The heating system should be at the end of your order of priority, especially with renovation, go for the low-hanging fruit first. Eco-minimalism as an antidote to eco-bling explains why insulation and airtighness and thermal bridge reduction are the first priorities. Once your heat demand is reduced, you can start to utilise free heat gains from occupants, cooking and latent heat in water vapour through your heat recovery ventilation. The ventilation system also manages indoor air and humidity is managed, especially important in retrofititing. Eco bling is never cost effective, insulation is the best investment money can buy.
So if you get your heat load down from 24W/m2 to about 8, it really dosent matter what you heat your house and hot water with, your running costs will be minimal and you would be a longtime waiting for payback on your bolt-on ecobling. Many building and design professionals are hung up on DEAP which prioritises renewable technologies over fabric and ventilation improvements, a better option for occupant comfort and future proofed value is to follow the passive concept.