@david-2 Rather sounds as though Mr. Octopussurveyor was having an off day! Your own and HG’s figures are in the same ball park seem to suggest which to go with. Regards, Toodles.

Posted by: @david-2

↑

I have just had 3 heat loss surveys, one by heat geek one by octopus and one that I did myself.

The octopus surveyor arrived and asked to be shown where the heat pump would go, he looked at the consumer unit and then the airing cupboard where my recently fitted unvented cylinder is. There’s not much room in here he said, I asked him why and he said that they had to install a new, bigger unvented cylinder and a buffer tank. I asked him if he meant a volumizer but he said no, octopus would be installing a buffer tank. This was before he had done his survey. He also said it was not an option to keep my cylinder.

 

Having lived in my house for 40 years and been present whilst any building works were carried out, I know the details of the fabric very well, so I offered to accompany the surveyor and tell him which walls were dry lined etc. He then asked me when the house was built and what was the date of the extension and explained that the way octopus worked was they imported those dates into their system and then scanned the room and the system worked out the U values based on those dates.

 I told him that they that the house was originally built in 1924, but we had just spent a lot of money renovating upstairs, a lot of which went on improving the insulation. We had dry lined walls, removed the plaster from the ceiling, fitted 70 mm of celotex between the rafters and 70 mm across under them, and so on. He asked me if I had any certification, I said I had the  architects plans for the extension which specified the insulation  and the certificate of completion from the council building control. He said that was not sufficient.

I had taken photographs of the insulation being fitted, but the surveyor said that he couldn’t accept those as they could have been taken anywhere. I pointed out that you could see out of the window in the photographs and see that it was the same room, but he wouldn’t accept that .

 

When he was finished, he said that he had calculated the heat loss at 17.5 kW and he was very sorry that octopus didn’t have a heat pump big enough.

When the surveyor came from Heat Geek . I went round the house with him and told him which walls were dry lined, which were solid, 9 inch brick, which were insulated cavity and so on.

He calculated the heat loss as 10 kW, which was quite close to my calculated heat loss of 9.5 kw.

 

Your house sounds a lot like mine.  2 surveyors each spent 3 hours to declare the loss to be 16kW, my own calculations (using MCS assumptions) came out at 10.5kW, actually its 7kW which I robustly established using measured fuel consumption.  I sought installers who would take notice of the measured results, had a Vaillant 7kW heat pump fitted, and its just right.  Double counting of some losses, overestimated air changes and failing to account for fabric upgrades were the main issues.

Do you have any figures for fuel consumption to do a sense check, this is exactly the sort of house where it matters, possibly quite a bit.  That said the Vaillant 10/12kW (which I presume HG will offer) seems to be reasonably good at dealing with oversizing.  I think is now single fan, dont know if that has changed its ability to deal with oversizing.  For sure however it would be good to do a sense check.