We just started our first continuous kiln up and the project engineer says we can load one track with dimension lumber and the other with 4x6's. Has anyone tried this or have any idea what the push rates would need to be? Will this even work?? Don't want to have a lot of downgrade due to high moisture content.

Henco is correct concerning the airflow. Just know that with one track of 4" and one track of 2" the 2" will get less flow than if both tracks were 2" and the 4" will get more airflow than if both tracks were 4".  How much? You would have to test all 3 sets of conditions to know that.

Bonedry I have and usally am running two differant products in my continuous kiln. In the past I have had 6x6 on one track and 5/4x6 on the other. What you will see is that a very slow rate on your timbers (say 1.5' per hour) but will make up time on you 5/4 From say 5' per hour to 6' or more). This is due to temp in the kiln rising. If your temp keeps getting hotter you need to adjust your speeds on your side that has demensional lumber. the temp you set your Kiln at is what you want to maintain. If it gets high or low its giving you a sign that the lumber is wet or dry. This is just a way I see whats going on with out a big surprise when the product starts exiting the Kiln. You want to make sure the fans in you main chamber are reversing every 2-4 hours. I prefer 2. This is just some things I have found with our Kiln going on 6 years old.