Method for renewing a building heating system of a building, and renewed building heating system

A method for renewing a building heating system of a building, comprising steps of:

• a) disconnecting an existing boiler of the building heating system:
• from an existing fuel source,
• from an existing fluid line for conducting fluid to be heated by the boiler, and
• from an existing air inlet pipe connected to an existing air inlet opening, to allow air to be led through the boiler, and
• from an existing flue gas discharge pipe connected to an existing flue gas outlet opening for discharging boiler generated flue gas,
• b) removing said boiler, and
• c) connecting an air source heat pump:
• to the existing fluid line,
• to the existing air inlet pipe and/or the existing air inlet opening, and
• to the existing flue gas discharge pipe and/or the existing flue gas outlet opening,
• connecting at least one heating tube, directly or indirectly, to the heat pump to provide additional heat energy to the fluid to be heated, and
• d) connecting said heat pump to an intermediate working fluid line for heating a working fluid conducted through said working fluid line, wherein said working fluid line comprises at least one water heat exchanger for transferring heat from said working fluid to water conducted through at least one water line of a building water system of said building, and wherein said at least one heating tube makes part of the working fluid line, and wherein the at least one heating tube is configured for flow-through of the working fluid, such that during flow-through of the working fluid the working fluid can be heated by the heating tubes.