JohnMo

Cylinder for a 4 bed do 250 to 300L 1. Unless mad set on UFH don't, do radiators with a design temp of 35. You will get push back from installers, but your running costs will be very good. 2. No 3. Wall mounted fan coils, these would give summer cooling as well as heating and smaller than 35 Deg radiators. But more expensive. A2A heating system (Aircon) would replace the whole wet system, but you would need to think about DHW heating as separate thing. 4. Costs Do not accept a system design that includes Glycol - it requires a higher flow temp and more pumping power to move it about the system compared to water. Buffer, volumiser is ok to achieve 20L water per kW output of heat pump. Thermostat in every room, so a zoned system - needs to be fully open single zone ideally. Third party control, need to manufactures controls only. Suspect most your plumbing will get replaced.

The most economical way to do hot water is to heat just before you need it, then reheat again only when you are likely to need it again. We are pretty consistent, wife showers in morning I do so at night. Hence my heating times, also both are in cheap rate periods. You can heat once per day, but you have a trickle of heat being lost all day, you also need a bigger cylinder. Heat just before you need it with a suitable sized cylinder, your daily standing losses drops as your cylinder spends most the time cooler.

Never seen the point of a sitting room, living room and a snug. From an energy perspective the form factor is rubbish - I did the same. So insulation needs to be way better than you think to compensate for the exposed walls and more roof area

And if you have PV export, just export and leave the heat pump to do DHW at a CoP of 3+. And leave the cost of the diverter in the bank

Mine went from 50 to 13 at the sensor, after the wife's shower this morning (15 to 20 mins) - high flow shower head doesn't help. I just set the times when no-one is likely to use hot water. Morning heat 5am and afternoon heat 2pm. The main advantage of pdhw is the two distinct running temperatures. I also tried to heat on demand, think it tried to heat cylinder 4 or 5 times in a day and used loads of energy. Reverted to timed slots the next day. A gas boiler depending settings can just ramp up to 70 to heat cylinder so you don't get the cooling effect of an ASHP. When I did hybrid DHW I set the boiler to ramp up slowly so it stayed in condensing mode as long as possible. Cylinder heating took 20 mins and boiler never went above 60 degs.

Difficult to answer really. But have attempted to above. No it's unlikely to happen your heat pump isn't going to be big enough to do unlimited hot water. Heat geek have their mini cylinders which will produce a steady flow of hot water enough to full a bath or a single shower on demand. They use a bypass valve to force ASHP to flow at a high temp before being added to cylinder, the cylinder is not an UVC it's more thermal store, small water content high coil size. But not sure I would risk it, I'm in the same boat as @marshian I would be carrying my head around the first time it didn't perform.

Maybe? But when you look at how the ASHP heats the cylinder it starts at the lowest temp it can, based on return temp. So if bottom of cylinder is 20 degs and top 45. Heat pump will flow at 25 (dT5) plus the temperature difference across the coil walls, so more like 30 degs, at the start of the heating cycle, then ramp up as return temp rises. So it's more dependant on the coil configuration, mine is a slimline cylinder and the coil runs from very bottom to nearly the top. Have thought about the bypass valve arrangement, but think it would kill CoP. Return water would also drop the flow temp as soon as the bypass opened.

I thought that until I tried it. Scheduled DHW heating at same time as a shower. As soon as the heat pump kicked in to heat cylinder, the hot water cylinder got churned up and the stratification went, so did the hot shower. That's heating via a coil not a PHE.

Does anyone really need unlimited hot water, maybe not, most likely not. They may think they do. 15 to 20 mins in a high flow shower can easily eat through 100L of hot water if stored at 45 to 50 degs. The hotter you store the less hot water you get through. So 400L would allow 4 long showers (just about). I'm normally done all I need to in under 5 mins. Wife nearer 20 mins. You can get a big cylinder, have waste water heat recovery, low flow shower heads. A combination of or all three. Heat it hotter is the other option. You can heat more than once per day. Big cylinders take a while to heat up, smaller one take less time. It's just a matter of balance to suit your circumstances. Not mentioned it yet, but as you brought up ASHP. Assume OP is a new build Gas fire - thought those stopped being installed in the 80s, who needs one in a new build. No-one. Cook by gas, just do LPG no gas standing charges. Or better still move to induction. Gas boiler - in this day and age, you need an ASHP, especially with all UFH. Size it right, SCoP of 4. Shop about, you can install a heat pump for the same, or close to the same cost as a decent gas boiler.

This why they state to get a heat pump close to the actual heat loss and with good modulation. Then the cycling reduces you get less standby losses etc. I've run gas boiler, hybrid and just ASHP only thing changed is the heating source. For us the cheapest is ASHP, by a considerate margin. We have PV, battery and use octopus cosy, so we are on average paying 13p to import electricity, get 15p to export, which at this time of the year, off sets import costs by about 50%. Add into the mix solar generated. So overall cost this week for all electric for the house was 2p per kWh. So already way cheaper than gas without taking into account the standing charges for gas, and CoP gain by ASHP. Obviously in the depths of winter PV is rubbish. But even so a CoP of 3, is still cheaper than gas, plus you are not paying a second standing charge.

Here is an copy of the weather compensation curves for our Atag boiler, can be run as low as 20 degs. This may be a boiler specifically designed for the UK market. Where S and Y plan are the norm. So it does CH and cylinder heating at a single flow temp. The cylinder is normally a small coil area, so rubbish heat transfer at low flow temperature. So to be able to run CH at low flow temps you need a boiler that runs two flow temps (like a combi) or a system boiler that is priority domestic hot water enabled. This can be a 4 pipe boiler or a system boiler set to X or W plan - not S or Y plan.

Quick google and its located here https://mcscertified.com/mcs-has-published-an-updated-version-of-mcs-020/ Interesting that the wording is somewhat different "Contractors shall be under a duty to ensure compliance with MCS 020 a) in relation to any installation carried out as permitted development. The MCS may impose penalties or sanctions if an MCS Contractor fails to ensure compliance with this Standard prior to undertaking an installation." It does not state the contractor has to be MCS cetified etc. Only is an MCS contractor sanctions will apply if you don't follow the rules. So following the exact wording - you need to follow the noise rules - but you do not need to be MCS certified - so anyone can comply you just do the certificate. Which I will do for install and file away.

That is correct for a non condensing boiler. It has been law that all replacement gas boilers are replaced with a condensing boiler since 2005 and oil boilers since 2007. So a non condensing boiler should no longer be able to be bought or installed. However nearly all new boilers are installed using the same mind set as a non condensing boiler. Even though the government at the spent millions on training. A condensing boiler has a heat exchanger in the flue gas stream, heating return water passes through the heat exchanger. The Flue gas is cooled. If the return water is below the flue gas dew point (53 degs) the flue gas releases water - moving from a gaseous state (steam) to water. This phase change releases energy (latent heat) which is utilised by the boiler to add efficiency. A boiler with big plumes of white smoke from the flue is running above condensing temperature. The white smoke is the water vapour escaping, with energy it carries. Efficiency drop 10 to 15%, compared to running as described above by @marshian. His flue gas will be invisible or almost.

Here you go 120L tank to support 2 showers

What is your heat source? What temp do you run at?

Used Travis and Perkins a few times and prices came from a random number generator. No rhyme or reason for for some if the prices. Started to use mkm after that - zero issues, consistent prices, nice friendly. Plenty of websites selling to self builders.

No one has permitted development rights, while you are under a planning notice. As they make the planning process meaningless. Suspect adding PV becomes a minor change

Simple way With UFH you need low flow temperature, so weather compensation is ideal. To get weather compensation you need to priority domestic hot water (so X or W plan). Definitely do not go the normal S or Y plan. To keep boiler happy and not short cycle you need to run zone fully open system. So switch your head off to multiple thermostats one will do. Cylinder choose a heat pump cylinder - yes a heat pump cylinder. It will have a 3m² coil so hot water recovery is quick. Boiler choose, Viessmann, Atag, Intergas. If you plumber looks blank at you when you ask for priority domestic hot water, get a different one, they won't do you any favours. @marshian will be able to tell you facts about figures on the reduction in gas consumption going this route. A other way to do hot water with a combi boiler is to have a pre heat cylinder. It moves away from the single shower situation and does DHW. Alfa boilers sell a stand alone cylinder, but Vaillant, Viessmann and others do storage combi boilers. This will give you never ending hot water and with an external sensor weather compensation - a simple solution. The important bit is look at min turn down rate, you don't want a boiler kicking out 12kW for a house that needs 4 or 5kW or less. 2 boilers - no

But isn't the OP a new build, UFH only on ground floor. So 6kW and below heat pump, 22mm pipe from ASHP to high kvs 3 port diverter, to cylinder and UFH manifold. Return pipes tee back together, decent low pressure drop filter (not a Y strainer or ball valve strainer), expansion vessel and PRV. Add a few isolation valves and drain point, fill with inhibited water, job done. Wouldn't even bother with anti freeze valves.

You would pay nearly that for a bog standard car battery. Similar offering from other companies many times more expensive. The battery is tiny compared to similar offering on eBay (150Ah version)

And a house full of the thermostats and short cycling boiler, that's using twice the energy it needs to. Then complain about the price of gas, while having a pint, down the pub. The way things used to be before I built a house.

I quite like these the Pro version https://uk.ecoflow.com/products/stream-ultra-pro?variant=50839891280211 Not the same from a price perspective, but plug and play, charge in a cheap tariff period. 1.92kWh and 1200W output. But just under £1000

A 100m² floor at 100mm thick holds about 5 to 5.5kWh energy for each Deg you raise it's temp. If the floor is warmer than the room this energy will pass into the room at a ratio of the room to floor dT. Run a 6kW heat pump for 4 hours, it will raise the floor temperature by just over 4 degs (100m2). It makes heat pump selection quite fluid, as long as you have around 20L of engaged water per min output kW of heat source you won't have any cycling issues. The floor is just a massive thermal store. You just need to brave don't listen to the people that have never experienced a thick screed. Plenty of people on here have and wouldn't change it.

Had a look at the notes and they were held in place with framing anchors. Thinking back we were supplied with enough to build several houses.

Our is currently at a lowly 23, heat pump selected to heat, a while ago, as I didn't need cooling. Circulation pump is on, floor dropped to 20.1 overnight, but is currently at 20.8, soaking up the free sunshine. Heat pump actually ran about 5 days ago as overnight it dropped to 4 degs after a dull wet day. It just looks after itself as @Nick Laslett says.