What Is a Chimney Cleanout Door For?

Where cleanouts are and what they serve

In many older houses the cleanout sits a foot or two below the point where a boiler, furnace or water heater pipe enters the chimney. That space below the pipe is a catch basin for everything that falls down the flue: soot, oil scale, flakes of tile, leaves and the occasional bird. The door is how it all comes out.

Below a fireplace there may be a different kind of cleanout. The firebox floor has a small ash dump, a hinged plate the ashes are swept through, and they drop into an ash pit with its own door at the bottom. On many New Jersey colonials, Long Island capes and Delaware ranches that door is outside at the base of the chimney; in rowhouses and brownstones it is usually in the cellar. A stack with several flues can have several doors, so it pays to work out, once, which door belongs to which flue.

Why the door has to seal

Draft depends on the flue being a closed column of warm air rising from the appliance to the top. A door that is warped, loose or missing lets basement air pour into the bottom of that column. The exhaust is diluted and cooled, the draft at the appliance weakens, and a heating flue can struggle to clear the burner's exhaust.

The leak can run the other way too. On a calm day or a cold flue, soot and fumes can drift out of a gapped door into the basement. An outside door that does not close lets rain and snow in, and mice and squirrels treat an open ash pit as a ready-made shelter.

Outside doors take the weather as well. Water that gets behind a loose frame freezes, expands and pushes the frame a little further out of the brick each winter, until the door no longer meets it.

Opening it safely

Looking inside a cleanout is a reasonable job for a careful homeowner. Turn the heating appliance off and let it cool first, and leave a fireplace ash pit alone for several days after the last fire, since ash holds live embers long after it looks dead.

• Wear gloves and a dust mask, and put down a drop cloth
• Open the door slowly; debris may be piled against it
• Scoop the material into a metal container with a tight lid, not a plastic bag or bucket
• Set the container outside on a non-combustible surface, away from the house and the deck
• Close and latch the door before turning the appliance back on

What the debris tells you

The bottom of a flue keeps a record of what is happening above it. A little fine soot is normal for an oil flue. A thick pile of soot suggests the burner needs service or the flue is overdue for sweeping. Curved pieces of orange or tan clay mean flue tiles are breaking up. Sandy grit is mortar washing out of the joints.

Rust flakes or metal scale point to a corroding liner, connector or cap; grey or white powder can be a corroding aluminum liner. Water, wet debris or a rusty puddle means rain or condensation is getting into the flue. Twigs and nesting material mean the top is open to birds. Mention any of these when you book a sweep, because they tell the technician where to look first.

A useful habit: before clearing the base, take a photo of what is there. Comparing it with next year's photo shows whether tile is falling faster or water is new, which is exactly what a technician wants to know.

Ash pits below the fireplace

Ash pits fill slowly, and in older houses some have not been emptied in decades. A pit packed all the way up to the ash dump stops working: ash backs up into the firebox, and the dump plate cannot close. An overfull pit can also hold dampness against the masonry and smell of old smoke in humid weather.

Some ash pits were built with wooden forms that were never removed, or sit next to framing. Hot ash against wood is a fire risk, so an ash pit that has been in use should be looked at during the yearly inspection along with the fireplace above it.

Clearing a long-neglected ash pit is dusty work. Old ash is fine and drifts everywhere, so it is often easier to have it emptied during a sweep, with the damper closed and the basement protected.

When the door needs replacing

Cleanout doors are usually cast iron or steel, and they live in a damp, acidic spot at the bottom of the flue. Over time they rust, warp, crack or work loose in the brick. Some were never proper doors at all: a sheet of metal leaned against the opening, or a cover held by a brick or tape.

Replacement means chipping out the old frame, setting a new door and frame of the right size into the masonry with mortar, and checking that the door closes tightly and latches. It is a small job, often done during a sweep or as part of a liner installation, when the base of the flue is open anyway.

The new door should suit the size of the opening and close flat against its frame, with a latch that holds it shut while the boiler runs and the flue is under draft.

If you cannot find a cleanout

Not every flue has one, and some that do are hidden. Basement renovations often plaster, panel or brick over a cleanout to tidy up a wall, and the door is forgotten until a sweep goes looking for it. A covered cleanout hides exactly what it was built to show: fallen tile, water and blockage at the base of a working flue.

Where a heating flue has no usable cleanout, one can often be added, and when a liner is installed the bottom tee needs to be reachable through an opening in the brick for future cleaning. If a finished wall is in the way, a small access panel in the wall is far better than no access at all.

Cleanouts and the yearly sweep

Under NFPA 211, a chimney gets an inspection every year and a cleaning whenever deposits have built up. The cleanout is part of that visit: the sweep brushes the flue from top to bottom, clears what falls to the base, and checks the door and its frame. On a lined flue, the cleanout gives access to the cap on the bottom of the liner tee.

Oil flues and fireplaces with heavy use may need the base cleared between yearly visits. If your door is missing, loose or held shut with tape, mention it when you book, and a new one can be included in the written estimate for the visit.