Very few modern homes are being built with wood burning fireplaces, instead builders are installing vented gas log fireplaces. These cost a lot less money and time to install. These gas fire places still need a “chimney” or flue just like their wood burning cousins, but with a difference. If the fireplace is on an exterior wall the flue pipe can be that metal square (see photo).
The to get rid of the carbon monoxide generated by burning the gas logs the flue pipe can be horizontally vented out through the wall. This termination is called a direct vent.
The only part of the flue visible will be a termination cap or vent on the exterior. The termination cap is installed to keeps birds etc. out of the pipe. The cap is usually embossed with the word HOT, which it becomes when the fire place is in use, hot enough to burn a child’s hand.
Frank Scurio says
I just installed an ashley hearth wall heater with direct vent. The vent consists of a 4 inch flue surrounded by a 6 inch air intake. The 6 inch is very heavy steel and the 4 inch is very thin aluminum. I know aluminum is not code for gas fired appliances. So why is it used here and is it safe, especially being so thin?