Vented Vs Non Vented Fuel Cap

The non emissions caps freely vent the tank to the atmosphere which can waste gas through evaporation.

Vented vs non vented fuel cap.

The vented gas cap has a one way release valve that is pressure activated. Ventless logs do not put off these emissions so no chimney or flue is needed and the heat is more likely to stay in your space. All modern vehicles use a non vented cap. Both styles of caps provide vacuum relief.

Look at the front of tank at the axle for a u shaped metal vent tube about one inch in diameter. The vented gas cap is designed to vent small amounts of air into the car gas tank line. Gas fireplaces come in two configurations. Gas caps have not been vented since the introduction of evaporative emission controls smog control on cars many years ago.

Vented gas logs produce carbon monoxide emissions so your fireplace must have a chimney or flue. If that tube is not present then you need a vented gas cap. In these systems the tank incorporates a third vent line that is routed to a cannister inside the engine compartment that is designed to capture and recycle gases formed in the fuel system. Vented caps only vent one way into the tank to allow air in as the fuel is used to prevent a vacuum from occurring.

When the pressure reaches a certain point defined by so many pounds per square inch the valve opens by a very small amount relieving some of the pressure. Emissions gas caps have a built in pressure relief valve that will only vent to the atmosphere if the pressure gets too high. A non vented cap is just that no venting at all and will not let air in or out so unless you have an eec tank or other vent setup elsewhere you ll have some issues.