sharpener

FWIW I received this comment from @mk1_manyesterday: "Air2heat highly rate Panasonic units especially the new R290 versions." They operate an MCS umbrella scheme and are in Shropshire.

I don't think we even had EPCs 20 years ago, this article says they were introduced on 1 August 2007. Michael Podesta's blog on predicting HP size from gas consumption dates from 2022, and the extension of the idea to EPCs first appeared yesterday AFAIK.

Do you have a reference for this? It was new to me. Yes. If for example you are looking at houses to buy they will have to show you (or you can look up) the EPC and from this you might then get a fair idea of HP size. As you also could using the Heat Geek cheat sheet. And then you could work out where it might be sited. (The installers who came yesterday are proposing a big Stiebel Eltron mounted over a passageway on wall brackets). But you cannot retrospectively ask for a year of weekly meter readings to be done, at most you might get quarterly gas bills and of course in that case the result would be more accurate than using the EPC.

The three that you have to extrapolate in this seem to be rather different from the first three so I would be a bit sceptical about using them but I suppose taking the median helps. I take it these are perhaps smallish ?terraced houses (or maybe bungalows) of identical floor area? In which case an HP of 0.4 x 5.9 = 2.4 kW sounds plausible, whereas your 1 does not.

Well clearly if you have got all the underlying data then it is of course better to use that in Jeremy's Spreadsheet or Heatpunk or Heat Engineer. I have been impressed by Michael Podesta's use of degree-days to calculate HP size from gas consumption. Essentially this method just estimates gas consumption from the EPC figures which can then be used to imply a certain HP size. The old GINO adage always applies, Garbage In Nonsense Out.

No, I think you have got the dimensions wrong, but I am not sure I follow yr calcs, the product is the HP size in kW not kWh.m2.Year-1. Don't know what yr 1.75 is. Should kWh.m2.Year-1 be m-2?

Mine issued 22/5/23 doesn't, in fact it does not have numbered sections at all. It just has (separate) estimates for total annual heat requirement in kWh like this: Estimated energy needed in this property is: • XXXXX kWh per year for heating • YYYY kWh per year for hot water I haven't been able to find an example online that looks exactly like mine. There are several links to this format which appears to date from 2012, however somewhere I read it was discontinued in 2017 so not a lot of help. Your method is fine @JohnMo so long as your EPC shows such a high level of detail, what date was the EPC survey done? Can you find a similar published example or could you post an anonymised extract so I can see what the relevant bit looks like?

Here is a thought-provoking result: Estimated Heat Pump size in kW = 0.4 x (Total EPC annual energy requirement in MWh) For the reasoning behind the formula see this post in Michael Podesta's blog. It would be interesting to know whether anyone on here has results which agree with it, or otherwise!

And when you draw the cables through also draw a second messenger so you have always got one in the duct for the next cable and so on...

and there is also this which I have taken from the HG site (though IIRC it was not originally theirs), the other significant axis is turnover rate. Personally I think the risk in domestic premises is vanishingly small. We use filtered and UV treated rainwater and even when we are away the PV keeps the tank at 55C all the time, so have never had a problem with it in 17 years.

Would that be 90 mins? Maybe the button is faulty or there is a loose connection having the same effect? But only on Mondays, no I am stumped, ask yourself what else (apart from the cleaner) is special about Mondays? Perhaps the button gets knocked when you get the clean sheets/towels out of the airing cupboard? Or bang it with the vacuum cleaner, I am grasping at straws now.

Could it be that your cleaner comes on Monday mornings and routinely boosts the immersion heater or something like that?

Yes but since the OP wants two zones he will mostly likely be fitting a VR71 wiring centre and this has 3 separate outputs for up to 3 zones in addition to the HW. So no relay needed in his case though I appreciate the advice was useful and intended more generally.

That's what might be inferred from this incredibly unhelpful piece of publicity material but AFAICS it will be entirely adequate when fitted with this H-box 12 or similar, this is the "third party control" referred to. The H-box does indeed have the voltage-free relay output you need, which is an OR-function of the individual room stat demands. As it says on that spec sheet, any one room stat will then be sufficient to call for the HP to run. So you just need to wire those two terminals to the FTC2BR, job done. The Mitsi instructions are very easy to follow and personally I would have no hesitation in tackling the wiring as a DIY. BTW I take it you mean a mechanical tempering valve on the manifold, not an electronic one which is unnecessary given you do not have any rads. Yes although @mk1_man is in some ways in a similar position I had worked out it was yr own thread.

Am no Mitsi expert but having read the FTC6 instructions in connection with this thread I had a quick look at the FTC2BR, it is what is packaged with the smaller Ecodans and I think should be sufficient for your purposes as you do not want to control multiple circuits or mixing valves for which the FTC6 is required. AFAICS it will do WC and accept a voltage-free input assuming that is what the Wunda Hbox setup provides. As many have said in the past the best approach is often to utilise the individual zone stats more as a high limit set to 22C or so and drive the whole house as a big open circuit (whether using WC or fixed temps). That way you can avoid using a buffer - subject to the total volume being sufficient for defrosting. The room stats can be trimmed down as a later adjustment to allow for solar gain or lower temps in bedrooms.

For a new system it's entirely reasonable. For retrofit less so but then if you have been told you need a new cyl then the odd valve is down in the noise. Many ppl seem to be against pre-plumbed, they are intended to be foolproof so fools can install them, but constrain the layout as all the ch flow has to go via the cyl location whether sensible or not. Fine if there is a central plant room but not good if the cyl is going in the loft. Also the Vaillant FB page has reports of poor quality control, no 100% end-of-line pressure testing and hence fittings leaking on arrival. Used to be made by OSO, maybe they have changed to a cheaper supplier? Gledhill ditto, reports of leaks and also rattling noises from inadequately supported coils. Recent Honeywell valves as well, reports of balls becoming detached.

Heat lost from the top of the slab is not wasted as it is within the thermal envelope, and to take @Tim S's recent example 37 tons of concrete beats any plausible amount of water even though it has only 1/4 the specific heat. Several ppl on here report good results, as mentioned below:

Octopus Cosy is well suited to this, you get 3 hrs overnight and another 3 hrs 1300-1600 which is ideal for a recharge before the evening peak. It will need some more modelling before I know if this is a better bet than Intelligent Octopus Go.

Because as @JamesPa says that was the deal to get early adopters to invest in PV. We paid £14k in 2011 which was a lot of money and would not have done it without the incentive. The breakeven point neglecting the cost of capital was 6 years which I think is about right. I worked for the DTI at one point and like many other government grant schemes this one was in part designed for political purposes and with hindsight could have been a lot better. In particular rewarding Total Generation not export has never made a lot of sense. And IMO it should never have been allowed on agricultural land when so many commercial and industrial roofs are still out there. Nevertheless I think it achieved its objective in that domestic PV is now commonplace.

Yes, thermal storage is defo much cheaper than batteries and I agree in principle, but as you demonstrate @Originaltwist you have to do it on a heroic scale for it to be truly worthwhile. We only have room for a 260 litre thermal store, the economics are analysed here but in brief you have to assume 20% inflation in electricity tariffs to get a 10 yr payback. I am planning on doing it as much as an interesting experiment as for its economic value. The other issue is that MCS installers are not used to thinking like this and in a sellers' market mostly want to throw in standard systems at maximum profit rip-off.

What about the sparky who has done the house wiring in yr new building, you must have a relationship there or is he one of the above? Or send a Building Notice to yr LA for £200 and then DIY, they will come and inspect the work later which should keep insurers happy and might forestall any major warranty problems. The IET On-site Guide has all you need to know. If the building has its own supply get the DNO to disconnect while you fit an isolator (or pay them to), then you can turn off the supply to work on it all in perfect safety. Presumably If you can fix up a temp supply to immersion htr you won't need much in the way of space heating until September, for emergencies we have kept 1 x convector heater and 2x fan heaters (inherited from two sets of parents!).

Well it does cover lots of options (inc how to cascade up to 6 units!). Maybe for the next candidate you should cut and paste just the bits he will need.

How about an industrial size louvred grille (like a Mapvent but bigger) or a slatted window shutter, or even a venetian blind as an experiment. Or make something out of treated wood.

Just had a read, the FTC6 manual is one of the best and most comprehensive I have seen and the diagrams for common system configurations are very easy to follow for both sparky and plumber. Should be no problem even for someone who is new to HPs.

I don't think something like the pic would cause unacceptable back pressure or harm the HP. Once the exhaust air is a bit mixed with the surrounding air it will disperse pretty quickly. I take it the pic is an example from somewhere else entirely.