How to read Bosch heat pumps and air conditioners serial numbers
This covers Bosch. The serial number is on the rating label on the unit. On a mini split it's on the side of the outdoor unit.
Reading it yourself
22 to 24 characters. The three characters after the first four are a date code. Bosch's own table turns each code into a month and year: 278 is October 2022, and 720 is April 2017.
Example:
3520-278-0000289-7738007421was made in October 2022.
This is the date the unit was made. It was usually installed soon after, but it can be later. If a serial doesn’t fit any of these patterns, look on the label for a printed manufacture date.
Sources
Checked in October 2026.
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