Nick its closer to 1/3 heat loss.

Pipe it to the top, no the bottom is better as you have no condensation
provisions in your pipeing, it could fill with water ruining the motor.
Best is a constant angle down from exaust port.

Depressurise the room, exuast the gas inside the building, a rube
mononberg idea. Lets see, insurance would be cancelled and an inspector
would deem house uninhabitable. Your idea will kill people. Also a fire
hazzard of running a gen inside, but you never heard of leaking carbs,
cracked fuel lines, stuck floats, gas fumes, spilt gasolene etc etc etc.
Gasolene anything, does not belong inside.