I understand that installing ducting can be inconvenient, messy, overwhelming, and might even seem unnecessary. Why can’t you use what’s already there? I am no stranger to attempting to improve efficiency while decreasing the work it takes.
However, a dryer vent is not the place to do it. There are specific rules to follow when it comes to venting dryers, especially gas dryers. Since these are there to keep you and your home safe, it is all worth the effort and mess.
It is against IRC regulations to vent a gas dryer through a chimney. Not only is it illegal, but it prevents proper exhausting by impacting airflow, and it’s dangerous. Lint, moisture, and gas byproducts are harmful to health and home. Lint is also highly flammable.
Venting Through a Chimney is Prohibited
The International Residential Code (IRC) provides clear regulations for dryer exhaust ducts and how to vent them. Not only that, but it explicitly prohibits the connection of a dryer exhaust duct to a chimney:
“Clothes dryer exhaust ducts shall not be connected to a vent connector, vent, or chimney.”
Section G2439.3 (614.4)
As you can imagine, forgoing the ducts altogether and just using the chimney is also not going to be permitted based on this regulation.
Additionally, Section G2439.1 (614.1) states that the dryer must be completely independent of other systems. To connect the dryer to the chimney means it is sharing an exhaust system with whatever appliances or installations that the chimney serves.
The IRC, Section G2439.7.1 (614.9.1), says that a gas dryer exhaust duct must have a smooth surface and be made from metal. A chimney can be made of metal, and this pipe for your furnace might have a smooth interior, but what about if you have a brick fireplace chimney?
There is also a section (G2439.7.2 (614.9.2)) on how to connect the ducting sections for a dryer exhaust. One can infer from this description that connecting it into a chimney or just directing it up through a chimney is not up to code standards.
It is always important to note that there can be local adjustments to the code regulations, which means that state building codes vary. However, it is unlikely that there will be any states that will allow a setup that vents a dryer like this.
Why Gas Dryers Cannot Be Vented Through Chimneys
It’s Against the Code (Illegal)
The International Code Council (ICC) created the building codes as a comprehensive guide and model code for the safest installations and practices for homes. The people behind these codes come from international councils and committees of professionals that complied their knowledge and expertise.
What makes these suggested regulations laws is their adoption by a state’s governing bodies. Adjustments are made to increase the local applicability of these codes, and currently, Wisconsin is the only state that has not accepted the codes.
Since the legal bodies in the other US territories have standardized the ICC building codes, they are law. It is according to these codes that home inspectors conduct their examinations, and municipalities issue permits and approvals.
Non-compliance with codes, including those regarding your dryer exhaust duct, can result in fines and demands that you bring your constructions and installations up to code (which will cost you, especially if you have a time limit).
Another consideration is that, since using a chimney constitutes an illegal installation, you can have problems with insurance.
Venting a dryer through a chimney is a fire hazard. This can void any insurance claims if a fire occurs and can even impact other claims for damage when the inspection reveals the system.
Compromised Airflow Efficiency
Dryers are designed to work with a specific sized ducting with a balanced air pressure system for the exhaust system to achieve optimal airflow that will transport hot and humid air, gas byproducts, and lint out of your home.
A too-narrow opening, too-long ducting run, and a textured surface (as with bricks) increase static pressure (resistance), which slows the airflow.
This increases the depositing of lint and condensation as air remains in the channel for too long and cools. Textured surfaces also provide more places for lint to gather.
Another thing to consider is that your dryer is not meant to connect to a chimney. You are going to have to Frankenstein the connections. Compromised or excessive connections can also interfere with the pressure system and create more areas for lint to gather and velocity to be lost.
Lint Can Gather in the Chimney
Fine, short, soft fibers are lifted from clothing during washing and drying. However, these fibers, which compose lint (including some other fluff and substances on your clothes), are mainly lifted as the clothes dry.
As hot air evaporates moisture from the clothes, it also picks up and blows lint out of the drum, where it passes through a lint filter. This removes the majority, but some still gets past it.
These fibers can build up in an exhaust vent (or chimney); the previous section shows that most improper exhaust systems increase lint gathering.
Lint acts as kindling when it combines with heat. Since it’s already a fire hazard, adding it to a chimney (attached to a fireplace, furnace, or heater) means taking unnecessary safety risks.
Not only can this lint be blown down into your home and around a fire, but it can also be blown through your house once alight.
Thus, it is incredibly dangerous to have lint gathering in inappropriate places, like a chimney, and that is why terminals and clearances for the dryer vent are heavily regulated.
Dryer Exhaust Can Enter Other Appliances
If your furnace or any other gas appliance is attached to the chimney, you want to keep humid or lint-ladened air away from the appliance. This air will interfere with the furnace’s operation, and clog the filters, which can result in overheating and breaking down.
Lint near the heat of a fuel-burning appliance is also a shortcut to starting home fires, which is dangerous.
If you connect a dryer where it isn’t supposed to go, you run the risk of creating a backdraft for the fuel-burning appliance. This pushes the exhaust products like carbon monoxide into the house.
Carbon monoxide is a toxic gas that can impact your health, so it should be removed from the furnace to the outdoors where it isn’t harmful. Even carbon dioxide (the main gas byproduct of a properly functioning gas appliance) is not the good for you in large amounts.
If your chimney is brick, you are subjecting yourself to extra maintenance as the moisture from the dryer will cause damage and increase blockages.
Moisture, Lint, & Harmful Gases Can Enter the Home
Dryer vents are supposed to terminate outdoors for a reason. This is to help keep you safe and to prevent damage to your home.
I have mentioned that lint can enter your home through a chimney, which is highly flammable and can be inhaled. Especially if you consider that the dryer duct is likely to be too short to reach the top of the chimney.
This means that, without the exhaust system’s power, the dryer exhaust will stay in the chimney, where it can cause problems.
You also risk backdrafting through the chimney, directing unwanted byproducts into your living space.
Gas dryers also exhaust their own gas byproducts through this vent, which won’t be disposed of correctly and can also get into your home. Symptoms like headaches, nausea, dizziness, and confusion are associated with carbon monoxide.
Moisture is undesirable in your home. You do not need the damage to structure, paint, and furniture that this moisture and condensation can cause. You are also increasing the risk of mold and mildew problems, which can be challenging to clear up.
Thus, all the outcomes of venting your dryer through a chimney will result in damage to your home and negative impacts on your health (particularly your respiratory system). Therefore, it is not worth skipping a code-compliant ducting system.
Sources
https://www.cdc.gov/co/faqs.htm
https://www.finehomebuilding.com/forum/ok-to-vent-a-dryer-through-a-chimney