IMO you are too close to the max ouput of the heather and it is also too small.
My shop I went with a mobil home furnace. They are about 80k BTU. They can be had for the same or less as what you are paying and run for much cheaper on LP, NG or oil.
I then added a wood furnace and linked the fans between the two. Gives me a choice of one two fuel or I can run both. When either run, both fans blow.
