JamesPa

I have one fancoil in an otherwise all radiator/ASHP system, installed because I couldn't fit a radiator large enough in the available space. Its a wall mounted Mitsubishi Ilife 2 Slim, made in Italy (as are quite a high proportion of the available fancoils with stylish enclosures). Nice (but expensive) piece of kit capable of heating or cooling. There is a view that you can dispense with condensate drains if you keep the cooling flow temp above the dew point, which some heat pumps can do automatically. Obviously you get less cooling this way. Fan auto adjusts depending on load, so better to get a bigger model if fan noise matters (because fan will then be slower). Its audible, but quieter than eg my fridge. With 20:20 hindsight I wish Id fitted a couple more so I can get a decent amount of cooling. Hope that helps

That's indeed interesting. My contacts were about 18 months ago, perhaps they have changed?

I would check this directly with Mitsubishi tech support (who are very helpful). If it is the case, which I frankly doubt, don't use ecodan, seriously. "It's mandated by the manufacturer" is an excuse some installers use to do what they want to do for their benefit, not yours, knowing you are unlikely to check.

@timhowes Whatever else you do and whether you get a grant or not please do not: Get a buffer and more than one pump (including any pump in the outdoor unit). A 2 port volumiser in the flow is OK. Don't get or any other form of system separation, eg a phe or llh, between emitters and heat pump either. Get a massively oversized heat pump, unless your loss is say 3kW or less, in which case you have no choice and anyway it doesn't matter because of the low consumption. Get external controls (exception - those specifically designed for heat pumps IE havenwise, homely or adia) If you do any of these it's highly likely you will be back on this forum complaining about poor performance. The understanding and technology of heat pumps has moved on a lot in the past 5 years, sadly some installers haven't kept up and are still following outdated practices for their own benefit not the benefit of the householder. There are of course some specific circumstances where one or more elements of the above advice doesn't apply, but they are rare in domestic situations.

Why do you want buffers and 3 pumps? Unless your house is very unusual no buffering and one pump (often included in the heat pump itself) is the way to go assuming you don't want to increase running costs by 15% or more for no benefit to anyone other than the installer. Also no fancy controls unless specifically designed for heat pumps (which currently means only homely, adia or havenwise sofaik). The bus can save money certainly, but not if you accept unnecessary components and/or a grossly oversized heat pump because any installation savings will quickly be consumed by increased running cost. My personal advice is take the bus, but not at the expense of being saddled with the wrong system. Shop around!

You won't do the second but you can avoid the oversizing (well I did anyway). In brief. I had two full three hour surveys done both getting to 16kW. Fortunately I paid only for one. My own calculations using mcs assumptions got to 10.5kW. Difference accounted for by double counting of room to room losses and the fact the surveys ignored fabric upgrades that I made a point of telling them about. Measured loss based on 2years of smart meter readings (gas boiler) is 7kW, difference accounted for by air change rate assumptions. I found 2 installers who would use my readings to infer a lower ACH than MCS default, both anyway believe ACH is often overestimated. They aren't alone, I have since heard several installers make this observation. Result was 7kW Valiant installed by mcs installer, bus grant claimed, heat pump capacity matches actual house loss. In my second round of seeking quotes I provided the evidence of measured loss up front and also told them I wouldn't accept anything bigger (and also that I wouldn't accept any system separation). That filtered out the grant harvesters and left those who genuinely want to do the right job. I ended up with a local installer on Vaullants approved list (obviously other manufacturers also have approved lists, but by the time I got to this point I had pretty much decided on Vaillant). He was already very sensible but possibly recognised he might learn a bit from the experience. My second option was someone more distant but totally switched on, he didn't get the job solely because of distance, but nevertheless I would recommend them.

Eon didn't ask me for proof of ev ownership or even the model, and doesn't require you the have a dedicated EV charger (IE the eon rules allow you to charge from a 13A socket). Can they tell the difference between your battery and a battery on wheels? will they bother?

For me (no battery, ev, ashp, pv) I can't better eon next drive and eon export. 7hrs at 6.7p, the rest very slightly more than the best fixed rate without tou. 16.5p export. So I charge the EV, do the washing and washing up, heat the dhw and bake bread at night whatever the season as the revenue from export exceeds the cost of nighttime import. This has the distinct advantage that it's simple to manage (like the one you are on). I don't even need a smart ev charger, just a 13A EV rated socket. With a battery and no EV I think I'd end up doing the same, but I can't make the business case for a battery work. I did a spreadsheet comparing the various options. The differences between the various tou tariffs weren't that large by comparison to not having a tou tariff at all, and the simplicity meant I didn't need any smarts other than the smart meter. Of course the numbers will depend on your own usage.

I went through this loop (being quoted a silly price to remove gas), albeit with a community centre (so possibly classed as commercial) not a house. In the end the gas pipe stayed in place for a couple of years until we could conveniently change 'supplier' to one who would remove it all for free (BG I think). Crazy I know but in the end it was removed and we didnt pay a penny.

On paper, but many houses need circulation pipes, radiators replaced, My list was the things that (judging by what we hear here and on other forums) generally go wrong and mess up the performance, not a recipe for the whole installation. Fixing these is simple and my point is - why do we make excuses for the industry and try to shift the blame for the piss-poor performance of some to government, particularly given the farce of the condensing boiler roll out that the industry foisted on us. With a lower electric price, why wouldn't all the above stay in place, except 45 Deg. The lower unit cost allows the 45 degs to become higher, you can run a wider dT on heat pump and still have tolerable running costs. Completely agree. In fact I have long advocated engineering a modest reduction in the electricity/gas price ratio so that designing for (eg) 55C is possible from a running cost standpoint, and still offering a 45C design as a value-add cost saving upgrade. I have also long advocated reusing existing DHW tanks where there is one (again offering a new tank as a value add upgrade), NOT needlessly replacing pipework and generally simplifying rather than insisting on the gold plated (but sadly not always gold standard) approach we currently have. Finally I have long advocated allowing unvented DHW tanks heated by ASHPs and with an external (not internal) element to have external protection instead of the D1/D2 vent arrangement, a change in practice (not regulation - this can be done within existing rules) which would cut half a day or more off an installation in many cases. These changes alone could significantly reduce install time and disruption, with value added upgrades offered if the householder wants them, However I have been consistently shouted down on all of these ideas, with few practical alternative ones proposed. However to achieve 5p/kWh (suggested upthread) is unrealistic in terms of the subsidy it requires, and unnecessary. Perhaps a good compromise might be to (a) shift the policy costs from electricity to gas (its madness that electricity users pay for green policies) and (b) offer a limited subsidy for say 10 years for electricity consumed for heating by ashp (maybe instead of the grant). The risk of course is that just encourages the industry to deliver installations that perform even more poorly. That fundamental still needs fixing. not excusing, IMHO.

Ohh .. I remember having to do that - convince my time served boss that he needed to change work practices. Various occasions come to mind, but most memorably the novel idea that staff (in a technology company!) should be offered computers so that they didn't have to write long articles out by hand (and literally 'cut' and 'paste' when they wanted to revise), all for a secretary to type. It probably didn't help that he was in a relationship with the secretary!

To halve the price of electricity would, at present, require taxpayer subsidy @JohnMo - it doesn't remove the subsidy it just shifts it. And where is the evidence that our electricity prices are 'the most expensive in Europe', thats certainly not the case if you believe Eurostat. @marshian is right. Why are we even talking about tolerating unnecessarily poor installations when its SO simple, in most cases, to do it right: NO system separation, RIGHT size, design for 45C or less, NO external controls other than TRVs in the bedrooms if you insist (with, if you wish, Homely/Havenwise or the like specifically designed for heat pumps), adjust the WC properly = SCOP 4, job done! If you also tell the homeowner to get a sensible tariff, they will likely be quids in. Surely we aren't going to use the fact that we totally messed up condensing boilers as an excuse to mess up heat pumps (and then deflect the blame from industry failings to the government), or are some parts of the the industry (I say some parts because there are clearly a fair few good installers out there) really that piss-poor, that lacking in conscience and that unable to learn from its own mistakes? If the MCS closed shop cant make it happen right, scrap them and let competition sort it out. I do agree that a readjustment of gas vs electricity prices is needed, but please lets not use that as an excuse to tolerate continued industry incompetence. Time for the industry and its acolytes to cut the crap excuses and get its house in order. Early mistakes are excusable but domestic heat pumps have now been around for long enough for the 'professionals' to work out what to do, so JFDI or get out.

Im presuming this comment is intended to be funny and/or a poke at incompetent installers, in which case well said. If not then i must apologise that i dont understand it, so perhaps you could clarify?

Definite no here. Having just retrofitted an ASHP to my 1930s house there is no way I would bother with gas in a new build. Its cheaper to run by about 20%, much more comfortable (because there are fewer thermal gradients due to the way it works) and can do cooling as well as heating. Whats not to like? Incidentally, ignore the people who falsely claim that hydrogen heating is the way forward. Hydrogen does have a place but not for domestic heating, its for applications where there isnt an alternative. There is a very simple reason for this - to be green (which is the argument for swapping to it in the first place) it has to be made from electricity, and this is a factor of 3 less efficient than a heat pump, so is guaranteed to cost much more. 'Hydrogen ready' is just filibustering by vested interests in the oil industry so they can continue to sell gas boilers.

My suspicion is that the architect isn't confident about designing an ASHP based heating system so has taken the easy route out. BTW I have encountered more than one 'M&E consultant' that is similarly clueless. @johnmo is spot on the money with his comments above. Having retrofitted an ASHP to my 1930s house (solid walls, with partial fabric upgrades, good loft insulation, uninsulated floors, 200 sq m, 7kW loss) there is absolutely no way on earth I would fit a gas boiler if I were doing a new build, and I would frankly be reluctant to go back to a gas boiler if I were purchasing another 'second-hand' house. Get an ASHP design right (basically follow the principles set out above and size it correctly), and you wont regret it. Consider also if you want light cooling, an added bonus with the correct emitters.

@Dillsue thanks for the comments. It's going to take a few more read throughs before I respond with any confidence. In fairness to the people drawing up the regs they seem to be trying really hard to allow as much flexibility as possible without compromising the integrity of the initial FIT scheme. It does make me wonder whether they should just offer a buy out option, basically (eg) 90 pc of the remaining expected fit revenues in return for no ongoing commitments on either side. I can however understand why this would create all sorts of complications given that it's government sponsored. This does also highlight how complex 25 year contracts are in a landscape where the technology is forever shifting! I genuinely don't envy the people constructing contracts with wind farms and nuclear power stations, with perhaps a 50+ year life expectancy. The only certainty is that whatever the context is now, it will be totally different by the time the half way point is reached (even without the politics)

Hmm, interesting (and thank you). This is a later version of the guidance than the one I have previously read, and does indeed seem to omit many references to MCS. However the requirement to pro-rate based on total installed capacity seems to depend on the definition of the latter, which is apparently given on Page 65 in a way that involves certification by either MCS or Roofit. I think this might mean that you can install a DC coupled battery without MCS (because, although the metering requirements will change, the TIC doesn't) but you cannot increase the solar export capacity without MCS (because the TIC does change). If so that would, in itself, be very helpful. I may need to read this document a few more times to understand whether swapping an inverter (which, practically speaking, potentially changes the TIC) does (in terms of the rules) change the TIC in the circumstance that the inverter has the same limit (eg G98). Am I right in thinking (as I did with the previous version of the guidance) that there is nothing to stop you increasing the capacity of the panels above the output capacity of the inverter, and thus claiming FIT on the generation as clipped by the inverter (even though this will be greater in aggregate than the generation with the original panel capacity), on the grounds that the 'total installed capacity' is set by the inverter limit. Complex this stuff!

Have you got the figures to support that statement(either half) or are your assertions just speculation or a repeat of something that some journalist claims, also without evidence. Do you know how we compare with other countries with similar levels of public services? As regards the first part of your assertion (for which these is some evidence, albeit only by a tiny margin and even that dependent on whether you believe the Office of National Statistics or the Organisation of Economic Cooperation and Development), do you think by any chance that it might have anything to do with an ageing population and thus a reduction in the proportion working (state pensions count as benefits and are paid for out of current taxation not historical) . What do you suggest we do about that (which, btw, is predicted to get worse), other than the obvious which is to encourage a higher level of immigration?

@dilsue @mk1_man thanks for those very helpful comments which I will certainly factor into my personal choice. Im thinking that if I self install (unless I self install it definitely doesnt cost in.) I cant DC couple, because to DC couple requires changing the generation meter and inverter on the existing PV and that requires MCS to retain FiT payments. However DC coupling and a hybrid inverter means that one inverter controls the export so it can remain within G98. But if I AC couple, which means I can leave the existing PV alone and thus potentially self install, I need G99 unless I can find a certified way to link the PV inverter and the battery inverter to ensure that, together they, remain within the G98 export limit (even though in practice they certainly will). I wonder if any battery inverter supports that. Alternatively I can wait until the solar inverter fails and I am forced to replace anyway. They were guaranteed for only 10 years but mine is still going strong, I wonder what the practical lifetime is in the real world.

I can easily believe that this case with zero export payment. My current leccy prices are basically 7p from midnight-7am, 26p from 7am-midnight and 15p export. Since the night time import rate <daytime export rate, I charge my EV, do my washing, breadmaking, washing up and water heating at night, and don't worry if I export during the day. I don't currently bother with 'setting forward' my ASHP to benefit from the night rate, but neither do I set it back; bedrooms are just set to be a couple of degrees colder by adjusting the LSVs. For me at current electricity prices batteries would need to be <<£250/kWh installed to make sense, currently they are closer (at least in the South of England) to £400-£500.; In a few months time I will have years worth of daily records of peak rather and night rate usage, which will enable me to d a more accurate calculation, but I can already tell that its not going to justify a 'professionally' installed battery just yet, but I am keeping my eye on self install prices. One complication is that with solar already present any export by a separate battery inverter puts me into G99 territory. Currently I have no realistic option other than to AC couple, given that I get FIT - ie generation - payments as well as export payments.

I agree entirely. That's one reason I haven't bothered with a battery, with current tarrifs it makes no sense for me and I can't predict future tariffs. Only if either batteries come down significantly in price or the gap between export and import prices widens significantly (and looks to remain wide) can I justify this particular investment. Furthermore I wouldn't be surprised if, by the time that happens (battery prices don't seem to be falling that fast!), getting a cheap leaf with bidirectional charger turns out to be a great second car solution. Obviously the numbers vary from person to person.

I installed solar panels over 14 years ago. If I were installing panels now I would Fit as much panel capacity as the roof will take - as others have said you can have greater capacity than the max output capacity of the inverter. My only regret about what I did 14 years ago is I could have had more panels, and of course I cant now match the panel design Limit export to the G98 value (16A/3.6kW) per phase for simplicity. You arent going to exceed this very often (never if you have 3 phase) Get a decent export tariff (eg I get 15p/kWh for export with EON, Octopus do similar) Use DHW (ie a solar diverter) as the only on-site storage... ...unless you have an EV which is frequently at home during the day, in which case then rigging up a simple 'divert to EV if export > (say) 1.5kW' is worth considering - I did this for a while with a granny charger, Home assistant and a Shelley relay, but now don't bother as I have a night time import tariff that is less than my export tariff, so its easier just to charge on import at night. I would probably fit a hybrid inverter however, ie one that enabled (DC coupled) batteries to be added later, but I wouldn't bother with the batteries until they get a lot cheaper. With a decent export tariff you have to worry less about self consumption, so managing the use becomes easier, and the business case* for batteries more or less vanishes (at least for my usage pattern). Of course export tariffs may reduce with time, but then the case for a battery will be stronger (and batteries anyway cheaper) hence why I would consider fitting a hybrid inverter now. Modelling accurately in the real world house is rather difficult, so simplifying the question may help. ----- *Unlike solar or an ASHP, the environmental case for batteries is at best arguable, possibly non existent, so my current personal take is that they need to justify themselves financially.

The rads all fit comfortably under the windows (with a gap either side for curtains) and are either type 21 or type 22. There are just two exceptions: I fitted a type 33 by mistake, at a point in an extended process when I thought the heat loss was much bigger than it actually is. 22 or 21 would have done. I have one fancoil where a sensible sized rad just wouldn't fit. As I say my only regret is not fitting a couple more, just because of the fact you can use them for cooling. You can indeed mix down for UFH but from an efficiency point of view it means you are running your ASHP at the higher temp demanded by the rads, so if you are going to do this rads may be no less efficient. Of course UFH has its own advantages. Yes you can. After some experimentation I now do that in one bedroom only (used as a guest room) but not the others. The others are simply 'balanced' down on the LSVs to a slightly lower temperature 24*7. The best controls, particularly for an ASHP, are simple controls, and the low and slow mode from ASHP (or UFH) anyway facilitates and works best with simple controls; low temperature heating has a significant element of self regulation (if the room warms up the output of the emitters decreases and vice versa). I also get significant solar gain. The room with the most solar gain has the fancoil, so it simply switches itself off. All but one of the other rooms is run with TRVs disabled, ie permanently on (they remain fitted to the rads for aesthetic reasons!). I did a bit of balancing on the LSVs, but but rooms share heat much more than the manufacturers of fancy controls like us to believe Most of the year I run on pure weather compensation with no room influence at all, In April, when solar gain became significant in comparison to the base heat demand, I switched to what Vaillant call 'expanded' mode, which basically turns the ASHP off altogether when the room in which the room sensor is located gets more than about half a degree above the set temperature. I will switch back once the heating season restarts. So essentially its left on pure Weather compensation for most of t he year, with TRVs inactive. The result is much more stable than I ever achieved with the fancy controls and a gas boiler, and without the fiddling previously needed. The key is that the fabric heats up properly and serves to moderate any temperature variations. The house is 1930s 200sqm, originally with solid walls. IWI and a couple of modern extensions mean that the walls are now ~80% insulated, but 20% remain solid. Double glazing and 300mm loft insulation completes the picture. Floors (a mix of suspended and concrete) are uninsulated. 7kW loss, Vaillant '7kW' heat pump. Why did it work well? No system separation (ie no buffer tank, plate heat exchanger or low loss header between ASHP and emitters) ASHP capacity correctly matched to house loss Design for a reasonably but not excessively low flow temperature - radiators have to fit!, simple controls ie the controls native to the ASHP only Operate 24*7 choose a sensible tarrif (in my case essentially economy 7 ie 7 hrs cheap leccy in return for about a 10% uplift during the day. ie Nothing 'clever', just keep it simple but sensible. I could probably do a bit better still if I operated a 'set forward' at night to take better advantage of the cheap night-time leccy, but I cant currently be bothered!

You should question that assumption. Obviously it depends on the achievable rad size. I sized my rads for ft45C at the design temp of -2 , am actually running at ft42C with an ashp which is costing roughly 20% less like for like than my gas boiler. None of the rads are intrusive in any way. The house, now heated throughout 24*7, has never been more comfortable. Even I have been surprised. My only regret is not adding a couple more fancoils (I fitted just 1 where it was absolutely impossible to fit a sensible size passive radiator). They are great for light cooling.

@johnmo thanks for flagging this. So its a plate heat exchanger built into a plinth, especially designed to increase householder running costs by perhaps ~15% - 30%, targeted at those least able to afford it and institutional specifiers who haven't got a scooby. The voiceover to the ad is worth listening to for a laugh. Apparently the device also means that radiators will not need replacing (in a parallel universe presumably, where the laws of thermodynamics don't apply) Isn't free market capitalism wonderful!