I've been in touch with scores of installers and heat engineers over the past 12 months discussing a lot of renewable heating things, and one of the biggest industry problems is that companies and installers oversize heat pumps for properties because they don't fully understand how they work or they can't be bothered to do accurate heat loss calculations. An oversized heat pump, from what I understand, would be a complete waste of energy and electricity (as well as money). 

I'm glad you got downsized at no additional cost for the work (and hopefully you were charged less for the smaller pump). What heat pump do you have?

The general consensus amongst heat engineers is the same as your summation, in that MCS are not hugely beneficial to ensuring that heat pumps are installed correctly.

Mine's the Grant Aerona 9.1kW. COP of 2.66 with air at 7 deg and water at 55deg.

During the period between initial commissioning and the MCS inspection (about 3 months and while other building work was being completed) our first electricty bill was £1k. So I was glad the too big pump was swapped out.

@mike-patrick, that's a hefty electricity bill. Yikes! What's it dropped to now? Have you considered dropping your hot water into the 40s?

@editor Electricty uage settled down to a sensible level. But I have a whole post to do on electricity consumption, mostly arising out of my winter of 2021 experience.

@mike-patrick, I look forward to the post on your winter consumption - ours was insanely heavy.

As an aside, would you consider wiring a review of your 9kW Aerona to appear in the reviews section of the site: https://renewableheatinghub.co.uk/category/reviews

I’ve just spotted that Ian Rippin is leaving MCS as CEO this week after eight years in the role.

He won’t disappear immediately, as he’ll remain with MCS full-time until the end of the year to support the transition, with Lisa Cooke taking over as Managing Director next month.

Posted by: @mike-patrick

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I've come to the conclusion that the MCS scheme sets a fairly low minimum standard for installers.

I personally would characterise it as a process/standard designed such that, by following it 

a) MCS is protected 

b) the installer is protected 

c) the customer is protected

In that order of priority (most important first).

Your example of heat loss is classic.  A process is mandated and provided the installer follows it they are protected.  It relies on definitions from a British standard, so MCS is absolutely protected.  However in a practical retrofit scenario this will require assumptions to be made which are frequently incorrect, but such that the installer will almost always be able to side step any criticism by saying that something wasn't visible so they were 'forced' to assume worst case. That's why heat losses so frequently overestimated.  MCS protected, installer protected, customer exposed 

@jamespa A cynical view but, I fear that it is  a fair summary….. unfortunately. Regards, Toodles.

Posted by: @jamespa

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However in a practical retrofit scenario this will require assumptions to be made which are frequently incorrect, but such that the installer will almost always be able to side step any criticism by saying that something wasn't visible so they were 'forced' to assume worst case. That's why heat losses so frequently overestimated.  MCS protected, installer protected, customer exposed 

I suspect this is why HG has massive ventilation losses in their tech heavy heat loss report..

What saved us was the confidence in the 2 year long gas usage data…