RomyD

I had a look at the Eddi manuals and examples. Far better documentation than i-boost and very informative. Tks.

I am now thinking the diverter should maybe wait until we have the battery etc installed and see how much we actually end up exporting...

Tks very much for the replies, its really helpful. Self use of free (well kind of.....) electricity and little to no export is EXACTLY what we are trying to achieve so the i-boost or another PV diverter is a must then and it saves the ASHP from short cycling too. The idea really is to be as self sufficient as possible but its proving quite difficult to get consistent answers from various suppliers. For example we've had "MCS" accredited installers suggest ASHPs with capacities from 12kW down to 6kW. Our heat loss is about 5kW according to JH spreadsheet. We are currently planning on battery storage too, an 8.2kWh Givenergy system recommended by the electrician. A bit worried now you say its complicated Jack...8/ Complicated seems a bit of a problem right now... ProDave, how is your system configured to work the wireless 700W heater? it sounds like you are doing exactly what we want to. Our idea is to have the solar charge the battery first when there is excess, then the hot water. Maybe the other way round. If there is still excess after that a regular heater sounds sensible. Confused I Am (CIA i am not). But getting there. Tks.

So if the legionella cycle is pointless, the only reason to have an iboost/pv diverter is to have a back up hot water heating method? Is a diverter really that appropriate for a ASHP based HW system then? surely it would be better to simply use the PV generated power to drive the heat pump during the day instead of the immersion and take advantage of the ASHP efficiency? In the event of an ASHP failure, presumably the immersion can be just manually switched on?

do you mean connect the immersion heater directly and only to the iboost? tks

Sorry to resurrect an old thread but we have a similar plumber issue. Ecodan and preplumbe cylinder and plumber says it wont work with an i-boost. I don't quite understand the solution described here. Have I understood it correctly in that the output from the Mitsubishi FTC powers the immersion heater (for legionnaires control) periodically and that all that is needed is to wire this power to the 240v i/p on the i-boost? So now the FTC will (if the option is turned on) do the legionnaires boost thing (if there is no solar) and the iboost will top up the cylinder temperature in any event when conditions allow? I've looked for a wiring diagram but I cannot find anything useful. Hope the questions makes sense. tks,

? Tks for all the replies. Tbh if it really was a problem aI suppose it would be well known because there must be loads of people off mains sewerage using softeners.

I'm finding all sorts of conflicting recommendations one way then the other. There are two types of septic tho, aerobic and anaerobic. Treatment plants are aerobic whilst the regular tank/soakaway arrangement is anerobic I think. Different bacteria apparently so maybe that's why.

Hi, We are making good progress with our refurb and we are now close to first fit plumbing. Our builder has suggested fitting an aquabion instead of a softener. I am a bit sceptical about this kind of device and know that salt using softeners do work. We would prefer a regular real softener but are worried about the effects on the septic tank and soakaway. Hs anyone any real world experience of using a softener in a very hard water area with a septic/soakaway? We are in Suffolk and water is very hard. Thanks in advance

Yes I get it now. Tks!

Tks for the advice everyone. I think I may have made a mistake on the heat loss calcs. I used 21c and 10C for the delta on the floor but I suppose I should have used the UFH set temperature. Is that right?

Thanks for the tips. I've had a look at these. They sound great but i don't like the idea of sacrificial anodes as a consumable that will get forgotten about. The Dimplex Edel which looks like the best of the bunch doesn't use such a thing but still only has five year tank warranty. Is a 5yr tank warranty a bit stingy or does it sound about right? And then there's the COP. Dimplex claim 3.21 which from their spec sheet isn't the sum of the power out divided by power in which is 1650/700=2.36 Have i got that bit right? And why cant a multi split system do A2A internal units and DHW somehow? Sorry for all the questions, I am still getting my head round all of this.

Mines a renovation and with only 75mm floor insulation it seems UFH is probably wasteful so A2A or rads. Really don't want rads. Quite like the idea of A2A. HW is the next problem.

I quite like the idea of a split system with a pair of internal units. The layout of the bungalow is a large lounge/ kitchen/ diner open plan area of about 55sqm and a hall with the bedrooms hanging off it. One unit in the hall and one in the kitchen/diner area might just do it. We don't like overly warm bedrooms, just a zillion tog duvet does just fine. Most of the glass, windows and bifolds is south facing too.

Maybe other countries that didn't benefit from huge gas reserves needed something else and gas is indeed too cheap. I suppose coal was once the enemy and now it's gas. They will need to migrate the green surcharge away from electricity and on to gas. Anyway UFH would be nice but we can only fit 70mm floor insulation (upgrading from 20mm EPS). Is 70mm enough for UFH? The other thing that puzzles me is that swimming pool A2W heat pumps are also not covered by RHI and appear much cheaper but don't work when it's really cold. Is RHI code for Really Highly Inflated pricing?

Having realised that RHI will not assist financially with our bungalow renovation due to timelines, we have been looking at alternatives. We considered storage heaters which I expect are much better these days compared to when many of us experienced them years ago, but then Iceverge on here suggested A2A either single or multi split units. To use A2W we would need rads or UFH neither of which are currently installed so additional expense there. A2A avoids all this. A2A multi split seems like an ideal solution but why is it not a more popular choice considering how cost effective it appears to be?

Having had a google fest this afternoon, those A2A multi split multi room systems look really interesting. Could be the perfect solution for us.

I think you are right about the string thing. Each case has its own upsides/downsides but I think its useful to use the storage heating costs as a baseline for comparison. Its a simple sum. Anything to do with heat pumps gets harder to work out and I think the equation and debate has been distorted by RHI. If you can get someone else to pay for your system over a few years of course its a no brainer but those days have gone away. A2A sounds interesting but isn't EAHP much the same as MVHR? No gas where we are so has to be electric or oil, or biomass etc.

Storage If I put the leccy price I have been quoted into your sums for storage I get: E7 13p System £2000 Total £25,400 For ASHP I get: Assuming your leccy costs Pump and UFH, £22k as I have been quoted 20yr cost £34k If was able to invest the cap cost difference I could earn; Loss of investment return on £20k, 2.2% @20years, £11k Total ignoring investment loss £34k Total Inc investment losses £45k So ASHP over 20years comes out at around £8600 more best case or £19600 more with a modestly performing investment. Even using 18p for e7 storage heating so 20yr at £34400 gives an ASHP saving of just £400 with the higher cap costs but that ignores potential investment returns of £11k so still £10k worse. Conclusion: Get storage heaters and stick the savings into you pension pot and unless your retired you'll get 20% tax relief, maybe 40% too. Just thinking out loud really and I am not a financial advisor and this is not financial advice!

I too had a very small house in the early 90s, two up two down type of thing. It was our first place and had a single woefully inadequate storage heater. I wonder how it might have performed had it simply been a bit bigger, but the real problem back then was it was simply a terribly inefficient building. It's not a no brainer in my mind. The cost to run it is only part of the story isn't it? Up front capital cost without any subsidy at all for many, is now much more relevant than before, especially if you don't have any radiators to start with.

Is it fair to think of storage heaters and immersion heaters as having an economic efficiency of about 200%? (Depending on the supplier tarrif). Whatever the outside temperature. Assuming the heaters will still produce heat into the evening which I think a correctly sized system ought to these days. Has anyone done say a twenty year cost benefit of ashp Vs good old fashioned e7 based storage and immersion heat?

You could try Origin. They are aluminium with quite thin (49mm iirc) frames. I love the style of Crittals but cannot find any with sub 1.0 u-values.

DCM is a banned substance in Sweden. Used to get it in paint stripper IIRC. Paint stripper has never been the same since.

Thank you for your responses all. Very helpful and now I have a bit more thinking to do.

But the two studies, on very ordinary housing stock, that I linked to in my first post show ach via leaks, extractors and vents as generally less than 0.5, which suggests much lower ach numbers should be used even if there has been little attempt at airtightness improvements. what am I missing? I totally get that uncontrolled air leaks are bad - and get worse the older i get but the less said about that the better.....