(a) downrate the delta T 50 output by the correction factor for your delta T. As you can see, a delta T of say 30, the output is just over half (0.513, or 51.3%) of the delta T 50 output. This is my preferred way of doing things, you have rows for each rad, one column has your delta T, which can be set by a reference to two cells containing the LWT/RWT (so the delta T cell has a formula, LWT - RWT), allowing you can adjust at will, and then another column for the rad's type and size, and then in a third column you do a lookup for that rad in the two tables in the screen grab, first lookup uses the rad type/size to lookup the delta T 50 output, and then the second lookup gets the correction factor for your delta T, and the you multiply the two together to get your rads output at your delta T, which you then compare to the room's heat loss, you can use conditional formatting to make it change from red to green when it is sufficient, and tweak as necessary. This method achieves accurate results that are specific to the particular rad.

(b) the other method is to use the inverse of the correction factor, the oversize factor, which tells you how much bigger your rad needs to be at your delta T. Again, using delta T 30 as an example, a rad that would be OK at delta T 50 needs to be almost twice as large (1.95 times larger) at delta T 30. I find this method clunky and less intuitive, and so use the output conversion factor method, but the oversize table itself is a useful reminder that ASHP systems generally need rads MUCH larger than fossil fuel system rads, typically by a factor of 2 of more.

(a) it is surprisingly effective, reducing U values from typically around 5 to around 2.5 W/m²K. It also greatly reduces condensation and somewhat reduces noise. Both the plastic sheet itself and the air gap it creates contribute to the insulation. The ideal air gap from a performance point of view is a moot point - as ever, authorities do not agree, and the calculations are far from straightforward eg larger air gaps may have better static performance, but end up shooting themselves in the foot because of convection currents. From my point of view, mounting the secondary glazing on the window frame, typically creating a 30 to 50mm air gap, is good enough. Even better ie lower U values are possible using specialist materials and fittings, but those are beyond my ken (and wallet).

(b) it significantly reduces draughts from old leaky window casements that are simply not sealable short of permanently injecting a high quality sealant, thereby making it impossible to open window  

(c) it can be used in listed buildings without needing listed building consent because it doesn't permanently alter the fabric of the building

(d) it can be removed for example in summer so the windows can be opened 

(e) DIY installation is possible, making it very affordable; alternatively there are firms that will fit it at a cost

If you are going to do it yourself, there are a number of considerations:

(a) there are a number of plastics that can be used, all with minor pros and cons. I used 3mm PETg cut to size by the supplier, widely available online. Having it cut to size by the supplier makes it easier to transport and it generally makes sure the edges and corners are cut square with a clean finish. When sizing the sheets, you need to allow an 1/8 inch margin (more is also of course OK), as PETg expands in warm weather  

(b) 3mm PETg up to about 1m² can be held in place by 12mm (1/2 inch) magnetic strip, larger sheets will need a wider magnetic strip. Larger sheets also start to get a bit more awkward to handle so if the window is large, and the frame allows it, ie there are landing places for the magnetic strip, divide the sheet into smaller panels. Almost all my windows are less than 1m² meaning in most cases a single sheet is fine. The magnetic strip comes in two rolls, in effect a North and a South pole, that will hold themselves together when in a particular alignment (out of alignment they repel). Both are adhesive backed, one gets stuck to the perimeter of the of the PETg sheet, the other to the window frame. The strips have a thin foam backing which, along with the flexibility of the sheet, allows it to adapt to minor irregularities in the frame, thereby achieving a reasonable seal, which is how secondary glazing helps reduce draughts. The backing foam is whitish in colour, and so blends in with a white painted window frame very well.

(c) I used an A4 paper size guillotine to cut the magnetic strip to length, making it easier (and quicker) to get square ends. The procedure is: (1) cut and fit the sheet side strips in place (2) cut and fit the frame side strip to the strip already on the sheet and then, and only then, with the strips in magnetic alignment with each other (3) peel off the protective strip from the frame strip and fit the sheet to the window. I used glaziers rubber suction cup glass holders to quite literally get a grip on the sheets, because there isn't room to get your fingers between the sheet and the window reveal. I also used temporary spacers to rest the sheet on at the bottom to get the sheet lined up and level (many of my windows are neither square not level)

(d) by a long way, by far the most time consuming part of the process for me is frame preparation. If the paint finish is less than perfect, it makes sense to redecorate, and if there is any rot or other damage, that needs cutting out and repairing first. Many of my windows clearly have lead based paint on them, making redecorating far from straightforward, and in some (most) cases any rot tends to affect the corners where there is exposed end grain, meaning repairs are also not straightforward, you need at least a modicum of woodworking tools and skills, which luckily I have. Often the frame is not square, and so extreme care is needed ensure you have a square 'bounding box' that your rectangular PETg cut sheet will fit ie be very careful when measuring up, to the extent of cutting a template in lining paper or whatever if not sure, to be sure the cut sizes you order will fit. Use a builder/roofer's square and spirit levels to keep things square and level. The other two snags are frames that have steps on their inner faces (maybe one side has a face or trim that protrudes a small distance, it may only be 1/8 inch, but that's an 1/8 inch too much) and window furniture that gets in the way of the PETg sheet. Both of these snags can be fixed using small packing pieces fitted to the frame before redecorating, and once the paint is on, they are invisible

(e) if all else fails, you can apparently use sharp hand tools to trim the PETg sheet. So far I haven't needed to do that, all the time spent measuring up has paid off (apart from the order in which all the cut panels were exactly 24mm undersize - for some bonkers reason I subtracted the width of the magnetic strip from the sheet before sending in the order, luckily it was only a small order). Think thrice, measure twice (and then twice again), cut once. 

All in all, somewhat fiddly and very time consuming work, but affordable and very worth while. Of course, if you can't or don't fancy doing it yourself, there are plenty of firms that will do it for you at a cost, no doubt some of them good, but others decidedly dodgy, so make sure if getting someone to do the work that they know what they are doing. You will in effect be dealing with double glazing sales people.

PS @editor - if you want to move this to its own place, that makes sense, but also leave a link to it here?                   

Would you mind providing details of the secondary glazing that you are installing, I think many others may find the information useful.

At the moment it looks like I can get a job lot of 600x1200 type 22's and stuff one of those in every room and 2 in the north facing lounge.

Many of the houses I can see from my windows are just like mine, small old stone cottages. They will all have exactly the same problems as I have had when they try to fit ASHPs. Many will be told by those who should know better there is no way an ASHP will work in their homes. As I said above, they can work, with compromises, and realistic expectations about energy usage, given old leaky buildings all other things being equal will always use more energy. 

I know you will know this, but others may not, if you have the choice, always go for the higher output rads. It gives you more options for running at lower LWTs. The constraints I had, limits to the practical size of rads that could be fitted, meant the system had to be designed to run at a high-ish LWT, with the efficiency penalties that entails. It is a heating system, and it just as important that the rads can deliver the heat to the room, as it is that the heat pump and circuitry can deliver the heat to the rads.   

Similar to our install, 1946 block/block construction with a 2" cavity, that has been blown. Double glazing, suspended timber floors and a chimney running up the middle (that if I had my way, would be removed and sealed up)... Old and leaky but typical of a lot of building stock.

Freedom toolkit gave us 6.6kW at -3 outside, heatpunk software gave us 4.8kW at -1.5 outside... A bit more rad sizing to do and I'll be cracking on next spring.

Apart from obviously needing a new heating system given my oil system was on the way out (after 25 years or more of use), and Argos type heaters had shown themselves to be expensive to run and not effective enough, and not wishing to spend ££££ on a fossil fuel system that in a few years time might look like something of a dinosaur, my main driver for going with an ASHP was to see whether one can work in an old leaky building. I think this matters, because a lot of our housing stock is old and leaky, maybe not as old and leaky as mine, but still not text book ASHP homes. If anyone is serious about installing a lot of ASHPs, then they have got to be made to work, and shown to work, in these less than ideal properties. My property is also listed, and that was another hurdle, no permitted developments for ASHP for listed buildings, so needed both planning permission and listed building consent. The later was a major factor is the choice of heat pump, most >10kW units are tall and narrow, but Midea's are short and wide, making them less visually intrusive.   

I did my research, and on paper there was no reason why an ASHP shouldn't work in an old building, but there would need to be compromises, eg higher end LWTs, and an acceptance that old leaky buildings are always going to lose more heat, and so will be more expensive to heat. But that applies whatever the fuel/system is in use. One possible positive which I hadn't spotted in advance is that, although the house takes a long time to warm up from cold, once it is up to temperature, the fabric acts as a huge heat sink/store, and that helps level out the temperature (most of the time, there have been some exceptions).

One thing I learned very early on in the process is that there are a lot of chancers and cowboys out there. I did my own heat loss calcs when I fitted central heating using a solid fuel boiler almost 40 years ago, and they got updated when I had an extension done (just before the building got listed!), so I know the basic principles, and it was obvious not all ASHP installers do proper calculations. There was also a huge variation in potential design solutions, from 'it can't be done' to over-complicated (and expensive) solutions to obviously inadequate solutions that used the old rads and an undersized heat pump. The installer I chose, as well as being helpful and accessible, was roughly in the middle, definitely not an outlier. I also had a prolonged and increasingly unpleasant experience with a LAD grant preferred installer which end up with me saying I would not let them within 10 miles of my property on pain of being shot on sight, and going back to my preferred installer.

It's still early days, and that matters because by and large my system has only been running in mild ambient temperatures, and I don't yet really have a proper feel for running costs, but from a heating and hot water point of view most of the time it is fine. The necessary caveats are I don't know whether it will be fine in colder weather (on paper it is borderline), and it does have periods of a few days up to a week when it just decides to run colder, maybe with rooms about 3 degrees below design temps. This has happened twice, once in the spring, probably linked to cold weather at the beginning of April, and once at the beginning of November, with no obvious explanation except possibly it was immediately after a period in which I was balancing the rads, maybe the Midea controller got confused. It wasn't the balancing itself, I went from valves fully open to closing them as needed to get rad temps and more importantly room temps balanced. I may also be in for a nasty kWh usage shock if when we get cold weather, I just don't know yet.

Sorry, rather a long answer to a simple question which I seem not to have answered!         

1. As the Samsung controller is currently stuck on my hot water tank it will need to be moved elsewhere and the cable is short. Can it be used wirelessly?

2. Is 'disconnecting' the Hive as simple as changing a setting on the Samsung controller to say its not using an external thermostat?

3. Does the Samsung have the ability to set a temperature schedule for different times of the day? I need it to be hotter in the evening (when the wife is home). At the moment I can't nosey around in that menu as it locks you out if you have an external thermostat set up.

If anyone has answers to be the above I would be very grateful.

One last thing, I did speak to the TADO support team at the time and they said that the TADO is not compatible with the Samsung MIM-03 controller.

Attached is the samsung gen6 manual as supplied by midsummer wholesale. Their installation instruction and wiring is more advanced than that from Joule/Freedom in that they talk about the primary pump being PWM (speed) controlled and show the settings needed to run the samsung controller as the room stat.

The freedom samsung gen6 videos that are floating around on youtube make passing mention of the PWM wiring to the pump but GH says in the video 'we played with this, it didn't work so ignore this wire'.

You'll need to remove the samsung controller from the front of the tank in the airing cupboard and fit it nicely somewhere downstairs. You can use the two core cable that's currently running the hive to connect the controller back to main PCB.

Yes, I'm pretty sure the gen6 controller will have a scheduling capability.

I should add, I'm an electronics engineer and this stuff doesn't phase me. If you're not technical and aren't happy working in and around your house electrics then please find someone who is.