Tahir: good luck with the build, if you want to compare notes you are more than welcome to come and have a look at the build so far. The frame is 2/3 complete built with masonite beams. The builder I'm using is Wilkinson Builders, I came across them when looking for airtight buildings in Masonite. So far their attention to detail has been very good, but the airtest will give the final verdict. The windows from Thermotech and should be fitted in about a month. I'm just finalising the solar combi, biofuel boiler and WHV with heat battery.
David: Is the reason that thermal stores require a higher temperature because they use an indirect heating element rather than heating the contents of a pressurised store directly? Should a condensing boiler be able to load either vented or unvented and stay in condensing mode? The choice between vented and unvented store will probably be dictated by the solar combi system I can fit. I intended to use a Consolar unit but couldn't find a Consolar trained fitter who would install in my area, as a result I'm probably going to use Sonnenkraft.
I've not come across Mike Garnham, does he specialise in heating or is he a general builder?