Building codes are often a sticking point for anyone looking to do some home improvement or additions. I know that the cross-referencing of sections and all the exceptions or special considerations used to make my head spin.
So, I always try and make the building code easier to understand and follow by putting what you need to know about a matter in one place. This includes why and how far a dryer vent should be from a furnace intake and the primary safety consideration for this particular case.
A furnace intake is an opening into a building. A dryer vent must be a certain distance from this opening as per specific instructions from the manufacturer or, if there are none, at least 3 ft away, according to the IRC. This distance is important for safety reasons.
Dryer Vent Duct Termination Code
A furnace intake counts as an opening to your house. Therefore, this opening must be taken into consideration for dryer vents that are required to terminate at a specific distance from openings to the building.
According to Section M1502.3 of the International Residential Code (IRC):
“Exhaust duct terminations shall be in accordance with the dryer manufacturer’s installation instructions.”
However, if there are no specified locations for the terminal, the duct cannot terminate within 3 ft (or 914 mm) of any opening to the house, in any direction. But you should be sure to comply with the manufacturer’s directions, as long as it is a listed (approved according to the code) product.
Always Check Local Codes
Some states adopt the IRC with amendments in order to ensure that the regulations for safety work best for the different areas they are applied to.
For example, according to the California Residential Code, water heaters are strapped throughout the state because the whole area is within the earthquake risk zone. Other states (like Colorado) only require strapping in certain regions at higher risk for earthquakes, but it is not necessary for all areas in these states.
This is why I always advise checking your local codes. It is vital to be aware of any amendments that individual states have made to the IRC, including for any specific dryer vent distances regarding furnace intakes. This will ensure you are correctly following the regulations that are made for your health and safety.
Why Manufacturers Get the First Say
If you are wondering why the manufacturer gets the first say, it all comes down to practicality.
With the ever-changing models and designs for different types of dryers, the code would constantly need to change to try and keep up. This is why it is easier to outline the safety guidelines for dryers in the building code, but leave the specifics to the manufacturers who know their products best.
Giving manufacturers this authority is safe because they rely on their products being up to a certain standard for selling. In fact, they benefit most from providing the best direction for the installation, maintenance, and safe usage of the product. If products keep causing trouble, no one will want to buy them.
This is why the building code defers to manufacturer instructions; they are the experts on their own products, and they should be thoroughly familiar with the codes that regulate the installation and use of their products.
If the building code had to account for every type of dryer as well as the instructions and safety guidelines for each model and make, the code would be very difficult to create, use, and keep updated.
By providing code approval to products (specifying the product must be listed and labeled), the building code can reliably leave the directions beyond basic regulations for issues like dryer vent clearance from a building opening (i.e., furnace intake) to the individual product-based directions. This limits confusion and improper use.
Dryer Exhaust in the Furnace is Dangerous
Lint comes from organic fibers used to make clothing and other material items and develops naturally as the item wears and rubs against things. However, it comes loose when water from the wash cycle lifts it from the material, and then this becomes dehydrated in the dryer and is deposited as a clump of lint.
Dryer lint is a fire hazard and can be dangerous if you have a gas furnace that has a flame. This is because the fibers that make up your bit of lint are soft and short, making lint an effective kindling.
However, the more prominent issue with a dryer exhaust in or too near a furnace intake is that it can become blocked by lint build-up.
Carbon monoxide (CO) is a byproduct of furnaces as they operate. Furnaces are properly vented to keep this from being an issue, but if lint were to compromise the intake vent (it may also reach other parts of the ventilation system), resulting in CO building up in your home.
This, in turn, can lead to carbon monoxide poisoning. This is highly dangerous as CO gas is hard to detect unless you have a CO alarm.
Blocked vents or clogged and dirty filters in the furnace will also impact the appliance’s functioning. Without sufficient airflow, your furnace will have to overwork to counter the lack of airflow, which will cause overheating and will cause damage over time. It can also heat up the basement uncomfortably.
This is why it’s important to keep your dryer vent an appropriate distance from your furnace intake and to also clean the lint filter frequently to minimize the expulsion of lint from the vent.
For more information, check out: Dryer Vent Clearance Requirements (Complete Guide).