Opinions wanted on the following ASHP decisions (specs at the bottom). Currently we have EWI and MVHR too recently to get accurate bill data so working from estimates. Planning to get it in within 3 months to avoid refilling oil tank (price has gone up 50% since 2021). Also getting new heating pipes since they are end of life and small microbore
(leaks keep happening). DHW uses immersion heater which will go.

1. Heat pump hot water cylinder of under 130L recommended by eco energy retrofit report but quotes all suggest 200-240L. We have 1 mixer shower and second shower may be mixer or electric. Which cylinder size is best - small or large? Is the large cylinder worth trying to use to store extra hot water as an alternative to a second battery for the solar PV we have planned? ASHP shift will move us 100% to electric and main heating need is daytime (I am housebound so always home, get cold fast and very little solar gain).

2. Cylinder location: no garage, can't use space boiler or current hot water cylinder currently use. Is it really really bad to use a bedroom alcove? Possibility covered by acoustic access panel and nicer boxing in. Another option is far end of kitchen but this crosses a doorway and it can't go under solid uninsulated flow - pipes would need to go in ceiling void above doorway then around corner and down - a long pipe run on coldest side of house.

3. See photo - could space 850mm x 450mm be used for cylinder? The 450mm wide is the frpnt, basically next to MVHR. Is there enough elbow room and plumbing room? If not would solar PV 2 inverters and 2 batteries fit here? Second inverter should apparently allow solar PV use during our very very frequent power cuts (30+ gets you a cheque from energy network company).

4. We would be looking at around 8kw solar PV and ASHP between 7.5 - 15 kwh plys obviously some stored hot water. We already use electric for hob and oven, if we have ASHP connected to solar PV with batteries are we going to have enough power to actually run the ASHP (colder temp ok)? This is for daytime since I am home all day, housebound and easily get cold.

5. Upstairs and downstairs zones for heating - any thoughts? Atypical use means lounge and downstairs office are used all day (I am housebound and get cold easily) and very very little solar gain. It seems daft to heat bedroom when it is empty. MVHR helps kitchen and bathroom temp a lot.

6. The Gulf Stream looks set to collapse or become dramatically unstable within the next 20 years.. causing Artic temperatures in the UK. We already have -10C several nights a year here. Is it worth getting the larger size of heat pjmp suggested (15kw) rather than 8-11 kw and will the larger size be environmentally much worse? Local experienced plumber always overspecs and suggested 15kw but is not familiar with our degree of insulation or MVHR and Internorm triple glazing. Aira also said the same. Others are in the 8-11kwh range. We have accurate plans (dwg) and accurate U values but energy needs are estimates (only 6 months since EWI and MVHR). Do small or large?

Basic details are
1830s stone house, 3 bed 2 bath, 150 sq m
Full repiping needed, microbore is at the end of its life and like spaghetti
loft 0.11-0.13 U, walls 0.60 U (EWI), MVHR in use
no floor insulation and too little head height for underfloor heating
Oil use should be approx 16,000 to 18,000kwh/year maybe less (from eco report) - because MVHR and triple glazing to near EnerPhit standards
Water heating 1,800 kwh/year - scrapping immersion heater

If you've got concerns over the reliability of your supply then maybe keep the oil boiler and go for a hybrid system with a small generator to keep the lights on and run the boiler indefinitely. Your own battery bank isn't going to last too long running a HP.

thanks all for the replues - I am still digesting them but have more clarity on some

Location - we can maybe fit the cylinder under the stairs (depends on heighy)/are actually (surprisingly) at the far end of the area set aside for possible future ensuite (or far end of kitchen which would be less flexible), still unsure of noise but the super large (1.5m tall) acoustic access panel we have elsewhere is good. This leaves MVHR room for solar (conveniently next to electrics).

Chat with engineer today told me MCS standards stays minimum cylinder size, and since we are thinking of Aira that means probably 250L all-in-one unit so 600mm x 670mm.

Heat pump quote from a few years ago was clearly calculated as 15kwh based on MCS calcs before EWI etc, checking recently its 7-10 kwh almost certaintly. Since the original quote was from full calculations (which we didnt keep a copy of hopefully this tine things will be lots clearer. We have exact plans from a survey including all ceiling heights so btu calculations can be done (I'm jumping ahead with guess work on my estimate above).

Looking at costings, looks like a dead cert to get solar PV at the same time due to its really good payback time - house wil be 100% electric by then. Just checking our consumption pattern from bills, it looks like a second battery for solarPV won't be worth it since we will be using all we generate for 6 months of the year. It wont be enough surplus to be using a second battery.

Yes walls are highish at U of 0.60 - 55mm of Diathonite Evolution - its vapour open and a big plus for the damp, could feel the difference before it was dry. One wall has less since it enchroaches on neighbour's.

Are heat geeks really that good? Any ballpark figure on what they charge? I saw that they were against zoning which concerned me with our atypical daytime usage.

Rads with TRVs are a poor substitute and the chance of a signal to all of them is pretty much zilch. A timer on rad may be some help but that takes away central control. And fancy TRVs are another thing to break and maintain Hmm..

Cheaper electric at off peak means needing a regular smart metre signal which is highly unlikely given location of meter, thickness of walls, terrible radio and 3G/4G signals. Everyone here is on same mobile provider but only some parts of house have a signal so we can't bank on that.

Floor insulation will be limited but we are going to try in 2 maybe 3 rooms, some floors are below ground level already and we have beams.

Posted By: stonecoldCheaper electric at off peak means needing a regular smart metre signal which is highly unlikely given location of meter, thickness of walls, terrible radio and 3G/4G signals. Everyone here is on same mobile provider but only some parts of house have a signal so we can't bank on that.

It's the supplier's problem to make suitable arrangements that ensure a good connection to the DCC. You don't need to worry about it.

@philedge checking into Newark cylinders helped me realize that I needed at least 10cm more width than I have or a really high ceiling rather than an unusually low one. Cylinders are cylindrical so they don't sell rectangular ones so I think we need to look at the loft space.

The gap between the wall with the door in it and the front of the MVHR unit turned out to be nearer 350mm... so no chance unless we knocked a wall out which is daft...

I wonder if there might be a little flexibility in the MCS standards, like there are in building regs based on what is practical in a 19th century house?

Posted By: stonecold@djh lol. It might be the supplier's problem but actually knowing how to sort it and bothering to do something about it is another matter entirely in this area.

Complain to the Ombudsman if the supplier isn't doing their job.

Re. TRVs - you might not need them - we don’t - use weather compensation + at least one indoor temp sensor, + if needed, a time program to reduce room temp nighttime. All this functionality is already in your ASHP’s control module. In fact, if you don’t have a buffer tank, then TRVs can be a problem - the heat pump might suffer from reduced flow issues if you have e.g. partially closed TRVs.