Three common instruments found in a flue gas analysis kit include:

1. Combustion gas analyzer: Measures various components in the flue gas such as oxygen (O2), carbon dioxide (CO2), and carbon monoxide (CO).

2. Flue gas temperature probe: Measures the temperature of the flue gases.

3. Differential pressure gauge (manometer): Measures the pressure difference between the reference point and the flue gas sampling location, indicating draft conditions.