Very clear video and helpful What if the fan is not running or damaged or not connected does the burners will turn on with no air flow ? Or it will shut off the gas automatically.

Hey Mike, How about using some mastic to seal up those holes so you don't have a possible negative pressure near draft hoods in a CAZ zone, you already determined that there isn't enough combustion air and make-up air for that space. Change that filter and better inspect for leaks or cracks in those heat exchangers, if it's been hitting the high limit like that and not moving enough air across the exchanger, my agency just changes anything out with a draft hood, standing pilot, and over 900ppm.

Is the right side of the furnace against a combustible wall? Wood? Doubt if it’s 0 clearance on the sides. High limits are usually set for 180 degrees.

And the filter made it quieter not beccause it's rubbing against anything it's probably Just so dirty that it's not giving you enough return air so your blowers working harder to get the air

That old Johnston should have been replaced years ago. It must be about 60% efficient. Looks like the gas valve was recently replaced. That thing don't even have a/c ! Ask the customer "Are there any registers closed"? They'll say no but when you go check about half of them will be closed. Put them in a Trane XV 95 and a 16 seer a/c and save them some money.

What's an ok level of CO safe to work around?

I didn't know Eric Wareheim from Tim and Eric Awesome show did HVAC work.

Ya get a new furnace

What dumpy tools brother. My analyzer is 12,000 dollars. Start buying Ecom.