Container Data

Packet ID	Direction	Mojang Name	MCP Name
`0x69`	Clientbound	`ContainerSetDataPacket`	`Packet105UpdateProgressbar`

This is sent by the server to update the furnace GUI's progress bars.

Clientbound

Field	Type	Description
Window ID	Byte	The incremental ID of the window. Ranges from 0 to 99
Type	Short (Type)	The type of data.
Value	Short	The value of the data.

ID	Name	Range	Description
`0`	Smelting Progress	`0` to `200`	The progress of the current item being smelted. This counts up from `0`
`1`	Burn Time	`0` to (fuel duration)	The progress of how much fuel remains. Starts at the burn time of the used fuel, then counts down to `0`.
`2`	Maximum Burn Time	`0` to `20000`	Sets the max burn time of the current fuel (defaults to `200` if not sent)

All of these are sent only if they've changed, which means 0 and 1 can be sent every tick while looking inside of the Furnace Interface.

See the smelting page for more info on what counts as valid fuel and for how long said fuel burns.