I don't know how you guys can burn so little and be in colder places than me!
I burned about 7 cordof maple, locust and cherry that was barely 10 months old from
Nov 1st thru end of March, ( about the same the first year with even less dry wood)
View attachment 111853
that may be part of the problem...10months old wood?

of maple, locust and cherry that was barely 10 months old from
another 900 sq.ft. garage to 45 
You are going to need well seasoned wood for your gassification boiler to perform nicely. 