JohnMo

That's strange when I went into it, came up with my floor area, and all the U values and came up with a strange kW required. Refering to the SAP report the TER (target emissions rated) wasn't even as high as the quoted figures. It also stated I would need a new EPC, even though the one I have is only a year or so old.

Dream on, unless you do a massive coil and heat slowly over an hour or two, then you may get that. 3 to 3.5 is more normal.

Think you will struggle to get the heat transfer. The 16kW rating comes from flow temps circa 80 degs. The alternative to replacing the cylinder is to use a plate exchanger. One side goes to the heat pump. The other to the hot and cold tapping at bottom and top of cylinder. You would have a circulation pump suitable for DHW on the cylinder side. When you get a call for heat the heat pump starts and so does the circulation pump. The bigger the heat exchanger the better the CoP. So something like this https://beetbg.com/products/dhw-plate-loading-20xplate-kit

How do you know either until actually delivered and you have paid the import duty? Are really saving enough for the possible hassle you may have especially if you have issues?

When you need heat it unlikely the PV will produce much, especially in winter. Gas will cost you 5p per kWh, electric 25p. Even on the best tariff electric will still cost you more, it will also deplete a battery quickly. Effective depends on what criteria you apply, if you just want warm feet quickly electric, if you need to heat the room either. Efficient both the same really. Unless you consider cost to run - Cost gas about a 1/5th the price of standard rate electric.

Just tried the link Even though the full heat loss calculation in the SAP report says 3kW heat loss, the shrunkpunk says 8.7kW, no idea where it's getting that info from?

Doesn't mean you don't need to balance, that is still needed. Balancing is required to ensure each radiator works as it should, without that the water could just circulate through a single radiator, boiler gives you dT 20, but house is cold because you have bypassed most the radiators. Still not sure what you are trying to do?

In a new build SAP report there is an as built heat loss rate. So assuming the SAP is correct or near, you could use it quite easily. Mine after a bit of ping pong, correcting assumptions made, isn't far off. But judging most EPC reports I have done for previous houses, they are mostly rubbish in rubbish out. So wouldn't trust them at all.

dT is a combination of how much heat can be taken away compared to how much is being generated by the boiler. If your radiators can only transfer 4kW (dT between them and the room for example) and you are generating 16kW something has to give and it's dT. Reducing flow may cause the boiler to short cycle, increased flow will reduce dT. The lower the flow, more heat is extracted from the water flow for a given heat input. On the cylinder with a small coil and high flow rate your dT is always going to be small. Bottom line is what are you trying to achieve?

Really not seeing the difference, if the suns out battery will be charged after any usage that exceeds PV power. Battery does a full cycle every day. A few days per year, on a long day solar day, it may not do a full cycle, but they are not many. On Sunday when we had a good solar day PV stopped at 15:50 and then was on deplete mode and battery was down to 16% before being charged again. Interesting Sunsynk, actually have this feature of full load to the immersion built in to the their hybrid inverters.

Been there that failed also Correct So are you saying people shouldn't put the oven or kettle on either? The general situation is especially in winter is the battery is generally depleted over the evening from the 95%

Hence the cost. Maybe if immersion is keeping warm, then heat pump doesn't actually do anything.

Go around new housing estates, many houses are that size and smaller

That's bigger many new houses! And that's just the hall

From heat pump alone you should be getting a CoP of 3 or so for DHW. So if only heating for 30 mins a 6kW would be using 1.0kWh. if you are actually heating continuously by immersion your usage will be way higher. And lead to high energy usage and high running costs.

Really depends on heat pump size. A normal heating cycle for me with a 6kW heat pump is anywhere from 50 min to 1.5 hrs. Or @PhilT has a big heat pump and small cylinder?

I think Any house with two or more floors will always be cheaper and have a lower risk of escalating costs. The biggest unknown on all buildings projects is what you find when you start digging. 200m² single storey has twice the risk of hitting something expensive at foundation level, than a 100m² foundation for a 2 storey house. Other factors - form factor for heat losses, nearer a cube the better. Space usage, stairs take up space, but so do long corridors to get to the large footprint of single storey. So you are trading one for the other. Future proofing - single storey will always have easy access to bedrooms if stairs cannot be used. At the end of the day it's about what is right for the site, ours was single storey, long frontage and not very deep. Rubbish form factor, more expensive to heat. Has a long corridor. But great views from all rooms.

4.30am to 5.00am isn't long enough to enable a heat pump to heat a cylinder, unless it's very big heat pump. So I would suspect the immersion is kicking in if you are seeing high electricity usage and have plenty of hot water. I would get the instructions book out, or download if you don't have a copy. Heating once is ok, but I would give it 1 to 1.5 hours to heat - depending on water usage. Make sure the set temperature is 50 or below, to get a decent running cost. Make sure the immersion settings are off - this will depend on you risk (or perceived risk) to legionella, plenty of info on here, do a Google search. But key is you don't want it coming on during normal heating of cylinder. I heat once, and it's just enough for the day, I have heated twice and had lots of hot water, but cost more, did leave on all the time, that used loads of electricity.

Assume you have zero floor insulation? If so don't do it, you will spend more money heating other things and not the house.

Taken a long time to get head around it, didn't come that easy. A breakdown forced my hand. Next job is sort more diverted electric dumps, thinking about towel rads next. Ended up with a cylinder up to 73 degs, couldn't get it any hotter, and 14.5kWh in the floor.

Update Have now got the system fully automated, after a few iterations of home assistant automation. 2 diversions have been set, have a higher flow temp setup on ASHP which is selected via a shelly relay. So that clicks on if forecast temp minimum is below 9 deg, battery is above 96% and generating more than 500W, it runs for 20 minutes minimum and after stopped if battery is below 94%. And immersion similar to above but without weather forecast temperature requirements. Immersion gets the full 3kW instead of small amounts, so seems to get the water hot in no time. It has no time limits set just switches off when battery drops below 94%. So the way it runs, battery charged overnight, keeps house in energy until PV starts up, PV recharges battery to 97%, once there we start to use immersion or ASHP, if generation is enough it keeps going for as long as needed, or clicks of when battery hits 94% - repeat. Getting way less energy slipping past, making its way to the grid. Original PV diverter would only step in, once batteries fully charged and exporting above a set number of watts. Battery fully charged on E7 overnight. At 1pm we have generated 8.3kWh PV. 8kWh of heat added to floor via ASHP. 3.7kWh added to DHW - cylinder at 65 degs. Have had a cooked lunch And battery is sitting at 95% PV is generating 3.5kW. If you have a battery, a commercial PV diverter is not needed and isn't really that good at optimization of battery usage if you don't paid for export. Charging the floor doesn't seem to overheat the house, it does push back ASHP normally restarting on WC for many hours. DHW hasn't needed to be heated for a couple of days now, it's all being done via the immersion, which didn't happen very often before.

The loads imposed will be purely downwards and any sideways loading is taken by the cable ended. So all it's doing is limiting the downwards droop of the steel.

Are the isolation valves either side of the pump open? With pump on, do you see flow on the flow meters - behind pump. Your mixer valve - altering that, does it change anything?

Have exactly the same one. Built all our internal stud walls, exterior cladding, fences, clad pallet sheds and more besides, before I got round to changing the first blade. Have a smaller one also used that for cutting stone slips - with the correct cutting disc and coolant.

Sounds a lot of work and something you will never look at a month after moving in. Nice place for spiders to live.