The ever delightful Dennis Brady never fails to entertain. His latest on using a window AC unit as a source of fresh air from LE:
Air is air. A specially dedicated incoming air supply is a lovely thing but is NOT essential. Whether or not air coming in through a heater or AC is sufficient replacement depends on the volume and consistency of that incoming air. If there’s enough volume to replace air being exhausted, and it comes in fairly steadily, it will work perfectly.
A separate concern is if the incoming AC or heater is blowing air around to create a turbulence that interfers with your exhaust. You may have to install some form of deflector to reduce the likelihood the incoming air flow will push fumes away from being exhausted.
The source of fresh air according to the building codes adopted by all 50 states in the United States clearly state that a local ventilation system MUST have its own dedicated source of fresh air and CANNOT rely on the fresh air supplied by any heating or ventilating system.
Dennis seems to be stuck on this turbulence issue…and it again points to his lack of experience and knowledge of ventilation issues. The ONLY TIME turbulence is going to be an issue is when it moves the flame around on your torch. A properly designed ventilation system will easily handle any turbulence inside its capture area.