I agree that appliances should be vented to the out side .
They say they must and this is incorrect.
Two examples are Gas cook stoves and unvented Fire places.
Will not have either in my home.
“One thing to remember that is critical to your safety? Fuel burning appliances *must be *vented to the outside.
Negative pressure conditions can result in a back-draft of combustion appliances. And
negative pressure can kill.
Carbon monoxide, otherwise known as the ‘silent killer’, is produced when fuels do not get enough
air to burn completely. It is an odourless, tasteless, non-irritating poison that displaces oxygen in the
body, causing the nervous system to completely shut down. Symptoms are similar to those of the flu
and can include headache, nausea, dizziness, weakness, disorientation and/or confusion. It can
knock you unconscious or worse – lead to death.”
I’m thinking this must have been an old standard efficiency furnace. I believe mid and high efficiency furnaces have a pressure switch to protect against this.