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A pointer, please. I'm building new and I have opted for ASHP (I've seen nothing especially wonderful about ASHP, but it seems to deliver at a comparible cost to oil, and easier to get BC/SAP on board, but this is not the point). I'm in N Ireland and have 3 prices from installers that use their suppliers design service (Grant, Warmflow and another). None of the 3 can provide any detailed information on what their proposed system is, basically " in case the design is copied". I want to know a lot before i decide, from pipe size to zones, to controls and equipment, coz i get one shot at this, its expensive, and must work without me having to get a degree in Turning-On-The-Heat!!. Until this moment, I assumed the supplier was the cautious one, but as I write I realise that does not stack up because having designs with their equipment out there is good. Anyhow, has anyone else had this issue? Do I just hold a tight reign, or is there a better way to choose?

I have finally come to the conclusion that we are going to fit an ASHP and cylinder to our property. Over the years we have been drawn to the Sunamp, Sunamp and Willis heater courtesy of @TerryE but with the recent problems encountered and the uncertainty of how the system works if/when you have a problem does not appeal to us (Apologise to all those Sunamp owners out there). So having chosen ASHP it brings with it the problem of designing/installing the system and even though I have plumbed houses and fitted central heating systems the thought of this seems quite daunting.I have never fitted a cylinder before so this in itself is new territory so I am appealing to people who have done this themselves @joe90 , @ProDavefor any guidance you can pass on to me and may be some more help from @Nickfromwales and @PeterWif you can spare the time. I am struggling to get anybody locally who can just fit this low KW ASHP with cylinder without wanting to double the capacity, have it interact with the space station for telemetry and spend a whole week on fancy control systems. I have looked at the plug n play systems from the likes of LG and Samsung which would be very easy (ish ) to set up but would cost quite a bit more. I know I need an inverter in the ASHP and a blending valve(!) now so you can see I need quite a bit of advice to be able to understand the system and what I require. The house is Passive so will be minimum heating and I intend to keep the DHW temp low like Joe and Dave so I am trying to give you as much info to help with your advice hopefully. I know people have bought their cylinders from Telford but not sure what cylinder to buy? We will be doing solar PV at some point just not sure when. @joe90has mentioned having a buffer tank but he is not sure whether he actually needed it although he has his immersion in this tank I know you can have an immersion in the main cylinder and if I had a Willis heater as an immersion heater this could double up as a stand by if I ever have ASHP problems but how does this all connect together!! Hope you understand my dilemma and hope you can help me design and understand my DHW and UFH system from the start to the finish!!

Needing to focus on my next project after my UFH fiasco and being in a holiday rental place where the DHW is very hit and miss reminds me that I need to get some specs laid down before I start ordering stuff! Having read so much over the past couple of years, I feel a lot more informed but also a bit bamboozled at the same time. UVC or TS, buffer tanks, what size..... So my main questions (so far): 1) what type of gas boiler to go for? 2) Thermal store or UVC? 3) Buffer tank needed? My setup will be: 4kw solar PV Mains gas 2 UFH manifolds (upstairs and groundfloor - so I can choose the flow temps accordingly to get the maximum comfort levels) Room stats in all areas 2 Bathrooms (2 showers, 2 baths) MHVR Although not going to be a passivhaus, I’m hopeful it'll be a bloody whole let better than your standard newbuild: 2 SIP extensions 300mm EPS floor insulation 3G windows/doors 100mm EWI on existing house DHW requirement: 2 adults and two soon to be teenagers (so they will hardly wash reducing the DHW figures a bit) 2 morning showers 2 evening baths Hot water for washing up (though may get a boiler-type tap for most hot water needs in the kitchen) Occupancy: Wife and kids out and I although I work from home, my office will be one of the sheds out the back so main house can either be set to off or very low temps during the day. UFH demands: Groundfloor: Water volume: 129L; Estimated loading: 9.45Kw Upstairs: Water volume: 25L; Estimated loading: 2.03Kw BOILER QUESTION: Before I start getting plumbers out to fit a boiler system, I’d like to get people’s advice on whether to go for system or combi. Combi = don’t need a water storage cylinder = no need for cistern in loft = combi boilers don’t supply enough hot water = better to use a separate cylinder for the hot water supply. = combi boilers can be quite noisy. System = Store hot water in a cylinder, so they can feed several outlets at once at mains pressure. = no need for a cistern in the loft and the expansion vessel is built in. = Flow rates will be high as water is delivered at mains pressure, and hot water is instantaneous. I'm thinking to go for a system boiler at this stage (easier/quicker install) and then to use excess PV with the cylinder. THERMAL STORE OR UVC? My thoughts so far are to have a 300L UVC fed partly by the solar PV during the day (using an Immersun type of device) with maybe E10/E7 at night and then also the gas boiler. I would end up with two circuits – one for DHW and one for UFH. The boiler would kick in for the UFH when the UVC doesn’t require heat. BUFFER TANK? I'm also thinking that if I go for a UVC rather than thermal store (from what I have read on here) I would need a buffer store seeing I will have UFH. But I've read that if I opt for a TS, that can be my buffer tank also. So perhaps I should go for a TS rather than a UVC? Confused.... Hoping someone (AKA: @Nickfromwales etc) is able to assist..... Thanks, OB

Due to some of the astounding quotes for UFH and DHW systems, I have decided to have a stab at designing and specing our own system! This is the first draft, possible due to this forum and the Building Services Handbook recommended by @curlewhouse - an awesome book, I've left in the page #'s from where I've done capacity calcs. Even so, a sanity check is very welcome! It's currently a bog-standard unvented system + system boiler that is scaled for the DHW only. You'll notice I'm one of the converted to @Nickfromwales's Hep 20 Manifold setup, though I'm not necessarily sure that the 2nd hot water at 48'C manifold is necessary for us. Principle question here is whether it's safe to pass the output of the UFH back to the main cylinder, or will that have to be discharged? We're unsure as to how we're going to supply heating however, whether we scale up the boiler / cylinder capacity, or whether we go via the ASHP or Solar Panels/Thermal Store. We're looking at ~2100 Watts for the UFH based on our heat losses during the winter here in Oxford. There'll be no other heating in the house save for some electrical UFH matts in the upstairs bathroom. ASHP with a good CoE running overnight to take advantage of the E7 scheme sounds grand, though we're concerned with the noise and another hole in our external wall for this. Could this be plummed directly into the UFH, or would a separate cylinder be needed to store the output? Solar Panels sound grand, but we're concerned the timing of the heating will be at odds with when we'll need to heat the floor. Also, the initial outlay appears quite steep so we'd likely need to install it retrospectively when we've the money. Scale up the Boiler to ~18kW to supply the UFH along with everything else FYI: I used MS Visio 2016 which has several Pipes & Valves stencil sets out of the box. Very useful! Heat Losses calculated thanks to @JSHarris's calculator.