This plate is needed to isolate the outdoor boiler from the indoor? Unless you are running the indoor one 50+ degrees colder than the outdoor I don't see how a 10 would work. (Unless it is a 10" x 20" plate heat exchanger.
I don't like to use 10s at all because they have way too much head pressure loss.
If you want to try a 10, I have a used one on the shelf you can put to see how it works but I really don't think it will do what you want.
Here is a chart of plate heat exchangers. The last number is the pressure drop. Multiply that by 2.3 the get feet of head.
Model Btu/hr Flowrate GPM Hot Inlet ℉ Hot Outlet ℉ Psi
LB10 40,000 6.20 180 160 5.175
LB20 80,000 7.44 180 160 3.5
LB30 110,000 8.93 180 160 1.7
LB40 156,000 10.71 180 160 1.02
LB50 220,000 12.86 180 160 0.7
LB60 300,000 15.43 180 160 0.56
LB70 400,000 18.51 180 160 0.42
LB80 538,000 22.22 180 160 0.36
LB90 710,000 26.66 180 160 0.3
LB100 930,000 31.99 180 160 0.24