Hi all,
I just got a 22.5' Weber Kettle and have trouble keeping it hot (350 F
and higher).

I use two chimney starters to start the coal. When its white hot, i
place two piles of coal along opposite sides of the grill for indirect
heating.

I use an oven thermometer for monitoring the heat.

Keeping the bottom and top vents all the way open, the grill heated up
to about 375 F. 15 min. later it went down to about 330 F. I added
more coals in the hope to get the heat back up. However, another 15
min. later the temperature was down to 200F!

What am I doing wrong?

Thanks,
Christoph