That's very interesting. Thanks.
How likely would a COP of 3.5 be knowing the radiators would need above 50°c flow temps? I think a good COP would be achievable running the UFH but I'm worried the radiators would ruin it.
Looking at the cost of a 12kW ASHP it seems like quite a big investment. I asked the plumber to install a solar unvented cylinder when he moved our boiler so I'm pretty sure it's a simple bolt on job but even so looking at the prices is it fair to say this isn't a sub 5k job? We pay 13.5p for electric so I think your cost per day is accurate.
I do plan on doing that but I need to talk with my neighbours about it as it's an estate. I fear that one of them would have signed a contract and FloGas will tell me tough luck.