What is so special about insulation for heatpumps? You need that insulation anyways.
EDIT: ok so the best interpretation I have is that it has just been so cheap with gas that people have not bothered insulating their houses.
EDIT: ok so the best interpretation I have is that it has just been so cheap with gas that people have not bothered insulating their houses.
A heat pump’s max output in heating mode decreases when the outside temperatures are low enough (whereas a gas boiler has a roughly constant max output and it’s quite inexpensive to size a wall-hung combi for 150K BTU/hr [44 kW] if needed).
Buildings that are fine on the coldest design day with a gas boiler may need more output than a heat pump can provide on that day.
Adding insulation can reduce this gap, which is why you’ll often find a heat pump project needs insulation, while a boiler replacement like-for-like would merely benefit from additional insulation.
The UK government back in 2010 actually had major plans for nation wide insulation, but famously the prime minster at the time, David Cameron, ordered the cutting of "the green crap" (widely reported to be his words) to help resolve some short term political problems with the budget in the early 2010s.
So technically it would be possible to install a heat pump with the same capacity as the existing gas boiler, but it would costs a ton more and it would all be upfront.