If so, you may need/want to put a small restriction in the line going to the lower unit so that the flow favors the higher unit. This would be especially true if the lower unit was less capacity than the upper unit.
On measuring the flow: Since you have two outlets, you'll need a friend and two 1 gallon buckets or containers. As the unit runs, fill each container until almost full, then dump out quickly. Record the count and continue to do so for exactly an hour. The only math you need to do is combine the recordings of the two measurements. Simple.
Sponsors