 2 or 3 brands, often most of efficiencies is down to control set up and system design, if a company has installed 50+ of the 3 brands they do its likely they have the controls set up fine tuned.  

Lastly, if you owned 300 houses and had an ASHP in every single one I think it is unlikely we would have designed in a buffer that is connected to break the system, it is very likely you own one of the 299 homes that would never need one, so if you get offered one say exactly this, why would my home need a 4 piped buffer when the other 299 homes don't need them as you would be the 1 in 300, if they answer anything to do with manufacturer, power or distance please make sure you except this if you have 30 radiators on a 200m pipework over your 7 floors or the manufacturer you are choosing is somehow able to boost the performance of the machine by utilising the 25l of capacity stored energy that has a value of less than -4% in fact it is nearly always going to create an energy loss at the exchange, if the 1 in 300 scenario happens any good company could explain exactly why you need the buffer as they would have had to do some special mathematics to calculate the correct pump curves or curve controls to make the 2 pumps work correctly and together before they install then system.

Buffers protect ASHP from old systems not working properly, demand a modified system set up correctly to match your chosen ASHP so you don't need a buffer, simple as that. 

 Volumisers are buffers piped as volumisers this is not the same as a 4 pipe buffer and never has 4 pipes (3 and 2 are common uses), these just help with return volume for defrost.

@ashp-bobba I agree that as an installer you probably don’t want to be the cheapest.  There is plenty of work out there.  If you charge more, you can afford to work more carefully and do a better job.  Of course, a good installation benefits you as well as the customer - fewer call-backs, fewer complaints, less hassle, another good customer reference.

The aspect that mystifies me is why an installer would be motivated to install a buffer tank, duplicate control system, or anything else that adds complexity.  The complexity adds cost, which surely translates into an increased price and the risk of losing the job? 

Installers seem to perceive that buffer tanks and other potentially unnecessary design features reduce risk.  However, as a general engineering principle, complexity usually increases risk.

I wonder how much installers typically learn from their installations.  Margins in domestic work can’t be that high, so can you afford to make follow-up visits?  Obviously, if the customer complains, you will deal with the complaint, but if the customer is slightly unhappy, he might not say anything.

My installer tells me that a slightly nerdy member of his team sits at home most evenings checking the performance of systems they have installed.  That is invisible to me.  Similarly, I am all over our system, fine tuning it.  That is probably invisible to him.  Happily the system is working so well that, after a few early exchanges and one return visit, we don’t need to communicate at all.  

Posted by: @editor

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@jamespa, excellent point.

And it's also worth sharing what you said or asked an installer that was the moment when you decided "you're hired" or "see you later".

@editor like @jamespa, I had a list of test questions:

1. What SCOP will you design for?  Can you show me evidence of achieving that SCOP on your installed systems? I hoped for a number above 4, or at least in the high 3s.
2. What flow temperature will you design for?  I was looking for no more than 45C.  
3. How will you control the performance of the system?  I hoped they would say “with weather compensation”.
4. Do you intend to install a buffer tanks?  I hoped they would say “no”.
5. How many zones do I need?  I hoped for 1.
6. How many heat pumps do I need?  Our house came out borderline between 1 and 2 heat pumps on the heat loss calculation. I was determined to have only 1.

The installer that I chose actually told me that I would have to use weather compensation and run the system with a single zone open loop.  He said I could have TRVs but only in bedrooms and one sunny room that gets very hot.  

He presented this as an ultimatum and looked slightly nervous, as if he was expecting a big pushback from me.  This was music to my ears.  I readily agreed to all of it and we have got on very well.

Thats what happens when you ask Mars to recommend a supplier!

Some interesting comments here on buildhub.  If SimonD is correct in his analysis/statements it pretty much explains everything (bad) we observe.

We should also consider the importance of the manufacturer's role in setting design guidelines for installers.  
As an example, Grant UK seem to recommend low loss headers in this case study on their web site:
https://www.grantuk.com/about/news/heat-pump-and-low-loss-header-are-a-winning-combination/
It is entitled: "Heat pump and low-loss header are a winning combination" and dated July 25, 2022
"A Grant Aerona³ air source heat pump has been installed as part of a new heating system for a bungalow which has been refurbished in Kent. Alongside the heat pump, a Grant low-loss header has also been fitted which is designed to support the efficient, reliable operation of the Aerona³...
"Alongside the heat pump, NCC Southeast Ltd also fitted Grant’s combined low-loss header/volumiserwhich is creating hydraulic separation, separating the heat pump from the rest of the system and helping to maintain a correct flow rate through the heat pump unit.
“Installing a low-loss header and using it for hydraulic separation is our preferred method when installing a heat pump system,” continues Neil. “It does involve a bit more planning during the early phase of an installation but the benefits it delivers are worth this extra time. Provided space inside a property permits, we fit a low-loss header but when this is not possible, Grant’s external volumiser serves a system well when space is limited.”
 

@grahamf I think in the last 3 years and due to heavy social media coverage many manufacturers and designers now design buffers out, in 2019 when I designed a 400m2 open loop full UFH system on 2 ecodans with no buffers and submitted, installed and commissioned the system we were considered outside the norm, taking risks and were told it would not work by the manufacturer as like many they designed them in back then. My only response at that time was "heat loss is heat loss, if I put the heat in it and can move the water evenly around the building I don't need a buffer and it will keep it warm" don't mistake buffers for anything than in the way and causing distortion. This system runs today and runs well. 

You see, for 26 years I have been designing and installing HP chillers which are the same as very large Ecodan's and just about every other ASHP for domestic with a couple of extra controls on top and you know what, we did not even put low loss headers or buffers on 200kW systems so why would we on 10kW system? these systems were design with balanced return valves and pumps specially selected to handle the curve, now these return valves were a bit more sophisticated than what we use on domestic design today but in theory the same as balancing rads by hand. The difference is I would employ a specialist water commissioning engineer to balance every leg and reg return valve to design rather than this touchy feely hand on rad and call it a commission. I would also have to pay them around £2,400 to commission this water flow but it was worth it on a 7 story building. 

We AAC commission your home like a commercial building, we measure the F+R leg + M Av value of every rad, we IR camera to prove even flow and saturation as well as we data log performance of every rad all included in the installation and thats why we take AV 5 days to complete an installation as day 5 is 7hrs to commission up to 12 rads.

The issue is, we need engineers better than the manufacturer for application, its the designer that is supposed to know the building after the heat loss survey, the designer is advising you best kit, best application and best practice and the designer should be assisting and checking the engineers installation. I understand why the manufacturers specify a buffer as it will largely protect their equipment from an incorrectly designed and installed system connected to their HP but the manufacturer never visits the house after the installation.

It worth remembering as many complain about the fee, but the aprox £300 you will pay for the heat loss survey and design is your best asset right at the beginning of the journey and before you have committed to the larger installation, if that paperwork says you need X rads and X flow with X performance and you accept this design, as long as the system performs this way you have exactly what you signed up for, at this stage you can ask as many questions as you would like about application, performance timings and even estimates on running costs with small caveats.     

I agree the advert is misleading to a point as there is no need to advertise it like its the best solution if it is only one solution that suits the manufacturer but most of what they say is true. A buffer does ensure correct flow through the HP as the house circuit cannot restrict it now, it often does make it more reliable (HP ONLY) they are not talking about the whole system here, and efficient yes as whom decides whats efficient is? Anything over 100% is efficient so even if it only generates a SCOP of 2 it is still efficient just not as much as a 4+. The trade off here is better protection for the manufacturers equipment V a slightly more expensive cost to run for the home owner. We should also not get hung up on SCOPS of 4+ 5+ and so on, each system should be a good outcome for a reasonable price with the customer driving preference. If you want top end SCOPS and lowest runnings costs then this can be designed in but will be bigger rads, larger pipe, more of a retrofit. If you want an av but good performance go with the biggest providers that design everything at 55 deg C and will not budge as it makes the installation as cheap as it can but reasonable cost to run an finally if you want to go with the cheapest for capital cost just double check they are offering you a reasonable installation that will run at a reasonable cost and hope they are much cheaper as they have no overheads or there is some kind of promotion rather than its all done on day rate speed, subbed out or corners cut.

I cannot see where a buffer would fit in to a domestic system unless you had to place undue stress on the HP primary water circuit but this is just because the system works better when the HP has control of the hole house circuits and can modulate the flow across the building or better maintain a constant flow curve and these systems work better and more efficiently when they modulate. This is the magic of this technology, how it can move from delivering 3kW to 10kW on a demand curve that follows some clever math to track heat loss. This is steady-state heating or what we try to target is steady-state but you need to be one of the best to get it near perfect. Our definition of a good ASHP system installation is one that can be designed to perform as a quasi-stead-state heating system at a pre-set desired temperature across the building at is designed criteria.

Now how you find a designer that is capable of this level of design and application eludes me, perhaps a register of excellence "MCS" or more badges, I joke we don't need more badges thats for sure. 

I had fun writing this, I could have written 12 more pages 🙂