JohnMo

In simple terms To get the grant the heat pump has to be capable of heating the house and got water at the lowest design temperature. So using easy number 3 kW heat demand, AND requiring 2 hours for DHW heating, that leaves 22 hours for heating. 3 x 24, is 72kWh. You now need to put 72kWh into the house in 22 hours. 72 divided by 22 is 3.3 kW. Now add your numbers to those and see what you come out with.

A quick look and the next size down is 8.5kW, so by the time you have allowed for DHW heating, it would be too small.

No - but is the output of the heat pump a your design outdoor temperature?

No way I would do a borehole without it. Never know what could come out the ground. Not sure I would be comfortable drinking the water without boiling it, without the UV.

I wouldn't put the condensate out the roof it really needs to be down a drain, it also needs a drin trap. Otherwise it will suck outside air in also, adding to the issues. I can spiral wound duct without insulation, not good. If the supply and extract flows are poorly balanced the flow temperature gets messed up, these figures should be within a degree.

My boiler in 2020 cost a £1000 in a pre COVID sale, around £400 off. In 2023 I swopped over to ASHP all self funded. The asap cost £1300, some other bits and pieces added to that cost, but not much. Running costs are cheaper than gas overall for me and I get summer cooling. Win win

I am currently running about 30% cheaper on ASHP, compared to gas boiler. When comparing all electric usage, to gas and electric. Battery and E7 helps, but neither would help with a gas boiler.

Me also, assume you UV treat and element changed annually, that wil kill anything anyway.

A copper tail - then convert

Get one with 3m2 Yes Not needed 2x 2 port one normal open one normally closed or 3 port diverter - not mid point Two ways balancing or amount of pipe in the floor, or a combination I use a Computherm Q20RF at 0.1 hysterisis and charge floor at a set temperature, not WC, once 0.5 degrees below target it switches the heat pump off. Run on E7 tariff. Download the Chofu manual and install as per their instructions not Grants, use their controller to control temperature - no need for any external controls.

If electric boiler is being proposed a well designed heat pump would cost a 1/3 to run. Storage heaters would be a better alternative to an electric boiler.

I assume you are talking gas, oil or LPG not electric?

Or these, cheaper than making them, just add screw as many sections together as you need. No need to reinvent the wheel. https://www.screwfix.com/p/reliance-valves-4-port-potable-water-manifold-15mm-x-3-4-/248TY?tc=TA5&gad_source=1&gclid=Cj0KCQjwwMqvBhCtARIsAIXsZpbeISzhvFO7hmEFMvAOeigrG2p8bINv9aaj4gLrCuFMPsFQidtZfR8aAhEmEALw_wcB&gclsrc=aw.ds

Been there got a t shirt. High temperature required, rubbish and avoid (mine had a further 150mm of insulation under it). Even with fantastic levels of floor insulation, your downwards heat loss is at least 20% more than radiators. With minimal insulation it becomes a money pit. Not really an issue, you really don't want to be zoning things to death. Boilers don't like it. Couple of things to consider Run a boiler the same as you would a heat pump, assuming you go that route. Have a boiler suitable for priority hot water or X plan. Your heating run at low temps with dT25 radiators and hot water production is at two different temperatures to get best efficiency out of the boiler. Use a heat pump UVC store water at 50 degs. Fast recovery through a big coil. Ventilation needs to be considered early. Especially if changing windows. Best in my head is dMEV with humidity activated trickle vents. A low wattage fan in each wet room running all the time with automatic boost based on humidity. Cheap to install only ventilates as required. Greenwood CV2GIP are good, silent and generally cheap of eBay.

Not sure in a domestic setting there is a legal requirement, but get the facts and do a risk assessment. We reheat our cylinder generally twice a day because we use the contents, not because we loose the heat. If you are consuming the cylinder contents daily there is zero risk. If you go away for a few weeks at a time, you may want to use a sterilisation program to keep you safe. If you have anyone with a weak immune system, avoid the risk use a sterilisation program. Not every case is the same, do the research make your own mind up. Commercial property is different.

Not really sure that is actually true. It's the stopping and starting that breaks machinery, steady running doesn't and never has. It's basically the changes in temperature of the moving of parts, breakdown of boundary lubrication as bearing parts start to lift and be supported by lubricant, that what kills mechanical equipment.

The heat loss test basically heats cylinder to 65 degs in a 20 deg room and maintains that temperature for 24 hrs and measures how much energy is required to keep it at 65 degs. But storing water at 45 to 50 your losses become really low. Reducing by around 50% for both cylinders. I would think the biggest difference to cylinder heat loss, is the piping install and insulation which is never mentioned or included in the heat loss figure. Store at a lower temp and don't worry about it. But some perspective the oso delta geo coil is £1800, my slim line cylinder was £1000. It would take 40 years of savings to make up the cost difference.

When I compared my boiler and ASHP install. If I had just installed the ASHP and not the boiler, my overall cost delta, would have been an additional £500 for the heat pump. No grants taken. New build, heating system and plumbing is the same cost, cylinder the same cost. So the only change for me was the cost of the ASHP over the boiler I purchased and some additional outside pipework. Shop around. You really don't need to pay Vaillant prices.

Do all your hot and cold in no bigger than 15mm, otherwise you will waiting for ever and a day for hot water. You don't need separate feeds, unlikely to use all three colds in the ensuite at the same time.

Because there is only 24 hours in a day. If you are heating DHW for say 3 hrs that leaves 21 hours. So instead of dividing by 24 you really need to divide by 21. Undersized is really as bad as oversized, especially if it starts trying to activate immersion heaters to help it cope. Quite like a Hybrid heat pump, smallest heat pump topped up by gas when you get the frequent defrost temp and below (about 3 degs and below).

If your fans not doing to the job and you need to dehumidifier. Your fan is rubbish and needs to be replaced. Cheap ones are cheap for a reason...our last house the builder installed cheap no brand intermittent extract fan and after the first year it would not hold a piece toilet roll in place running at full speed. My first port of call would be the extract fan. Greenwood CV2GIP are ace through wall or ducted.

For the renovation yes, or extension. Doing UFH correctly on a renovation so you get really low temps isn't easy and if you do the rest of the system flows at a different temp, so it a fudge, your heat source efficiency doesn't gain. Fan coils, set your flow temp at 35, your heating is sorted, set a heat pump at 12 to 15 and the cooling is sorted also. UFH will always include an additional chunk of downwards heat loss, that you don't get with radiators or fan coils. Example I have a floor U value of 0.09, so pretty good and the floor sits at around 23 to 24 during the heating season, with a room temp of 20, my downward heat loss automatically increases by 15 to 20% because of it.

You need to add the allowance for DHW heating also to the 3.08kW. Plus the 3.08kW is an average figure it doesn't account for the worst heat day or the design case, of around -3. So DHW will add 0.5kW and doubling up the consumption to allow for the coldest days gets you to, 6.7kW ball park. Now the bit missed by a lot of people, is every manufacture uses a different scale to size the marketing size of the heat pump. So you need to look at the technical datasheet for each specific heat pump and look at the max output at the coldest design day temp. Based on the above an 8kW at -3 het pump is close to what you need, but that's only a ball park, you real heat loss calculation to size correctly

Done plenty of experimentation with my house, tried Weather compensation etc.Find the cheapest to run by far is E7 tariff, run heat pump at 35 degs starting at around midnight then run until the thermostat says stop. The heating then stay off until the next start time of around midnight. Why that big on a new build? Are you sure you need that big, my 6kW is huge, and it only puts out 6kW max, the Vaillant puts out way more than 12kW when you read the specs.

Good for Australia, not so good here