Hello David, I’ve just seen your response to my post. As Timbones says, minimising the target ASHP exit temp (consistent with room comfort) is the single most important factor in keeping down running costs. Here in central southern England, I run my (Samsung) weather compensator at 40degC exit temp for summer (20degC ambient) rising to 45degC exit temp for winter (-2degC ambient). This has worked well so far, but I may have to tweak up the winter setting (the next few months will tell…).