I'm not sure what the exhaust temp would be but I had my big smoker under a lean to and it discolored the painted metal above the stack(only 6'' of clearance). If I was using a tarp for a roof I would leave as much room as possible between them and I would make a heat shield/ deflector about 8-12 inches above my stack. I'm talking about something makeshift just thrown together, a small piece of scrap metal/tin and a piece of pipe or a stick, something to keep the heat from directly flowing on the tarp. jm2cw
To measure the temp coming out stick a themometer probe across the stack while using the smoker. Big T is spot on with the deflector above the stack between the tarp. jm2cw
I like the deflector idea... Especially if I have at least 2 feat clearance above the stack.. I'm planning to have 3ft clearance with a fire retardant tarp. Add a thin piece of metal for a heat shield and I should be in business!
I don't care about discoloration... I know the smoke will do that.. I just want to be comfortable walking away from the smoker for a bit. Inside to cool off, wash some pans or cut up some meat.. Whatever.
So I dropped a probe into the stack about 4 inches.. Basically as far as I could get without it touching or burning my hand. It read around 325 while the thermometer on my pit read around 300. I raised the probe about a foot above the stack, still in the stream of heat/smoke and got a similar reading to the Pit thermometer again. Above 1 ft the smoke started to dissipate and spread out so the reading dropped a lot. Based on this, at 2 feet clearance I'm good, and at 3 feet prob don't even need the heat shield especially with a fire retardant tarp.