Thanks for the reply. I actually had a survey/quote last year by them which I declined, but the price is now nearly 1/3 of what it was…they’re still doing a fresh survey though, probably a different install team to last time.
~100m2 4bed semi '70s build - It’ll be interesting to see how much the survey differs vs last years, when 8x new radiators were proposed.
Hi Peter,
By the looks of it you have about two thirds the radiator output that I currently have under their proposals, about 6kW at 50c flow.
They are quoting the same heat pump that I am having problems with.
Your heating requirement is about the same as mine and the house is a similar size.
You are going to have a worse experience than I am having.
I am about to double my radiator capacity and the heat pump will still be too big.
I predict a disaster if you went with that.
what @matt-drummer said.
I have higher heat loss and more emitter capacity but our 11kW Daikin still doesn’t modulate low enough in milder weather (the 9kW is the same unit as the 11kW, 14kW and 16kW unit - just software de-rated it seems to limit max output)
I’d suggest you want the 8kW Daikin unit (a 4kW, 6kW and 8kW unit is software restricted on the other max ratings, and basically the same thing)
These seem to offer 35-50% of the minimum input electrical energy of the 9-16kW units
Here’s an interesting plot that compares 3 Daikin heat pumps, COP vs. temperature delta (right handside = colder weather):
Baskingstoke (blue), Cambridgeshire (green, only 8 days) and Ipswich (red)
I’ll let you draw your own conclusions…
I like it, red to match my anger 
Thanks Tim,
It demonstrates very clearly what you get when you strap a heat pump that is too big to a house that is too small for it with no way to get rid of the excess heat available.
I deliberately avoided saying a house with radiators that are too small because they clearly aren’t for the house, they are just too small for the heat pump in the outside temperatures represented here.
I agree, feels like there is opportunity to put together a useful resource with all that’s being discussed here. If @glyn.hudson and I can facilitate that and hopefully contribute as well, we would be more than happy.
Making the most of octopus?
They can tick all the boxes to access your tax rebate (BUS) and install without explicit planning consent (MCS).
Anything and everything else is a bonus; starting with them not screwing up the design, through them actually fishing the job, to their being in the slightest bit interested later.
They have a great brand in energy retail for a reason. (they’re good at admin, or the very least the least worst at it)
They’re trading on that brand for heat pumps though. (the evidence appears to be they’re as useless as your average MCS installers)
You’ll need to do the design work for them, hold their hand whilst they catch and carry all the parts, and then check they’ve fitted and configured them correctly yourself.
It’s probably still a good deal.
They’re not paying the installers much or making much money on these jobs. Cheap labour as long as they’re willing to follow instructions.
I’d ask British Gas (PH Jones) too whilst at it.
I got further with them than octopus (their self proclaimed experts stated that heat pumps don’t work with microbore when I enquired) and the surveyor appeared quite happy to follow customer led sizing etc but ultimately couldn’t buy an install because my cold water pressure wasn’t enough for their liking. (won’t touch anything less than 20L/min at 1bar in order to avoid complaints about lack of flow on an unvented cylinder even if you were happy with a combi)
Thanks again. The previous quote included the old, leaky, unused conservatory, which has a radiator in there but is permanently off.
I guess it makes sense to ask them to not include this in the survey this time, or am I missing something?
Hi Peter,
I also have a conservatory but it is actually pretty easy to heat.
It does, however, mess with the heat loss a fair bit.
At first they wanted to exclude it but then changed their minds and said it would be ok.
But, one of the strange MCS rules is that any radiators in unheated areas or radiators that they cannot ascertain the heat output of must be excluded from the calculation and removed from the property on commissioning.
So, in my kitchen, the designer radiator had to be removed at installation as they couldn’t determine its heat output and no alternative was available. I end up with an unheated room that pushes up the heat loss.
Of course, the kitchen is actually heated in reality because the radiator is back now.
They would have done the same with the conservatory.
Honestly, yes do that.
Should bring your heat loss at design outside temperature wayyy down (hopefully), getting you in to the range of the more appropriate (smaller) Daikin 4/6/8 kW outside unit.
I told them where to go when they tried that trick on day one of the install as the conservatory (not long for this world!) was explicitly not included in the heat loss calcs, and said when the install started they’d take the radiator off in there, and leave out the front (and alluded I could get someone back to refit it once they had finished).
They relented when I told them to stop works as this was a deal breaker and that I was going to cancel the project.
I use it in milder (> ~7C) weather as it’s useful given minimum output constraints discussed at length. Set to barely come on and keep room above 8-10C when colder.
MCS rules have a lot to answer for, and there appears to be little room for discretion. I guess that’s an attempt to protect consumers from cowboys (at the expense of rigid rules)
@matt-drummer - just re-read this, and I wonder (out loud) if this (including a conservatory in heat loss calcs) may be part of your issue with being provided the oversized (for rest of your property) heat pump? Could we be onto something here?
Hi Stephen,
The conservatory is included in the heat loss calculation and obviously loses more heat per floor area than the rest of the house.
But, I have been heating it all the time we have lived there and my maximum gas usage of 110kWh in a day included heating the conservatory.
So you could be onto something as I don’t know what the heat loss of each room was calculated at.
They may have got the rest of the house right in terms of heat loss and then doubled it by including the conservatory, let’s say 3.8kW for the house and 3.5kW for the conservatory giving 7.3kW in total.
If that is what they have done then it was always going to be a problem.
They are supposed to be experts at doing this, how can you design heating systems that use heat pumps without being an expert?
Would any installer be stupid enough to base the size of the heat pump on a conservatory? Surely they would realise the problems that would cause?
I think this may have been the issue 
To illustrate: our small conservatory dominated the MCS heat loss calc I just added it to:
With conservatory (Octopus were told not to quote including this):
My actual MCS calc I did prior to them showing up that did NOT include the conservatory (so I had a good idea as well as actual smart meter half hourly data use that corroborated ~8.5kW peak load):
Do you have the radiator schedule they provide in your quote pack? (This seems to be the closest they provide to a heat loss value)
Thanks Stephen,
It’s interesting.
How big is your conservatory?
Mine is about 15m2 so about 30 cubic metres of air.
They cannot have included 3.5kW in my heat loss calculation for this?
Half my heat loss to be provided by one radiator?
EDIT:
They did not do this I have just found the error in my heat loss calculation.
I will post my radiator schedule with the heat losses on.
So here is my heat loss and radiator schedule prepared by Doug from Octopus!
My lounge has two radiators in it but he has included the heat loss of the lounge twice! He put in the full loss of the room against each radiator rather than halving it. Ooops!
The heat loss appears to be 7.791kW but he has included 1.441kW for the lounge twice so his actual answer should have been 6.350kW
…you may have grounds for a smaller unit replacement - error is on their side.
On the contrary.
There’s no enforcement even if you as the customer want enforcement. (compliance is optional)
And there’s no right of entry to inspect if you the customer would prefer MCS to piss off once you’ve got your £7.5k.
Therefore infinite room for discretion. 
I’m afraid not. They’re not supposed to be experts.
They’re supposed to tick MCS boxes. That’s all their contract with you really says.
The terms and conditions offered that you signed up to say nothing about having a clue or ensuring an efficient system.
They’re good at lawyering. Unfortunately.
The difference between what they contractually agree to provide and what they would like you to think they provide is marketing.
Hiring a handful of actual experts who have no involvement in the everyday business; knocking out a prototype Ann Summers inspired grit bin of a heat pump etc all cost nothing in the grand scheme of things. The true cost (the one that makes up the bulk of the business expense) are the apprentices that they send out to survey/design/install.
They’re good at marketing. Unfortunately.
