-rick-

Damn it! I really should have waited. Could've saved a load. Not sure if the TRVs are really worth it. I got two, partly for temperature sensing but they seem to add complexity and not sure the wiser interface makes managing them great. Link?

I think these two statements is the crux of my disconnect with your points. With all UFH there is a potential for a kinked/damaged pipe during install but once the floor is down and the pipes are known intact then I don't think there is anything to worry about with them. If gunk gets in they can be cleaned. If some lump of metal gets stuck in there then that loop can be isolated and a mildly corrosive liquid can be put through the loop to dissolve the metal. PEX is pretty much inert and as long as it's intact once the concrete sets you shouldn't have issues. (If the concrete moves sufficiently to cause problems then you have a bigger issue than the pipes). I know there have been issues with some other materials used in the past, but PEX has been standard for a long time now and it's properties are well known. I still don't see why you would want redundancy in terms of extra loops. To me this is violating the idea of keeping things simple. We see a lot of designs on here that only have a few loops. If you want to build in loop redundancy you either add one more loop, which if you have to isolate one loop would still leave quite a large area unheated which is not a satisfactory answer or lots of extra loops which pushes up costs quite a bit and maybe reduces overall efficiency. My argument is that a failed loop (post install) is a very low probability and in the event it does happen having extra loops doesn't really buy you much over just running the system with a higher flow rate/temperature to compensate, neither option would likely be satisfactory. *A failed loop at install time likely leads to a repair being made before the concrete has fully hardened and certainly before any finished floor surfaces are laid. Over 50 years you would likely be replacing the heat source and controls 3-5 times. Each time flushing the system of any build up. I'd argue that over the life of the pipes the overall efficiency is likely to increase as technology improves and the mechanical/control aspects are replaced with newer technology. There is a limit to the amount of heat you can put in a floor due to finishes but if you've designed for low and slow then there should be a very siginifcant margin that could be used to compensate for other issues at the cost of efficiency before that being a factor. It entirely depends on the layout of the property. The cost of installing a rad is likely lower than digging up the floor to fix a damaged loop and there are lower cost electric options.

Installation couldn't be simpler if you already have all the right wiring setup. I removed my old dumb Honeywell controller and re-wired the base and installed the new one, only to realise that the Honeywell base was exactly the same and I didn't need to rewire anything. Basic setup in the app is easy, two annoyances: 1. The base doesn't support 5G wifi and I had to re-enable 2.4G to have it connect (this is the older V1 model that is currently being replaced by a V2 - partly why prices are getting discounted - but the V2 is more expensive and is sold as a more comprehensive smart home hub rather than a heating system. I think the wifi is the only real limitation that affects me. 2. The way they setup scheduling is frustrating to edit. Currently my system is still not fully set up as I want to change over to opentherm for CH while keeping the HW at a higher temp*. Because of this I'm still running the system in manual mode without the advanced features. Turning off all the scheduled times was time consuming. * I'm not 100% sure I can fully use opentherm in my setup. I know it's supported with combis but with a S-plan system boiler I need to verify things. Unfortunatetly my installer really ballsed up the wiring and I'm not even running properly as S-Plan right now (there is one signal line to the boiler, not two) and thats before adding opentherm cabling. Royal Mail literally just rang my door and walked away before I could get to it with my delivery of stuff needed to change the wiring over. So guess I now get that delivery on Monday and will be able to report back how things go later in the week.

Tado seem to want to charge a subscription for their AI features. I've just got a Wiser system whose advanced features are entirely free (at least at the moment). Not had it long enough to recommend but suggest you at least look at it before comittiing. Screwfix are selling it at a discount right now (wish I'd seen it when I bought mine). https://www.screwfix.com/p/drayton-wiser-wireless-heating-1-channel-thermostat-control-kit-white/7785v

'Infrared' in this context is marketing nonsense. There is a point to exposed infrared emitters but you are going to bury these emitters underneath other surfaces so the infrared emission properties will be of the surface not this graphene nonsense. Any electric underfloor heating will be the same efficiency as these graphene ones and likely cost a lot less. Electric UFH mats are really cheap and theres no reason to pay more. Now, electric UFH is a pretty poor way to heat a space, especially if the floor and house isn't well insulated but if you are only installing it as a way to take the edge off cold tiles then its running costs should be manageable with the right controls (ie, timers to limit its use to short periods).

Impressive!

Would have thought you could load shift the hot water and bulk of heating, especially as you are targeting most usage during summer when heating less needed?

You've said stuff like this a few times and everytime I try to understand what you are getting at but I'm afriad I'm not really getting your point. In case it doesn't come across in the way I indend, the below is not having a go, just trying to understand your argument. The pipes buried in concrete (at least in low energy houses) are going to be able to cope with almost anything thrown at them and will last a very very long time.* A lot of what we discuss here is how to get the maximum efficiency out of a system and the theme here to achieve that is minimum controls, low water temperature, system on most of the time with weather compensation (a technology that has been standard in all heating systems in other countries for literally decades). Even if you add lots of fancy controls on top of the basic system, the fundamentals of the system are such that you should be able to remove those controls and still get a very functional system. Similarly, if the heat demand of the house increases then worst case you need to up the flow temperature in the pipes to compensate. Again, most of the designs talked about here for new builds are based on very low temperature heating. If you can output sufficient heat with the water in the pipes flowing at less than 30oC then if some cataclysimic climate change happened and suddenly we were all living in -20C then upping the temperature in the pipes to 40-45C should still be able to adequately heat the house. Obviously if people want to extend the house then any extension would need work, but thats no real difference to any other system. If you have a low and slow design the system shouldn't care too much where the walls are if they needed to be moved. I do think that any 'smart' stuff added to a house should always be removable while maintaining the basic function of the house. Maybe you lose convenience or a little efficiency, but things should still work. Again, in the vast majority of cases, the systems discussed here are of the type that could be removed without significantly reducing the basic function of the house. Therefore, it is easy to offer any future buyer of the property the option to have all smart systems removed before they complete any purchase. So these shouldn't have a negative impact on the price of the property. * Plastic pipes don't corrode and UFH systems should have much less metal in them overall reducing corrosion of other parts and build up of gunk. They can be flushed if there is a problem. Even in the unlikely event of the pipes developing a problem, retro fitting radiators or even electric heating to affected rooms would be unlikely to dramatically change the sale price of the house. I do see a concern about whether rafts can be relied on to last as long as traditional foundations, but this has nothing to do with UFH.

If you claimed a self-build CIL exemption for your build and move out before 3 years after completion you may become liable to pay CIL. It can be a lot of money so check this as well.

Lots of inverters (not all) come with a controllable relay output that can be used to signal things like excess energy available. Your Panasonic likely has an input that could be programmed to set a higher temperature when there is a signal present. So combining these two could likely do what you suggest without any extra geekiness. But still requires some set up and knowledge. Whether it’s worth doing vs doing the work to export and sell excess to the grid idk. A 3.6kw system with 5.6kw of panels should generate a decent amount of power that likely justifies the £250 charge to get export approval with Octopus (for a non MCS system).

A single inverter with two MPPTs will handle two strings with different condition (and importantly different voltages/number of panels).

The doc suggests a £2500 govt contribution to an overall £4500 cost so not free, just discounted. Bet their require MCS certification to do the install though so there goes your saving!

I don't think most people put anywhere near that much thought into their systems. We on this forum are not representative. I can see this happening, but not because the bulk of people have analysed the costs but through inertia. ie, "the boilers broken, lets just use the AC for now and decide what to do with the boiler later". They'll stick on the immersion for hot water and then forget about it.

Nothing in the doc that Simon posted suggests that the new A2A element requires removal or disabling of the old system. To me that seems like one of the biggest changes. In the end I suspect this change if stands as is likely means almost everyone just installs new A2A and uses the cooling but continues to use gas in winter (possibly less). Not sure how MCS will work with A2A stuff either. Most of the existing MCS contractor base is not f-gas and don't think there is much crossover to A/C installers.

Now show a modern equivalent mediteranian design. It will have large windows too (though also plenty of shading/overhangs most likely). Old houses has small windows because glass couldn't be manufactured in large sizes. Once large glazing panels became viable people everywhere wanted to use it with varying levels of solar gain mitigation, from brute force carbon intensive mechanical forms to passive approaches.