SimonD

Oh, it's great. I've got everything to basin/sink/toilet cystern on 10mm in my house, then just 15mm for everything else from a manifold. The 10mm completely negates the need for secondary return. When I offered to put in some 10mm for a customer having a new bathroom so they didn't have to use the excessive 22mm supply to the bathroom for their basin, the plumbers doing the bathroom install wouldn't have, telling them they had to have 22mm as it was coming from an unvented cylinder!

10mm, 15mm 20°C 60°C 80°C Easy-Lay PB - Horizontal 500mm 400mm 300mm - Vertical 800mm 600mm 500mm Has to be done if you're installing a gas boiler on PDHW. Still more than double the requirement of MLCP even at 20C flow temps and triple that at 60C Yeah, this is the general criticism you get from the super copper zealots of heat pump piping, and those making pretty videos on YouTube showing miles of lovely copper in the cavenous plant room, even regarding the Hep2o inserts. 😉 I always use the Hep2o inserts, even though I use Speedfit push-fit out of preference. I found out directly from a pipe manufacturer that as long as the pipe and fittings are to the correct standard, they're interchangeable. Hence I use Pipelife PB pipe as it has the same guarantee that Hep2o and Speedfit but it's half the price. I know some will say no-no to this but a lot of purchasing decisions are made thanks to clever marketing and companies wanting you to buy in to the entire eco-system, just like in tech. I just go by the principle of minimising fittings and using the natural capacity of the pipe to take bends - with MLCP it's a much easier task than both copper and PB/PEX. I have an MLCP ratchet hand bender which is compact and easy to use so makes this a really simple job - unlike with a copper pipe bender you can often use it in situe. So overall the pressure loss through the system is not a problem at all. The problem as I see it is more the lazy approach to plumbing you see so much nowadays. Recently I was asked by a customer why their cold water pressure was so rubbish and I opened up the cupboard in the utility where the rising main was only to find a silly circuit of 15mm pushfit with about 12 elbows and a handful of Tees to get the pipe going through a water softener. It's definitely requires a change of thinking about piping workflow, but I have to say I now wouldn't go back. Piping up a full system install with copper press-fit is just so much nicer, cleaner, less smelly, and quicker. The welding torch stays in the van unless it's an absolute emergency. Even with the odd cock up I've found resolving it is pretty quick and straight forwards - even when the system is wet and full of water. The trick is to do as much dry fitting as possible first and then go through the pressing. Well, I'm a relative newbie to the heating industry. I've only been in it about 5-6 years now. However, it's never sensible to develop your perspective based on one person. All I can say is that I have no doubts whatsoever about installing a new heatpump, unvented cylinder, pipe and radiator upgrades using MLCP safe in the knowledge that I won't get a callback due to a leak and that the system will perform as intended. But better to look at how much the stuff has been used in industrial settings and domestic settings throughout Europe for a very long time. I though it was interesting when I watched a technical heatpump video on heatpump system balancing and refining weather compensation curves that was filmed in Germany. Everything in the example plant room was in MLCP and not a single sign of a piece of copper.

In terms of redundancy, what exactly are you referring to? Is it to run extra loops in parallel - for example, if I need 300mm spacings, I add additional loops so that I essentially have 150mm spacings - or is it something else? I'd like to know more Gus as I'm keen to understand your perspective and reasoning for this. What are the thermal characteristics that are better and how is the system output controlled once it's in? I'm from the school of calculating heat load requirements in the room and designing emitters to satisfy this at a low temperature as possible and avoiding external controls as much as possible although I recognise and use room influence where needed. This approach does use the method of designing both radiators and ufh to the demand of each space. I'd like to understand more from your experience.

Obviously your flow rates & dt need looking, but also be very patient. I commissioned a new installation at the beginning of December that has very thick stone walls and had no heating for 3 months. Initially I thought I'd messed up the installation, but it's taken until the last week or so to find its balance. This is todays: This is what it looked like just after installation:

Yep, I have 100s of meters of the stuff in my store and it's very good. If I'm doing large installation work, MLCP and the fittings are what I pick up in preference of both push-fit plastic and copper. However, if I'm having to run new CH pipework through existing floors and joists, plastic layflat push-fit pipe is my choice as it's easier to work in these kinds of situations than MLCP. But in other situations it's not as good because it expands much more at high temperatures and the clipping distances are silly short - like 300mm on the horizontal - and it doesn't self support, so it sags. With MLCP clipping distances are over 1m and it has inherent stiffness and memory so when you bend it, it stays bent. Plastic doesn't stay bent but has a very annoying memory (even the layflat PB type) The big disadvantage with MLCP is that you typically need an expensive press-fit tool along with expensive jaws for each size of pipe you use. But you can now get manual press tools that are a lot cheaper and some manufacturers now have compression fittings available - I've even seen a German manufacturer with a push-fit fitting for MLCP but no sign of it over here. With MLCP you can also get pre-insulated pipes which save time and effort where you need insulated runs for the installation. Your other advantage with both plastic and mlcp is that you can run continuous lengths and minimise joints throughout the installation. Copper is very expensive now, requires lots of joints, and if you have runs in existing floors, it's just a pain. Even if it is pretty when first installed and polished, this tarnishes over time. Overall, with the brands I use, MLCP actually comes in at better value than plastic, believe it or not, and it has slightly reduced installation time overall even in retrofit jobs. What's also nice about MLCP is that you can dry fit all your joints without fixing them and then when you're ready go through it all with the press tool. Another small thing, that can sometimes be really important is that the sealing of MLCP is on the inside of the pipe. On plastic, it's on the outside, so you have to be careful you haven't damaged the surface of the pipe. With MLCP this isn't a problem. Since I've used MLCP I haven't had a single leak on an installation. That's more than I can say for copper and solder! And there's no hot works or stinky soldering!!!

Here is the technical sheet for Stelrad cast iron. There 4 column are about 100W mark per section at 760 high. 28968_Stelrad-HS_Cast-Iron-Column_Web-PDF.pdf

I gave that figure, which was chosen randomly, to provide an example of the difference in output of floor coverings for the same given MWT. This was to illustrate why you need to know what floor coverings you need. It was not in any way a suggestion of what you need. Yes, this is a good thing, but look at your chart. If indeed your output needs to be 17.8W/m2, the chart you use shows output with a screed floor with a covering of R0.1, this is the equivalent of 1 TOG carpet tiles or hardwoord flooring - so if you have tiles it will give more heat. You may have a problem here, because you can't run the heating system with a return temperature less than the room, so you're probably looking to reduce the heat output of these floors. Remember, your heat loss is calculated at an outdoor temperature of -3 to -4.6 in Somerset.

It depends on the control system, some of which are pretty advanced where you can specify which heat pump delivers what proportion of heating and how they share DHW demand. With Nibe systems you can even integrate ASHP with GSHP.

Ah, okay, I'll keep that in mind. Thanks. 🤣 What is the world coming to. I wonder if BH can cope...

No it doesn't skip over those bits of information, it provides you with the foundations for your design. Without it, you can't do any of the rest. The length of your pipework is actually irrelevant right now, that is just selected on the basis of pressure drop, not heat output. The heat output is given by the formula I provided. But in your design, you also need to know things like down losses, which is more involved than just knowing the thickness of your floor insulation because it depends on the proportion of external edges to floor area and the shape of the room. But it's not just down losses to the outside, it's also downloss in intermediate flooring because otherwise you can provide excess heat to the room downstair. And it's not just your floor downloss but the heat load of the room, which means you need your heat loss calculations. These will give you a required W/m2. Then you take the formula I gave you and you can calculated the average floor temperature and work back from there to determine mean water temperature and pipe spacing. What I gave you was a suggestion of book that provides you with a very easy way to determine what you need with simple nomographs - all you need to know is your pipe spacing, which you have on GF and the heat load in W/m2 and then you can find your mean water temperature for that system - it includes a standard screed and a spreaderplate. Or you can do it the other way round by selecting your mean water temperature and knowing your W/m2 requirement, you can find the pipe spacing. All you need to do is spent 25-30 pounds on the book and use a ruler. However, this just gives you a basic guide. You need to know your floor coverings why? Take a screed floor fairly standard covered with ceramic tiles a mean water temperature of 30C and target room temperature of 20C. With 150mm spacings the output of that floor will be about 55.5W/m2 and average floor surface temperature will be about 25.3C. If you instead had hardwood flooring you're looking at an output of 33 W/m2 and an average floor surface temp of 23.3C. As mentioned above, in some instances a resistant floor cover may give rise to greate down losses in intermediate floors. I work in the business and even though I have the industry guides to do the design so I can pull out the figures above, I still wouldn't sit down a do it myself because the UFH suppliers do the design for me and they have the software packages to do it. This is why you're not getting or finding a spreadsheet.

No, I haven't used the Ivar sets. It's good to know about these as a fallback - I'll investigate more! The weather compensation deals with it. The 'mixed' circuit just has different flow temperature parameters by setting min and maximum temperature in the controller and then this is adjusted as the whole house weather compensation does its magic. This has the advantage that the whole system remains open. But you can also set these things up to work based upon a set flow temperature with circuit always open, or with a room stat, or even have the circuit activated/deactivated based on the weather compensation curve or water temperature sensor.

TBH, on mine, if I lean forwards and go over a bump when my main boom is fully retracted, I almost get head butted by mine. I've been meaning to get new pins & bushes but like you say @ProDave it stll works fine, just with a good few clunks sometimes.

Normally what you would do is design the heating system to do this naturally. Each room would have its ufh output designed for the specific heat load - this means you might have different pipe spacing etc. The problem with a manual mixing valve is that it only works reliably with fixed flow temperatures, and many of them only really work well with high flow temperatures. They don't work well when you have modulation from the heat source that you will get with weather compensation. Using an electronic mixer is not the same as zoning, because you are not cutting flow to the zone, think of it as a heat area instead. What you're doing is controlling the constant flow of heat to that area, appropriate to its heating requirements. So, for example, on a cold day you might need a flow of 45C but on a mild day, it might be as little as 27C, depending on the house heating co-efficient (W/K). Therefore the house is still being treated as a single thermal envelope. The issue with target temperature is down to the floor buildup. If you have a buildup that has a higher TOG value, you need a higher flow temperature - and this may still be the case, even if your target room temperature is lower. None of us can answer this question because we know so little about the house design conditions. The reason we're suggesting a mixed circuit as a possibility is because you already have the existing one in place and we don't know anything about its design other than it's at 150mm spacings. We also don't know about the proposed design for the FF - is it going to be using speader plates, or is it screed too? There are so many variables you need to consider and then put together your FF design that complements the existing GF, then you'll be able to decide whether you actually need to have a mixed circuit or not. I think the whole mixer circuit thing was suggested as the alternative to hydraulic separation, not as a dictate about your design. So at the moment, if you're going to attempt the design yourself, spend your time learning about the design and then complete that process, including reverse engineering your existing UFH installation and go from there. Don't spend your time right now worrying about mixers. That will come later.

DM me if you want to. I've got 4 500mm ones taking up space - these are with 1" bsp elbows . If you want 750mm ones, then unvented components sell then uninsulated. Everyone seems to only sell them insulated now.

Both. Most of the new ones have pwm pumps. It's also useful to confirm minimum flow temperatures as some are 25C some are 20C, but in some cases this really doesn't matter.

Grant Aerona 290s are really straightforward for this, for example. You just order the installation pack with the mixer and then it's just a few wires in the wiring centre and then just wire in the temp sensor. You can also assign a room stat to that zone for room influence. The Grant, however, only has one weather compensation curve. As long as the open volume is sufficient, there should be no problems and no need for volumiser. My 6.5kW unit actually modulates down to 1.4kW

Just like I said, the heat pump controller is controlling the flow temperature of the 2nd zone with the mixer. It doesn't bypass the manifold, it regulates the mixing of flow and return water to provide the right heat input to the zone in question.

Not necessarily. If you're using spreader plates and then have carpet, the flow temp may actually be higher even with less heat load. It's all answered by the initial calculation and designs. The mixers aren't proportional or relay valves as such. They mix flow/return fluid to reduce the flow temperature of the system. So the strategy is not about controlling flow, it's about controlling system temperatures. Your system is then still one giant emitter.

You don't need separation. As @JohnMo says just a heatpump and controller that can deal with 2 zones using an electronic mixer.

If maths makes your brain hurt, the best thing you can do is just buy a copy of the CIPHE Low-temperature heating and hot water guide as it has a load of nomographs (see examples here) so all you need is a ruler and this gives you a good start. If you want to do the calcs yourself you can use this calculation here: Q (W/m2) = 8.92(Average Floor Surface Temperature - Room Temperature)1.1 But this is really just the start because to then calculate the Mean Water Temperature for that average floor temperature, you need to know the correction factors for both the screed and the floor coverings. Why is this important? Because if you have say a carpet, you might need a flow temp of 45C to give you 27C floor temp, but with another surface like LVT you might only need a flow temp of 37. This is really why you need the design documentation from the UFH company, but I know from experience that a lot of companies out there provides pants documentation, if any at all. One customer of mine used a company from Bristol when they were in a hurry and I was away and their company gave them diddly squat. I then repiped their system with hydraulic separation but left it there as I dind't want to take responsbility for a system I knew nothing about. Really, your plumber should also be able to take you through this, together with any references being used if you're going to tackle this yourself. But I have to say that nowadays, if I'm contacted by someone who has problems with their UFH and they've done it through the builder/plumber I usually walk away. Get yourself a decent UFH company to do a proper design for you.

I've seen it done with a dremmel. Or very carefully use a reciprocating saw. There's been once or twice in my time on other vehicles I've used a sharp pin to drive in behind a bushing to make it fold, but this obviously risks some damage to the surface and your bushing thickness may just make this impractical. I'm guessing you've got some kind of rig to bear the boom?

Indeed. Have you been there recently? The place is in almost as bad a state as we are, though at least they're now rebuilding, but last I saw it was causing some chaos.

Yes, absolutely. The Adia came to mind mostly because of the continuous monitoring and adapting of the heat pump output etc. as well as the additional pump. The customer wants monitoring of the system they can access and see. I'd sketched up a pipe system to first try it with the single pump and then if necessary switch to CCT with a small additional circulator should it be needed.

You want to look at Germany, but according to their figures, there's not a whole lot of difference with the rest of the EU. Courtesy of Bundesbank June 2025:

No worries, that's what we're here for I'm all for that. It's been my life experience in all contexts where I've worked, from global companies to individual athletes that the focus gravitates towards technical and tangible issues. Even when they open up to acknowledge the softer side of things they struggle and try to box them into tangibles like soft skills or psychological techniques. Psychology generally has its problems in that it for much of the time it tries to turn qualitative data in quantitative data, which of course is rubbish and undermines the findings and the field. It's a very difficult area to tackle but has to start within openly sharing experiences so everyone knows they're not alone in theirs.