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Still mulling over my final choice of Sunamp variants... Considering Dual vs HWi+i in combination with an ASHP. In the event that my ASHP goes offline (more likely if I get a cheap import) then the Dual is offline too whilst the HW+i can still be charged electrically. Does anyone have the HW+i unit? Am I correct in thinking that the charging of the unit can easily be switched from charging between electric or a heat source? The Sunamp guide states: "The UniQ HW+i and UniQ HW+iPV heat batteries are designed to be heated primarily by an external heat source (e.g. boiler, heat pump) and for producing mains pressure hot water heating in buildings. Therefore, these heat batteries are equivalent to indirect unvented hot water cylinders or hot water only thermal stores. The UniQ HW+i models are fitted with standby electric heating elements to heat hot water when the main heat source fails." Are these units designed to only be charged electrically for short only durations? Or is it fine to use them primarily via electric heating? I was planning to have a low temp ASHP that will charge my UFH. I am thinking that in those times that there is no call for UFH heating, I could use the ASHP to at least raise the heat in the Sunamp unit to say 50c? Now if I understand, the std units need to be charged to at least 58c, so is it possible then to charge the PCM to 50c (from the ASHP), and then the electrical heating element to take the PCM temp to the required level of 58c? If that's not the case, then no point in considering the HW+i model. Other idea is to go for Dual model (does DHW and space heating) and then use a HT ASHP to charge that to the required temps. I can then utilise that to do both DHW and UFH. If the unit is fully depleted in the evening from showers etc and there is a demand for heat, then at least the ASHP can kick in to feed the UFH directly via means of a blending valve. And if I go E10, I can ensure the ASHP is charging the Sunamp units and slab. Just means that I choose to go for a Dual, then I am more inclined to go for a non-cheap import ASHP!

Yes, @JSHarris, having been literally been burnt with some cheap Chinese LED lights, I think I am leaning towards a big name (unless I can get a unit for under £1k). This particular outlet came back to confirm that the warranty is with them so for me is no good as I would want to know that they will be around during the warranty period. And I should probably be looking at having more faith in my heat loss calcs and size a bit more appropriately as 30% modulation seems standard on most brands so a 10kW unit may not make sense when heat loss indicates around 6000w.

Yes, saw that one too. Probably a case that you end up with a Copeland rather than a Mitsu: Not that I am qualified to compare the two brands though! But for another £100 and the fact that you have a 5yr warranty... Actually, I re-read the listing. You get a Copeland if you go over 11.6kW. And as far as i can make out, only the 18.7kW model has an inverter. As the Dragons say "and on that basis, I am out" (on these units). Looks like people already reviewed the seller here: Will see what my installer comes up with, but will probably be a fair bit more ££££!

Just resurrecting this thread as now looking to get my ASHP. If I go with pessimistic heat requirements, then that points to 10Kw input. Do I need to slightly oversize in any case and then run it slightly lower? ASHP will only be heating up the UFH (DHW will be via sunamps) so no cylinder needed. I presume also that I should be looking for an inverter controlled unit so that it's not simply turning on/off all time? Anything else I should be looking for? I have an installer in mind but don't want to be sold something I don't need! And most likely won't be going the RHI route unless his install price is really good. Haven't seen any Carrier units on ebay but did see this 10kW unit: https://www.ebay.co.uk/itm/Ex-Display-AIR-SOURCE-HEAT-PUMP-WATER-HEATER-10kW-EVI-Heat-Pump-Works-to-25/113863582069?hash=item1a82cc6175:g:S1kAAOSwSk5dLwgp Anyone know the credentials of this unit?

Thanks @JSHarris! I have used the longest path principle for most rooms where practical. The eaves in some rooms meant that some vents had to be some distance closer to the doors but on the whole I am happy with most of the positions, taking into account potential placements of future tall wardrobes, bookshelves etc. Just thought I would check on the bathroom and kitchen positions as was not convinced the positions indicated by BPC were optimal. So will re-locate the vents for both rooms. Was a bit concerned of having a dead zone in the bathroom at the bath end, so planning to move the vent closer to that end of the room. At least it's only 34c in the loft now!

Great time to be doing the final ducting work in the loft. Probably 50c in there at the moment.... Kitchen: This will have a re-circulating hob extractor, so no connection to MVHR. Is the location of the MVHR extract in the best location? Probably 1m from hob? Bathroom: Should the extract be closer to the shower or more central in the room? I was going to go for position A. Both rooms will have a 'boost' switch to cater for cooking/showering periods.

@Nickfromwales Hi Nick, any more thoughts? ? https://forum.buildhub.org.uk/topic/10802-is-a-16kw-ht-ashp-really-needed-for-my-ufh-with-these-heat-loss-figures/?tab=comments#comment-183019 Alternatively, when are you next in Kent? ?????

Just added that as worst case. Those UFH calcs were from Wunda, who base them on 'standard' build regs. My existing PV was an MCS install. So really no point going for another MCS install without the FIT incentive, so just looking at spending 2k for a DIY install.

Hi Nick, I am speaking to the installer tomorrow hopefully so any tips/advice you may have would be appreciated. Most of the info is on my introductory post. Supplementary info: DHW requirement: 2 adults and two soon to be teenagers (do they wash?) 1 morning shower; 1 bath 1 evening shower; 1bath Hot water for washing up (though may get a boiler-type tap for most hot water needs in the kitchen) though dishwasher for most items. Occupancy: Wife and kids out and I although I work from home, my office will be one of the sheds out the back so main house can either be set to 'off' or very low temps during the day. UFH demands: Groundfloor: Water volume: 129L; Estimated loading: 9.45Kw (as per Wunda calculations) Upstairs on separate manifold: Water volume: 25L; Estimated loading: 2.03Kw (possibly won't have the upstairs UFH on as it's only 1 bedroom and one bathroom which will have an electrical rad). I decided on Sunamp as wanted to limit heat loss (so didn't go down the UVC/thermal store route) and wanted to maximise 3.8kW PV setup. I have limited space internally (the two 12kW Sunamp units pretty much fill up the 'plant room'). So originally Sunamp designed my setup so that the eDuals would cover DHW and UFH to some extent with the knowledge that I would have to supplement charging the sunamps with grid electricity during winter months. Both units were received this year but had to go back due to a production issue and now on the cusp of delivery they suggest going for an additional 16kW HT ASHP plus UNIQeHW9. Obviously these can't be charged by water (i.e. ASHP) so they would be reliant on PV and grid (e7/e10). The ASHP would be purely for the UFH then but 16kW HT seems overkill for just the UFH, and not sure why HT if the eDuals or eHW unit can't be charged by ASHP? Indeed, can the eDuals be setup for the DHW as well as the UFH? I doubt we would be needing fully charged eDuals for DHW every day, so possibly use some capacity for the UFH as well. Winter months would see the DHW being reliant on e7/e10 grid and any sun during the day could be utilised to partly run a 8-10kW ASHP for the UFH. Obviously very little output from PV in the winter so reliant on the grid, but the long term plan would be to expand my PV setup with a further 5kW DIY system.

Yes, that makes sense. Then having the ASHP to also charge the sunamps during the winter months rather than relying on the grid. I don't think you came inside that time you were here Mike, but the house has a north and south wing, so setting up the ASHP to cool the southern slab would be good. I was also thinking to use the UFH to shift solar gained heat from south to north wing if required but not sure what additional items would have to be built in. All rooms will have their own stats and I have a temp sensor in the slab in the south side and one in the north side slab. slab is 140sqm and is 100-110mm. Presume high temp is needed to charge the sunamps rather than just the UFH. My presumption now is that it will do both, blending down the temps to the UFH and/or using the eHW sunamp as a buffer. I don't really want to add a further 9Kw eHW sunamp just as a buffer for the UFH. Think i read that getting an ASHP as a twin unit, one would heat temps for UFH and the other for the sunamps? So looking at the sunamp manual, the eDuals should only be charged by electric means: Hence their additional Sunamp eHW requirement now. So the eHW unit is purely to act as buffer for the UFH then. So the ASHP would not be charging the eDuals for my DHW in winter then and would be 100% reliant on grid (so e7 would need to be looked at again) unless there is a better setup? In any case, will talk to the installer tomorrow to see how this is all meant to work efficiently.

Not actually clear from either Sunamp or the installer, but I thought DHW would be powered by PV/grid and then UFH solely by ASHP. I am speaking to installer on Monday so will find out. Sunamp did actually come back to me this year and say that they recommend "16KW HT ASHP with 2x UNIQeDual 12 and 1x UNIQeHW9". No way can I afford a further outlay for another UNIQ unit for HW! And of course this can only be confirmed after a £500 energy assessment. Things were certainly different with Andy at the helm of customer servicing! I did pick up a pool heat pump the other day so wondering whether that could be used to test a lower kW input requirement. Will need to check the spec on that.

My ordered (2x)UNIQ eDual12 eHW12 should arrive in the next few weeks. Originally these were going to be used for DHW (occupancy of 4) as well as my UFH. It's a renovated/extended bungalow with 300mm slab insulation, 3G passive windows, 100mm EWI and 150mm spaced UFH. After getting a potential Sunamp installer to talk to Sunamp, the recommendation is for me to now also get a 16kW HT ASHP that will purely heat the slab. I always knew that I would be reliant on grid electricity over the winter months when my 3.8kW PV would not get sufficient sun. Using Jeremy's heat loss tool, I am looking at the following heat loss figures: Main issue will be the ACH that I may have imputed on the high side of 2, but despite taping, siliconing and sealing as best I can, there will be some leaks that I will have missed. I may still be able to tackle those when I do an air leakage test. Most winters don't achieve -5c here in Kent and when it does, it's for 2-3 days during which I would just switch on the 4.9kW LPG (balanced flue) gas fire. So a temp max temp difference of 20c would be more realistic during the colder months when the average OAT is around 5c. I know @TerryE has his willis heater set up with UFH, but he has a passivhaus set up (iirc) whereas mine won't be that close so I don't think a willis heater instead of an ASHP would work (though I lie the idea of it as a backup!). Not sure whether I want to go down the e7 route either just yet. So looking at the figures above, would a 16kW HT ASHP be overkill?

@Da-Dad I was in a similar situation as you. Renovating bungalow with 2 extensions that were going to have UFH, so needed to tie that in with the bungalow heating system also. So wanted UFH throughout. Looked at various options, tried to squeeze in as much insulation, but it still meant I was wasting a huge amount through the old concrete slab (that had no insulation - a 1950s bungalow, DG and poorly filled CWI). I almost went for a retrofit, overfloor UFH system that quite a well known online UFH specialist firm were trying to convince me would work fine with their minimal insulation. I ended up digging the whole slab up down to 1/2m below floor level and laying 300mm+ of EPS/celotex, then with UFH meshed in concrete (turned out to be a nightmare as the guy who did the pour, was an utter muppet...another story). So it can be a lot of hassle for having UFH. Those modern oversized radiators can look good on rooms if you site them carefully where they won't be in the way if you ever decide to change room layouts. Have you considered, EWI to reduce the heat loss through walls? And supplement your loft insulation if needed.

And now I want a paint sprayer......

Thanks all! Never really used MDF for anything so will take all advice on board!

Have read mixed reviews about water-based primers and as I have a large-ish mdf sheet to paint I'd like to get it right first time. I know a few here have used Rustns MDF sealer. I would have thought an oil-based primer would have been better than water-based? I really don't want the 5.5m length bulging/splitting! Any tips @Onoff? Think you have experimented with the TS stuff? Final coat needs to match plastered matt white wall as best as possible, so was simply going to seal the MDF, then use Dulux Diamond white Matt. TIA!

First pic is mine, the timber approach pic is from the net. Edge of windows will be 'covered' with insulation (100mm EPS) and this will be rendered. The alu cills fit onto a bottom 'rail' that you can just make out (see grey): Above pic is for my SIPs extension, but the windows have the same cill profile underneath.

Depends on the weight of the windows. Some of mine weighed over 200kg so standard window straps will likely fail! There are bespoke EWI window supports that you can get (I got mine from Fischer) but they'll be beyond your average double-glazing window fitter to work out (I ended up having to fit most of my windows as they were clueless). A bad pic, but you can just make out the brackets: This was cavity wall, but the brackets are better suited to solid wall as you have more fixing points. There is also the option of timber supports: But that also introduces a cold bridge. There's also another product like foamglass (indeed it may be foamglass) that will support the windows. I think someone on here may have used it...

Yes, I was watching the auction the other week, lots of pods, garden houses/offices etc. Started nice and low and then quickly jumped up during the last few days. I wish @Ferdinand would stop bloody promoting these auctions on here!!!

Some of these opening bids appear ambitious, take the Freya bath (£200 opening bid) plus 20% hammer price + 20% VAT which gets you close to £300 on top of which will be your transport costs (unless you live near Sheffield to collect). And it could be ex-showroom quality. New from soak.com is £400 inc delivery! Be interesting to see what it goes for.

£90 reduced to £18 inc del for shower valve! https://www.bathstore.com/products/square-thermostatic-shower-valve-20007015720.html? And found some baths in there also if anyone's looking: https://www.bathstore.com/products/bathstore-sale/massive-stock-clearance#price_range=m0&f_product_category[]=Bath&sort=price ASC&page=1 It's no wonder this place may be going down the plug hole. Local store always have 50-80% "plus another 25%" discount signs on the windows (and if you'd go in and ask about the reductions they just didn't add up and were certainly not the massive discounts that they appeared to be advertising.

I also went through BPC and went for the Vent Axia Kinetic Plus B, which was a bt more £ than the others that they offered me, but did have the summer bypass option, easy to install, efficiency was better than the others IIRC. There's also quite a few people on here who have gone for that option, so I thought I wouldn't be too far wrong with that choice. Not quite installed it all (loft is too hot) but also plan to site it on top of platform on the ceiling joists. Maybe with some rubber matting to reduce noise/vibration. If that fails, suspending it from rafters.

Well, maybe that is where Fischer come in. Then there's always the likes of Everest Glazing they could push these units through...

Talking of technical support, does anyone have a contact at Sunamp that they could PM me? People that used to be there aren't there any longer and then when I am told that someone should be in touch, no contact is ever made. The guy who's installing my 12kw eDual units, needs some technical support! Or perhaps Sunamp have sold that part of the transaction to Fischer as well! Sunamp really need to sort out there customer support if they continue to sell direct to the public or even trade.

Building control are going to love that staircase! ?