Gabriel

Thanks for the reply.

Air source heat pumps have been considered and it's my understanding that they're quite large - like a big air conditioning unit, stuck on the outside of the house - and noisy. Also, I believe that they work well with UFH as the circulating water temp - 40 - 45 degrees I think - is lower than conventional rads which require about 80 degrees, and in order to get sufficient heat from a radiator it's surface radiating area needs to be almost doubled. Having said all that the major consideration I have is budgetary.

With regard to the load test, already done and satisfactory.

(Just looked at the Danfoss site and see that the unit has a much smaller external footprint than I thought. Still, the budget....)

Anyway, I still need to think this through before committing to electric so any more advice from all out there appreciated.