Changing from electric storage heaters, best fuel option? Air source/gas/oil/biomass?

Good afternoon, Personally I would advise against oil unless it's your only option, for a couple of reasons. Oil is expensive and will only get more so, arguably less environmentally friendly and in addition, less convenient. You would see much better savings, quickly, by having gas. However... Air source heat pumps can be excellent but usually only in more modern properties, as the temperature that they produce is not as high and is therefore better suited to well insulated, modern properties, usually combined with underfloor heating. I'd have to investigate a little to refresh my memory here but I don't believe that they are suitable for heating your hot water. I think you need to have gas or some other means of "topping up" the heat as I recall that the maximum temperature is around 40-45 degrees, whereas 60 degrees is needed to heat hot water, conventionally speaking. This is to kill the potential bacteria from legionella. I would suggest that you investigate the cost of connecting up to mains gas - you may be surprised. In an older property I think this would be your best bet, excluding the alternatives that you've already mentioned. I hope this helps! Regards Philip Walters Walts Consulting Ltd