The Watchung ridges put a lot of the houses around Bridgewater on sloping ground. The mountains cross the hilly northeast corner of Bridgewater Township around Martinsville. Watchung borough takes in part of the first ridge, the one George Washington used to watch British troops in Perth Amboy, and the second ridge cuts Warren in half, with the Washington Valley between the two. A chimney on ground like that works in moving air, so when a fireplace up there sends smoke into the room, the hill is a fair suspect. It is one of four, though, and the fix for one does nothing for the other three.
Does it smoke only while the fire is catching?
Start with the timing, because it splits the causes in two. A fireplace that puffs smoke for the first few minutes and then draws cleanly usually has a cold flue. Cold air is heavier than warm air, and a column of it sits in the chimney until the fire's heat can push it up and out, which takes longest in a chimney built against an outside wall. Open the damper, hold a burning roll of newspaper up near it until you feel the draft turn upward, then start the fire small and hot. If the smoke stops once the flue warms, nothing needs fixing. If it smokes the whole time, only on windy days, or only when something else in the house is running, the cause is one of the other three.
Is the house pulling air in through the chimney?
Everything a fire sends up the flue has to be replaced by air from somewhere. In a house with tight newer windows, the kitchen exhaust fan, the bath fans and the clothes dryer all push air out, and the house makes up the difference through the easiest opening it has, which is often the fireplace. Tall houses add stack effect: warm air rises and leaks out near the top, which draws outside air in down low, and a fireplace on a lower floor can turn into the intake. The test takes a minute. With a fire going, switch off every exhaust fan and the dryer and open a window a crack in the fireplace room. If the smoke stops, the house is short of air. Keep the window cracked and the fans off while the fire burns, or ask about an outside air supply for the fireplace.
What does the hillside do to the top of the chimney?
Wind does not flow smoothly down the far side of a ridge, a roof or a tall stand of trees. It tumbles, and in the eddy behind the obstacle the air can push down instead of lifting. A chimney top sitting in that eddy gets pressed on, and smoke that should be leaving comes back out of the firebox. On a hillside lot the obstacle is often the ground itself, the slope rising behind the house, or an uphill neighbor's roof that stands taller than your chimney.
New Jersey's residential code sets a minimum height. A chimney has to rise at least 3 feet above the highest point where it passes through the roof and at least 2 feet higher than any part of a building within 10 feet. That rule counts buildings and nothing else. It says nothing about the hill behind the house or the oaks along the property line, so a chimney can meet the code and still smoke when the wind comes over the ridge from the wrong side. The giveaway is a pattern: a fireplace that behaves on still evenings and smokes on gusty ones, often in one wind direction.
The fixes for wind belong to chimney repair. A cap built to shelter the flue blunts the downward push; some have a solid top and open sides, others turn with the wind. Replacing a cap whose screen has clogged with soot and leaves often helps on its own. When the chimney top sits deep in the eddy, extending the chimney until its top clears the disturbed air is the larger and more dependable fix. Branches over the stack get cut back first, by the homeowner or an arborist.
Could the flue itself be the problem?
A flue narrowed by creosote, a nest left from spring, a mat of leaves or a clay tile that has slipped out of line cannot carry all the smoke a fire makes, and what it cannot carry spills into the room. A damper that no longer opens fully because its hinge has rusted does the same. That is why chimney cleaning comes first on any smoky fireplace: the sweep clears the flue and the smoke shelf, and the inspection that follows shows whether the damper, the tiles and the cap are sound.
Size counts as well. One of the code's two sizing methods ties the flue to the fireplace opening, calling for a flue area of at least one tenth of the opening for a square flue and one twelfth for a round one. An opening that is large for its flue smokes along the top edge. A strip of metal or glass fixed across the top of the opening, or a set of glass doors, makes the opening smaller, and a sweep can measure the flue and the opening before you buy either.
Wet wood makes every cause worse
A smoldering fire makes more smoke and less heat, and heat is what drives the draft. The EPA's Burn Wise program says wood burns best at a moisture content under 20 percent, needs at least six months of seasoning, and keeps best outdoors, off the ground, with only the top covered. A moisture meter answers the question before the wood goes in. The same EPA page says that if you regularly see or smell smoke, you may have a problem.
Smoke in the room is a carbon monoxide question too
The Consumer Product Safety Commission lists fireplaces among the household sources of carbon monoxide and describes the gas as colorless and odorless, so the amount of smoke you see says nothing about how much of it is in the room. The CPSC advises an alarm, battery operated or with a battery backup, on each floor of the house and outside the bedrooms. If one goes off, its advice is to leave for fresh air first and then call 911 or the fire department. For heating systems it advises a yearly inspection that looks at the chimney and flues for anything blocking them, rust, and connections that have worked loose or come apart.
What a visit for a smoky fireplace covers
We ask before we climb, because the pattern points to the cause: when it smokes, for how long, in what wind, and what else was running. Then we sweep and inspect the flue, check the damper and the smoke chamber, measure the opening against the flue, and compare the chimney's height with the roof and anything built within 10 feet. Outside, we look at what the code leaves out: the slope, the uphill roofs and the trees. The U.S. Fire Administration's standing advice is a cleaning and inspection every year, and on a hillside that yearly visit is the time to mention how last winter's fires behaved.
Around Watchung, Warren and the hilly side of Bridgewater, work through it in order. Rule out a cold flue and a house short of air, have the flue swept and inspected with chimney cleaning, and only then put money into chimney repair aimed at the wind.