Smoking fireplaces part 5: fireplace smokes on wet day

It is one of the most valued features in our homes. And all too often, the fireplace is labeled "non-working" and sits unused, because the homeowner doesn't know what to do about a smoking problem. Here I will show how most smoking problems can be handled relatively easily, with little or no expense. We'll cover:

 Here's a trick for monitoring smoky fireplaces: If you can't see the smoke spilling from the fireplace, shine a flashlight across the fireplace opening. The light reflecting off the smoke particles will make it easy to see. 

Fireplace smokes on damp or rainy days

This can be a real nuisance. Here is what to look for: 

Cold, wet fireplace flue

Wet chimney flues are much harder to heat than dry chimney flues. This is because it takes an enormous amount of heat to convert water to steam. The water absorbs so much heat that the flue doesn't warm up effectively. The tall column of cold air in the flue wants to sink, drawing smoke into the house. 

Try pre-heating, or priming the flue. Sometimes, by pre-heating the flue with the priming technique, you will overcome the problem. 

Other things that will help include a good chimney cap to help keep water out of the flue, and a water-repellent treatment for the exterior masonry work. 

A word about water repellents: Don't use a foundation or masonry sealer on chimneys. Burning wood creates moisture, and the chimney needs to "breathe," to allow the moisture to escape. Sealers lock this moisture in, causing gradual damage to the structure. Instead, use a vapor-permeable water repellent designed for use on masonry surfaces. Ask your chimney professional for a quote. 

Fireplace chimney is too short

Especially on damp, wet days, when the temperature and pressure differential between the inside of the chimney and the outside isn't ideal for chimney draft, it is important for the chimney to be tall enough. You need a tall column of warm air to drive the draft. (See above for details on the height rule.) 

Current building standards require a minimum chimney height of three feet above the roof penetration, and two feet higher than anything within ten feet of the chimney. If your chimney doesn't meet this standard, have a professional add height to it. 

Sometimes even when the chimney is tall enough to meet the building standard, its overall height isn't adequate. Especially for short chimneys in one-story homes, extra height above the required minimum is a good idea. But talk to your chimney professional for advice before you spend money on adding height. 


Smoke Signals: Have a question about your chimney?