From King’s Cross St Pancras, take the Piccadilly line directly; if crowded

https://telegra.ph/Bus-Routes-to-Heathrow-Airport-Local-Services-Night-Buses-and-Fares-08-17-2

From King’s Cross St Pancras, take the Piccadilly line directly; if crowded, consider one stop on the Circle/Hammersmith line to an easier interchange at Paddington.