Another easy way to determine if there's an ongoing backdrafting issue is to look for rusting around the flue or any melting of plastic components on top of the WH.

Can I get info on the smoke pencil you are using in the video?

Won’t exhaust fans, such as bathrooms and the range hood, change the air pressure dynamics of the house and possibly the gas venting ?

I wonder, in this case he opened the door to change that air pressure. Do ppl have to create a permanent door to stay open to fix the issue?

What door you open

What about when newer, efficient water heaters just short cycle, and there is just too much cooler air along the entire run of of the flue venting? There is just not enough time for the water heater exhaust to warm that air and create a proper updraft.

The pipe should be 12 inches in length before the elbow. If they have a 200 amp service they should just switch to a tankless electric water heater.

What if exhaust from the kitchen stove is on is there any backdraft will happen?

If you have carbon monoxide detector, will backdraft set it off?

I would cut a high low grille into the room or leave door open.

Does anyone know the brand of this smoke gun?

True...whats the smoke tool called..very nice tool

What is the best solution? Keep your water heater in an open space ? Or keep your mechanical room open ?

This video is junk. If building code and fuel gas code are followed this doesn’t happen A. Opening the door is doing what the hack who constructed the room failed to do. Supply adequate combustion make up air. Hire professionals. B. If you’re producing “toxic gasses” aka CO over 100 ppm, then there’s burner problem. Hire professionals. C. NFGC allows 5 minutes for the chimney to prime before measuring draft. Hire professionals.