Proper fireplace dimensions can prevent smoke
Tim Carter
Q: I have a masonry fireplace that puffs smoke into the room when a fire is burning. It gets worse as the fire dies down. I've spoken with three bricklayers who build fireplaces and have received three different answers.
Confusion reigns at my home, and my wife is none too happy. Can you share what might be wrong and if there's an easy fix to the problem?
A: Smoking fireplaces are a nuisance and, unfortunately, the solution is not always easy.
The physics that are involved in chimneys, drafting and smoke prevention is quite complex. The Brick Industry Association has tackled this topic in no fewer than three detailed white papers that show exactly how to build a fireplace that will work perfectly and not smoke. The white papers also help you diagnose why your fireplace might be smoking.
The issue is that some masons who build fireplaces have no clue about these fantastic, easy-to-understand documents. A mason who has been building bad fireplaces for years might, without realizing it, pass on his faulty knowledge to the young apprentice working for him.
It's important to realize there is a distinct mathematical relationship between the width and height of the fireplace opening for a standard fireplace. All the dimensions and shape of the firebox, the throat, the smoke chamber height, the flue size and the total height of the chimney This stone fireplace doesn’t smoke because it matches the necessary dimensions.
are determined by just the width and height of the fireplace opening.
Here's an example. Let's say your fireplace opening is 32 inches wide. The height of the opening should be
29 inches. The depth of the firebox, less the outside facing material of the fireplace, should be 16 inches. The width of the rear of the firebox should be 19 inches. The smoke chamber height should be 24 inches and the nominal flue size should be 12 inches by 12 inches. The height of the chimney using this flue liner should be 19 feet.
You can sometimes solve a smokingfireplace problem by making the chimney higher. But before you go to all that work, you need to be sure all the other dimensions of the entire fireplace are correct. If there are significant design flaws in the firebox and the smoke chamber, it's possible the entire fireplace will have to be rebuilt.
Q: Water is leaking through a crack in my foundation. I've tried to patch it with regular mortar, and the leak is diminished but still happening. Is there something I can use to stop the leak permanently?
A: Many homeowners have water coming through their foundation or crawlspace walls. Often it enters around water pipes, cracks or other penetrations through the wall.
The good news is there's an easy-to-use product that usually solves these leaks within minutes. I'd start with hydraulic cement. Hydraulic cement is a powder that looks like typical Portland cement but it's radically different. Once you mix hydraulic cement with water, an irreversible chemical reaction occurs and the plastic mix expands in volume. As it hardens, it retains this change in volume and exerts pressure against the hole or crack so normal water pressure can't leak through.