The film describes in great detail how the installation of so-called residential heat pumps offers the tenants space heating and warm water for relatively low costs. The heat pumps are efficient, plus they run on green electricity: one kilowatt-hour of electricity is converted into 4.5 kilowatt-hours of heat. As a result, after the house has been renovated, tenants only need about 1,000 kilowatt hours of electricity for heating a 100-square-meter apartment. And that includes hot water. The interaction between the geothermal probes, heat pumps and heating system has been tweaked to perfection. Hydraulic balancing optimizes the entire system. So it's possible to move away from oil and gas, even in houses that are more than a hundred years old.