SimonD

For radiation you need to ignore the air (as that can actually hinder radiative heating and cooling). It's the radiation of heat between different bodies. For UFH the warm floor radiates heat to our bodies and the surrounding walls/floors which then radiate the heat back into the space. A similar thing happens with cooling. When the floor temperature is reduced, the walls and ceilings, and our bodies radiate heat toward the colder surface. Hence we feel cooler (even if the air isn't necessarily any cooler). It's the same reason intermittent heat isn't very good for comfort because it heats the air not solid bodies so when the heating is turned off, it feels cold very quickly because the surfaces draw heat away from the body through radiation. Passive cooling using radiation can be very effective but it has to be carefully designed for cooling. If you happen to have the infrastructure, like UFH and your heat pump has the necessary controls/sensors for relative humidity and dew point calculation, then of course you can use it. I've had conversations with the tech people at a couple of large and well known heat pump manufacturers who, whilst they confirm the heat pumps do cooling, it's not like aircon, it will temper the room temperature. In many circumstances this is okay. And the other side is finding the design resources to do the cooling side properly - if heating using heat pumps is difficult, just imagine trying to find the knowledge and skill for cooling. And I'd argue that if there is any risk of condensation forming on pipes, then detailing the system is even more painstaking than insulating for heating.

Like I said: If you're going to run fan coils with a flow of 6C then be prepared not only for condensate drainage throughout, but also to very carefully lag all pipework through the house etc. So it's a lot of work to make sure the system is properly installed.

You're not far off. Cooling effectiveness of ASHP isn't that great, you may get a few degrees drop during the hottest days, so it might take the house from uncomfortably hot to okay, but that's about it. If you're in a position where you need to drop time, money and resources on infrastructure for an ASHP to do cooling, you're better of just getting a split a/c unit. I made that choice.

The MCS design and installation requirements are that the Heat Pump can provide all the heating/how water requirements, which does mean the unit has to be sized according to the heat loss, but that doesn't necessarily mean that your heat pump will be over-sized. Good design also makes sure that the heat pump can modulate down far enough to deal with typical temperatures without short cycling.

Difficult to say as there are issues with both and I wouldn't trust either of them. If you can bear the pain of re-inputting your data, you can use OpenHeatLoss.com (which I have developed) to complete a calc and design to current design standards. This also provides the ability to look at your ufh design in relation to heat loads etc. The only thing it doesn't do right now is Fan coil sizing

As an installer, I can tell you that many products aren't even designed for the sole benefit of the installer, but that of the manufacturer, so we have to fiddle around unnecessarily and deal with call backs, hence why you get to spend a long time finding the products you stick to. When you find the good ones you find they're for the benefit of both installer and customer.

Full RdSAP10 (from June 2026) construction library is now in the tool. It's under the U-value library similar to floor u-value calculator.

I'll need to think on this as the logical extension would be to add this function to all internal elements and party walls. It could be done by changing the workflow so that all rooms are added, like U-values, into a library and then the following the tab is elements - that way each element can be tagged for adjacent room and dT between those spaces calculated and auto applied. It would require quite a bit of change, but definitely worth mulling over.

Yes, I agree. That's all coming, but as an ancillary support doc/instruction videos with links from the app itself, rather than notes within the app itself. This is already there - it's a full EN 1264-2:2021 output calculator. If you input ufh into a room, when you go to emitter sizing, you can either import exiting UFH or Add New in there. You'll then see then full options available. This is currently so unusual, that yes, if I get a number of requests, I'll build it, but at present, it's on the back burner. This one is a bit of a difficult compromise. My original design did do auto save on blur, but when it was deployed to the cloud app server together with a linked database server, performance was not very good. I though there was too much lag, so lots of functions were re-scripted to calculated and produce local results for better ui/ux. The project doesn't need to be save constantly, just before closing the project of closing the browser. You can navigate between tabs and complete a whole project without actually clicking save, but for back up purposes I save when moving from one tab to the next, or when leaving the pc for a bit. Personally, I wanted to confirmation that the project has been saved when I clicked. This is probably more down to user instruction on when to save? In what sense? You can add your target design air permeability in the measured/tested tab - which could do with the addition of Design to the tab or associated note? Is this what you're referring to? Or something else?

I think you must live on a different planet, Nick. I see series plumbed all the time with absolutely no thought whatsoever. Plumbers (who do very good quality work) who mindlessly just go, 'oh it's unvented so that needs 22mm to the bathroom, bla, bla, bla. Show them a manifold and the tilt function goes into overdrive and they ask wtf? Yes, radial all the time for me. And just like you, rads should also be connected through a manifold - ideally with flow regulators

No, it doesn't. All it presents are long term disadvantages and dissatisfaction for you. Even with the immersion you appear to need to compromise, and even then, if you're reheating during the day, you've got a long reheat time at just 3kW, or you're having to deal with control between heat pump to a certain temp, and apply immersion over, but then you're better off just using the heatpump to max output. There are plenty of slimline cylinders to choose from and sometimes twin slimline cylinders can be made to work. Presuming that this is as little work as required, then this hardly sounds like zero disrupt prices with zero upgrades. What have they actually detailed in the quote? As a gas install comparison, the 6.2k you're talking about is probably enough to cover a boiler and cylinder installation, depending on where you live. Sounds to me that you have too many questions about their proposal, you need to speak to others to get comparative prices. If your job is this straightforward as you say, then the other big players plus an independent are worth speaking to.

Are they proposing to plate load the cylinder? Even then, as an MCS installer myself (with the full Heat Geek training) I'd be seriously suggesting a cylinder upgrade, especially given the existing one is 15 years old and having lived with high storage temps, and given you've got them in on BUS Grant and zero VAT now.

That's amazing, thank you very much. I totally understand where there needs to be better notation and explanation of the tool. The instructions are one of the next big steps. So too is a methods for importing measurements. I decided against Lidar as the kit is very expensive (if you don't already have the top of the range phones or tablets) and it's still a bit fiddly to work. So I'm working on a way to use bluetooth lazer measures that import into an app and can then export the data, but this may be some time. U-value data is being structured and imported as we speak, so maybe there by next week. And then next step will be the radiator library too. Noted on the links to room below or above as you have to hold that in mind quite carefully while inputting the data. I tried one other app that did this is a semi drawing/semi text way and it fuddled my mind - I found it even more difficult than without the facility, so need to give it some careful thought on implementation. But thanks again for your input.

Are you going for Zero disrupt? How many people is this cylinder serving and do you have any data yourself on hot water usage?

The Aerotherm 7kW catalogue output at -2 is 9kW and the heat loss calc is probably on the conservative side, so in theory, it's just about right. The only question to run by them is the known percentage of under performance by Vaillant units which could put you very close to the edge. You can have a geeky look at the data here: https://energy-stats.uk/vaillant-arotherm-performance-data/ But generally, you can trust Heat Geek designs especially if you're going through them and the performance assured route. If it doesn't perform, they will sort it out.