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Before specifying your kit, you need to go back to first principles. 1. On you heat pump size, don't just look at peak output at design outdoor temps. You need to also look at the unit's minimum modulation to see if it will run at your average outdoor temperatures with your heat loss at those temperatures. With a peak demand of 3.7kW you could be well below a lot of heat pump's minimum modulation, so check with the manufacturer, and if they can't give you the figure, go and find someone who does. 2. as has already been suggested, the value of a pre-plumbed cylinder is questionable, unless your doing this commercially and you save yourself a day or 2 in labour - sometimes worth the extra cost in headache time too. calculate the open system volume to determine whether you need to add more system volume using a volumiser Carefully consider your control strategy. If you're going to go for lots of zones, then a buffer is something that you're likely to need to help the system run efficiently (I know I'll get flamed but the actually decision between a buffer/no buffer is more nuanced than most people understand and they're not necessarily the no-no people seem to think they are). If you decide that you don't want lots of zones, or you have a couple of mixed zones on different curves, then you may not need it. As already mentioned, very carefully consider if you really want fan coils and ufh to be duplicated. It's not always the plumbing that's the issue but the control and whether your chosen system has adequate control to do this (even though the additional plumbing for fan coils can be significant if you want full cooling capacity from them because you may need condensate drainage as well as individual power outlets etc). But also consider whether UFH cooling would suffice and then as @ProDave said using ufh downstairs and fan coils upstairs where you're most likely to want the cooling too. Carefully consider your DHW sizing. The MCS size calculator is quite crude and for a family or 4 you'd get to something like 250l anyway, but the new CIBSE method is much more detailed based on taking some time to calculate draw off compared to likely consumption, lower storage temperatures etc. For example in my instance, MCS calc gives 220l requirement so a 250l cylinder. Using the CIBSE method recommends a 400l cylinder. As a basic calc you can use 45l per person plus 40l as a start.

Because with the eps suspended floor systems the slab kind of has to act as a raft on top of the eps. It can't just crack anywhere

Doh! You are correct. Sorry I think you mentioned that in a previous post. I was thinking this was a first floor.

If using a Panasonic, you don't need flexis and you don't need the feet, just bolt down to a slab, but feet are okay if you haven't got choice, or they sell a metal stand up frame. But also and more importantly, don't narrow down your choices on the DHW cylinder. Also, the Panasonic system by default use the DHW for defrost, although you can switch it to use the CH circuit, but DHW cylinder is a good way to deal with it. Heat pump cylinders from Gledhill have gone down a lot and ex. VAT are around £800 for a good family sized cylinder. For the sake of a few hundred, it's just not worth it long term with a direct. If you ever want to change, you're then talking either a new heat pump cylinder or a plate load kit and you've lost a lot of money compared to just going for an indirect cylinder to being with. Heat pump installations do require building regulations approval, which like with all things you can pay for through your BCO, or use an installer who's registered with a competent person scheme to do this. Is that over 12k after the grant or before it? And what heat pump and cylinder did they specify. And then what control system? See above, a 3-port diverter for your cylinder is about £100 and then you just need flow and return pipework to the cylinder, D2 and a sensor back to the heat pump. I don't think a direct cylinder is even a sensible option. Does the OP have family? What's the likely DHW use. For example, we're a family of 4 and have dhw on continuous top up, no schedule through the heat pump. Our dhw cost us a mere £129 for the last year using our average electricity cost, or it would be £220 if using our expensive rate of 30p/kWh I had some more thoughts but something else is distracting me now so forgot......

Thank you - it's a bungalow, and I've read (on this forum if memory serves me right) that unless you have 10cm PIR below UFH, all you're doing is heating up the floor void.

Sure, but if you do that you've still paid for the heat pump cylinder and all the valves/plumbing involved. You are not saving on installation this route.

Not really - design wise and plumbing wise the heat pump has to be capable of heating the water - but, of course, once installed, you can set the heat pump to heating only. We do this.

We're doing a Danwood build and the house goes up in about a week. Groundworks guys have all said they don't need power so my ideal would be to get the slab in, then bring the power up through it with a temporary cabinet on the slab. Once the house goes up I'd get rid of the cabinet. SP Energy are going to price the options up for me (well, I've asked them to!). The RPAs plus driveway dictates the trench routes so the distances I quoted are the actual trench distances involved. Without the RPAs it would be a lot simpler! I would imagine that my responsibility starts after the meter but it's a fair shout that the cable from meter to the house would still likely have to be larger than normal. Thinking about it, this would mean I better put a decent sized duct in. What comms are you thinking of? Not a thing I'd considered so I'm assuming I've missed something

Not sure this really makes sense in your situation but throwing it out there just in case: If you are thinking about putting thin polystyrene in the floor and boarding over it, then think about whether you could use one of the thin UFH products (pregrooved polystyrene that acts as a template for the pipes). That might solve your radiator issues (and generally UFH will be cheaper than buying a load of vertical rads). Important note is that the insulation layer is not thick enough for an external floor (would be very expensive to run), but if all you have below the floor is another habitable room then the small amount of insulation might not be a big deal. It would certainly solve the cold feet issue. The floor still won't be as good as a screeded ufh setup but everything is a compromise. The biggest issue in your case @tetris is likely that you want to do this quickly while living in the place and doing that with the floor might be tricky and certainly requires careful thought.

All I can really say is it has worked for us for the 9 years since we built it and moved in.

If you are a heavy hot water user (especially if that means you need to heat the water during expensive electricity hours) then heat pump will heating will likely win. But if, as John is, you are able to heat the water overnight (and potentially use solar to heat the water during the summer) then the install would be significantly simpler and cheaper using direct heating. This all assumes you are not getting the heatpump grant. If you want that you have no choice, you have to have the heatpump heat your water.

Yes, and it was as recommended by Hanson. Can't recall the exact mix, but pretty sure it was glass fibre strand.

I suspect for the longer run the DNO would size a larger cable, probably 95mm2 With an external joint to reduce to normal size to enter the meter box. What are you going to use for a building supply if you don't have an external kiosk and don't want a temporary building supply. It sounds like you want to wait until at least the shell is up then get the supply installed?

Worth asking SP Energy a few things before you pick. First, whether the 35m limit is measured along the actual cable route from their main to your cut out, because digging around root protection areas can add a lot to the real length. Second, what the quote difference is between a larger single phase cable and a three phase supply. Three phase only really earns its keep if you want big loads like multiple EV chargers, a large heat pump or an induction hob setup, otherwise a larger single phase cable is usually simpler and cheaper to run. On the meter, the real issue with a 50m run is voltage drop and who owns what, so ask where their responsibility ends and yours begins. If the meter sits in a kiosk and you run 20m of tails or armoured cable to the board, you will need to size that cable for voltage drop and the maximum demand, and your electrician needs to calculate it properly. Duct everything now while the trench is open, and add a spare duct for comms. If the kiosk is the only way to avoid damaging roots, a low profile one can be clad or screened with planting, but check the DNO rules on access first.

An UVC can be direct or indirect, so immersion or cylinder coil. A heat pump cylinder can deliver reported CoP of about 5 (Heat Geek Cylinder), we got a reported 3.6 most the time from our normal ASHP cylinder. But when you start to compare the actual electricity input, yes the immersion does consume more but surprisingly not a lot more. We were heating the cylinder twice per day and using about 2kWh per heat (4kWh a day on average), getting a CoP of 3 to 4. Doing it directly via immersion. I was doubtful so did a one test, dismissed it, then a month or so later did a longer test over about 4 day and then left it like that as I wasn't seeing much change in energy usage. The immersion is set to run twice per day it does one heat that takes an hour and other time the immersion comes on for 10 mins a couple of times over 3 hours. So I am using about 4kWhs, somes 5kWh. So really not that much difference in reality On E7 you have a 7 hour spell to heat your water and ideally heat the house, yes you can use the battery but most of the year you can heat the house in the 7 hours. But you will struggle to heat house and heat DHW in the same window with the heat pump. Doing one DHW per day on a small heat pump can take 1.5hrs and that is 1.5hrs less time for heating. Cost, a direct UVC cylinder is £5-600, it can be way smaller than a heat pump cylinder also. A basic heat pump cylinder is £1500 and heat geek ones start at £2500. That cost difference alone buys a lot of E7 electric.

Just trying to understand my options and implications around a 'long' connection from the main supply in the road to the house. Ideally, I want the meter inside the house in the technical room, and from the main supply in the road to that location will be around 50m. SP Energy have said that anything over 35m will require either 3-phase or a larger cable. I'm awaiting a quote on these, but is there any advantage of one over the other? The second option is to have an external kiosk housing the meter which would be at the side of the house and about 30-35m from the supply in the road. Due to root protection constraints we don't have much choice on location of this kiosk. From the kiosk to the distribution board in the technical room is around another 20m. We don't need a temporary site supply and we are quite tight on space at the side of the house where the kiosk would have to go so if I can get away without one I would do so. We had an external kiosk on our last build and I hated the fact it was there! So, what are your thoughts/views and is there anything else have I not considered?

Not steel. That is way ott. Your floor isn't structural or a waterproof tank. Why fibres at all? They are nasty to work with and are only for crack control which in your case is entirely cosmetic. I agree with all (?) the above. Walls in first. Insulation, pipes and screed follow. The downside is a day of cutting in the insulation to walls, and the cost of controls. Upside is a lifetime of temperature control to suit the room purpose, personal preferences, room aspect.... and running costs dropping accordingly. And no worries about screwing sole plates onto pipes, plus the walls will be easier to build and stronger.

You do have to pay more for hard-wearing, which will last years. If you don't mind the utility look then carpet tiles . In office quality they will last you out, and allow kids' wheely toys, and for any accidents, plasticine or damage, can be taken outside to clean. I have some salvaged from an office after 7 years of heavy use, used in a corridor, gym, workshop area. It is on an uninsulated concrete slab. I put an underlay of 10mm down first. The theoretical insulation (by U value) is low but much better than nothing, and the effect on feet comfort and warmth is significant.

With young kids carpet is so much more practical for playing on

Brilliant. Presume designer knew about ufh? Which fibres did you use think you can choose steel or others.

You can, it needs to be thermally poor, so not sure how it ends up feeling under foot, may feel and look like cheap carpet, but won't be? We have carpet in the bedrooms and the wife insisted on wool carpet, that does a really good job of killing the UFH output. We have oak floors in living room and a large rug - it all works fine

Mind you, for a 60sqm bedroom wing, I'm looking at about £1.2k for the styrofloor thing, or as little as £800 if I buy xps and chipboard separately... Appreciate this is not comparable to 10cm PIR, but will probably feel better than 2mm LVT glued to concrete. I imagine at the rate we're going, this time next year we'll be paying £800 for a tank of diesel. Biggest issue is the 4-6cm reduction in door height.

Why is this? The heat pump can heat hot water at at least 150% can it not? I do intend to use TOU and I have a quote for a great economy 7 rate and 32kwh of battery storage so I am hoping to make the system cheap to run. But I also intend to use the immersion element when it is expedient to do so. What is the advantage of a direct cylinder vs a typical UVC?

No, we stuck with 70mm but had the fibre reinforced mix.

Can you get carpet that works ok for ufh? I don't want a lounge room with hard flooring.