It seems like many of the calls that we receive from homeowners in Houston and the surrounding areas this time of year are concerning smoky chimneys and fireplaces. Most of the time these types of problems fall into these categories: pre-existing, new, or irregular chimney smoking problems.

If you’ve recently bought a home that has a chimney and it tends to smoke, there is usually a pre-existing condition from that carried over from the initial construction. Chimneys must be built at least 3 feet above the nearest point or another roof within 10 feet of the chimney. Taller chimneys ensure stronger drafts. A good draft is important for the combustion of the chimney and most of the experts agree that a good draft is between 10-20 Pa (1-2 mm VC).

I’ve seen that shorter chimneys may not have enough draft even when they are built to be three feet higher than a neighboring roof. In those cases, sometimes increasing its height by a few feet will solve the smoking problem. Another reason that a chimney smokes is the relationship between the area of the fireplace opening and the area of the flue. The chimney flue carries the smoke outdoors.

According to the International Code Council which is dedicated to helping the building community and construction industry provide safe construction, the fireplace opening should be no more than 10 times the area of the flue. One test that you can try is by inserting a piece of sheet metal or a row of bricks. If decreasing the opening size eliminates the smoking problem, then reducing the opening might solve it if there aren’t any other problems

Smoky fireplaces can also be found in houses that don’t have enough ventilation. I’ve seen this with newer houses whose construction doesn’t let in enough air to replace the air drawn out by the chimney. In most cases opening the window nearest to the fireplace will help with the smoking. If ventilation seems to be the problem, adding a vent will make it easier for the fireplace to receive combustion air or leave a door or window cracked while burning. If you have a newer home, look in or near the fireplace to see if there is a closed air inlet.

The next thing that I usually check for are obstructions such as leaves or branches that are blocking the top of the chimney or are blocking air from escaping the chimney. In some cases animals may have crawled into your chimney and they will have to be removed by a professional. Obstructions are usually the reason for your chimney smoking when it’s a new problem. If you haven’t had your chimney swept recently, your chimney might have creosote buildup. Creosote is that sticky, foul smelling, corrosive substance that is composed of the volatile gases that are given off in the burning process and coat the insides of your chimney.

Irregular or intermittent smoking problems are the hardest to detect. There are many causes to intermittent problems such as ventilation and drafting issues caused by trees. One solution is to install a chimney caps that have been specially designed to protect against downdrafts. In some cases intermittent smoking can be caused because you’re too eager to have a fire. The differences in the temperature of the air in the chimney and the air outside might cause the chimney to draw air at a slower rate. In those cases, you can try to prime the chimney by rolling up a piece of newspaper, light one end, and hold it way up in the damper opening. It might take a minute or two when you feel the draft reverse and as the warm flue gasses start to move up the flue, you can light your fire. If the newspaper trick doesn't seem to be working, try leaving the damper open for half an hour or so which allows the heated room air to gradually reverse the flow. Please dress warmly as it might get cold!