Hi   I'm trying the decide whether to replace our oil fired boiler with an ASHP, the main drivers being that the current boiler and tank will need replacing soon, the oil tank takes up a lot of room, and I'd like to have a modern more ecologically friendly system. However, I can't tally the sizing requirements I've been quoted with my own figures.   It's a five bedroom house, built in 2004, with a total floor area/volume of around 300m2/700m3 and a footprint of 150m2 (some of