Hi RV3,

It is always difficult to provide advice about heating systems, because there are so many variables that need to be considered.

From the information supplied, I would estimate that you should not need to upgrade your electricity supply from single phase to three phase, unless there is a phase balancing issue in your area. When you say that you are rural, exactly how rural?

For me, your starting point would be to try to improve your insulation.  Reducing your heat demand has a knock on effect for everything else, including costs.

What solar thermal do you have and why is it not working? This is a good source of free energy and should be utilised if at all possible.

Now that I have repaired my old gas boiler and recently installed an Air to Air ASHP, so that she who must be obeyed is now warm and happy, I can continue with some ideas I have been working on for improving efficiencies. So watch this space as they say.

As you have no doubt read, ASHP's suffer from lower efficiency at exactly the time when higher efficiency would be much appreciated. This is a particular problem during the 3 Winter months. From Spring through to Autumn you should be trying to get most of your hot water from your solar thermal and hence you would be able to run a ASHP at lower water flow temperatures which gives much better efficiency.

Have you consider solar PV? Solar PV can be used to help power a ASHP during the day and if there is an excess of power available could also be used to produce hot water.

Let me give you an example of what can be achieved.

Since repairing our gas boiler, it now provides our heating overnight at 21C. At about 9:30 this morning, when I arose, there was sufficient output from our solar PV panels for me to start our ASHP. As the ASHP heated up to the 23C setpoint it pulled back the controller and shutdown the gas boiler. There was sufficient output from the solar PV to also heat the water in our hot water tank up to 65C.

For 8 hours during the day we imported only a very small amount of electricity and gas from the grid. As the Sun was going down and the output from the solar PV was insufficient to power the ASHP, I switched off the ASHP and allowed the gas boiler to take over heating duties. In this way we used the maximum amount of the free energy from the Sun and hence reduced the amount of electricity and gas that we imported.

Obviously this arrangement works well for us, but may not be suitable for everyone.

Another thing that you may wish to consider is your electricity supplier. I know that some of the members have switched to the Octopus Agile tariff which provides lower prices for much of the day, but is quite expensive between 4pm and 7pm.

I hope that this is of use, but please feel free to ask any further questions.

Regards,

Derek.

Thanks Derek - appreciate the thoughts and v useful.

We live in a hamlet - couple of houses nearby - then some more about 500metres away etc.

Definitely going to try and get the solar thermal sorted out. The pressure has dropped right down so going to get it serviced and then see where we are.

Not sure how to improve insulation. The one company I've been able to get out said not worth doing much more. because we have stone walls have been advised cannot get cavity wall insulation.

Your set up sounds great, not sure I'd have the skills / confidence to start thinking about a twin set up like that though. Going to also start looking into solar PV as well.

Thanks again much appreciated.

Welcome to the forums @rv3 and thanks for the kind words.

As Derek says there are a lot of moving parts when it comes to ASHPs and what works for one house will not work for another. I've read through your detailed post and will comment later this evening, and we've made some huge strides with our ASHP heating this week - these insights may help.

It's going to be a long day outdoors today taking advantage of the splendid weather. 

Your w/m2 losses is shocking. As a comparison our renovated house has a loss of 34 w/m2 and our house is actually bigger at 261m2

I would advise you really do look at insulation first, before you do anything else. If you are going to spend £17k on anything, wrapping the house (and loft) in solid wall insulation is 100% going to be better than anything else. 

According to your house size I'm going to assume its a square, so you need 60m of insulation and at 2.5m high so 150m2 of insulation board - it would cost £3,700 for this 70mm outside insulation board (35 packs). Plus you would need some kind of cladding so lets say £8,000 all in. You will dramatically reduce your heat needs this way and reduce your losses. Then an ASHP would make sense. If you get one before you reduce your losses you are, pardon the phrase, pissing in the wind.

Our bill for the ASHP and all our power should come to around £800 @ 11p/kw - almost 25% of your cost. The insulation would recoup itself in a couple of years based on your bills.

Hi RV3,

As Batalto says, start with improving your insulation.

Look on the forum for posts by NeilSondhi which details external wall insulation.

I assume that you have solid stone walls so do not have a cavity.

Regards,

Derek.

Thanks @batalto and @derek-m.

Will need to do some homework on what w/m2 is but I get the drift. 

Totally take your points re insulation. I picked up that insulation is key - right at the start of this  did get a firm out who were meant to be one of the best in the region - he basically seemed to think there were no easy improvements (really difficult to get firms out to have a look and reliably quote?) . Lofts already done though not brilliantly. Solid stone walls so no cavity options. I'll look again at the external stuff, I'd initially thought this would mean a big alteration in external appearance but need to do some homework on that.

I think then we thought ok well if insulation is not something we can easily improve - and renewable could run at a price that wasn't more expensive than LPG - it would still be a positive step rather than getting new LPG based system. But when you then start getting the full picture re ASHP it's a more complicated picture.

Like I say - will go back to trying to think the insulation thing through. Maybe just need to try and get someone else to come out. Everyone is very clear that the insulation question is totally fundamental. Just not sure we have many options.

Really great to get feedback and help us focus on stuff though - much appreciated.

@rv3 Its just your heat loss per m2 of the outside of the building e.g. what is the replacement number. You can then multiply this by the size of your house and you get the total heat loss of the building.

Its just a number you need to size the heating system. The lower the number the less heat you will need to warm up your house. As an FYI, if you are still renovating, have you considered insulated plasterboard?

Hi RV3,

If you do not wish to change the outside appearance there is also interior wall insulation that may be an option.

Regards,

Derek.

@RV3 I have a heat loss tool you can use to work it out yourself. Its fairly straightforward, but needs a little background knowledge about walls/roof etc. As an FYI if you know your current use and efficiency you could probably work out your heat need - you literally have the heat use figures at your fingertips

Thanks @batalto. 

I probably don't have the background knowledge though. We have old parts of the house that have high ceilings and exposed beams, hard to know what's gone in there it's not accessible. We've got newer parts where you can see insulation wool but it's only about 150mm. Then we've got other parts which are kingspan. The insulation guy who came out stuck a camera in the wall and it looks like we have foil lining in there - but hard to know how consistent this is in all areas. 

Time wise and expertise wise I probably just need to try and find someone else who'll come out and maybe do a proper heat loss calc for me - advise re what practical steps we can take re the insulation. I got the last guy out though and I think they have that much work on that this kind of bitty job - they either quote you out or sort of pass you on.

@derek the @neilsondhi thread re insulation was interesting. I tried to get a firm out for the bead insulation but three wouldn't come out as we were a stone property - one asked for pictures - really helpful guy but said not suitable as well. I'll keep looking at options.

Hi @RV3, welcome and here are a few of observations/comments from my recent installation and research.

• Our DNO just required a simple form, with some basic details of existing use and some information on the ASHP power supply requirements that your installers can provide.  They got back within a few days with an answer.
• We had a wood burner that was attached to the old HW cylinder.  The installers just disconnected and drained it.  It  works fine like this. 
• Our 3 suppliers all gave an initial quote from our EPC.  Two did it remotely; one (the one we went with) visited.  The quotes were all subject to a full survey, when they do a room by room heat loss model of your house.  This could change the quote; mine changed because I needed 2 more radiators than were quoted for but the ASHP spec was the same.  
• Your Ecodan quote - mine was almost the same number but was for the ASHP, 250l cylinder, 11 radiators, pipework and all installation. It's also worth saying that my EPC number for space heating is c. 21000 so a 14kW Ecodan is going to be working harder in your house than mine. My house is 165 m2. 
• You won't achieve the quoted SCOP figure.  As far as I can see 2.5-3 is a more realistic aim, maybe a little more. 
• People have commented on insulation; what's your house like for draught proofing? - that make a big difference too.   

Good luck.  You'll probably get the maximum RHI so that takes the edge off the large upfront cost a bit.  And of course in your case it'd be one more fossil fuel burner removed. 😉