Empire Comfort Systems DV-210-7SG - Manual (Page 12)

Page 12 12433-5-0606
On the main burner, the burning gas forms a primary flame and a
secondary flame. The primary flame is blue and about 3/16" (5mm)
high. The secondary flame is very pale blue, 3 inches (76mm) to 5
inches (127mm) high. Dust in the combustion air will produce an
orange flame. Do not mistake it for an improper yellow flame.