SimonD

TBH, I don't really care whether the BCO will let something past, I care about the quality of the installation and how it can be serviced over time when necessary. This is explicitly allowed for in the regs guidance: "the bedding of any pipe and associated pipe joints in a closed system of underfloor space heating....in screed.....is generally acceptable if the pipes...etc. can be exposed by removing layers of screed. Pipe located in chase within a a solid floor are only generally permitted with heating pipes and should not be concreted in." So like I said the regs apply to pipe as fittings and they should not be installed below a solid floor at ground level - because we're talking about potable water and domestic hot water. If it's a new build then it takes a matter on minutes to install ducted pipework. The marginal cost is so small, there's no point even arguing about it. Which is what bemuses me here. A few months ago a customer of mine phone me about a leak where they'd got some emergency plumber in who had to dig out a whole load of concrete floor and in the end they had to get the original build in to take up a load more. This is a multi-million pound house. If they'd done it properly to begin with, the pipe could have been whipped out of the duct and replaced. Sh1t does happen.

Assuming that you have full load to your manifold and therefore lets say 30m from heat pump to manifold and 22mm copper pipe - assuming 5C delta T- will give you: Pressure drop of 9kPA (.92 Meters head) Flow rate of 0.191l/s (or approx 0.688m3/h) And a velocity of 0.61m/s This includes a 20% allowance for fittings and a water temperature of 35C (viscosity of water changes with temperature). With pipe sizing you don't really want to drop your velocity below the industry figure of 0.5m/s due to risk of debris settling in the pipework and you would do this if you used 28mm or 32mm MLCP. You could use 25 or 26mm MLCP and have roughly the same results as with the 22mm copper. This means that you could get away with 22mm copper and just make sure the nearly 1m head is okay with the rest of your system index circuit pressure drop and the pump residual head. It's so common for installers to think you need much bigger pipes. I've recently installed a 9kW heat pump (that can put out over 10kW) with a 25m long header to the house using 32mm MLCP and that's currently running a scop of 5.4. In this instance my header pressure drop is 1.1m head and flow rate of 0.8m/s well within the limits of the max 1 or 1.2 m/s maximum depending on which brand of MLCP used. Index circuit is just over 2m head with a pump with residual of 7m so really no problems at all. In your case, at 4kW the figures for 32mm MLCP would be: Velocity 0.36m/s Pressure drop 2.59kPa So even with 22mm copper you have some headroom if the heat pump can output more than 4kW and it'll save you a good few quid v 28mm.

Nick, the term "fitting" includes pipes! What I posted up includes reference to pipe too! FFS, I give up....🙄

Here are the regs. Really you need them ducted - you are after perfection after all 😉

So this is what I said earlier, which you may have missed: First, you need to confirm exactly what barrier pipe they're referring to. Is it the MPDE barrier pipe that is design for COLD water services, or are they merely referring to Hep20 or Polybutylene push-fit pipe. As a distinction for you. PEX is the push-fit pipe that has memory and it's a pain in the arse to work with. Polybutylene is the lay-flat type of pipe that has less memory, but memory still. Second, MDPE service pipes, including the barrier versions are design for cold supplier. Their specifications usually state: based upon a 50 year design life at 20˚C. Any increase above 20˚C will result in a reduction in the maximum allowable operating pressure or lifetime or possibly both. Polyethylene pipe systems should not be operated above 60˚C. Your intended purpose as I understand it is to carry domestic hot water in your kitchen. Therefore MDPE Barrier pipe is completely unsuitable for this. PEX and Polybutylene as well and MLCP (whether PEX or Pert) are tested to over 100C and are designed for hot water.

Yeah, pull the other one. You'll be swearing for a month of Sundays getting it straight and keeping it straight even if it is lay-flat. So you believe the marketing blurb of these but not the technical documentation for MLCP? Well, here you you go. As it's going to be in insulation, the 9mm thickness will be absolutely fine? What diameter would you like sir? 16 Blue and Red https://www.plumbingforless.co.uk/plumbing/unipress-mlcp/unipress-mlcp-pipe/unipress-50mtr-mlcp-16mmx2.0-9mm-red https://www.plumbingforless.co.uk/plumbing/unipress-mlcp/unipress-mlcp-pipe/unipress-50mtr-mlcp-16mmx2.0-9mm-blue 20 Blue and Red https://www.plumbingforless.co.uk/plumbing/unipress-mlcp/unipress-mlcp-pipe/unipress-50mtr-mlpipe-20mmx2.0-9mm-red https://www.plumbingforless.co.uk/plumbing/unipress-mlcp/unipress-mlcp-pipe/unipress-50mtr-mlpipe-20mmx2.0-9mm-blue Oh, and here you go, Wolseley, pipe in pipe Mlcp: https://www.wolseley.co.uk/product/uponor-mlc-insulated-pipe-13mm-25-x-25mm-50mtr-blue/ And it confirms that: This Uponor MLC 13mm, 2.5mm thick pipe-in-pipe is designed for integration into a building structure and can be safely covered with screed. Withdrawn without causing structural damage, this water regs compliant pipe-in-pipe is supplied in 50M lengths. Product features Suitable for hot and cold and heating systems Suitable for recirculation hot water systems PE-X material construction Meets BS EN 13501-1 Complies with water regulations 1999 Any decent plumbers merchant will be able to order some in from one of the multitude of manufacturers out there and the good thing is that it's often cheaper than standard plastic PEX of Polybutylene. But hey ho, go with your barrier pipe...even if the world is moving on.

It's in the Water Regulations:

No, it's only aimed at UFH because that's where we mainly use it in the UK. This stuff is used right across Europe from small domestic installations to huge industrial ones. Here's another articles (obviously with manufacturer input) about it: https://www.installeronline.co.uk/plumbing/multilayer-composite-piping-mlcp-what-installers-need-to-know/ https://www.cibsejournal.com/technical/smooth-operator-multi-layer-composite-pipes/ https://www.bdonline.co.uk/buildings-design-and-specification/lets-be-specific-mlcp-qa-with-james-griffiths-uponor/5126836.article https://www.uponor.com/en-gb/products/drinking-water-systems/innovative-projects-utilising-mlc-and-pex-pipes This product is not a bodge and it's not only for ufh.

Most installers do use app to do the calculations, so that's not necessarily a bad thing at all. Yeah, that's not good. If they're not doing zoning and what is called open-loop, this is a positive indication actually. Was that for the cylinder size? Yes, okay, that's lazy. They should talk to you. There are good and not so good bits to this. What you could do is send a message to the man at Renewable Heating Hub to see if they've got anyone on their database around you? https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/struggling-to-find-a-top-heat-pump-installer-we-can-connect-you-with-the-best-installers-in-the-uk/

So this is very much where we diverge Nick. I wouldn't let anyone near my house if they told me they'd design my system with their fingers in the air because they had so much experience. That's partly why I do what I do now. Now, everyone develops experience and knowledge so of course you get to know approximately what size pipes carry what loads etc. but you still have to back that up with the numbers. It's like a seasoned SE will know a lintel will take the load but they provide the calcs to confirm it under those specific circumstances. Every heating engineer needs to do the same. And the problem with rules of thumb is that over the years they diverge from reality through Chinese whispers and become useless and wrong - that's partly why people put in 30kW boilers into new builds when they don't need anything more than 6kW.

Oh, no, did it go that badly?

It's not about complex maths. None of the maths involved is complex. It's actually pretty straightforward and it's not about box ticking here. It's just about good old transfer of heat. If you've got a low energy build, lets say 30W/m2 at design outdoor temp, your mean water temp in a screed floor is going to be about 29C, now consider what that needs to be when you're at the average outdoor temp of 7C in England. The mean water temp requirement is then below the required floor temperature to even produce heat into the space because there's then no MW-AT difference and it'll probably below the minimum flow temp of the heat pump. You then have to rely on controls to switch flow on and off, which we all know is not the way to be running a heat pump. TBH finger in the wind look at it and call it, is exactly why we're in the situation we're in here in the UK, because very few heating engineers and possibly M&E Consultants are up to basic design and so many systems are shite and inefficient when they don't need to be. Just a bit of maths and thought is all that's needed at the early stage.

Congrats, must be an amazing feeling. I like the adjustable spot lights you've used, especially on the ceilings - what brand are they and where did you get them from?

Yes, so they should be telling you that they'll produce a heat loss calculation based on your drawings and the SAP report you have. Then you should get a figure of a total output for the heat pump and a report telling you the heat load of each room and that will feed into a design of the underfloor heating (UFH), radiators, fan coils etc. If you're going for UFH on its own or with fan coils, keep an ear out for if they ask about cooling too, as that could be very handy for you.

And yet the pipes are all still at 150mm and no variation between rooms. Whilst we have seen the design we don't know the heat losses the design is supposed to cater for. If this is a properly insulated house with low losses and in particular low down losses, the 150mm spacing is frankly silly, It'll end up overheating the house and then the installer will start telling them they need a 1000l buffer or something to prevent the heat pump from cycling when all the actuators start closing down and it all unravels from there. Instead they could do a proper job of UFH design. But show us the design numbers and I'll be open to correction! 😉

What are they talking about? Of course MVHR is taken into account in the designs and you can use whatever flow temperature you want as long as you can demonstrate in the design that the system provides the heat to heat the house properly. With MVHR you use the calculation methodology from SAP where the efficiency of the system is taken into account to calculate ventilation heat loss. This is really important because often ventilation losses make up more than the fabric losses. Where do these people come from? BTW I know this because I'm MCS Certified for design and installation of ASHP.

SAP is about calculating energy use not about sizing the actual heating system or emitters (Radiators / Underfloor Heating / etc) . But the new standards for heat loss and system design do use aspects of SAP (e.g. designed or measured air permeability). You do need a heat loss calc and system design.

I'm not sure what you mean? MLCP pipe is absolutely suitable for hot & cold supplies and at 13mm insulation thickness it's good enough for your purposes, but if it's exposed to external temperature it needs to be minimum 19mm insulation. Here is a link to maincor's technical brochure about MLCP: https://www.maincor.co.uk/wp-content/uploads/2022/02/Maincor-MLC-Pipe.pdf You can then also buy the pipes that are designed to be buried and are preinsulated and ducted as complete units, either with one pipe or 2. Here is maincor's sheet on that kind of pipe. https://www.maincor.co.uk/wp-content/uploads/2025/09/Maincor_AUSTROFLEX_2025_web.pdf The issue is that with water regulations you shouldn't really embedd the pipes unless you absolutely have to. So use some ducting and thread MLCP pipe through the ducting to the outlets. This is high quality stuff.

Okay, here's another link - 9 13 or 26mm insulation https://www.maincor.co.uk/pipe-systems/products/ or this: https://wavin.com/gb/p/f38c1cf7-cf05-4844-9e65-3529628340c8/tigris-pexcalpe-pins13bl-25x25-l25?systemId=C05_F001_S278 All manufacturers I will use from time to time.

Ah, yes, if no insulation below, then it's a problem. Oh, you do test me 😉 https://www.bes.co.uk/riifo-multilayer-pre-insulated-fire-rated-pipe-coil-16-x-2mm-x-100m-blue-27351/

I think you've just described properties in the opposite of the order most people put them in. Most people will think less about spending huge amounts of money on kitchens and bathrooms, but will then skimp on a heating system, unless it's a flashy column radiator..

It's fine for this kind of use as it's only to reduce heat transfer between pipes and not to insulate the pipes from external conditions. The MLCP insulation is usually 13mm which is in line with indoor pipe insulation. My assumption is the pipe in the OP will be well surrounded by the insulation being installed around them though?

I'm guessing the proposal is to lay all the water pipes in ducts? As Water Regulations does state that no fittings should be embedded in a floor or wall, but people do. I don't know what they're talking about regarding barrier pipe unless they're referring the plastic pipe that has an oxygen barrier as I see no need for the barrier pipe you're referring to - it's confusing. You can, however get pre insulated MLCP which is going to be easier to thread through the ducting, just do it before you introduce bends to make installation easier.

We're still 4, two teenage boys who disappear for an eternity when they have showers! But, with DHW there is actually a detailed calculation method which should be more accurate, but I doubt a lot of designers will spend the time completing those calcs. Now, for a moment I was about to respond on your question about the rethink, but I then wonder whether the industry really is that responsive? It's only taken them 9 years to implement a hybrid version of the 2017 standards....and even then they still haven't ratified the national annexes to the standard, so you can still, according to MCS just use BS EN 1283-1:2017 for your heat loss calcs, for example, and ignore the new CIBSE guide because MCS only require calcs to be to that standard. So still a bit of a mess, but a step in the right direction. It'll be interesting to see what the fallout will be because if I now update a design just completed for a customer, the airing cupboard is not going to fit a 400l cylinder!

I've just got my hands on a copy of the new edition of the domestic heating design guide and it's a major revision. Totally different approach to calculating ventilation heat losses, comprehensive tables for calculating floor perimeter to area ratios and then applying those with fabrics of up to 400mm insulation. And even new guidance on DHW cylinder sizing, which is probably the easiest to illustrate here. Typically the DHW cylinder size calcs use for heat pump training courses is either 45 x number of rooms + 40, or 45 x number of occupants x 40, so in our house we have 4 x 45+4= 220l so we had a 250l cylinder installed. The new CIBSE guide suggests that for our house/occupancy/bathrooms and storage temperature of 50 we should now, with 4 × bedrooms, 2 × bathrooms or 5 × bedrooms, 1 × bathroom (maximum occupants, 6 persons)according to their table have a minimum size of 577l. Now, we have no problem at all with hot water provision, but is this new sizing table taking things too far?