USSC 6500 Venting question

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New Member
Jan 22, 2021
Hi all,
I have a USSC 6500 that I am going to be using for my central heat. The question that I have is about the vent setup. With where the stove will be sitting the vent will be coming out through the roof. Due to the length of the vent I will need to use 4".

The issue that I looking to solve is that the exhaust venting comes directly out the back of the unit about an inch or 2 above where the return air plenum attaches, See the pics below. They are snips from the manual. A side and top view. This causes all kinds of issues regarding return plenum placement and T-cleanout placement. My thought to solve this is to come right out of the back of the stove with a 90* elbow. Run a piece of 18" pipe horizontal off the 90 to move the vent stack out to the side of the stove. Then put the cleanout T there and run 4"straight up through the roof.

This is where I was wanting input. Should I be good at converting from the 3" outlet to 4" at the cleanout T, or do I need to convert the vent to 4" directly off the back of the stove (18" sooner)? Keeping it 3" for the first 90 and 18" would give me more room for the air return plenum.

I'm not sure what the designers were thinking with this vent placement.