End-of-Season Chimney Care

Why the end of the season deserves its own routine

On the last cold night of the year, the chimney holds the most deposits it will have all year. If nothing is done, those deposits sit in the flue for five or six months of warm, damp weather. Three things follow from that.

• Odors. CSIA explains that the smell many people notice from a fireplace in summer comes from creosote deposits in the chimney, and that it is usually worse when humidity is high and the air conditioner is running. See why a fireplace smells.
• Corrosion. Residue plus moisture is hard on metal. DuraVent's instructions for its DuraTech Premium chimney explain that sulfur in coal deposits combines with moisture to form a highly corrosive acid, and tell coal burners to have the chimney cleaned within 48 hours of shutting the stove down for the season. Stove maker Contura gives similar advice for wood stoves in plainer terms: ash and soot left in a stove for months can trap moisture and lead to rust.
• Time. Anything an inspection finds in April can be repaired over the summer. The same finding in October competes with the first cold snap.

The last fire and its ashes

There is no special way to burn the last fire. Let it burn down completely and leave the ashes in the firebox or stove until they have had time to cool. Fire officials in Montgomery County, Maryland, tell residents to treat every batch of ashes as hot, even ones that seem to have had plenty of time, because buried coals can rekindle days later.

When you clean them out:

• Use a metal container with a tight-fitting lid, never a bag, a box or a plastic bucket.
• Set it outside, at least 10 feet from the house and other buildings.
• Do not use a household vacuum to pick up ashes. The same fire officials list that as something to avoid.

The full routine is in our guide to getting rid of fireplace ashes safely. Once the ash is out, take a flashlight and look at the firebox: cracked or missing firebrick, open joints and rust are easier to see in a clean firebox and worth mentioning at the spring inspection.

Shutting down a stove or insert for the summer

1. Let it go fully coldGive the stove body and the ash bed a full day or more; a stove that feels cool on the outside can still have live coals under the ash.
2. Empty the ash and brush out the fireboxContura recommends emptying the ash pan and brushing out loose ash from the firebox at the end of the season, because residue left in place can trap moisture.
3. Look at the wearing partsDoor gasket, glass gasket, firebrick, baffle and, on catalytic models, the combustor. The U.S. Department of Energy advises inspecting a catalytic combustor after every two cords of wood burned, so the end of the season is a natural point to do it. Order any parts now, while there is no rush.
4. Let air move through itContura suggests leaving the air controls slightly open or the door ajar over the summer so air flows through the stove and moisture does not build up. Check your own manual first; it is the authority for your model.
5. Leave the connector and chimney to the sweepThe pipe and liner hold the season's creosote. They are cleaned and inspected as part of the chimney visit.

For the stove-cleaning tasks themselves, see cleaning a wood stove and its pipe.

How the fireplace should sit through the summer

An open fireplace spends the summer as a hole in the house. What you do with it depends on the damper you have.

• A throat damper sits just above the firebox. Close it after the ashes are cold. It cuts the flow of air between the house and the chimney, though a worn cast iron damper may not seal tightly, and it does nothing to keep rain or animals out of the flue above it.
• A top-sealing damper closes at the top of the flue with a gasket. Closed, it keeps rain, debris and animals out as well as limiting air movement. Check that the cable and handle work before you rely on it all summer.
• No working damper, or one that is rusted open, leaves the chimney open to the house all summer. That is worth raising at the spring inspection.

If the fireplace has glass doors, closing them over the summer is another layer. Our guide to throat and top-sealing dampers explains the differences.

One caution: never close off a flue that a furnace, boiler or water heater uses. Those flues stay open year-round, and many of them still work through the summer when a water heater shares the chimney.

Booking the inspection and sweep in spring

The national standard is an inspection once a year, and the sweep when the inspection calls for it. When in the year is up to you. Spring has several things going for it:

• The flue shows the full winter's deposits, which tells you how your burning went and helps set next year's interval. See how often a chimney should be swept.
• Removing deposits before summer takes away the source of most fireplace odors and the residue that holds moisture against metal parts.
• Repairs found in spring, such as a crown, a liner or flashing, can be done in warm, dry weather with the whole summer to work in.
• Fall still needs its own pre-season look at caps, nests and alarms. That routine is covered in getting your chimney ready for heating season.

Oil and gas heating flues can follow the same calendar. Late spring, once the heat is off for the year, is a convenient time to have a furnace or boiler flue cleaned and checked without leaving the house cold. See furnace and boiler flue cleaning.

Before the swifts arrive

Chimney swifts are small birds that nest inside masonry chimneys, clinging to the flue walls. The U.S. Fish and Wildlife Service says the birds reach the U.S. in March or April, head back to South America in August or September, and they are protected under the Migratory Bird Treaty Act, which makes it illegal to harm them, their eggs or their nests. FWS advises cleaning the chimney every year outside swift nesting and roosting season, which for most of the U.S. means between September or October and March or April.

That makes early spring a natural deadline for a sweep in an uncapped masonry chimney. Once swifts are nesting, the chimney has to wait until they leave. If we find active swift nests, we recommend waiting too.

FWS also asks homeowners not to cap chimneys or screen them just to keep out nuisance wildlife, so swifts can keep using them, while noting that metal-lined chimneys need caps so birds do not get trapped. Whether to cap is a choice with trade-offs, since a cap also keeps out rain, debris and other animals. Our guides to animals in the chimney and chimney cap types cover both sides.

Gas fireplaces at the end of the season

A gas fireplace has no ashes, but it has its own end-of-season decision: what to do with the pilot. Natural Resources Canada notes that a standing pilot light can consume 600 to 1,500 Btu of gas per hour when it runs continuously. Whether to turn it off for the summer depends on the appliance. Follow the manual's shutdown and relighting instructions for your model, and if you are not comfortable relighting it in the fall, leave that to your service visit.

Before summer, look at the outside vent termination from the ground for nests, plants growing toward it or damage. Annual service of the appliance and its vent can be scheduled at either end of the season. See gas fireplace and gas log service.

Write the season down

The most useful five minutes at the end of the season are spent on a short note while you still remember the winter:

• How much wood you burned, in cords or the size of the stack.
• Roughly how many fires, and whether they were short evening fires or all-day burns.
• Moisture readings, if you used a meter.
• Anything unusual: smoke in the room, smells, a fire that would not draw, sounds from the chimney, water in the firebox.
• Parts that need replacing on the stove.

Bring the note to the spring inspection. Put next to what is actually found in the flue, it turns next year's sweeping interval from a guess into a measurement. File the findings and photos from the visit with it.

Questions homeowners ask

Sources

1. Chimney Safety Institute of America: Frequently asked questions (summer odors)
2. U.S. Fish and Wildlife Service: Chimney swifts
3. DuraVent: DuraTech Premium chimney installation instructions (PDF)
4. Contura: The end of stove season checklist
5. Montgomery County (MD) Fire and Rescue Service: Cool your ashes (PDF)
6. Natural Resources Canada: Gas fireplaces

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