Hi Stuart,
By all accounts the RHI payment will exceed any future grant system in terms of financial benefit, and will close next March, so I’d recommend getting in on that before it closes. You should be able to get an ASHP installed for an average house for £8k- you need to get a few quotes to show how serious you are about getting a good price, and negotiate. If you do that you should be able to get it paid off in the 7 years of RHI payments and energy cost savings…