How to Close Up a Fireplace for the Summer

Why a fireplace needs closing at all

An open flue is a straight path between the living room and the sky. In winter, the warm air in the house rises up it. In summer the direction often flips: the house is cooler than the air outside, and warm, humid air settles down the chimney into the room, picking up the smell of old soot and creosote on the way. On muggy July days in a Brooklyn brownstone or a Philadelphia twin, that is when owners first notice the fireplace smells like a campfire nobody lit.

The same opening lets cooled air from the air conditioner escape, and gives birds, squirrels, wasps and other insects a quiet, dark shaft to explore. Closing and covering the fireplace properly stops most of that, and it keeps soot from blowing onto the floor when windows open and the house pulls air down the flue.

Start with a truly cold firebox

Ash insulates embers, and a bed of ash that looks gray and dead can hold live coals for days. Before you shovel anything, wait until the fireplace has not been used for several days and the ash is cold to the back of your hand held just above it.

Ash goes into a metal can with a tight metal lid, and the can goes outside on a non-combustible surface, away from the house, the deck, fences and stored firewood. A cardboard box, a paper bag or a plastic bucket is not a safe container for fireplace ash, however cold it seems.

This is also the moment to look at what the ash tells you. A fine, light gray ash means the wood burned hot and fully. Lumps of black, half-burned wood and a sticky, tar-smelling residue on the firebox walls point to damp wood or smoldering fires, and to a flue that has probably collected more creosote than usual over the winter.

Step by step

Once the firebox is cold, the closing routine takes well under an hour.

• Shovel the ash into the metal can and set it outside, clear of the house
• Brush loose soot off the firebox walls and floor and vacuum the hearth with a vacuum suited to fine ash
• Close the damper fully and look up to check that the plate sits evenly
• Close the glass doors, if the fireplace has them
• Fit a cover or plug if you still feel moving air or smell creosote
• Put the grate, log rack and tools away so the hearth is clear for summer

Check that the damper really seals

Most older masonry fireplaces in the region have a cast iron throat damper just above the firebox. It was never designed to be airtight, and after years of heat, rust and the occasional summer of rain coming down an uncapped flue, many of them barely close. The plate warps, the frame rusts at the edges, or the handle slips so the plate hangs partly open.

A simple test: with the damper closed, hold a stick of incense or a strip of tissue near it on a breezy day. Smoke or paper drawn up or pushed down means air is moving through. A visible line of daylight around the plate, rust flakes on the firebox floor or a handle that turns without moving the plate are signs the damper needs repair or replacement rather than a cover.

Fireplace covers, magnetic and otherwise

A fireplace cover closes the opening from the room side. Some are insulated board cut to size, some are fabric panels, and some are inflatable or foam plugs that press up into the throat above the damper. Magnetic covers are a thin sheet with magnets around the edge, and they only work where there is a steel surface to grip, such as the frame of glass doors or a metal fireplace front. Plain brick or stone will not hold them, so those openings need a snug-fitting panel or a plug.

Whatever you use, treat it as a summer part. It has to come off before any fire, including the first chilly evening in September. A bright tag hanging into the firebox or a note on the mantel helps everyone in the house remember.

Covering the top of the chimney

People shopping for a summer chimney cover usually need one of two things. A chimney cap is a metal hood with mesh sides that stays on year-round: it keeps rain out of the flue and stops animals moving in, while still letting the fireplace and any heating appliance vent. A top-sealing damper is a hinged lid on the top of the flue, opened and closed with a cable from the firebox, and it seals far tighter than an old throat damper because it has a gasket.

What you should not do is block the top of a flue still serving a heating appliance such as a boiler or water heater. Those appliances run all year, and a blocked flue can push exhaust, including carbon monoxide, back into the house. In many older homes the fireplace flue and the boiler flue share one chimney, so it is worth knowing which flue is which before anything goes on top.

If the fireplace still smells in summer

A closed damper cuts the smell but may not end it. Creosote soaked into the flue gives off odor whenever the air is humid, and bathroom fans, kitchen hoods and clothes dryers pull air into the house through any gap they can find, including a fireplace. If the smell persists after closing up, the usual causes are a flue that was not swept at the end of the season, a damper that leaks, rain coming down an uncapped flue, or a nest or animal debris on the smoke shelf.

Baking soda or charcoal set in the firebox can take the edge off for a while, but they do not remove the source. A sweep and a cap usually do.

Use the quiet months for repairs

Spring and summer are when chimney work is easiest to schedule. The flue is cool, roofs are dry, and there is time to fix a cracked crown, replace a rusted damper or fit a cap before the next heating season. If the last winter left heavy smoke, a strong smell, black flakes in the firebox or debris at the cleanout, book the sweep now instead of in the October rush.

Our own crew can sweep, inspect and look over the damper and cap in one visit. If anything needs repair, you get it in writing with time to plan, rather than a scramble when the first cold snap arrives.