Hi! Long time lurker. Midway through build at the moment, and ASHP quotes are coming in super expensive - they are also coming in at different sizes! And generally don't seem to know much about what they are selling. So I am wondering is it possible to avoid the RHI altogether and go for a self/plumber/heating engineer install. I've watched the Vaillant youtube videos and it rather looks like it is plug and play. So a plumber and electrician used to heating systems should be able to do it? I'd probably rather a cheaper up front cost than receiving the RHI over 7 years- provided it is a reasonable saving.
So far, I've had a 14kW, 13kW and a 5kW recommended... The house is single storey, built to building regs (wall 0.24 floor 0.1 roof 0.15 u values) with not excessive windows. I suspect air tightness isn't great, and the ceiling is vaulted so a bit of extra volume there, but I just can't understand why two such massive ASHP are being spec-ed. Also the quotes are fairly wild.
I've downloaded @Jeremy Harris v helpful calculator and put in my figures, getting a heat loss of just around 5000W @ -10 degrees outside and 20deg C inside. To my mind that shows heating requirement, and bearing in mind outside temp of -10 for the calculation, surely a smaller say 7kW Vaillant would be more than sufficient? I'd also like a 300l cylinder, as it is a 4 bed, albeit one shower is electric.
I can pickup the Vaillant easily enough, and it seems very capable unit. Surely the install cost can't be £6-7k, or that complicated? The youtube videos make it seem that it is really just connections that need to made to get it going...