The initial warm-up time for a Bunn coffee maker is about 15 minutes, according to Bunn-O-Matic Corporation. After the initial period, the unit is designed to remain on and plugged into the power supply, providing instant hot water.
Bunn coffee makers do not operate like most other units. Each unit has a lower reservoir of water that stays hot (200 degrees Fahrenheit) at all times and an upper reservoir for cold water. As soon as the lid on the upper reservoir is closed, the hot water flows through a spray head over the coffee grounds to brew fresh coffee. The cold water refills the lower tank, and the water is heated and stays at the correct temperature to brew the next pot. When the water is hot in this tank, coffee brews in three minutes.