JohnMo

Your build is basically the same size as ours. My opinion is the pipes all grouped together will make a hot area, I just deleted any loops on the hall and used the pipes going to the different rooms spread across the hall floor. Our hall is internal, so no outside walls, so takes no heating really. But it keeps the hall the temp as the rest of the house. So don't insulate use the heat to your benefit. If you operate as a single zone, no need for a buffer.

KISS, is really a single thermostat, no actuators, no manifold pump or mixer and no buffer. Then run the whole lot on either WC, or a modified version for batch charging the floor etc. But if you are keeping the zones, have a look at at Salus SQ610, fits a standard wall box, they look nice and lots of good fuctionality for UFH. It has built in control algorithm for UFH so it learns how to stop and start the heating to keep things stable. It needs the Salus ZigBee unit to function, but once commissioned there is no need to be internet connected but you can be if you want.

In Scotland, you explicit approval from SEPA to install a treatment plant and soak away. Full design details need to be submitted and approved. Just do a proper job, teeing off another pipe will just end up with you or the other person getting a dribble out of the tap, if the other runs their tap at the same time. If you want to build, do it properly or not at all.

Trouble with that rule of the plumbers thumb, the gas boiler is nearly always way too big for the property, in my case it was 11x too big for the max heating load. So it lived in short cycle mode, until I got the first gas bill and nearly fell over. I then added a 160L buffer to keep it happy.

If you really need a 15kW, which I very much doubt, unless you are doing a very poor quality build that doesn't comply with any regs. Then 28mm is way too small for a heat pump primary piping. Go on the heat geek site, they have section on heat pump pipe sizing, which should give a good steer.

Flow rate from combi boilers can be rubbish. The figure published is not a real UK figure, as it's based on a summer only rate, where incoming water is warmer. The UK models have a flow restriction added so it can cope with colder winter water incoming to the boiler. This reduces max flow rate all year. There are ways around it. Have a read of the attached. From real experience they work exceptionally well, I have one, as an eBay buy.Canetis-SuperFlow-Product-Sheet-WE-050318.pdfCombi-SuperFlow-White-Paper-v1-2-4.pdf

You would have a dark ugly house! Everyone would laugh at.

Lucky you, mines a nice new smart meter that cannot communicate. So I'm slowly moving towards E7.

We had similar issues in our last house, the diaphragm in the expansion had failed. The plumber should just replace like for like.

It certainly would.

The way I do is to force the nozzle into the gap, and slowly withdraw. Keep the flow rate nice and slow. Repeat. Spraying a mist of water make the foam expand more. Slow and steady. I never bother cleaning, just close the nozzle, so when you press the trigger nothing comes out. Do not remove the canister until it's empty. The next day any hard foam I just cut off with a knife.

All you need is a spray foam gun and spray foam. Fill the gaps, trim an hour or so later. Tape all the joints with aluminium tape.

Looks good, but get the gaps in the insulation foamed up and taped, while you have access. The gaps undo all the hard work being done.

So glazed is ok, so long as the rest of the house is improved, quite a bit. (Para 10.10)

Had a look at this early today and worked out I would need two very large radiators at dT5, and not enough space for that. If I go to dT10 I assume the UFH would be ok. Using reasonable heating kWh required and 3 days electric usage, the CoP looks to be averaging a little over 5.1, that's including all the electrical equipment used to heat the house (pumps, thermostats and valves) and all standby losses and the crankcase heater.

Tested the intelligent startup this morning, setting the start time early this morning. The overnight garden room temp set to 16 degs, the day time temp at 21 degs. The thick solid band is where the heater started to heat to 21, which was about 1.5hrs prior to its program to increase from 16 to 21 degrees. This should self learn and get closer to starting just in time to have the room temperature when we need it. Interesting is the amount of stop starts the heater does to keep the room temperature stable. A bigger view, based on the 1/2 hr usage in kWh. The calculation for heat loss, says I should have been using 430W and the electric input seems to back that up quite closely.

And more on the subject https://www.rehva.eu/rehva-journal/chapter/hybrid-heat-pumps-saving-energy-and-reducing-carbon-emissions

Government report from 2017 on the hybrid situation Hybrid_heat_pumps_Final_report-.pdf

Daft question, how does a fully glazed extension get anywhere near building regs, min insulation values?

Are you trying to make things more complex than they need to be. It looks like your flow temp is too high and the system needs balancing. What are the external probes bringing to the party?

As far as planning is concerned the room is designated the same as the garage. Have read up on here, it may point you in the right direction and you may be able to apply for something retrospectively https://www.fmb.org.uk/find-a-builder/ultimate-guides-to-home-renovation/garage-conversions-the-ultimate-guide.html#:~:text=Search-,Do I need planning permission%3F,to make a planning application.

yes Is this the first time you have use for heating? Or has it been in for a while an been ok before?

Yes a structural floor, as the house is built on a sand hill.

Is it short cycling? Tell us more about your system. Is there a buffer, if so how is it controlled or is just dumb, i.e. does have a thermostat going back to the controller or not? If you have a buffer the system is basically split into two system. The heat pump feeding the buffer, the buffer feeding the heating system. They will generally operate independent of each other if controlled by a thermostat. If you don't have a buffer how much of the system is open to the heat pump?

To argue the case you would possibly need to know why it's stated as a gym and not something else. For example do you have heating in the gym, is the floor and walls treated the same as the rest of the house? The issues you have is the drawing as presented,m, shows the external wall to built to the same spec as the garage, so not insulated. So it's more like a sub division of the garage, and not within the insulated envelope, like a normal internal room. To be classed as habitable room the walls and floor and ceiling or roof would all need to comply with building regs. Unfortunately as presented they look more like a garage not an internal room.