[mft_]

Our house (in Europe) is relatively old and not well insulated by modern standards, and all of the advice we read and receive from experts is that heat pumps are not a good fit without additional insulation.

The gist is that we’d need to spec larger units and/or run them harder than usual, removing savings vs. gas.

[Panzer04]

It doesn't really matter. You should insulate anyway to save energy, but a heat pump will still use 1/4 the energy as resistive electric for the same heat. Depends on your gas prices as to whether it's worth it, but it almost certainly would be.

A worked example - In AU gas is metered per MJ - 3.6MJ/kWh. So 3c/MJ means that gas is equivalent to electric heat at 12c/kWh. Heat pump multiplies that by roughly 4x, so 48c/kWh is the Breakeven point for a heat pump vs gas heating.

Heat is heat, it makes no difference. insulation would save you money on all heat sources though, and can be a pretty cheap upgrade (insulating the roof space, for example).

[brnt]

They give that advice because 'experts' (you probably mean salespersons) have to simplify a somewhat complicated story in a single recommendation for their market.

We can assume that you currently have a high power (e.g. 28kW+) gas heater and radiators that can only emit that kind of power at high water temperatures. This system works in tandem (place where has is burnt and devices that emit the heat throughout the house). A leaky house typically needs a higher heating power in the interest of comfort: it'll have a higher power loss, and you'll want to not spend days bringing it up to room temperature in case the power was out or what not. These heating systems are usually overdimensioned, so any variability in the power loss of the house is compensated for by simply upping the power output.

A heatpump is lower power, and therefore slower, and therefore you'll want to limit the heat loss of the house, because when things go wrong (somebody left a window open in winter), you're gonna have to wait some time before the pump's caught up. Calculating a building specific optimal heat pump power is already trickier, and it's trickyness is increased without that insulation.

Which doesn't meant that you cannot do it yourself! You can simply accept that response times are going to be slower (so, if you flip the temp up from 17C to 20C that it's gonna take half a day). Best is to just set it to a temp and leave it there, it's no longer the advantage it was to modulate.

Most important is to not underdimension the heat pump. I've never seen a salesperson offer it, but there's online communities of people who can and do calculate it for older houses (gas consumption is a good proxy). One thing to understand is that heat generator power (be it a heat pump, gas heater, whatever) needs to match the heat emission power of the system that releases the heat (radiators and floor heating most likely). The water is gonna run at lower temps with a heat pump, so that means that your radiators will emit less heat, and probably not enough. You need to make sure that at the water temp the pump outputs economically the power output of the delivery system matches. This usually means putting in floor heating and/or significantly larger and more efficient radiators.

[manmal]

Isn’t insulating a house way more expensive than buying a bigger heat pump and paying for extra electricity?

[vladvasiliu]

It probably depends on what kind of insulation work needs to be done.

My parents' house in France is one of those hundred-year-old stone ones. It's fairly cool in the summer, but it gets quite cold in the winter. My father did the insulation work himself (he's not in construction) for fairly cheap and saw his gas bill halve.

[stephen_g]

The usual other option is to look at increasing the size of the radiators, then you can lower the flow temperature and you still get big efficiency savings.