A smoking fireplace can be a Homeowners Nightmare. The problem is, you don't know why it's smoking and you don't know how to figure out what the problem is or how to fix it. Thousands of fireplaces throughout the United States go unused for this very reason. The good news is, most of these fireplaces can be fixed to draft properly with some very simple and inexpensive solutions.
I burn my fireplace for a while and then it starts smoking!
The first problem we generally run into with a smoking fireplace is one of design and construction. Believe it or not, fireplaces must meet certain structural requirements to work properly. When a fireplace is built it starts with a good foundation, then the firebox and damper, the smoke chamber, and finally the flue. While the firebox can be constructed in any dimension you like, the smoke chamber and flue must be constructed to meet the the dimensions of the firebox opening. In most instances, a smoking fireplace is the result of the flue not meeting the minimum dimensions required to make the fireplace draft properly.
Here is what happens. When you light a fire, the fire creates smoke which goes up the flue. At the same time, the fireplace face opening takes in a certain amount of air from the room which also goes up the flue. If the flue is not big enough and cannot hold the volume of air and smoke being emitted, the flue will eventually fill to its maximum volume and causes an overflow of smoke into the room. As an example, think of your fireplace as a funnel. If you hold a funnel and begin pouring water into it the water will run through the funnel. If you pour the water to fast only so much can leave the funnel neck at one time. If you continue to pour faster than the water can get through the funnel , it will eventually overflow the funnel. This is exactly what happens with your fireplace.
So how do you know if this is your problem? Here is what you do. First measure the height and the width of your fireplace opening and multiply those two numbers together.
EXAMPLE: height= 27" and width= 34"..... 27" x 34" = 918 square inches
Next, you must measure the inside dimensions of your flue across each direction and multiply these two numbers together.
EXAMPLE: Width #1= 7" and width #2= 11" ...... 7" x 11" = 77 square inches
As a rule of thumb, your flue must have an inside area of at least 1/10 of the area of your fireplace opening to work properly. To figure out what size our flue should be for our example fireplace, take the 918 square inches and divide by 10.
EXAMPLE: 918 divided by 10= 91.8
This tells us that our flue should have an area of around 91 sq. in. or better to work properly. As we look at the area of our example flue, we see that the area is only 77 sq. in. and is too small for our fireplace to work properly.
The good news is that you don't have to rebuild your fireplace to fix this problem. The problem can be resolved with a very simple item called a Smoke Guard. The Smoke Guard can be used to reduce the height or width of the fireplace, making the ratio of the fireplace opening to flue size more compatible. The Smoke Guard is spring loaded, adjusts from 28 1/2" to 48", and installs easily with only a screwdriver.
In our example above, we can see that a 4" or a 6" smoke guard across the top of our firebox opening will reduce the area enough to meet the area of our flue and allow our fireplace to work properly.
