Can you share a chimney flue?

Author: Marlene Davis MD  |  Last update: Saturday, July 5, 2025

The type of fuel used (wood, gas, etc.) in each fireplace can impact the feasibility of sharing a chimney. Combining different fuel types in the same flue is a terrible idea due to differences in combustion byproducts and the potential for hazardous mixtures.

Can two fireplaces share the same flue?

If you want two fireplaces to use one flue, all the fireplaces will need to burn the same type of fuel. In addition, you will need a fireplace expert to design and install the system.

How many appliances can share the same flue?

A solid-fuel-burning appliance or fireplace shall not connect to a chimney passageway venting another appliance. In other words, only one appliance per flue, period.

Does unit share a chimney flue?

Each heat source needs its own pipe. Alot of times a chimney will have 2 or 3 separate pipes running up thru the chimney - but they're separate flues. The other option would be to just run it out the side of the house. Or if it's a 1 story home - you can just run a pipe straight up thru the attic and out the roof.

Can you have a shared chimney?

A shared chimney stack is commonly found in terraced or semi-detached homes. Often they qualify as party structures under the Party Wall etc. Act 1996. As such they are often jointly owned by the owners on either side of the boundary, and certain works require notification under the Act.

✅ How to Keep Fireplace Smoke🔥💨Out of Your House 🏠 and Up Your Chimney!

What is a shared chimney flue?

Combustion appliances, such as gas furnaces, produce combustion byproducts (flue gases) that need to get out of the house. A shared chimney flue means multiple combustion appliances vent their gases through the same opening.

Can you add a second flue to a chimney?

Chimney Design Considerations

In some cases, two flues within one chimney structure can accommodate this, allowing each fireplace to have its dedicated passage for smoke and gases. Two flues in a "chimney pot" are common in the United Kingdom and France.

Why would a chimney have two flues?

In older houses located in colder climates, it was fairly common to have one chimney with two or more separate flues. This would allow a homeowner to vent, say, an oil-burning appliance as well as one, two, or even three wood-burning stoves/fireplaces.

Can you use the same chimney for oil and wood?

If you have both an oil or gas furnace and a wood stove, make sure they have separate chimneys or vents.

How many flues can a chimney have?

Exception: Where venting only one appliance, two flues are permitted to adjoin each other in the same chimney with only the flue lining separation between them. The joints of the adjacent flue linings shall be staggered not less than 4 inches (102 mm).

What is the 7x rule for flue?

The flow area of the largest common vent or chimney shall not exceed seven times the area of the smallest draft hood outlet. Typically: many water heaters use a 3" flue, the largest area to connect the water heater should be 49" in area or an 8" x 8" chimney tile or 7" round chimney.

Can smoke get into second flue in chimney stack?

If the flue liners are broken, or shift, creating gaps, and no wythe is present, smoke can cross over into an adjacent flue. If that flue is cold, the smoke might be drawn back into the house.

How many bends can a chimney flue have?

Use no more than two right-angle bends in the stovepipe installation. Additional bends cause soot and creosote to collect in the stovepipe or chimney, block flue gas flow, and increase the danger of fire.

Can two stoves use one chimney?

If the chimney is wide enough, and both of the stoves are feeding into a similar elevation, and both are running hot, you won't have a problem. The problems mostly come from lack of shutoffs, and elevation differences, you don't want one stove inside on the second story and one on the base floor.

Does each fireplace have its own flue?

Each fireplace will have it's own separate flue which is divided by the mid feathers. The chimney breast in a lounge will usually house two flues; the lounge fireplace itself and also the bedroom fireplace directly above.

Can a furnace and water heater share a flue?

In short, yes.

What is the best firewood for chimney?

Top Choices for Fireplace Wood:

Oak: Known for its dense nature, oak is a standout choice. It burns for longer durations and emits consistent heat. Oak also leaves behind minimal creosote, making chimney maintenance easier.

Can I use existing chimney for wood burning stove?

Building regulations allow direct connection of flue pipe to chimney as long as there is no danger of the building catching fire and that the combustibles (smoke) are successfully taken away via the flue.

How do I vent my oil furnace without a chimney?

Direct venting systems eliminate the need for a chimney. An induced draft fan typically provides the draft required to exhaust the combustion products through a side wall. This system normally requires an air-flow proving switch to confirm that the required draft is present before combustion begins.

How often should a chimney flue be replaced?

The average lifespan of a chimney flue liner is about 15 to 20 years. If you lived in your home 15 years or more you probably need to get the entire liner replaced to make sure it is up to code. If there is damage to your chimney flue liner your home is at risk for a serious home fire.

What is a dummy chimney?

A prefabricated chimney, also known as a dummy, replica, false or reproduction chimney, can visually meet the planning requirements without the need for chimney breasts. Chimney breasts cut into a large amount of space in a room, which makes a prefabricated chimney the perfect choice for smaller builds.

Why does my basement smell like smoke when I use the upstairs fireplace?

A frequent issue homes have is smoke in the basement when using the upstairs living room fireplace. This is because smoke is crossing over from the upper fireplace and getting sucked down the unused basement fireplace flue. With your upstairs fireplace burning, it sends 250-500 cfm (cubic feet of air) out of your home.

Can I fit a chimney flue myself?

Yes. Most of our customers fit their stove and or flue liner / system themselves. You do not have to use a professional installer if you are competent to do the work yourself.

Can you reuse a flue?

The principle: an independent stainless steel pipe is inserted inside the existing flue, connected on one side to the stove and on the other to the roof outlet. The result: the existing flue is reused, the draught is good and the installation is safe and long-lasting!

Can a chimney flue be too big?

Improper flue sizes are a leading cause of poorly drafting fires. A flue that is too small won't allow the fireplace gases to exhaust properly, and a flue that is too large will be cool down too quickly, causing condensation and creosote buildup within the flue.

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