Gas appliances produce cooler, wetter exhaust than oil. In an old masonry chimney that's too big or unlined, that moisture condenses, mixes with combustion byproducts and slowly eats away at mortar and clay tiles. When a furnace, boiler or water heater is converted or replaced, the flue usually needs a liner sized to the new appliance.
What goes wrong
- Water stains and white deposits on the chimney
- Crumbling mortar and broken tiles at the base of the flue
- Poor draft, which can push carbon monoxide back into the home
The fix
A stainless steel or aluminum liner (depending on the appliance) sized to the manufacturer's venting requirements, connected at the bottom with a cleanout and capped at the top.
What about high-efficiency furnaces?
Many high-efficiency furnaces vent through PVC pipe out the side of the house and no longer use the chimney. If the water heater still uses the chimney alone, that flue is now far too big for it and usually needs a smaller liner.
More questions
Does a new water heater need a chimney liner?
Often, yes — especially if the furnace no longer shares the flue. An oversized flue causes condensation and poor draft.
Need a local professional?
Chimney Champs has been a local chimney company for 13 years. We provide chimney liners & relining in your area. Call (856) 300-9215 for a free estimate.
Sources & further reading
- NFPA 211 — Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances (National Fire Protection Association)
- U.S. Consumer Product Safety Commission — carbon monoxide safety
Keep reading
- Chimney Liner Types: Clay, Stainless Steel, Aluminum and Cast-in-Place
- How Often Should You Clean Your Chimney?
- 9 Signs Your Chimney Needs Repair
- Chimney Inspection Levels 1, 2 and 3 Explained
- What Is Creosote? The 3 Stages and Why It Causes Chimney Fires
- Why Is My Chimney Leaking? 6 Causes and How to Fix Them