GDAL, if its of any use, we live in a house the majority of which was built in 1760's, so thick solid walls, no wall insulation, no under floor insulation, 2 large inglenook fireplaces with wood stoves, about 3300ft2 in size . Luckily, its not listed. 10 years ago we carried out a fairly big renovation, so some of the older part has minimal insulation, new parts were insulated to the standard of the time, loft has lots of insulation, double glazing fitted etc..At the time we also fitted solar panels to the rear south facing roof and for heat/hot water we have been using a Daikin 16KW ASHP. The Daikin has been working fine, especially if its just left ticking over and particularly if youre going to use a woodstove as well. All our heating/hot water/cooking is electric (except the woodstove which is handy when the village has its powercuts) for which we are currently paying around £800 per annum. Hope thats of use.