Gas furnace venting is a ventilation system designed to remove carbon monoxide and other potentially dangerous by-products of combustion from the home. All gas appliances that operate indoors require a ventilation system, otherwise these toxic by-products can build up, displace oxygen and potentially cause death by asphyxiation.
When a hydrocarbon burns completely, the only by-products are carbon dioxide and water. Unfortunately, the conditions for complete combustion of a hydrocarbon are hard to maintain, so most fuels undergo incomplete combustion. One of the most common by-products of incomplete combustion is carbon monoxide, a gas that can cause headaches, fatigue, nausea, dizziness, difficulty breathing, loss of consciousness and eventually death. A ventilation system removes these gases before they can build up to potentially dangerous levels.
A furnace vent typically begins directly above the pilot light and burner and rises through the home to the roof where an exhaust vent allows the gas to dissipate into the atmosphere safely. There are specific guidelines as to the type of pipe required for each appliance, as well as to the configuration of the vent. This is to ensure that there are no spots where dangerous gas could escape the venting system or improperly arranged angles that might create a bottleneck in the vent where gases might build up.
As of 2015, there are three vent options for a gas furnace: natural, direct and sidewall power. A natural vent system is also called a Type B vent design and uses air inside a house or building to produce combustion. Because gases produced during this process are of a relatively high temperature, they can be vented through a vertical pipe system with relative ease and efficiency.