According to the PP people here: http://www.wood-fired-pizza-oven.us/italian-recipes/
When the over is already well heated, put off the fire, leaving the door open the temperature should drop to about 200-220° (390 – 430 Fahrenheit) that will be steady for about 2 hours even without the fire going. If you want to leave the embers in the oven, you should leave the chimney cap slightly raised and the front door partially open to avoid too much smoke. However, if you want to remove the ashes, you must close the chimney to keep the internal temperature for longer time."
However, here https://www.youtube.com/watch?t=37&v=p46zulun3IA
they say to just close it without mention of the ashes and embers.
When I roasted a chicken, I followed the first instructions and left the chimney lid up an inch.