It's the added cost. New rads all round?
Retro fitting. Need solar to actually be cheaper.
It's great it's greener but probably a long way off for me. Even though boiler is 20 years old it works well.
Doubling rad size would be very annoying the house isn't that big so it would be a noticeable loss of space. Do you actually have to double rad area?
The space for the outdoor part of the pump would be fine
its not necessarily double the size need to calculate the heatloss from the room then size accordingly but for sure the rads need a larger surface area because the water running through them is at alower temperature with a heat pump