SimonD

Can you explain what you mean by this?

Yes, if there are significant heating inputs that are not measured by weather compensation alone, and/or if the occupant want some control in rooms such as bedroom. In our house, for example, we can have the triple glazing on the north face still covered in ice while the upstairs has already been heated to 23C by the sun. In this instance, even if the MW-AT delta T is such that the radiators then don't theoretically add heat into that space, it seems a bit silly not to modulate the heatpump using room temp feedback as the home heat load has reduced. In ours this is easily by 50%. The idea around room influence is that an internal thermostat provides input to the heatpump to modulate. This can also be achieved using TRVs on radiators without modulating the heatpump, or with electronic mixers. Most manufacturers will provide 1 or 2 of these room stats but companies like Stiebel Eltron can build a system with up to 6 and it also provides the ability to weight system control input between weather compensation and room. Nobody here is saying that a heatpump installed with open loop and weather compensation isn't the simplest solution. It's just that get a heating system to work for its occupants may NOT be that simple, especially in highly insulated homes. Room influence does not make the system more complex. It can infact make it simpler for both the occupant and the installer. Room influence does not necessarily shut down flow and therefore reduce system open volume, except for at the extremes. Zoning, using relay type controls is a different matter as this does reduced system open volume and therefore the system becomes more complex. For me the issue here is the understanding of controls, what they, do and how they work, and then when to implement them - but that's a headache for the whole industry right now which is still learning. But most good decent installers will go for open loop with some room influence baked into the system in current designs.

Unfortunately you can't do that. You must be MCS registered and be a verified BUS installer. Your 1st option must surely be to go back to the installer and instructs them to sort the application - again? I'm a bit bemused why they haven't just said they'd do that and instead argue with you - perhaps they're one of these companies in trouble who don't really know what they're doing?

Okay, quite rightly, you're very pissed off! And yes, it's cearly down to the installer - their responsibility and their probelm. What was the other partly reason?

The company should handle this. You should have received an email from OFGEM granting permission for them to deal with it. Installers will often ask for the relevant information, particularly self-build, before this so it can be provided to OFGEM for any assessment. Did this happen? When they say they haven't received the grant, why hasn't it been granted? OFGEM will usually ask for any additional information reuiqred, so they must be able to tell you. There is some small print that if a grant isn't accepted, the installer can come to the homeowner for the outstanding sums, but I'd expect a decent installer will communicate with you to tell you what exactly is going on. You could contact OFGEM but you will need your application ID which you should have received when you provided consent for the installer. Tel: 0330 053 2006

The MCS rules require any supply and install company to provide a quote minus the BUS grant so you can see that it has been given. The supply & install company, or their umbrella scheme will apply for the grant on your behalf. You'll get a message from OFGEM when they apply where you give consent for the application. As has already been mentioned. If you purchase supply only, you have to pay VAT for all materials and then you'll have to pay VAT on labour because it's not part of a supply and install under the MCS scheme. Best thing to do is find installers local to you, and even try the larger ones like Octopus, Aira, Heat Geek and get some prices - on Heat Geek's site you can get an estimate straight away to give you an idea of costs. Get some quotes and then you can look at the costs and compare. If you can find an umbrella scheme happy to do the MCS side of things for you, you'll most likely be paying something like £1000 plus VAT for the MCS/design stuff, plus another £400 or so for commissioning too. They will usually supply all the heatpump kit from their supplier at their markups, so again best to go out and get price comparisons. With some of these services, you won't see change from your BUS grant and you'll have to complete the installation yourself and probably pay for all required emitters on top.

Lets back up a bit - yes, the OP is about designing a simple UFH, which you can do with both gas and heat pumps and you can make them both efficient. Radiators are relevant because they need to be there in the design library because UFH may not always be the best option for the given situation, whether you like that or not. The reality is that every house is different, it has its own climate context and it has its own users, all of which play into the design of the heating system. I designed my first system just a little before you, which was for my own house. I designed it with UFH in mind and then changed to radiators for several reasons. Mine is currently on gas and will be a heatpump in the next month or so. I also chose not to go down the route of pure weather compensation, but have actually implemented 2 main zones with room influence using Opentherm. My system has actually been extremely efficient and has this year, for example, used about 5000kWh less than estimated at design and that's even with a thermal store on PDHW sitting at 75C at the top for dhw. It's still a simple system and needs some changes, but this is quite good. Without blowing my own trumpet, I found I had a knack for heating systems and now run my own business doing them. And one area I've made quite a lot of money from is fixing UFH systems to run efficiently, especially with gas boilers - so I have a little knowledge about how they work and don't work. One of the things you don't seem to be aware of is that room compensation in controls can apply just as much to UFH as it can to radiator systems. Many heatpump manufacturers provide built in room compensation within their controls, including Grant, Vaillant, Stiebel Eltron, to just name a few. This is because it works well in unison with weather compensation which can and does have some limitations. The room compensation provides, as I said, additional real-time data for the heatpump to modulate output. This isn't to say that your solution isn't valid - I've already acknowledge I understand what you've done and why. It's just that this isn't about being a one trick pony, but acknowledging that there are other solutions out there. Your experience with your gas system is unfortunate and a reality for many, but that doesn't meant to say that you can't design and implement a gas system with ufh that functions well and is efficient and can be simple. Same goes for heatpumps, of course! Even in your case, there is a limit to how much self-regulation there is in the system and how flexible it is because as you say, the response times of UFH particularly when sitting in a big slab, are pretty atronomical.

I know this is a debate between you and @Nickfromwales but I feel compelled to jump in on this because I think you are mistaken. System control is the biggest headache in heating systems. It's something I have struggled with in my place because of surprising and significant solar gains, even with triple glazing. It's the main reason I opted for radiators rather than ufh. I know you have settled for a system that runs low flow temperatures and you have balanced your system to take advantage of the self-regulating effect of those low temperatures, but there are so many other factors that play into whether a heating system actually delivers the heat to the right place and the right time in the house to prevent both over heating and under heating. I have always been a fan of using room influence together with weather compensation because it adds additional and necessary feedback into the system and this is especially important when you have highly insulated buildings because basic activities such as cooking can have such a dramatic effect on internal temperatures. Not to mention the issue of solar gain already mentioned. Thankfully manufacturers are awake to this with newer systems providing the options in both design and operation to commission the systems with pure weather compensation and/or room influence to allow better tuning together with better tunability in defining the weather comp curves. In my designs, and especially after completing all the heat geek training etc. I always design systems with the capacity to have room influence, especially within bedrooms and areas subject to heat input. Now, the problem with many room influence solutions on the market is the tendency for this to be relay rather than modulating, especially in underfloor heating systems. I believe that the way to go is through moderating the flow rates so you still, at least theoretically, maintain decent open volume and more subtle temperature control. But this is a difficult balance to find. Like @Nickfromwales, I'm also doing this commercially, so I have to cover my backside, especially because I'm taking design responsibility. It is very different if you have both the time, knowledge and resources to spend countless hours tinkering.

Interesting, I'll have a look at that. Thanks.

Don't, we'll have @Pocster in on this thread with you in a minute, but maybe as acting mod in waiting, he'll put it all straight again.

Ah, you're both using the wrong merchants. Grant's local rep was down a couple of weeks ago with boxes full of Gregs stuff, and there's a regular tray in some of the local merchants. Then there's the doughnuts just about everywhere on different days of the week. I reckon round here I could build a good pie chart of local food distribution to keep me happily fed 5 days and weeks. Mind you, I'd probably end up a lot bigger than I already am! I started with good intentions. I kept a box where I threw all my receipts and meant to put them in a spreadsheet. The box is still there by the door in the garage. In the end I just went along with how much money did we have left and how could I cost engineer every purchase. Then we ran out of money after the post Covid price inflation spike, (*cough* Brexit stupidity) and I just gave up. But honestly, it depends so much on building decisions and fit out etc. - e.g. I saved us about 35k by making the kitchen myself and it'll be about 50k by the time I'm done as I still have half of it to make, as that's what bespoke kitchens cost around here at the basic level. Are you properly self building or are you fully design and build, and have you got complex groundworks? As I went fabric first, that's so far taken up the majority of our costs.

I know he is and that we do, that's why I'm pulling his leg a bit 😊...just to highlight that the boiler is part of the overall mess up there and isn't just fine. The last installation I did in a loft was actually to put in a UVC a few months ago and I spent 2.5 days building a completely new raised platform to 1, allow for very thick insulation upgrade over the existing joists, and 2, provide a proper solid, wide and safe access to the new cylinder from the loft hatch, 3, properly distribute the new loads across a wide area of the existing joists - the first part of the platform next to where the cylinder was to sit was anchored to the wall with a wall plate too. The platform was built with osb floor panels and with an additional layer of plywood under the cylinder. Then it had proper lighting and all wiring and plumbing was completely out of the way to remove any trip hazards and all fully lagged. I thought I had a photo but can't seem to find it unfortunately. I tend to avoid loft installations like the plague but if there's absolutely no other choice then it's got to be properly boarded with safe access and I quote for this work or they can have someone else do it - otherwise I'm off tbh. The last boiler installation job I did involving a loft was to take a bloody combi out of the loft and reinstate a system boiler and UVC so the customers could have proper showers for the first time in 8 years having previously been conned into how good combi would be - especially when it sprang a leak in the hot water heat exchanger and flooded the house over 3 floors.

That's what I said too. And if that's not there, the boiler shouldn't be up there - it's not safe, so it's not fine to be there. And regardless of this, I think it's poor practise to put boilers in the loft full stop. Would you have installed it like that and would you work on it like that? I'll bet you a pint or two you wouldn't...😜

I disagree with you there Nick. Gas Safe updated its technical requirments back in 2024 and they read as follows: Access and lighting The homeowner should provide measures as a minimum for their own safety and so that gas engineers can work in a safe environment. There should be a permanent means of safe access to the appliance. For example, this could be a permanently fixed retractable ladder to enter and exit the loft, with a safety guard around the loft access, which should be secured to the building’s fabric. The strength and design of the ladder should be such as to maintain safety. There should also be adequate fixed lighting. The flooring area from the loft access to the boiler should be sufficient to allow access for normal use, servicing and maintenance, and should be extended to under and around the boiler. Consideration shall be given to a guard in order to prevent contact between stored articles and the boiler, its flue and pipework. If the floor is of combustible material and supports the boiler, a non-combustible insulating base at least 12mm thick should be directly under the boiler. The chosen location in the loft/roof space must be able to support the boiler’s weight once filled with water. https://registeredgasengineer.co.uk/technical/boilers-in-loft-spaces/ If a customer asked me to service or repair that boiler, I wouldn't go up there. It's a completely unsafe working space. Now, I've worked on boilers in pretty awkward lofts, taken a few and out & replaced one or two in the space, so I don't always insist on all the safety guards etc. but I do insist on proper boarding so I don't have to balance on joist or loose boards randomly chuck on the floor.

Shocking thread. And shocking they think they can wash their hands of it through their subby. I'd love to see a judge's face when they try to say it's nothing to do with them to fix it when they happily took your money and subbed it out without your knowledge or agreement. It's all down to them and they know it's going to be expensive as the work looks like a total bag of shite. The cylinder isn't even fully supported and they've only used chipboard - great structural support when that gets soggy. I also have to say your boiler shouldn't be up there and it should have been installed with proper loft boards across the access area as a minimum to allow for safe servicing and maintenance. The sad thing about these sorts of things is my sister had an issue with a window company who dragged their feet as much as they could and it took 6 years and a court appearance (and the company didn't even turn up) to get the situation resolved. It wasn't just the company but also their lawyers that were scumbags. I've been burned before and it's a horrible experience - you have my sympathies. Hope you have legal insurance or some access to legal advice?

That's a difficult one. Our WF has a reaction to fire classification of E but then becomes B-s1 Do when rendered. I guess the E risk factor is because WF contains paraffin. We're okay because it's rendered. It was at one point suggested that we batten and clad but obviously chose a different path. Haven't heard of cavity barriers for WF. As @Redbeard suggests, maybe a coating of thin coat render - you'd only need 6-8mm with mesh done in 2 coats and no need for the silicon top coat. Baumit or similar would be simple enough to get. But with ours the buildup details show clad with ventilation gap but no mention of cavity closers https://www.schneider-holz.com/en/products/insulation/multitherm-wood-fibre-insulation-board/multitherm-140/ Have you contacted the manufacturer's technical department?

Yes, heat will rise. There are a good few people on here who have chosen to only have UFH on the lower floor and none upstairs - so if your house is well insulation enough, this could very well be a better solution. It all depends on the heat loss of the house and what you want to design for - so unless you want to geek out on all this yourself, you need to have a good long chat with your designer.

Yeah, I might just have to do that. My other thought was if I could get something that works like the kitchen sink as we have no problems there. Good old ChatGPT - I ought to try that more often. I'll have a look at those! Ta!

I've got two different basins. One is Ideal Standard and the other is Ikea. The Ideal has a lever pop-up mechanism for the plug and the Ikea one is a pop-up. Both suffer from repeated and regular clogging up so I'm forever having to take them apart to manually clean out. I've basically had to remove the whole plug mechanism from the Ideal one in the ensuite so my wife isn't happy. I've never ever had this problem before so must be down to designs? Are Macalpines good and reliable - or is there another brand I could use instead? Ta!

I think the first question has to be: what do you consider to be huge? And how are these impacting the space? In my experience so far, which is now a few designs using radiators, is that it is far easier to design for 40C (45C if retrofit) on radiators than 35 and more so the higher the target room temperatures. It's basically down to the old law of diminishing returns. Remember that this is also done at the design outdoor temperature so for the majority of the year your flow temp is going to be lower. At the end of the day, if you can manage 40C on the rads, it'll still be a good efficient system, providing the rest of the system has been designed, installed and set up properly. Here's a good video illustrating savings with varing COPs If your house is going to be highly insulated, I would forget about trying to design for different temperatures as the house will even out overall. I still don't understand the logic behind the MCS/CIBSE temps at all as they don't hang together very well between design temperatures and operational temperatures in the real world. In my house, I've had to design for 23 in the space my wife wants the warmth as she really feels the cold. My wife wants the bedroom warm and toastie in the winter and 18-20 doesn't cut it. I wouldn't be allowed to compromise on comfort for the sake of a few quid during the winter. I'm currently upsizing all my bedroom radiators because when I designed the system for 18C we never really anticipated the usage of these rooms would change to being more like study spaces and even though the heating works as designed, it doesn't work for sitting still for long periods for my wife and the boys. In my house, which is a deep retrofit rather than new build, I've designed to 40C but managed to oversize the rads by an average of 25% which will theoretically give me something like 36-37 at design outdoor temperature. But also keep in mind that some air source heat pump controllers might not provide the granularity in the weather comp curve to set it to a specific flow temp at design outdoor temp and if the necessary curve sits too high, you'll have to use room influence - so it can be a careful balance. If you're likely to end up with solar gain in parts of the house, you also want to consider room influence controls. It does sound like you need to have a good conversation with the system designer (is this your plumber or are they using a design company?) to understand and agree the strategy here 18 is the design indoor temp and 17-19 is the operational design temp. All defined by CIBSE

And keep everything to standard, off the shelf sizes

That has got to be the best self-builder quote in a while! So if my budget is 1m and the estimated build cost is 1.2m, then definitely a tight budget..maybe too tight and certainly no room for cost shaving 😉 But on the op - that is a tight budget in today's building space and would require some very careful assessment in the high risk areas as already mentioned, but also in decisions all the way through the build with materials etc.

I'd double check your figures and especially the assumptions in your project in Heatpunk. I'm just completing a trial of another design tool which came up with over 10kW on a property I'd calculated at under 7 in default mode. I'm not a million miles from you and have a retrofit rather than newbuild which has ewi on existing walls and therefore only 0.21 u-value and some other compromises. Our house is larger than yours and we have 4.6kW losses. You really need to check the minimum output and compare it to your house w/k to understand demand at more average temperatures. I think you're running the risk of lots of short cycling. Also, is -5 really the design outdoor temperature for Devon?

That's a very good point. Most manufacturer's don't publish output inclusive of defrosting - Nibe do publish these figures and I think more are on the way due to pressure from installers and customers. Speaking with some other designers it's the fear of defrosting that often drives the addition of a buffer, but again manufacturers are getting to grips with this and will now give better guidance on minimum open volumes without buffer to deal with defrosting - even if it ain't rocket science to figure this out anyway. At least one start is we're seeing better specification of output figures at the relevant design temperatures rather than just at 2/35 or 7/35, for example. E.g. Grant Aerona 290 heat pumps stated output is the actual output at -5/55C so a bit more helpful.

I do wonder whether it's to do with rules. It's also more important as their climates are a bit more extreme compared to ours? Who knows. Nibe publishes the data right in the installers manual so it's easy to find.