About this detail of the Tiger
This diagram shows the third kind of air vent in the Tiger's firewall. I don't know when it was introduced.
A surviving German drawing  shows how to upgrade an old Tiger. When it was drawn, it specified an upgrade to the second kind of firewall vent. But later the drawing was altered to specify this third kind of vent. So we know this vent was introduced no later than the drawing change, 6 March 1944.
A possible date for the introduction of this vent is September 1943, when the entire firewall was simplified [1, see 220.127.116.11] .
This is a detail from the design drawing  . All text relating to the second kind of air vent was struck out in March 1944. The dimensioned hole was drawn then, and a new paragraph was added above this detail:
"Seal the cutouts and threaded holes for the sliding vent respectively. Cut the hole for the door. See drawing 021 C 2701 - 370"
New text was written at the side of the drawing:
"l) The old air vent in the firewall is to be removed and a door (021 E 2702 U 206) according to diagram 021 B 2702 U 205 is to be welded on."
This design of vent was probably used until the end of the Tiger's production run. The surviving hull #251114 (the 'Saumur Tiger') has an example of this vent  . The door had a latch to close it firmly
On the engine side, the sliding panel and handle were gone. There was a limiter to prevent the door opening too far and becoming unreachable. I believe the curved arm above the door uses friction to prevent the door swinging shut during travel.
At some unknown time the clutch control lever was deleted from the HL230 engine. A new device, the cold-weather starter, was added in its place. This device had a thumb lever, visible at the bottom of the photograph; so the firewall door remained.
This door had a rubber seal around the edge. Since this door was not spring-loaded, the crew could simply leave it open if they wanted hot air.
The same kind of vent is found in the surviving Sturmtiger at Munster museum. This photo  , taken from underneath, shows the catch for the door.(The latest version of this article)