Dryer ducts are essential to the operation of vented dryer units. But although it is common practice to insulate HVAC ductwork, dryer duct insulation isn’t as popular.
If you’re still on the fence on whether you should insulate your dryer duct or not, here is a guide to help you make an informed decision. I discuss the International Residential Code’s (IRC) stance on dryer duct insulation, the best materials for insulation, why dryer duct insulation is a great idea, and the drawbacks to dryer duct insulation.
The IRC does not mandate insulating dryer ducts, although local codes may differ. There are many pros of insulating dryer ducts: noise reduction, drip prevention, energy efficiency, and increased duct lifespan. Cons include cost and maintenance of insulation.
Dryer Duct Insulation According to the Code
Section M1502 and Section M1601 of the IRC address the installation of exhaust and duct systems, specific to clothes dryers and in general, respectively.
The IRC doesn’t mandate or forbid the insulation of dryer ducts. Instead, it instructs that dryers should be exhausted according to the manufacturer’s instructions.
The IRC also instructs that the dryer duct be independent of all other systems.
The code also covers things like:
- Dryer duct installation requirements.
- Duct material and size.
- Duct termination outlet and passageway size.
Insulation Materials (Section M1601.3)
In Section M1601.3, the IRC provides requirements for duct insulation materials. The instruction covers requirements for the use of adhesives, duct coverings, linings, and, polyurethane foam.
- Duct coverings and linings should feature thermal insulation properties. The materials are supposed to have a flame spread index of not more than 25 and the smoke-developed index shouldn’t be over 50 according to ASTM E84 or UL 723.
- If adhesives are used, they should have a low flame spread index, not higher than 25, in accordance with ASTM E84 or UL 723.
- The application of polyurethane foam to the exterior of dryer ducts that are connected in attics or crawl spaces is allowed if the flame spread index isn’t more than 25 and the smoke-developed index isn’t greater than 450.
So, before picking an insulation material for your dryer duct, pay attention to its flame spread index and smoke-developed index. You can find more information about these two indices here.
The IRC aims to protect the health and safety of homeowners. Thus, it is important to adhere to its instructions, especially with regard to appliances that pose safety risks like dryers.
Dryer ducts can neither be installed nor insulated with materials like plastic (even thermoplastics like ABS) and flexible materials because of their tendency to collect lint, which is flammable.
Best Dryer Duct Insulation Materials
Dryer ducts transport humid air to the outdoors. So, they can only be insulated with materials that are heat resistant.
The best material for insulating dryer ducts is fiberglass. You can opt for either fiberglass rolls or batts, ideally products with thickness between R-11 to R-19.
When securing the insulation, do not use regular duct tape. Instead, use aluminum foil tape (amazon link). Aluminum foil tapes possess temperature-resistance qualities, making them suitable for dryer duct insulation. If you do not have a suitable tape, you can use aluminum twine.
For optimal protection, every inch of the duct should be covered with insulation.
If the duct isn’t installed yet, it’s best to use an insulated duct pipe. This would save cost and also reduce the installation time.
You can make your home more air-tight by using caulk to close any gap around the duct’s exit point.
Why Dryer Duct Insulation Isn’t Mandatory
Duct insulation adds a protective layer that doesn’t necessarily affect the operations of the duct.
Whether your dryer duct needs to be insulated or not would depend to a large extent on the positioning of the duct. If it is located in a conditioned area, then insulation would not be necessary. This is because the temperature in conditioned spaces doesn’t pose a risk of causing condensation.
The IRC does not mandate the insulation of dryer ducts. However, some cities might demand that dryer ducts be insulated. So, you’d have to consult your local building codes to be sure.
Insulating Dryer Ducts Is Recommended
Although it isn’t required in every dryer duct, insulation provides extra protection to ducts and will prove worthwhile over time.
If the duct is connected through an unconditioned space like a basement or crawlspace, it’s best to insulate the duct. Should you leave the duct uninsulated, the vast temperature difference can lead to condensation on the duct’s surface.
This can be avoided by insulating the duct against external influence. That way, even if your duct is connected through an unheated crawl space, the dryer will not suffer from drippy ducts and other problems that condensation can cause to your dryer ventilation system.
Here’s Why You Should Insulate Dryer Ducts
Insulation Reduces Noise
The passage of air through dryer ducts release sounds and this noise can be annoying, especially if your dryer features thin ducting.
Insulation involves installing an additional layer to the duct wall. Although it might not completely prevent the sounds from entering your living area, it would limit the amount of noise that breaks through the duct wall, improving the comfort level in your home.
However, issues like lint build-up or dislodged screws can increase duct noise to an abnormal level, so even if the insulation dampens the sound, the noise entering your room might still be high.
So, you would have to first address the primary cause of the problem. This way the insulation would be able to muffle the duct sound to an acceptable level.
Insulated Ducts Don’t Drip
The primary function of dryer ducts is to move humid exhaust air from the dryer to an outdoor location. So, the duct’s temperature will increase while the dryer is running.
Condensation occurs when there is a significant difference between the room temperature and the temperature of the duct.
For instance, if the room is chilly and it comes in contact with the warmer temperature of the duct, the humidity in the air would turn into water vapor and condense on the duct’s surface.
Dripping vents are usually a source of discomfort and can lead to moisture problems, like rocks and mold, if left unattended. Moisture on the duct’s surface can also cause the duct to rust and corrode.
But you don’t have to endure moisture dripping from your dryer duct because insulation prevents the condensation that causes drippy ducts.
The protective layer of insulation material prevents the room’s air from coming in contact with the duct, thus even if your duct is connected through a chilly basement, you wouldn’t have to worry about your duct dripping.
Your duct can experience major leaks due to clogged pipes, broken flappers, or duct holes. If this happens, you would have the fix the problem because if you do not, moisture can bypass the insulation into your living area.
Ducts With Insulation Make Dryers Energy Efficient
Dryers are one of the highest energy-consuming home appliances. Most household dryers consume between 2000 to 6000 watts of electricity every hour.
So, if you would like to decrease your energy consumption, it is of utmost importance that you make your dryer and its units as energy-efficient as possible.
Insulating your ducts does not only prevent the discomfort caused by drippy ducts, but it also prevents duct irregularities from leaking humid air into your space. This ensures that the quality of air in the room is preserved and your HVAC unit doesn’t have to work overtime to make up for contaminated air.
Proper duct maintenance is also important for the effective performance of the dryer as well as increased energy savings.
Another source of energy sink is the dryer vent. Dryer vents are sometimes responsible for up to 10 percent of a home’s heat loss. Moreover, a cold draft can also enter through dryer vents.
Both loss of heat and cold drafts could be due to a number of reasons but the primary cause is an unsealed flap or backdraft damper.
Most dryers feature a flap that’s installed over the vent to prevent air leakage. Sometimes, the flap doesn’t shut off completely and over time, lint clogs the flapper valve, forcing it open and leaving your house vulnerable to air leaks.
So, for optimal energy savings, in addition to insulating the duct, you should also install a dryer vent seal.
Increased Lifespan of Ducts
When you insulate your dryer duct, you enclose it inside a protective outer layer. This means that the duct is protected against external elements.
A common issue homeowners experience is condensation on the duct’s surface, especially when a duct runs through an unconditioned location.
Besides the obvious effect of condensation, which is drippy ducts, it can also cause serious damage to the metal pipe if left unattended for a prolonged period.
Moisture as a result of condensation can cause the duct to rust, corrode, and can lead to the growth of mold and mildew.
It could eventually weaken the duct and cause it to crack or break in areas where condensation is prominent.
Condensation causes the ducts to corrode and corroded pipes affect the appearance of a room. It can also negatively affect the air quality of the room.
Insulating your dryer duct helps it last longer than it would if it is uninsulated.
Drawbacks of Insulating Dryer Ducts
Insulating a dryer duct involves installing an additional layer on the duct. It’s a project that would demand your time and money.
The primary drawbacks homeowners have are the cost, installation, and maintenance requirements for insulating the duct.
The first thing that comes to mind is the additional cost that duct insulation attracts. Insulating the duct would cost between $1 to $5 for every sq ft.
If you’re a skilled DIYer, you could do the work yourself and would only have to spend on installation materials. Employing a professional would ensure a thorough job. However, it would attract extra costs.
The insulation automatically becomes an extended part of the dryer duct maintenance. This means that in addition to occasional duct maintenance and repairs you would have to invest in the maintenance in the repair of duct insulation.