How to Dispose of Fireplace Ashes Safely

Why ashes stay dangerous so long

Wood ash is a good insulator. When a fire burns down, the last coals sink into the ash bed, and the ash around them holds their heat the way a blanket does. Those coals can keep smoldering for days after the last flame went out. The top layer can feel cool to a hand held above it while the center is still glowing orange.

That is how ash fires start a day or two after anyone used the fireplace. A bucket or bag of ash is set in a garage, on a wooden porch or beside a plastic trash can, and when the hidden ember finally meets enough air and fuel, it catches. Treat every batch of ashes as hot until it has sat in a closed metal container for several days.

The right container

The U.S. EPA's wood-burning guidance says to remove ashes regularly into a covered metal container and store that container outdoors on a nonflammable surface. That is the whole idea: nothing in, on or under the container can burn.

A purpose-made ash bucket is a metal can with a tight lid and a handle, sometimes with a raised or double bottom so the heat does not scorch the surface beneath it. A plain galvanized can with a fitted metal lid does the same job. The lid matters: it starves any live ember of air and keeps wind from blowing sparks out.

Step by step

Clean out ash when the fire has been out for at least a day, and wear gloves. Cooler ash is less flammable and kicks up less dust.

• Open the damper so fine dust drifts up the flue instead of into the room
• Scoop slowly with a metal shovel to keep dust down
• Put the ash straight into the metal bucket and close the lid
• Carry it outside right away; do not leave it inside, in a garage or on a porch
• Set it on concrete, stone or bare ground, away from walls, decks, fences and firewood
• Wait several days, stir with a metal tool to check for heat, then empty it

What to avoid

Paper grocery bags, cardboard boxes, plastic buckets, plastic trash cans and garbage bags are the usual containers in ash fires. Even ash that seems cold can hold a buried ember, and all of these burn or melt. A household vacuum is just as risky: one hidden ember can ignite the dust inside the bag or canister, and fine ash can also damage the motor and blow straight through ordinary filters into the room.

Do not dump ash on the lawn edge, into a compost pile or beside the house while it is still fresh from the fireplace. Wind can carry embers into dry leaves, mulch and wooden steps.

What you can do with cold ashes

Once ash is completely cold, it can go out with household trash where your local rules allow it. Wood ash from clean, untreated firewood also has uses around the yard. It is alkaline, so gardeners sometimes work a thin layer into acidic soil, though it is wrong for acid-loving plants like azaleas and blueberries. Small amounts can be mixed into compost, and some people keep a can by the door to sprinkle on icy steps for grip.

Keep the garden for clean wood ash only. Ash from painted or treated wood, cardboard, trash, coal or manufactured fire logs belongs in the trash, since it can carry residues you do not want in the soil.

How much ash to leave in the firebox

Many people leave a thin bed of ash on the firebox floor during the season. The EPA's burn tips suggest about an inch of ash helps insulate the coals for easier restarts. Too much does the opposite: it chokes air under the grate, and ash heaped against the grate or the back wall holds heat against the firebrick and metal, which wears both out faster.

Clear ash out when it reaches the bottom of the grate, and clean the firebox fully at the end of the season. Ash left all summer absorbs moisture, and damp ash mixed with soot is acidic and adds to the musty smell many fireplaces develop in humid weather.

Wood stoves and inserts

Stoves usually have an ash pan or an ash lip at the front of the firebox. The same rules apply: empty the pan into a lidded metal bucket, not a bag, and take it outside. Check the stove manual for how much ash it wants left in the firebox; some designs burn better on a bed of ash and some want the grate kept clear. Close the ash pan door fully afterward, since a pan door left ajar can over-fire the stove.

Pellet stoves produce a fine ash that is easy to underestimate. It packs into the burn pot and the heat exchanger passages, and the stove's manual sets how often those are cleaned. Treat pellet ash exactly like wood ash when it comes out: metal container, lid, outdoors.

The end-of-season clean-out

When the last fire of spring is out and cold, give the firebox a full cleaning rather than leaving a winter's worth of ash in place. Remove all the ash and loose debris, brush the grate, and look at the firebrick and mortar joints while they are bare. Cracks and missing mortar are much easier to see without a layer of ash, and spring is a good time to have them repaired.

Close the damper once the firebox is clean, so summer humidity and insects stay out. If the fireplace smells over the summer even with the damper shut, that usually points to creosote in the flue or water getting in, which a spring sweep and inspection can deal with before the smell sets into the room.

What the ash can tell you about the chimney

Look at the ash before you throw it out. Pale, fine, powdery ash means the wood burned completely. Lots of black, charred chunks point to damp wood or fires that were starved of air, which also means creosote is building in the flue. Shiny black flakes mixed into the ash usually fell from the flue itself, and reddish clay fragments can be bits of flue tile.

Flakes and tile pieces are worth mentioning at the next chimney visit. They are a sign the chimney needs sweeping or that the liner is breaking down, and both are easier to deal with early.