I have a 92% heater in my attic and it condensates. The HVAC guy was an idiot. I have built a box made from foam board around the heater it it doesn't seem to be condensating. What are some fixes that are inexpensive. I am tired of throwing money at this idiots screw up.

92% heaters should condense water from the burnt gas stream. In my house, the condensation is drained into a condensate pump, same as the AC unit, and then pumped into the waste stack. Enough water remains so it has a trap. Is there a drip tray under the unit? If the water runs into that, you could connect a PVC or poly line and gravity feed it outdoors.