Should we use the Heatpump?
The Energywise website (run by the NZ Government agency EECA) has a calculator which allows you to work out how much electricity your appliances are using. https://www.energywise.govt.nz/tools/running-costs-calculator/#!/
According to this site a 6kW heatpump uses just over 1kw of power per hour. That means it costs about 28c per hour to run a heatpump. So here are some comparisons to get you thinking about whether you should use the heatpump and keep warm.

One $5.00 coffee
= 17 hours of running your heatpump
= running your heatpump for 1 hour per day for 17 days
So if each person in a 5 bedroom flat gave up just one $5 cup of coffee at some stage during the year, the whole flat could run the heatpump for 3 hours every day for 1 month.

One $20.00 Big Mac large combo delivered by Uber Eats
= 71 hours of running your heatpump
= running your heatpump for 2.3 hours per day for 1 month

$25 of liquid refreshments
= 89 hours of running your heatpump
= running your heatpump for 3 hours per day for 1 month
= running your heatpump for 6 hours per day for 2 weeks.
So if each person in a 4 bedroom flat gave up $25 of refreshments at some stage during the year, the whole flat could run the heatpump for 3 hours every day for 4 months.