Just picked up a used leisure line Pocono top vent and was going to install it in the basement with a fields power venter( SWG ). Another stove occupies the chimney. What would the proper size of the power venter be? A 4-HD is rated for 170,000btu or 1.10gph oil but this would reduce the vent size to 4" going thru the wall . Is that the correct one to use? Prices go up fast as you go up in size, and don't want to oversize the venter and and have to throttle it way down. Any help would be appreciated.