Why does my lower floor get smoking when I use my main floor fireplace?

We get this question a lot!

The answer can be a few different things, but they all revolve around one thing: negative pressure. Every home has its own unique pressure system. What I am calling the pressure system is the air entering and exiting your home.

There are two things that have the greatest effect on your home’s pressure system:

1. Appliances consuming and drafting oxygen - Every time an appliance, such as a gas water heater, furnace, or boiler run they consume oxygen through combustion and drafting. This drafts a substantial amount of air out of your home. Range hoods, bathroom fans, and clothes dryers mechanically draw air out of your home creating negative pressure as well.

2. The stack effect - The stack effect is a result of the warm air in your home rising and causing a higher pressure in the upper portions of your home and a lower pressure (negative pressure) in the lower portions of your home.

The air that is removed from your home needs to be replenished by your make-up air system. Make-up air is the air provided back into the home in order to make up for the air removed from the home by these other factors.

In a properly ventilated home this is achieved by a fresh air intake system, - a vent that usually consists of an insulated flex pipe or ducting that enters the furnace room from the outdoors - and usually has the end put in a 5 gallon bucket. (really? ) I don’t get it.

Some homes are not built with the proper make-up air system and as a result the home starts to pull the air from leaks in windows, doors, and fireplaces. The air always takes the path of least resistance and in most cases, it is the lower floor fireplace that provides that path. When you open the damper in the lower floor fireplace and feel cold air rushing down this is your home attempting to make up for all of the air it is losing.

The lower floor gets smoky as a result of smoke exhausting from the main floor fireplace and being sucked down and into your home instead of up and out of your chimney.

So, what is the solution?

You have a couple options:

1. A top mounting damper is sometimes a good solution to the problem. This product seals the chimney at the at the top versus the bottom minimizing the amount of smoke that can enter the lower floor flue from the top.

2. If that doesn’t work, it is likely a result of cross drafting between the tiles somewhere inside the chimney system. This means that the clay tiles lining your chimney have cracks or the mortar joints between the tiles have eroded and it is pulling smoke from one flue to the other below the chimney top. In this case your chimney lining will need to be repaired.

If you are experiencing any of these symptoms, please stop using your fireplace and call the Chimney Doctors right away. We will send one of our CSIA Certified Chimney Sweeps out to take a look at your system and come up with a solution to meet your specific needs.

Steve Trumble

Chimney Doctors Owner

C.S.I.A Certified Chimney Sweep # 6835

Christine Pheneger