There's quite a bit to deconstruct and address here. Since you've described your insulation as good, that's a good starting point. Initially, the single core rads may be too small, but that can only be confirmed during a site survey, and they'll work out if the rads will be able to emit enough heat to compensate for heat loss.

We can only really address costs and financials once we know what size heat pump will be required, and that's normally proposed by an installer. The fact that you're on a smart metre with a battery, supported by solar PV, will make a big difference to your running costs.

As for hot water, you will need to have your hot water cylinder changed when switching to an air source heat pump. In terms of efficiencies, it comes down to how hot you like your water. We've set our hot water demand to 42C. The rationale behind that is when we open the hot water, anything hotter than that (42C) is too hot for the skin to deal with directly, so you need to add cold water to make it more comfortable (which to my mind is inefficient). We have a legionnaires program on the ASHP unit that heats water to 60C every seven days. During that time you can see how inefficient heating hot water can be.

Staying on hot water, since you have a solar PV array, I would recommend looking into a product like iBoost that takes excess solar production (what is normally exported back to the grid) and heats the hot water in your cylinder. We have one, and it's very, very handy.

The next step is to get a few installers to come out and visit - they will carry out heat loss calculations and give you a proposal. The proposal should set out a comparison between you're currently paying for heating, versus the savings from the heat pump.

And definitely only contact MCS accredited installers so that you can register for RHI and get the installation costs paid back to you over seven years. Here's the link to MCS' installer finder: https://mcscertified.com/find-an-installer/

I agree with all Mars has said above its good advice. But please consider using a solar thermal system to heat most of your water. At an installation cost of about £2000 and especially given your location on the East side of the country it should work almost every day for you.. and you get RHI as well. I have a friend on the South coast who figured out that he would have paid off the installation costs in 5 to 6 years with the RHI payments.

If you're interested I would take a look at Navitron and their solar tubes, (Tubes will work all day long even on very cloudy days and will keep your base temperature in the winter about 20c so that if you do need to use the HP to heat water, it doesn't have to raise the temp by so much) they much more efficient than flat panels and as you may be installing a heat pump which will probably require a cylinder change, it will cost tens of pounds to change the requirement to a twin coil rather than a single coil.

Hope this helps,

Chris

@nredshaw, sounds like you have a good set up there.  We have a similar-sounding house, also in Lincs and are in the process of getting an ASHP (see my thread in this section).  We don't have any solar nor an EV but are thinking about it so may pick your brains.  

In a straight contest between gas and ASHP on price, gas would win but with your PV/battery setup it might be a closer fight. Going by my quote, if you can get £10K GHG then that would cover most (but not all) of the upfront cost, especially if your pipework and rads can be re-used.  Even a few new rads aren't that much.  

As we have no gas and are all electric, it works for us on price alone (hopefully).

Let me know if you want any more details of my installation. 

Kev   

Here's the link to Kev's project: https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/my-ashp-installation

@editor thanks for the info it’s a great help 

@chris-in-kemnay thanks it something to think about 

@kev-m thanks for info . Yer if you need any info or pictures etc just ask and when we’re free to travel next month hopefully you’re more than welcome to come over and have a look and maybe a ride in our car if you want ! 

@editor thanks for link