Val6 KBE5L Maintenance Manual page 24

Adjustment of air inlet for using the heater in high altitude
Picture 9
If dark smoke comes out or flame protrudes from the radiation disk in using the
heater in an altitude higher than 3,000 ft, you need to expand combustion air inlet
opening.
knob
1. Unfasten a knob and expand combustion air inlet
opening.
Standard Scale: 3
You need to expand combustion air inlet opening
gradually until smoke is clear away or flame doesn't
protrude from the radiation disk. (scale should be 4
or more)
2. Fasten a knob of combustion fan and put a burner
cover back.