ANATOMY OF A GAS CHIMNEY/UTILITY FLUE
Anatomy of Gas Chimney
Utility Flues
Did you know gas utility appliances have chimneys? That’s right, they do!
Your gas furnace and water heater vent through the connectors allowing exhaust/toxic gases to escape out the homes existing chimneys! It’s something many homeowners don’t even think about, but is critical to understand for a few reasons.
Knowing more about the parts of a gas chimney system is important to your annual home maintenance plan. The more you understand about the parts that make a heating system work, the better you can help protect your family from harm that could come from a lack of maintenance.
Gas Chimney Parts
1. Chimney Top Opening: at the top of the chimney the top clay flue tile extends outside of the crown and is open without a cap. Every chimney should have a cap installed to prevent water, debris, and animal entry to the home (cap not shown in the illustration).
2. Gas Furnace: an appliance used to heat a home that runs off natural gas. All gas furnaces must have a pipe (also called a “gas chimney” to vent the exhaust to the outdoors.
3. Gas Water Heater: the tank that warms water for your household use such as laundry and hot showers.
4. Draft Hoods: Designed to prevent backdraft and provide an escape route for gases, draft hoods are placed at the top of gas furnaces drawing air into the chimney as necessary to create a constant flow. The draft hood device is built into an appliance, therefore non-adjustable. It also helps neutralize the stack effect.
5. Water Heater Vent helps remove exhaust (gases) from your water heater to the outdoors. This may come from the atmospheric air in the house, or it can come through a vent pipe that pulls air from the outdoors .
6. Connectors: pipe connection for furnace/water heater. Condition of connector (or lack thereof) for the furnace and/or hot water heater to the utility flue is a critical part of annual inspections to maintain the integrity of your system.
7. Wye: Pronounced /wī/: when two separate connector pipes meet with a joining branch, at an acute angle it’s called a wye.
8. Thimble: A chimney thimble is a fire clay or metal ring which allows a connector pipe to pass into the flue. The thimble must be permanently cemented in place with at least 24 gauge thickness. A thimble cover that looks like a pie plate is often found where there once was a pipe.
9. Gas Furnace Vent: Most modern gas furnaces use Type B Vent and draw convection air naturally from the house. These furnace pipes should be inspected regularly to prevent toxic gases from back-drafting into your home.
10. Foundation & Footings: A footing is part of the foundation upon which the brick and mortar chimney is built. Footings are constructed of concrete or solid masonry and must be poured properly to be able to support up to tens of thousands of pounds of weight.
11. External Chimney: the outside of a masonry chimney consists of brick and mortar. (Stacks are also made of blocks or stone).
12. Clay Flue Liner: Similar to the fireplace flue, the clay flue is the passageway to exhaust the furnace and/or hot water heater in most homes. Liner types can vary and since its venting gas appliance could be called a gas flue liner.