Tom, i'm giving you the straight shit, man. Just vent the warm air through stainless or aluminized duct with a "Chinese hat" (the a funnel shaped cap for a vent stack. The metalic duct (stack) will not show the heat as they are are not good emitters of IR radiation. The warm as is also invisible to the IR cameras as long as it isn't vented right against the side of your shed (like a dryer vent).

Shov