@jords this is an excellent and detailed post... thank you for taking the time to share it. It really highlights some of the challenges homeowners face when trying to make sense of this industry. Three surveys, three different design temperatures, three sets of radiator upgrades and three completely different interpretations of your property. It’s no wonder people end up confused.

The sundries line item from the Heat Geek quote would have made me pause too, not necessarily because the total cost was unreasonable, but because a lack of transparency instantly erodes trust. If half the cost is tucked into a catch-all category, how can anyone have confidence in the design or the installer? 

Your observation about Octopus insisting on a buffer is also interesting. I’m not aware of any MCS guidance that specifically requires a buffer to be fitted, and I think you were absolutely right to question them on it. It’s a reminder that homeowners should always feel comfortable challenging design decisions, especially when they’re presented as “rules” rather than preferences or risk mitigation measures.

As for British Gas and its stance on the positioning of the R290 unit, I will ask them for feedback and comment.

And I guess the next question is where are you now? Looking at different options?

I'm recording an episode of our podcast tomorrow morning on this very subject and I will use your case as an example.

Posted by: @editor

↑

 

Your observation about Octopus insisting on a buffer is also interesting. I’m not aware of any MCS guidance that specifically requires a buffer to be fitted, and I think you were absolutely right to question them on it. It’s a reminder that homeowners should always feel comfortable challenging design decisions, especially when they’re presented as “rules” rather than preferences or risk mitigation measures.

The only reason Octopus may insist on a buffer, is because they manufacture the Cosy heat pumps, so maybe they have a blanket "safety" requirements in case a user decides to turn off 50% of the radiators.

When I was going through my boiler room (AKA the Cylinder Hot Water cupboard) after EPC installed ours, I found a piece of paper where it stated "Minimum Water Volume 50l", and they took that as gospel, and fitted a 50l buffer, even though my system has more than that. Part of my remedial work will be to convert that buffer into a volumiser, or just take it out.

If any of them do insist on a buffer, just tell them you want a volumiser instead, that should give you the additional volume, without the compromise and potential issues caused by the buffer.

Posted by: @drei

↑

Did you check their heat-loss and radiator workings, did they use a buffer in your system?

I didn't because the survey (also done by Regenertec) didn't recommend any radiator changes - and I was planning to install Jaga fancoils anyway, to allow lower flow temps.  Also I have triple glazed everywhere since the system was installed.

They installed a 14kW Mitsi unit which, given the above improvements, is oversized.  Heat loss seems to average 8.5kW on a cold day but tbh I'm not fussed about having the extra capacity in reserve.

Today with temps around 11C it's running happily and without cycling.

I have had the 100l Steibel buffer converted to a volumiser and plan to have a more powerful pump added to get the flow nearer to the 40 litre/min specified for the 14kW Ecodan.

@editor Heat Geek - 8.45kW, Octopus - 10.27kW, British Gas - 7.69kW

I’ll be honest I think BG have made a mistake somewhere as they wanted the most radiator changes yet they had the lowest total heat loss. If I add up all the rooms I get 9.7kW for BG so I think their headline figure is wrong. 

@editor so my plan is to go away and upgrade all the radiators myself using the highest heat loss estimate for each room. There is about 5m of main “vein” in the house I will upgrade to 28mm having done the flow calculations. Luckily all the branches are 22mm and then small runs of 15mm to each radiator. It’s all easy access the bit I will upgrade to 28mm. Then I will also put UFH into the kitchen. Then hopefully no emitters will need to be touched.

Then I will go out and find some more local heat pump installers to get new quotes. Think I will avoid the big companies. They seem to have a lot of red tape and their own additional policies.

Personally I want a R290 unit as that seems like the future. Probably a Vaillant. 

@drei good to know thanks. I think there should be more than enough volume in the system. I plan for open loop other than TRVs in the bedrooms in case things get too hot. But if they insist they can put a volumiser in.

@drei this is the formula i was using to rate the radiator output correct to the desired flow temp.

=ROUND((((((Flow Temp + (Flow Temp - 5)) / 2) - Target Temp) / 50)^1.3) * Watt Output ΔT50)

I’m planning to keep it all open. Majority of the downstairs is UFH and is already the warmest part of the house. 

Posted by: @jords

↑

@editor so my plan is to go away and upgrade all the radiators myself using the highest heat loss estimate for each room. There is about 5m of main “vein” in the house I will upgrade to 28mm having done the flow calculations. Luckily all the branches are 22mm and then small runs of 15mm to each radiator. It’s all easy access the bit I will upgrade to 28mm. Then I will also put UFH into the kitchen. Then hopefully no emitters will need to be touched.

Then I will go out and find some more local heat pump installers to get new quotes. Think I will avoid the big companies. They seem to have a lot of red tape and their own additional policies.

Personally I want a R290 unit as that seems like the future. Probably a Vaillant. 

Good plan and pretty much what I did in the end (there were still 4 rad upgrades to be done by the installer when I got the heat pump installed, but I had done the rest). 

The approach I took (in what was essentially the second attempt at getting quotes) was to work out the house loss by measurement of gas consumption plus my own fabric calculations, decide what I wanted (whilst remaining open to genuinely better suggestions), and ask for quotes making it clear what was and was not negotiable.  In fairness there was one quote towards the end of the first round (jn which I got about 10 in total) that was convincing and which I would have gone with had there not been a delay due to planning.  Obviously they were a prime candidate for the second round, but narrowly lost out on distance.   Of course, as a result of specifying what I wanted, I got the usual 'I know better than you for reasons you cant understand' cr*p, but that simply made it easy to rule people out!  It was and is my house and, at least in part, my money!

PS your formula appears correct, output proportional to (average rad to room DT) ^1.3