Furnace and Boiler Flue Cleaning

The flue most people forget

Many New Jersey homes have two flues in one chimney: one for the fireplace and one for the furnace, boiler or water heater in the basement. The fireplace gets attention because people see it. The heating flue runs all winter and often goes years without anyone looking inside.

That flue does steady, important work. If it becomes blocked or deteriorated, exhaust can spill back into the basement. Your heating technician services the burner. The flue itself is chimney work.

Oil and gas flues fail in different ways

Our guide to oil furnace and boiler flues goes deeper into how each fuel affects masonry.

Water heaters left alone in a large flue

When a home switches to a high-efficiency furnace or boiler that vents through plastic pipe out the side of the house, the old water heater is often left venting alone into a flue sized for both appliances. A small appliance in a large, cold flue may not create enough draft, and its exhaust can cool and condense before it leaves the chimney.

This is sometimes called an orphaned water heater. The fix is usually a properly sized liner. See the orphaned water heater problem for the background.

How condensation damages a chimney

Gas exhaust is largely water vapor. When it travels through a warm, correctly sized flue, it leaves the chimney as vapor. When the flue is large, cold or on an exterior wall, the exhaust slows and cools, and some of that vapor turns to liquid on the flue walls.

That liquid is mildly acidic. Over seasons it soaks into mortar joints and the surrounding brick. In winter it can freeze. The result shows up as crumbling mortar at the base of the flue, white or brown staining on the chimney walls, peeling paint in rooms next to the chimney, and spalling brick at the top of the chimney. Debris from the deteriorating flue falls to the base and can partly block the opening where the appliance connects.

This is why a heating flue is worth inspecting even when the fuel burns cleanly. Cleaning removes the debris. A properly sized liner is usually what stops the cycle.

Signs the heating flue needs attention

• Your heating technician mentions soot, poor draft or spillage at the draft hood
• Debris, tile pieces or wet material in the chimney cleanout
• Water stains, white deposits or peeling paint on the chimney in the basement or upper floors
• Rust on the smoke pipe or a connector that is sagging or loose
• An oil burner puffback
• A CO alarm activation in the basement or nearby rooms

How we assess it

1. Confirm what vents into the flueWe note the furnace, boiler and water heater connected to the chimney and how the connectors enter it.
2. Check the base and connectorWe open the cleanout and look at the connector pipe and the thimble where it meets the masonry.
3. Look inside the flueWhen the flue allows, a chimney camera shows tile condition, joint gaps, scale and blockages along its length.
4. Check the topWhen it is safe to reach, we check the crown, cap and termination for damage and debris.
5. Report with photosYou see the findings with photos before any repair or relining is scheduled.

Cleaning and what comes after

Cleaning removes soot, scale and fallen debris from the flue and the base of the chimney. For oil systems, it is usually coordinated with the burner service so the system is not disturbed twice.

Cleaning does not fix a damaged flue. If the camera shows cracked tiles, missing mortar or a flue that is badly oversized for the equipment, the options are usually flue repair or a new liner sized for the appliances. When a liner is needed, the type depends on the fuel and the appliance manufacturer's instructions.

Cleaning an oil flue also means clearing the base of the chimney, where scale and soot collect below the connector. If that pile reaches the connector opening, it can restrict the exhaust even when the rest of the flue is clear.

What we do not cover

Burner tune-ups, nozzles, filters, heat exchangers and controls belong to your heating contractor. We focus on the chimney and venting side and will tell you when a finding should go to your heating technician.

If we find a condition that affects how the heating equipment runs, such as signs of spillage at the draft hood, we will show you and recommend you contact your heating contractor. Some findings mean the equipment should not run until both sides have been checked.

Next step

The quieter months before heating season are a good time to have the heating flue checked, but any time you see warning signs is the right time. Request service and a team member will contact you to confirm a time.

Questions homeowners ask

Sources

1. CPSC: CPSC Recommends Carbon Monoxide Alarm for Every Home
2. CSIA: The Three Levels of Chimney Inspections