Absolutely fantastic Smogsy, and don't listen to the nay-sayers, you are completely right to get one property paid for asap, meantime you live in what can only be described as a top class Hotel Room with all the tech you could ever need!!! I'm quite fortunate in that I have a very large plot for Birmingham! As such I have a summer house similar in size to yours, and have just completed a 'workshop'. Somewhere I can do my woodcutting/gardening, without all the dust going in my tech! I use panel heaters a lot. They cost pennies to run all day, maybe as little as 2 or 3p a day per heater, however they keep my greenhouse warm, and mine is 10foot x 12!! They also keep my summer house and my workshop warm. They aren't the nicest looking, but nothing stopping you putting radiator covers over them, BUT my summer house is maybe 8 metres by 6 approx, 4 of these little babies keep it warm as toast even in the worst of the winter, and costs sod all. They are super easy to rig up to a thermostat. I'm betting you notice the electricity bill with the A/C, but I run like near 10 of these throughout Nov - March, didn't notice any jump in price on my bill and all the rooms, (even the g/h) are kept at a nice temp. They retail about £50 quid a pop, and touch wood all still working tirelessly 4 years later. Just a headsup, my folks have a home in Malta, they have aircon, in the summer it costs a fortune, but the heating in the winter is an outrage as to how much it costs!!! Unsurprisingly we now have panel heaters out there now, they won't really burn your hand if you hold them, but they are constantly pumping out the heat, and it's a 'dry' heat, so no condensation worries. My folks bought some nice radiator covers which we painted and they look great. Just a solution that I found by accident! I wanted to keep my G/H warm (well about 6-10C) during winter, I looked at all sorts of fan heaters etc and more importantly their cost to run, hence the panel heaters. I worked out using a top of the range G/H fanheater for a week equates to more than 10 weeks of my panels being on 24/7 lol. Thanks for sharing your space with us, a brilliant build and gives people like me stuff to aspire to! (Don't tell the missus) What's next? Subterranean swimming pool?
