A happy gas appliance is one that has
a good supply of air plus a proper way
to exhaust the byproducts of combustion.
Unfortunately, providing those
basic needs is not as simple or as
straightforward as it used to be.
In the old days (six to ten years
ago), things were easy. Those old 60%-
efficient furnaces and boilers produced
plenty of hot, dry flue gases which
could easily force themselves up
almost any chimney. Little if any
"design" was necessary for the vent system.
Today's gas appliances, however,
have improved efficiency which means
less flue gas at a lower temperature.
To ensure proper venting without
corrosion problems, the vent system
must be designed for the specific appliance.