I don’t personally have experience of Consumer Energy Solutions, though I have heard of them. Are they offering a funded Eco4 installation?
I’ve got experience of heat pump installations in old stone cottages and old stone mid terrace houses… both with little insulation but still very good performance (COP ~4) - both of those systems are systems I designed and installed myself (with help from @johncantor) so I got the sizing of the radiators, pipework, heat pump, control setup all right. My expectations were also aligned with how the system works.
I know several people who have had heat pumps installed in similar properties who have unfortunately had the opposite experience. With high bills and trouble getting warm, so it does need to be done carefully.
I’ve been helping a couple who live up the road in a Welsh longhouse to work out if their heat pump is working ok. They are getting a COP of 3 (which is towards the lower end of the range we are seeing on http://heatpumpmonitor.org) but still should at least give them a similar cost to mains gas. They do still find it too expensive and so it’s actually rarely on, which is part of the reason for the low COP as there’s a lot of standby consumption and hot water is a greater portion of their use, which requires higher temperatures. They prefer to keep their log burner going and are quite frugal otherwise. The increase in electricity costs have not helped!
I think a key thing to work out first is how does your friend like to keep the house at the moment with the oil boiler. Is it kept at a fairly even temperature all the time and how warm? or is the oil boiler only used very intermittently with the wood stove doing most of the work? It would be worth getting a clear idea of the bills as they are, both in kWh and £. Is she also happy and comfortable with the temperatures as they are at the moment? Does she zone the house at the moment, are there annexes with radiators turned off?
The next step is to get a heat loss calculation for the house from the company and to compare the calculated running costs and consumption at the standard indoor temperatures assumed, usually around ~20C with her current oil boiler running costs.
If they look like they are in the right ballpark and she is happy with the running costs that they project, that’s a good first step to establish. If there’s a big discrepancy, e.g she’s spending half of what they calculate she should be spending then that’s something to dig into. Is it because of lower temperatures in the house etc? If the calculated consumption and running costs is much higher that could result in an oversized system being installed and lower performance running it more frugally.
The next step is to get the radiator sizing and pipework right, to make sure that the radiators are sized to provide the required heat demand when it’s -3C outside at a flow temperature of at most 45C (hopefully less), my design flow temperature is closer to 42C. The installation company may be tempted to go for higher flow temperatures if it’s hard to get the required radiator area which will then result in higher bills.
The other bit’s to be careful about is the size of the heat pump itself in relation to the calculated heat loss and all the extra gubbins that seem to get installed with a lot of systems e.g low loss headers, buffers, lots of pumps etc, often meant to help with zoning which when coupled with 3rd party controls and the wrong sized heat pump can all get into a bit of a mess.
On a more positive note, it certainly can be done and it can be done well, giving good performance and running costs that are least in-line with oil or gas. There are just quite a few bits to take care and get right, which is a big reason for our efforts behind heatpumpmonitor.org to understand and hopefully get more heat pumps up to the higher end of the performance range.