@ashp-bobba fascinating explanation, thanks.

I have a physics degree and worked as an IT architect for 40 years, so I can understand this kind of system quite well.  My key questions for potential installers were 1.  Do you use buffer tanks? And 2. How do you control the performance of the system?  My chosen installer insisted on open loop and weather compensation, so we got on very well!

The customer’s problem with paying for a heat loss calculation is that we want competitive quotes from 2-3 potential installers.  If we pay all three to do this, then it costs a total of £900-1200.  I paid one company, but did not choose them.

I did my own heat loss calculations, because I didn’t trust any installer to get it right.  One installer initially estimated 24kW, until I pushed back.  Then, he spotted an error in the model, which reduced it to 15kW!  

I produced my own list of radiator replacements.  My installer had his list and we installed the superset of the two.  He also installed FRVs, which I am sure have made the system work better.

Arguably, I spent too much money on radiator upgrades, but now I have a radiator system with a flow temperature that will probably be below 40C at well below the outside design temperature.  I will probably never recover the investment, but I will still feel good about the efficiency of the system.

@grahamf I understand, unfortunately I think the only way to know you are starting with a good company or designer is if they are recommended to you by someone you trust, not much chance of having 3 companies recommended by 3 people you trust.

In your case it sounds like you have a good understanding so you could ask the right questions and make a good informed judgment.

@grahamf, what was your own heat loss calculation in the end?

@ashp-bobba, your point about design being the cornerstone of a successful system cannot be overstated. When there’s no proper heat loss, no clear plan and no methodical commissioning process, things unravel fast, and the disruption for the homeowner can be enormous. This happened to us two weeks ago as part of our heat pump retrofix: no design, no plan, no objective. Finger to the wind stuff and the end result was catastrophic. More details to follow in the weeks to come.

I think what you’ve highlighted here (that the manufacturer’s “default” recommendations are largely a safety net to protect their kit, rather than an optimal solution for the home) is absolutely spot on too. It underlines why the designer and commissioning engineer are so critical, because they’re the ones responsible for ensuring the whole building actually works as intended. I also believe manufacturers have zero to no confidence in the current installer base, hence the safety nets. 

Your approach to commissioning, treating even a domestic install like a commercial job with IR checks, balancing and datalogging, is exactly what sets great installs apart from the rest. It’s reassuring to see examples where systems are designed to run in steady-state without unnecessary buffers, and where efficiency is engineered in from the ground up. 

For homeowners, the lesson is clear: a few hundred pounds spent on a robust, independent design and survey at the start is the best investment they can make. It avoids all the heartache and wasted expense later, provided you are able to manage and oversee that the design is applied in reality.

@editor Agreed, I await the details of what went wrong with your retrofit as we work on rebuilds often and they can be tricky.

Some more interesting comments on the state of, and changes in, the industry by SimonD (who is obviously a professional installer) over on the other place.  Worth a read.  Ignore the picture below, if you click on it you go to the correct place, not sure what RHH has substituted this for the link.

https://forum.buildhub.org.uk/topic/45343-anyone-used-bpc-for-ashp-odd-statement-from-them-re-ashp-sizing-part-f/page/2/#findComment-633986

and

https://forum.buildhub.org.uk/topic/45343-anyone-used-bpc-for-ashp-odd-statement-from-them-re-ashp-sizing-part-f/#findComment-633824

Posted by: @ashp-bobba

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@editor Agreed, I await the details of what went wrong with your retrofit as we work on rebuilds often and they can be tricky.

Agreed. There’s tricky, and then there’s diving into a project with no plan or forethought… just slinging stuff at the wall to see what sticks. That kind of approach doesn’t just fail, it causes damage and, in our case, total heating failure.

@editor oh dear, very sorry to hear about that.  I hope you get it sorted soon.

Posted by: @editor

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Posted by: @ashp-bobba

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@editor Agreed, I await the details of what went wrong with your retrofit as we work on rebuilds often and they can be tricky.

Agreed. There’s tricky, and then there’s diving into a project with no plan or forethought… just slinging stuff at the wall to see what sticks. That kind of approach doesn’t just fail, it causes damage and, in our case, total heating failure.

I was so hoping that the recent work would give you the heating system you want and deserve. I hope there’s a round 2 to fully sort it out .

Posted by: @judith

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I was so hoping that the recent work would give you the heating system you want and deserve. I hope there’s a round 2 to fully sort it out .

We’re going to do a full retrofix in spring with @pirate-rich at the helm… there’s a mountain of planning to get it 100% right and we don’t want to commence as we head into the heating season.

@editor I hope you have at least a partially working heating system for the winter?

@editor Oh no, that sound like a disaster, sorry to hear that.