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Thanks all, yes a fair chunk of my budget is going in to that retaining wall. Builder has quoted me £85k to build a watertight shell which I was pretty happy with, I'll then be managing/completing the build myself inside. I I bought it off a older chap who lives in the other house you can see in the trees, it's been his project for several years hence the footings are dug (a big reason I was happy to proceed was that building control was ok with the excavation depth). Age and poor health brought him to the realisation that he was never going to complete the build himself... 2 days after the sale went through he had a Range Rover Sport and a new boat parked on his drive so he's obviously not feeling too poorly

It is strange that we don't design in basements in the UK. You would think that with our unrealistically high land values that we would. I supposed that it comes down to the marginal price. Mind you, with our shoddy building practices we would all end up with either cheap underground swimming pools or very large rainwater harvesting tanks.

Just came across this technology where they store energy in the form of ice to cool in the summer and turn it back into ice to warm in the winter. 10 meters cubed! http://www.viessmann.co.uk/en/residential-buildings/heat-pumps/ice-energy-store/ice-store-system.html Anyone have experience of this system or heard anything about it? I wonder if the phase change lasts the whole season? They see it as an alternative to geothermal.... Just when you think you've seen everything....!! "......you want ice...you got ice....!!"

What peter said. Ok...... A TS is basically a huge round radiator, full of primary central heating water, and stores zero dhw. Dhw is produced instantaneously via a coil which sits at the top of the TS which is simply heated by the surrounding water. The heated primary water can be drawn off via dedicated tappings, the same way heated primary water enters the TS from the boiler, and your Ufh would simply be drawn from those points. There is no 'pressure' other than the static primary pressure which would show on the gauge of your system boiler, which is simply showing that the system is sealed and full of water, aka pressurised. There is no force available to 'push' water to the manifolds, that circulation would be provided solely by the manifold pumps. For eg, if you connected the manifold flow and return to the TS, then unless it was by convection, no water would flow through the pipes as the body of water would be unified and therefore be at the same potential. Even though the boiler pump is pushing water to the TS, it's also pulling back at almost the same potential so that creates a circuit of flow to and from the TS to the boiler, only. To create external ( beyond the TS ) circulation you need to fit a pump, hence the ones on the manifold. @Temp spoke in detail ( on EB ) about this need for a second pump still remaining with certain manifolds / manufacturers, but tbh I still am unsure as to why the manifold pump wouldn't draw through regardless. Maybe Temp can reiterate that so we can identify the type of manifold which may need the secondary circulation pump. An UVC is the opposite of a TS. It has a coil, fed by the heat source eg boiler, which heats the tank full of clean drinking quality 'potable' water, the water that actually comes out of the tap. UVC's don't have additional tappings for removing heat as the coil which heats it simply couldn't deal with the additional demand, eg a bath being drawn plus all the Ufh calling for hot water to heat the house from cold etc. The TS gets heated directly via the open body of water so is far far better at getting the heat from the boiler into the primary water, plus it circulates it too, spreading the heat out evenly. The flow from the boiler also hits the top of the TS, which is where the dhw coil sits, so in essence provides a kind of hot water priority. This is why your second plumber is one is not consider using. He should have clearly stated all this to you as a reason for his suggestion, but I doubt if he knows what a TS is, let alone how it should be utilised. My bottom dollar is on him failing to explain that he intended to run your Ufh directly from the boiler, using 2-port zone valves, and a third zone valve for the UVC, as opposed to leaving you think that the Ufh could be fed from the UVC. If you were having Pv I'd have probably said upsize to maybe 400ltrs, but if you feed the TS directly with that size boiler you'll get instant, constant ( as in 24/7 constant running dhw ) from the 300. As it'll never be used as a heat battery from a Pv POV, pointless in upsizing and increasing the losses, BUT, if you do upsize it, drumroll please, you'll be able to run at a lower target temp and reduce the losses a fair bit so if overheating would ever be a problem that's one way to mitigate it ( say upsizing to 500L and running at 55oC, or 65oC at 400L ), Setting up for a lower flow temperature can allow you to ensure you hit the best condensing flow return temps and maximise boiler efficiency too, so this is a multi-faceted question which needs a bit more thought / input . With a fully modulating boiler you could probably get away with running the Ufh directly from the boiler and fitting an UVC for dhw, as long as the minimum heat load for the house ( when the house is up to temperature and the boiler is only offsetting the heat losses from the house itself ) doesn't fall below the lowest modulating point. The only problem would be sizing the UVC exactly to your anticipated consumption. This situation would see the boiler running all sorts of different flow temps though, and would reduce it's efficiency quite a bit, so my recommendation would be.... 400L TS fed from a 32kw boiler. Ufh fed from the TS. Have the 2 circuits of Ufh flow and return pipework split immediately after the TS so the ground floor pipework can be isolated from the upstairs via dedicated two 2-port valves. These are required more to stave off convection circulation ( a killer with TS's ) than to offer control for the heating. You will also require an additional 2-port ZV between the boiler and the TS (i) to have control of the TS temp and (ii) to stop backflow of heat from the TS to the boiler. Set the cylinder stat to control that ZV and that ZV will then fire the boiler. That can be set to get the boiler to fire for bursts at a temp suited to get the best efficiency, rather than constantly idling to maintain temp. Written on the move so hopefully makes some sense.