At the risk of continued letter ‘ping pong’, Jeremy Hawksley raises some important points.
Electric-driven vapour compression heat pumps are not regarded as direct replacement for off-gas-grid properties using oil, even though the new generation of heat pumps should be able to achieve system (not just unit) SPFs above the necessary level of 1.7 (eg BS EN 15316 calculation based on BIN temperatures or BS EN 14825 as EuP lot 1).
I agree that in terms of initial cost, it will often be cheaper to replace conventional oil-fired plant with condensing models, providing they are actually set and left in condensing mode and no other refurbishment costs are required.
But this raises issues of long-term running costs and, even more importantly, oil-fired plant will face similar issues to heat pumps, ie in order to be efficient the return temperature must be lower than conventionally, hence also the flow temperature.
Will the existing heat emitter system be adequate or will upgrade be required? If the latter there may be little difference in the additional costs.
I have always found this perceived issue of need for insulation for heat pumps to operate correctly rather curious.
There are some peripheral reasons why it is preferable, yet not essential, but definitely advisable.
Surely we should insulate and conserve energy whichever fuel is used, and even more so when paying 7.6p/kWh for energy delivered via condensing oil boiler as opposed to 5p/kWh for the poorest-performing MCS-compliant heat pump system.
There are already heat pumps performing some 20 per cent above this level and with newer models now 40 per cent better and able to operate at 65 deg C within the break-even window.
This is based on SPF4 metric, and therefore includes boost heaters (eg DHWS and low ambient operation).
As long as consumers understand that costs are subject to many factors and the combination of these factors can give very different results, sometimes for similar situations, we are acting responsibly.
What we probably both agree on is that users have choices and the information they are given to make an informed choice should be as reliable and even handed as possible.
Hopefully this series of letters has helped in this regard.
Graham Hazell, renewergy consultant