Separate meter and electricity tariff for air-to-water heat pump sensible?

I was always led to believe that we need two tariffs for the air-water heat pump and for household electricity. Is that not the case?

Normally not.

From when does the air-water heat pump draw electricity permanently or is this always the case?

As soon as it is on, it consumes electricity. In summer, of course, only when warm water is being prepared. In winter, partly also around the clock or for longer periods during the day. But the normal electricity consumption with a heat pump with a 5kW heating capacity (easily sufficient for a 140sqm KFW 55 house) is only about 1kW – thus manageable (heating element not considered, but that should not run with reasonable planning anyway).

Maybe I haven’t fully understood the principle yet.

The principle is quite simple. As soon as the heating is on (whether heat pump, gas, oil, or pellets), an energy carrier is consumed. For the heat pump that is electricity – either for preparing hot water or for heating.

ok, so it depends on the consumption. I was always led to believe that we need two tariffs for the air-water heat pump and for household electricity. Is that not the case?

You don't have to have 2 meters, we also initially planned only one meter. Then I looked into it and found that it pays off. 4000 kWh household electricity = €1042 per year, 4000 kWh heat pump = €826 per year, but 8000 kWh household electricity (household and heat pump, we have well over 3500 kWh consumption per year) = €2156 per year. That makes a difference of almost €300. Since I don't yet know how much consumption I have with the heat pump, I first started with 4000 kWh. If I only need 3000 kWh, there is still a difference of about €200. So it is worth it in any case.

With us, it pays off as well, about 200 euros savings per year with a heat pump 4500kwh annually and general electricity 4000kwh.

Perhaps we let the first year run through a meter to accurately monitor the consumption and then decide again.

Maybe we let the first year run on one meter to be able to check the consumption exactly and then decide again.

And find out what the second meter costs.

Perhaps we let the first year run through a meter first to accurately monitor consumption and then decide again.

And how do you want to do that with a meter? Assumption, 7250 kWh per year. How is the distribution between household/ heat pump?