Thought I'd come back with how the A2A journey has been going so far.   We fitted 2 x 2.5 kw and 2 x 3.5 kw indoor units with 2 outdoor in our bungalow to replace 5 storage heaters.  Aside from a couple of tests of the AC in summer, it wasn't until September they saw much action. We haven't changed energy tarrif so still eco 7.   I'd love to have some like for like stats on energy usage but there are quite a few moving factors.   - Old draughty double glazed widows