Outdoor fire
Hearth
Gas stove
Electric stove
Induction stove
Electric kettle
Coffee machine
Microwave oven
Vending machine
Solar hot water panels
Oven
Car engine
Computer processor or video card
Lens collecting sunlight
Nuclear reactor
Geyser or natural hot water springs
Volcano
I make tea from cold water
I buy my tea ready to drink
I never drink or make tea
Other