Proper sidewall venting requires installing separate vent pipes horizontally so that they vent to the outdoors through a wall of your home.
Can you vent a gas furnace through a wall.
The exhaust gas is too cool for it to rise.
So what does this mean.
I believe high efficiency furnances must be vented horizontally through a wall.
The diameter of the vent pipe should always be larger than that of the gas furnace flue ensuring that no gas escapes from the pipe.
Only units designed for it can have a vent go thru the wall and end there without a vertical stack.
Distances pertaining to the furnace combustion air intake and exhaust vent distances from the indoor furnace cabinet itself and nearby surfaces materials or combustibles.
Adhere to them even if you are building the vent on your own.
An 80 efficient furnace can be side wall vented per national fuel as code 7 3 4 with the use of a mechanical draft system of either forced or induced draft design.
The answer is yes and no.
The vent pipe must overlap at each joint to prevent gas from leaking.
I would be very leary of a hvac contractor would not do this.
You cannot just take the vent off an 80 efficient furnace and run it out a side wall.
Gas furnaces usually come with their own specifications.
When installing a direct vent wall furnace there will be two sets of clearance distances that must be respected.
These ventilation pipes should be isolated from the furnace combustion chamber and made airtight to eliminate the possibility of combustion gas leakage.