Ask the Builder: Why is smoke is billowing from a new fireplace?

Question: F. Tim, I really need your help. I just moved into my new home and have a smoking brick fireplace. It is 55 inches wide and has a domed opening that is 33.5 inches at the top of the arch. It looks like normal brick mortar was used for the firebrick.

For some reason it has two triggers and a damper on each. It smokes like an old steam locomotive and sends suffocating clouds of smoke into the house. Cracking a window helps but doesn’t solve the problem. Should there be only one fireplace? Should I just open one damper? What’s happening? – Tim Y., broken arrow, okla.

ON. When I opened Tim’s email and saw his fireplace photo, I exhaled heavily. I was flooded with a number of emotions. Frustration, sadness, mild anger, and sympathy were high on the list. It breaks my heart to get bad news, like Tim knowing it is so easy to build things, even fireplaces, that work perfectly. The science of how chimneys and chimneys work has been known for hundreds of years.

I would like to take this opportunity again to advocate that you work with your local school board to restore vocational training in both elementary and high school. In my opinion this should be compulsory and all boys and girls should be exposed to the same study material every year as they progress through the 12 grades. We need to familiarize students with how houses work – and the right ways to build and repair things – because as they age, they will all need a roof over their heads.

Vocational training not only gives young people the confidence to perform minor repairs and speak intelligently to contractors, but it can also prove to be a stepping stone for those looking to work with their hands in a rewarding lifelong calling. We have to bring new young people into the trade every year. That’s just common sense. Let’s expose the jobs to children and show them how rewarding it is to absorb this valuable knowledge.

Let’s roll up our sleeves and see what should have happened at Tim’s house when his fireplace was built. I’m sorry to say Tim’s fireplace is absolutely the worst job I’ve ever seen in my career. It was meant to fail from the start.

The Brick Industry Association has published clear and concise brochures for decades that show exactly how to build a home, wood-burning fireplace that never smokes. Not only do these brochures cover size requirements, they also go into great detail on how to properly size the fireplace and adjust it to the height of the fireplace.

It is important to know that the size and shape of the fireplace are directly related to the width and height of the opening to the fireplace. You can’t just guess like Tim’s Mason did. As crazy as that sounds, Tim’s bricklayer created a firebox with two short stub walls that protruded back into the firebox. Then the two walls went off at a 45-degree angle and met at a hard 90-degree corner in the back of the firebox. It’s no wonder smoke was rising in Tim’s house.

The shape and size of the firebox are critical, but what you don’t see above the firebox is even more important. The shape and size of the chimney’s throat, as well as the design of the smoke shelf, are of the utmost importance to ensure that all smoke and hot gases go up the chimney and not roll into the room.

The sad thing about all of this is that almost anyone with moderate hand-eye skills can build a no-smoking fireplace using the easy-to-understand information available for free from the BIA. It’s crazy everyone has a smoking fireplace when you think about how the technical drawings, specs, etc. are available.

Let’s talk about using common brick mortar in fireplace fireplaces. It is simply a mistake. The firebrick used in a firebox is a special refractory brick that is designed for high temperatures. It is entirely possible that the temperature in a blazing fire could exceed 1,000 degrees in certain situations. Normal brick mortar cannot withstand this temperature fluctuation from room temperature to 4-digit temperatures.

Fireclay is best for making thin joints between the firebrick. Fireclay is a special fine clay that you mix with water to the consistency of a thick sauce. Skilled masons carefully dip the edge of a firebrick into them to apply the perfect amount of firebrick to each brick. The joint between the firebrick usually ends up no wider than 1/16 of an inch.

With the wet fireclay on the edge of one fireclay brick, the mason then presses it against another brick, and the fireclay creates a refractory bond. This fireclay is not that different from the clay my daughter uses to make ceramics. She burns this clay in a furnace that reaches temperatures of over 2,100 degrees. It easily withstands thousands of fires for decades without crumbling like ordinary brick mortar does.

I have created a special page on where all BIA information is shared with you. Just put this exact url into your browser so you can have a no smoking fireplace:

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