If you install an air-source heat pump (ASHP) to heat your property, it will attract a subsidy called Renewable Heat Incentive, which is a payment to you based on how much CO2 emissions are saved by the installation of the system.
The calculation is done on the basis of the guestimated CO2 emissions numbers in your (less than 2 years old) EPC Report, taking potential savings by loft and cavity wall insulation (which you can often get done for free) into account. Naturally that means that if you upgrade your fabric by other methods, and have a new EPC done before you apply, your subsidy will be materially smaller.
Here is a comparison for 2 semi-detached bungalows, one with an EPC of 74-C, and the other with an EPC of 44-E.
Annual energy for heating: 6,577 kWh.
Annual energy for water heating: 1706 kWh.
Total energy: 8283 kWh.
Calculated RHI Payments: £530 for 7 years.
Annual energy for heating: 12,283 kWh.
Annual energy for water heating: 3421 kWh.
Total energy: 15704 kWh.
Calculated RHI Payments: £630 for 7 years.
What to do:
Get a new EPC report to document the poor status (about £50), and get your ASHP process done under that rule, rather than doing it later.
In the case of the small detached bungalow above, the difference is worth £700.
(Cynics Corner: The apparent truth that for such an install done the official way to get the subsidy - via an Approved Installer - seems to cost more than having one by a competent installer who is not Approved, by an amount which takes up most of your potential subsidy-gains, is not to be mentioned.)