Old Chimneys, New Gas Furnaces: Prewar Houses in Haddonfield, Collingswood and Haddon Heights

Haddonfield, Collingswood and Haddon Heights hold the oldest houses in this part of Camden County. Census estimates date roughly half of Haddonfield's homes and nearly half of Collingswood's to before 1940, and more than four in ten in Haddon Heights, and in all three boroughs most homes now heat with natural gas. That pairing, a masonry chimney built for coal or wood and a modern gas appliance venting into it, is where many chimney problems in these towns begin.

What these chimneys were built to carry

A Foursquare in Haddon Heights, a twin in Collingswood or a Colonial Revival on a Haddonfield side street was usually built with a brick chimney serving a coal furnace or boiler, and often a second flue for a fireplace. Coal smoke is hot and heavy, so those flues were large. Some were lined with square clay tiles set in mortar; some had no liner at all, only the inside face of the brick.

Coal gave way to oil and then to gas, one conversion at a time, and in most houses the chimney stayed exactly as it was built. The appliance changed. The flue did not. In Collingswood's two-family houses the arrangement can double up, with two furnaces and two water heaters in one basement venting into the same stack, so one chimney may be serving four appliances it was never designed around.

What gas exhaust does inside an old flue

Exhaust from a gas furnace, boiler or water heater is far cooler than coal smoke, and it carries a good deal of water vapor. Moving up a big, cold masonry flue, that vapor can cool enough to condense before it reaches the top, and the condensate is mildly acidic. Over years it softens mortar joints, cracks and flakes clay tiles, and sends grit and mortar crumbs down to the base of the chimney. Where the liner has gaps, moisture and exhaust reach the brick itself.

The problem gets worse after a common upgrade. When an old furnace is replaced by a high-efficiency model that vents out the side wall through plastic pipe, the water heater is often left venting alone up a flue sized for the furnace and the heater together, or for coal before either of them. A small appliance in a large flue drafts weakly and condenses more, which is exactly the wrong direction for an old chimney.

Signs worth a closer look

Some signs show from the outside: white or brown staining on the brick near the top, mortar that crumbles when touched, a crown with open cracks. Inside, look at the base of the chimney or its cleanout door for pieces of tile or piles of grit, at the water heater's draft hood for rust or scorch marks, and at walls and ceilings beside the chimney for damp patches after rain.

Treat any smell of exhaust near the water heater or furnace seriously. The Environmental Protection Agency lists leaking chimneys and furnaces, and back-drafting from furnaces and gas water heaters, among the indoor sources of carbon monoxide. A flue that is blocked, oversized or leaking is one of the ways that happens.

Cleaning, inspection and the liner decision

The EPA advises having a trained professional inspect, clean and tune up the central heating system, furnaces, flues and chimneys included, every year, and the National Fire Protection Association gives the same yearly advice for heating equipment and chimneys. Chimney cleaning is where that inspection starts. Brushing out soot, fallen mortar and old nests lets the flue be seen from top to bottom, and a light or a camera shows whether the tiles are whole, cracked or missing.

What happens next depends on what the flue shows. Sound tile with a few open joints can be repaired. A flue with cracked or missing tile, or one far too large for the appliance now using it, is usually relined, with a new liner sized to the furnace, boiler or water heater it serves. The old masonry stays in place as the shell around it. In a house with a fireplace beside the heating flue, each flue is judged on its own.

The crown, the cap and the flashing

The top of the chimney takes the weather. The crown, the slab of mortar or concrete around the flue at the top, cracks with freeze and thaw, and water that gets through it runs down inside the stack. A missing cap lets in rain, leaves and animals. Flashing where the chimney meets the roof loosens as the roof ages. Chimney repair in these boroughs is mostly about those three: rebuilding or sealing the crown, fitting a cap, resealing the flashing, and repointing the joints above the roofline.

Haddonfield's historic district and exterior work

Haddonfield asks for a Certificate of Appropriateness before an owner in the historic district changes the look of a building from outside, roofs and siding included, with design review by the Historic Preservation Commission and final approval from the Planning Board. The borough notes that the commission's chair can decide that some work does not need a full commission review, and it points owners to the zoning officer for borderline cases.

For a chimney, that means the parts people see from the street: a new cap in a different style, a rebuilt crown that changes the profile of the stack, or visible hardware on top of a new liner. Cleaning and inspection change nothing outside. It pays to settle the approval question before the work is scheduled rather than after the scaffolding goes up.

Fireplaces that see a few fires a year

Many of these houses still have a working fireplace that gets lit on a handful of winter evenings. Smoke rising through a cold masonry flue cools as it climbs and leaves creosote on the tile along the way. Occasional fires build it up more slowly than nightly ones, but the flue still wants a look before the first fire of the year, along with the damper, the smoke shelf and the cap.

Across all three boroughs, the practical rule is the same. If a gas furnace, boiler or water heater vents into an old masonry chimney, put chimney cleaning and inspection on the calendar every year with the heating tune-up, and treat cracked tile, a split crown or a water heater left alone in a big flue as chimney repair to schedule before the next winter, not after it.