not sure why my text wasn't included with the above pic. Anyway, I also built a stove from an oil tank, not to heat a building, but for boiling sap, and I also once tried the pipe with holes in it to get more air to the fire to help with the boiling rate; maybe I used too small pipe ( I think it was one inch dia) or insufficient blower, I dunno, but it didn't work very well. The next season I cut an opening below the door and positioned a squirrel cage blower over the opening and connected a variable speed control to the blower motor; simply blows air under the grates from the front. Wa-la! By far the number one change that significantly increased my boil rate. Found a sweet spot by messing with the speed control and varying the cfm to the burn chamber. A word of caution though when running AUF (air under fire) as they say in the syrup hobby.....you'll experience much higher burn temperatures and can have embers shooting out of the stack with excessive air being injected into the stove. Since that picture was taken, I have relocated the stove inside a building and went with multi-wall chimney pipe and a metal roof to minimize potential issues. I think you'll see an increase in the air temperature in those pipes by adding AUF. Good luck with the rest of the build.