Smoky woodstove: smoky startups

The most common type of problem with wood stoves is smoke spillage. It is tempting to blame the stove design, but usually the problem is a faulty venting system or operator error. Here we will cover the different types of smoking problems.

If your wood stove smokes when you first light it, but works properly after a few minutes, here are some things to consider: 

Wood stove dampers

Inside wood stoves or in the stove pipe, you will often (but not always) find dampers, movable metal plates that restrict the flow of smoke and gasses. When you light the stove, the damper(s) must be in the full-open position, to allow maximum draft for start-up, when the greatest concentration of smoke is produced (and the draft is weakest). If you have accidentally left a damper partly or entirely closed, the stove will smoke. If you are not sure if the damper is open or closed, figure it out before you light the fire! 

The two basic types of dampers are bypass dampers and pipe dampers. Your stove may have one type, the other, both, or neither, depending on the stove design. 

By-pass dampers

A by-pass damper is a moveable metal plate inside the stove, usually located at the top rear of the firebox near the flue collar

If you look inside the stove, you will probably be able to see the by-pass damper (if your stove has one), although in some stove designs it is hidden. 

When the by-pass damper is open, smoke and gasses by-pass the normal exit route (hence the name) moving directly out of the stove into the stovepipe and chimney. 

When the by-pass damper is closed, smoke and gasses are re-routed through a system of baffles or a catalytic combustor or some other type of system designed to increase the efficient combustion of the smoke and gasses. 

Pipe dampers

A pipe damper is a metal valve (essentially, a round metal plate) installed inside the stove pipe, which can be rotated by means of a handle on the outside of the pipe. Turning the handle opens or closes the plate by moving it parallel or perpendicular to the pipe (or somewhere in between). 

Note: Pipe dampers are deliberately designed to allow some movement of smoke and gasses even in the full-closed position. The plates are smaller in diameter than the inside of the pipe, and usually have holes in them, allowing about 20% of the pipe opening to remain unobstructed in the full- closed position. This helps prevent smoke spillage by making it impossible to completely block the stove pipe.

The purpose of a pipe damper is to retard the flow of combustion air, smoke, and gasses in the stove by reducing the flow of smoke and gasses into the venting system. 

Note: Some stoves incorporate a round or oval pipe-damper attached to the flue collar of the stove. These perform the same task as a pipe damper in the stove pipe. Most new, EPA-certified stoves are designed to be used with no pipe damper in the pipe or at the stove collar.

If your stove has either type (or both) it is essential that the damper(s) be in the open position during startup. Once the fire is established, you can regulate the burn using the damper(s). 

Cold Flue at startup

Warm air rises. Cold air sinks. So for a chimney to operate properly, the chimney flue must be warm compared to the outside air, so the smoke will rise through the chimney and exit the house. If the flue is cold at startup – and it often is, especially in chimneys built on the outside of the house rather than up the center of the house – smoke might be pushed back into the house. 

Often, once the flue begins to warm up, the chimney will start to draw the smoke out, but by that time you might already have a house full of smoke. 

The solution is to prime the flue before you light the fire. It's easy to do, and doesn't take more than a couple of minutes – and it can prevent you from having a bad fireplace experience. Here's how to prime the flue: 

How to prime the woodstove flue

Roll up a piece of newspaper, light one end, and hold it in the firebox of the wood stove, up near the flue collar. Don't stuff it into the flue collar – you want the ashes to stay in the stove, and not clog the pipe. You might need to burn two rolls of paper. You will soon feel the draft reverse, as the warm flue gasses start to move up the flue.

Once you have primed the flue, you can light the fire.

If the newspaper trick doesn't seem to be working, try leaving the stove door open for half an hour or so, allowing heated room air to gradually reverse the flow.

Blockages

Sometimes, a smoking problem is caused by a partial or complete blockage of the flue. Creosote buildup, animal nests, leaves and debris, or internal collapse of the chimney lining or brickwork can cause blockages. If you think your chimney may be blocked, or if you haven't had it checked by a chimney professional within the past year, make an appointment for a chimney check. Your chimney professional is qualified to identify and correct chimney blockages, and to check your chimney for other hazards as well. 

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