Creosote Sweeping Logs: What They Do and Don't Do

What these products are

The category is broader than the familiar boxed log. CSIA's 2001 safety bulletin on the subject refers to logs, powders and liquids that, when burned, are claimed to remove a portion of the creosote from a masonry or metal chimney. Some are burned on their own, some are sprinkled on a fire, and some are sprayed onto the fire or into the firebox.

CSIA's homeowner FAQ describes how they are promoted: for their ability to remove a portion of the creosote from a chimney interior through catalytic action when burned in a fireplace or wood stove. The chemicals released by the burning product travel up with the smoke and react with deposits on the flue walls, with the goal of making sticky or hard creosote drier and more brittle.

What CSIA says about them

The Chimney Safety Institute of America has addressed these products in three places:

• Its homeowner FAQ says the use of these products alone is not an adequate substitute for mechanical chimney cleaning and inspection, and that the best method is mechanical brushing combined with a complete evaluation of the system.
• Its accepted products list includes one creosote sweeping log, and states that this acceptance followed testing focused on product safety. The same listing says the log does not take the place of inspection and professional cleaning.
• Its 2001 chimney safety bulletin expressed concern about these products and stated that mechanical brushing, with removal of creosote as completely as possible, was the only adequate method known for cleaning chimneys. It acknowledged that some chemicals used under the direction of a professional sweep can make mechanical brushing more effective on persistent, hard-to-remove creosote.

Read together, that is a narrow endorsement. Safety testing means the product is considered safe to burn when used as directed. It is not a finding that the product cleans a chimney.

The 2001 bulletin's point about professional chemicals is also worth noticing. When chemicals do help, CSIA describes them as working alongside mechanical brushing, chosen and applied by a sweep who has seen the deposits. A product burned at home without anyone looking inside the flue is a different situation.

Reading the label claims

Packaging for these products uses careful language, and it is worth reading closely.

• "Reduces" or "helps remove" describes some effect on some deposits. It does not say how much, and it does not say the chimney will be clean.
• "Up to" a percentage describes the best result under some test conditions, not what a particular chimney will see.
• "Loosens" or "makes it easier to remove" raises a practical question: where does loosened creosote go? It either stays in the flue in a different form, waiting for a brush, or falls. Falling deposits land on the smoke shelf, the damper, the top of a stove's baffle, inside the connector pipe or at the base of the flue, and still have to be cleaned out.
• "Between professional cleanings", where it appears, is the most honest part of the label.

Follow the package directions exactly if you use one, including how often and in what kind of appliance.

Check your appliance manual first

Not every appliance can burn these products. Blaze King's owner's manual for a catalytic wood stove lists chemical cleaners, along with artificial or paper logs, among the materials not to burn, and states that doing so can damage the catalyst and void the stove's safety listings. Other stove and factory-built fireplace manuals have their own lists of approved fuels.

• Catalytic stoves and inserts: read the manual before burning anything other than natural wood.
• Factory-built fireplaces: the manual governs what may be burned.
• Gas fireplaces and gas logs: never burn wood, logs or chemical products in an appliance built for gas.

What no product can tell you

The bigger limitation is information. A sweeping log works blind. It cannot:

• show how much creosote is in the flue, or whether any of it is glazed;
• find a cracked flue tile, a gap in a liner joint or a deteriorated smoke chamber;
• remove a nest, leaves or a dead animal;
• check the cap, crown, damper or clearances;
• tell you whether a past chimney fire has already damaged the system.

CSIA states that all forms of creosote are highly combustible. When a product leaves a homeowner thinking the chimney has been taken care of, the next sweep and inspection tends to slip, and that is when deposits and damage go unseen. See signs you have had a chimney fire.

Where they can fit, and where they do not

A reasonable use is as a supplement in a chimney that is inspected every year and swept as needed, burned according to the directions, in an appliance whose manual allows it.

A poor use is any of these:

• instead of an annual inspection;
• in a chimney you suspect has heavy buildup, glaze or a past chimney fire, where the right step is an inspection before burning anything else;
• to fix a fireplace that smokes, smells or draws poorly, since those problems have causes a log cannot address;
• on a chimney that has never been inspected since you bought the house.

If heavy, tar-like or glazed deposits are found, professional chemical treatments applied directly to the flue, followed by mechanical removal, are a different process from burning a log in the firebox. Our creosote guide explains how those deposits are handled.

What reduces creosote more reliably

The habits that keep creosote down are the same ones CSIA lists as its causes in reverse: enough air, dry wood and a warm flue. Burn seasoned wood, open the damper fully, avoid long smoldering fires, and do not pack a stove beyond what its manual describes. EPA's Burn Wise guidance adds a list of materials that should never be burned, including trash, painted or treated wood and wet or rotted wood.

Then let someone look. An annual inspection, with sweeping when deposits call for it, is what actually tells you the condition of the flue. See how often a chimney should be swept and our chimney cleaning page.

Questions homeowners ask

Sources

1. CSIA: Frequently Asked Questions
2. CSIA: Accepted Products
3. CSIA Chimney Safety Bulletin #2001-11 on chemical chimney cleaners (published by Fire Engineering, 2001)
4. Blaze King Chinook CK24 catalytic wood stove owner's manual (PDF)
5. CSIA: Chimney fires and creosote
6. U.S. EPA Burn Wise: Best Wood-Burning Practices

This guide is general information. It can't diagnose a specific chimney; an inspection can.