Hi Ursula,

The Morsø Owl Convector has 3 air intakes, these are:
 
Primary air.
This is controlled by the level under the left hand side of the ash lip
(as you look at the stove) pushing the lever up closes the air intake
and rotating the control anti clockwise will open the air intake. The
primary control introduces air into the stove below the grate and should
be used when burning solid fuel (manufactured smokeless fuel).Secondary air.
The secondary air intake is controlled by the lever under the right
hand side of the ash lip and is operated in the same manor as the
primary control. The secondary air is drawn into the combustion chamber
through cast iron channels and introduced above the fuel via the air
wash manifold, this curtain of pre-heated hot air washes down the glass
keeping it clear. The introduction of hot air in the firebox will also
produce secondary combustion of the fuel gases giving a cleaner and more
efficient burn. Secondary air should be used when burning wood but can
also be used at lower levels to maintain a clean glass when burning
solid fuels. When wood burning allow a 2-3 cm bed of ashes to build up
beneath the wood and any logs with a diameter larger than 100mm
(4inches) will require splitting, all logs must be well seasoned. Tertiary air.
This is simply a third air intake; although there is a control lever
for this at the rear left hand side of the stove it is pre set in the
lower position and should not be adjustment. Tertiary air guarantees
sufficient air into the stove to give a clean burn when using wood.