Creosote is the result of poor draft. Offsets, (especially RF) need to breathe and if anything is keeping it from doing so wood will smolder instead of ignite giving you dirty smoke.
Start with a chimney of lit lump for a quick bed of coals and toss in a couple of splits, using only wood for your fire from then on out. Let the splits fully ignite and begin to ash over, then once the pit is up to temp add a split every 45 min. or so to maintain it.
Your intake damper should be 1/2 to 3/4 open and your exhaust should be wide open allowing plenty of draft. If you have to choke down on your intake because the temp is too high, your fire is too big. A small hot wood fire is the way to go here. Charcoal is designed to burn slowly in a cooker designed for that fuel, if too much air gets to it you end up with temp spikes and then plummeting temps when the charcoal all burns up while you're going crazy adjusting the intake damper. To control it you have to choke down on the intake and then any wood present begins to smolder, leading to creosote. Wood is the fuel that offsets were designed for and trying to use charcoal as a primary fuel in an offset usually leads to headaches.
The old timers used a secondary fire and shoveled coals into the cooker or pit and that would be great if you are set up for it but with a little practice you can get a good clean burning fire using the above method.:wink:
