Popping, Creaking and Ticking From a Metal Chimney

Popping While the Fire Heats Up

Noise usually shows up as a fire gets going. The Regency i2450-2 wood insert manual tells owners to expect some cracking and popping while the unit heats up, and says the noises become minimal once it reaches temperature. A factory-built fireplace's metal firebox and chimney behave the same way: thin steel heats quickly, and every part of it moves a little.

A second round of ticking as the fire dies and the metal cools is the same thing in reverse. If the sounds follow the fire, come and go with heating and cooling, and do not get louder from year to year, they are the system working.

Why Metal Chimneys Move

A factory-built chimney is a set of round sections locked together, an inner stainless flue inside one or two outer casings, held apart by spacers and passing through firestops at each ceiling. The inner flue gets far hotter than the casing, so the two grow by different amounts. DuraVent's DuraPlus page says that in a creosote fire its blanket insulation lets the liner expand outward, which shows how much a hot flue can move.

Each place a moving part rubs or catches can click: the snap-lock joints, the spacers, the firestop collar at the ceiling, the straps at an offset, and the storm collar at the roof.

• Snap-lock joints between sections.
• Wire or tab spacers between inner flue and outer casing.
• Firestop spacer where the pipe passes a ceiling.
• Support straps at an offset or a tall run.
• Storm collar and flashing at the roof, and the cap on top.

Noises That Point to Something Loose

Some sounds do not follow the fire. Banging or rattling on a windy day with the fireplace cold, a creak that changes when you push on the chase, or a metallic knock from the attic are signs a part is loose rather than just warm.

The makers' instructions show where looseness comes from. The Superior Pro Series manual has the installer check every snap-lock joint by pulling the chimney upward, requires supports for tall chimneys, and hangs the weight of an offset on straps nailed to rafters or joists. The Majestic MPL11 manual calls for a chimney support above a set height and, on roofs that need a tall chimney, a support strong enough for wind load. A strap that has worked loose, a joint that never fully locked, or a cap whose screws have rusted out all make noise first and fail later.

When a Noise Means Danger

Some sounds should never be waited out. If the noise turns suddenly loud and continuous instead of the usual ticks, or comes with smoke, sparks from the top or a hot smell in the room, treat it as a possible chimney fire. The Regency manual's instruction is to close all draft and damper controls and call the fire department, and the DuraLiner and DuraTech instructions add that the chimney must not be used again until it has been inspected.

A hard tick or bang that comes with the top of an insert or a connector glowing means overfiring; the Regency manual says to stop adding fuel and close the draft control. Get everyone away from the fireplace either way.

Logging the Noise Safely

Listen for when the noise happens and write it down: during heat-up, while cooling, in wind with no fire, or all the time. From the attic, with the fireplace cold and a flashlight, you may be able to see whether straps are nailed tight and the firestop collar is in place; do not move insulation against the pipe or climb across joists you cannot see. From the ground, look for a cap sitting crooked or a storm collar that has slid up the pipe. Leave the roof to a crew.

A pattern helps. Noise only during heat-up and cool-down is expansion. Noise in wind with the fireplace cold is something loose outside. Noise when someone walks in the attic or the room above points to a strap or firestop that has lost its grip. Bring that note to the visit.

What a Technician Checks

On a noise call we follow the chimney from the firebox to the cap. We check that every section is locked, that offsets and tall runs are strapped and supported the way the maker's manual shows, that the firestops are seated, and that the storm collar and cap are tight. Where extra fasteners are allowed, they go through the outer pipe only; both manuals warn against piercing the inner stainless flue. Damaged sections are replaced with the maker's listed parts.

Our prefab fireplace repair crew does that work with the fireplace cold, and puts what it finds in a written estimate after a free inspection. Noise calls need an experienced crew with a good ear, and ours belongs to a local, family-owned, Proudly American company. Spring Hill homeowners get a Proudly American family crew that tracks the sound to its source before replacing anything.