Chimney Questions, Answered Straight

Creosote is the residue left when wood smoke cools and condenses on the flue wall. Stage 1 is loose soot that a brush removes. Stage 2 is hard, shiny flakes that need a rotary tool. Stage 3 is a dense tar-like glaze that brushing cannot shift and that holds the most fuel if it catches fire.

Dry wood, more than any particular species. Split hardwood seasoned until its moisture content is around 20 percent or lower burns hot and clean. Freshly cut wood spends its heat boiling off water, cools the flue gases and coats the liner.

No, a very hot fire will not clean a chimney, and trying is how chimney fires start. Igniting the deposit inside the flue can crack clay tiles and warp metal liners. Controlled removal by sweeping is the only safe way to get rid of it.

No, creosote sweeping logs do not replace a chimney sweep. The chemicals in those logs can dry out some deposits and make them easier to brush off, but the material still has to be physically removed and the flue still has to be looked at.

With a throat damper, look up past the firebox lintel with a flashlight: you should see into the smoke chamber, not a metal plate. With a top-sealing damper, the cable or chain is released from its bracket when open. If in doubt, hold a lit match near the opening and watch which way the flame leans.

A column of cold air sitting in the flue acts like a plug, especially in an exterior chimney on a frigid day. Warming the flue first, by holding a burning roll of newspaper up near the damper for a minute, usually reverses the draft. A tightly sealed house or a running kitchen exhaust fan can also pull air down the chimney.

Burning with a cracked flue tile is not safe. The liner’s job is to contain heat and gases; a crack lets both reach the surrounding masonry and, beyond it, the framing of the house. The usual remedy is a stainless steel liner.

It is the funnel-shaped space above the damper that squeezes smoke from the wide firebox into the narrow flue. In many older fireplaces its walls are stepped, rough brick that traps creosote and disturbs airflow. It is cleaned on every sweep and can be coated smooth with refractory mortar if needed.

A chimney sweep visit for a single open fireplace in ordinary condition usually takes roughly an hour, including laying drop cloths, the cleaning itself and cleanup. Inserts, wood stoves, heavy creosote deposits and camera inspections add time, so mention them when you schedule.

Level 1 is a visual check of readily accessible areas for a chimney in continued, unchanged use. Level 2 adds a video scan of the flue and accessible attics, crawl spaces and basements, and applies after a sale, an appliance change or a damaging event. Level 3 involves removing parts of the building or chimney to reach a suspected hidden hazard.

When conditions allow, yes, because the crown, cap and flashing can only be judged properly from up there. Sweeping itself can often be done from the firebox with rotary rods, which is useful when the roof is icy or too steep to walk.

Yes, most chimney work can be done in winter. Sweeping, inspections, liner installations and gas service are done year-round. Mortar and crown work are the exception: cement-based materials need temperatures above freezing while they cure, so those repairs wait for a mild spell or for spring.

They do. The appliance has baffles, a catalytic combustor or secondary air tubes that collect ash, and the connector pipe or liner behind it has to be reached. Some inserts must be slid out of the fireplace to clean the flue above them.

Yes. A prefab unit is a tested system of metal firebox and matching metal chimney, commonly listed to UL 103HT for the chimney sections. Parts cannot be mixed between brands, refractory panels crack and need replacing, and the sheet-metal chase cover on top takes the place of a masonry crown.

It is the metal lid over the wood-framed box, or chase, that surrounds a prefab chimney. Galvanized covers rust through and pond water; the telltale sign is rust streaks down the siding. Stainless replacements with cross-breaks that shed water are described on the caps and crowns page.

NFPA 211 specifies a Level 2 inspection upon the sale or transfer of a property. A general home inspection normally does not include running a camera through the flue, so the two are not substitutes. See chimney inspection for what is covered.

Creosote absorbs moisture, and damp creosote gives off a sharp, sour odor. In summer, air conditioning and exhaust fans can also pull outdoor air down the flue and into the room. Sweeping after the burning season, a tight damper and a cap to keep rain off the deposits all help.

The white powder on chimney brick is efflorescence: salts carried to the surface by water moving through the masonry and left behind when it evaporates. The stain itself is harmless, but it proves that the chimney is taking on water, and the source should be found.

Spalling is when the face of a brick flakes or pops off. Water soaks in, freezes, expands and breaks the surface away. Northwest Indiana’s repeated freeze-thaw cycles make it common here. Spalled bricks are replaced and the cause of saturation corrected, as covered under chimney repair.

The usual suspects, from the top down: a missing or damaged cap, a cracked crown, porous brick and mortar, failed flashing at the roofline, and, on gas-vented flues, condensation rather than rain. The symptom guide explains how to tell them apart.

Raccoons, squirrels and most birds can be dealt with and a cap fitted to stop a repeat. Chimney swifts are the exception: they are protected under the federal Migratory Bird Treaty Act, so an active nest has to be left until the young have flown, after which the flue is cleaned and capped.

Fire safety guidance calls for one on every level of the home and outside each sleeping area. Follow the manufacturer’s instructions for height and distance from fuel-burning appliances, test them monthly and replace them at the age printed on the unit.

Get everyone out and call 911. If it can be done without risk, close the glass doors or the stove’s air inlets on the way out to starve the fire of air. Do not use the fireplace again until the flue has had a Level 2 inspection.

IRC M1502 sets a maximum of 35 feet from the dryer to the wall or roof termination, reduced by 5 feet for each 90-degree elbow and 2.5 feet for each 45-degree elbow, unless the dryer manufacturer’s instructions permit otherwise. Longer runs move air too slowly and clog with lint; see dryer vent cleaning.