I won't lie to you @suzyq, but ASHP running costs at current tariffs are very expensive. At the same time, all heating costs have gone up so it's all relative. 

Regarding your installer, please ensure that they're MCS accredited. You're welcome to post their details and see if anyone else has used them and what their feedback and opinion is.

I've heard very good things about the Mixergy tank, so that's a good move.

Thank you @mars. I can't stay as I am, so my choices are limiting.

At first, I originally decided on a boiler stove with electric boiler as back up (instant heat) but expensive to run at the time which is why looked into whether Ashp would be more suitable, now a couple of years on though. 

 I hope the government will do something about the rates for renewables - soon! 

Maybe solar pv to go with it?.

I think the Mixergy cylinder is set up for this. 

I will try post details of my installationn as soon as, the installer has confirmed Vaillant in stock. 

ASHP should be cheaper than straight electric, but I would advise getting whatever live power consumption and efficiency monitoring you can, MMSP or whatever. It would have cost a lot more and taken a lot longer to configure our ASHP more optimally with only the daily figures on the Mitsubishi controller.

@suzyQ, how well insulated is your house? I'm going to bang @derek-m's drum on this point since that's where you can potentially really multiply the effectiveness of an air source heat pump.

What I would say, however, is that insulating an old house is quite a specialist area. It's easy to get it wrong and end up with moisture-related problems and so there seems to be a prevailing assumption that old buildings should be left as is. However, there certainly are breathable insulation solutions which, in the hands of a company that knows what it's doing, will make all the difference.

You may well already know this, in which case I'll shut up.

Hi @suzyq I can't help with running costs, but would reiterate what @majordennisbloodnok says - be careful about insulating an old house - especially using modern materials. It's easy to do damage trapping moisture in "breathable" buildings. Have a read through this website for some really useful advice https://www.heritage-house.org/

We're doing almost the same as you - replacing a solid fuel heating system (Rayburn) with a 7kw Arotherm Plus in a 200-yr-old rubble wall cottage. The ASHP was installed last week, just waiting on a buffer tank to get it going. We're using a Vaillant UVC.

We've had radiator upgrades etc (upstairs) but tbh our plan is to use the ASHP to keep the UFH going - we're also looking at installing solar PV for summer use to offset costs.

We're with Octopus and I'm hoping they bring out a tariff for ASHPs (we don't have an electric car so can't get on the Octopus Go tariff which would have been ideal).

Make sure you've got decent insulation in your loft but I wouldn't stress too much about wall insulation.

Better to draft proof your house as much as you can. Old houses are a nightmare for draughts so make an effort to fill cracks and gaps and ensure air changes are as low as you can make them.

I'm putting in secondary glazing (free - using old glazing panels left outside a local window makers). I'm also planning to build a small porch on the front door and a small conservatory at the back - to provide a buffer and stop the worst of the weather blowing straight into the house.

If you have a wood burner that could help too. The boiler on our Rayburn rusted through last year so we've spent all winter with no CH - just a woodstove in the lounge and one small electric radiator. Thankfully it's been a mild winter - but and using wood (and some coal) we've been able to control costs.

If you have any damp walls go outside and check the ground level outside compared with the floor level inside. The outside should be lower than the inside - if it's not then it will cause a real problem for your walls as you have no damp course. This is another really useful website on that https://www.davidkinsey.co.uk/pages/damp.php

Good luck, hope you get yours installed in time for the RHI deadline.

This is the spec.  (had guidance with this, my knowledge is very basic)

Vaillant arotherm plus 7kw.

Vaillant 45L buffer tank

Vaillant Hydraulic module station w Vaillant expansion vessel inside 

Vaillant Sensocomfort 

Vaillant SensoNet 

Mixergy 185 litre hw cylinder w non-branded.expansion vessel

 

 

The cop has been worked out at 3.55 at 50 degree flow. I know this is too high, so I will have to try get this down lower. 

 

Due to it being an old house, small 2 up 2 down. I have ufh downstairs and change 2 radiators upstairs.

 I am still on with trying to improve insulation. 

Once installed and checked all working. I can't see me having it on, 

now Spring is here and all doors and windows open until a bit more renovations have been done.

Any advice please or offer your experience and suggestions 

To try and limit any problems, pitfalls with the installation where possible.

The soakaway for Vaillant. 

What size should it be, depth etc. 

Looking at the installation guide sketch I find it difficult to tell what it's made up of, the pipe seems far down past the gravel or is it soil?!. 

I have checked with Vaillant,. They cannot help with any guidance. 

 

I have purchased 2 radiators for upstairs. 

I wasn't sure what to buy, Trvs?, good or bad?

manual turn on turn off or would it be better for a smart thermostat (I do not know anything about any modern gadgets!). 

 

Do you recommend any other room temp monitors and where is best to put them. I think the sensocomfort will be used for my ufh downstairs!?.

 

The installer will be setting the weather compensater. Is this the right thing to do?. 

 

The soakaway is usually a gravel bed.

Thank you @Saz i downloaded the installation guide yesterday but could not see the dimensions, so appreciate you posting this, with the guide. 

@suzyq I think a buffer tank and low loss header do a similar job - preventing the ASHP from short cycling - but others with much more technical knowledge will be able to give a better explanation. Do a search this forum and others for the pros and cons of installing a buffer in the first place. If the installers think your system will work with a low loss header then then personally I wouldn't wait around...

If you're hoping to claim RHI payments then you have a far more pressing issue - to get the system installed and commissioned before 31 March when the RHI payments change. If you don't get your application in by 31 March you stand to lose thousands....(mine would have gone from £11k to £5k). Personally I'd say go with whatever it takes to get it installed asap - they can always tweak the system afterwards.

The other advice I'd give is to double check the MCS form for mistakes once your installer has completed it.

My system was installed two weeks ago (we were also waiting on a 45l buffer tank - it took over a week and lots of calls to get one).

But the installer ticked the wrong box on my MCS form and put my system down as "Metered for Payment" instead of "Metered for Performance". I didn't pick it up when I filled out my RHI form and only realised after I'd submitted it. 

It's taken two weeks to resolve it and get the paperwork changed....though they accepted the date I put the amended paperwork in as my start date. It did cause me the odd sleepless night though. 

Also double check you have all the paperwork you need - is your EPC certificate correct and up to date? Make sure it doesn't recommend fitting loft insulation. 

You don't want to be filling out the paperwork at 5 minutes to midnight on 31 March and discover you've missed something.  

Good luck

@suzyq, our soak away is also into gravel and it’s very effective. 

The buffer acts as a low loss header. In terms of holding out, it’ll be very specific for your property and set up. This is, however, behind my personal comprehension and I can’t really comment beyond that.

@derek-m has a very good grasp on this, and maybe he can share his insights if he has a moment.

I have found some better pictures which show it is gravel over water-permeable course rubble as I don't think the previous pic was clear on materials used. All the best with it all 😀