How Leaky Air Ducts Affect Your Heating and Cooling
Air leakage in your duct system can have a poor effect on your heating or cooling unit, reducing the efficiency, lifespan, and performance of the system. Air duct leaks can increase your energy bills, create excessive dust, and cause poor indoor air quality. In order to fully understand how air duct leaks and a leaky duct system can affect your unit, it is important to know how the duct system works in conjunction with the unit to heat or cool your home. Let’s use this example for cooling your Phoenix AZ residence, instead of heating it, due to our summers being so brutal, it’s easier to understand.
When you turn on your air conditioner through the thermostat during the summer months, the A/C turns on and the fan motor sucks air through the return ductwork to the inside of your unit. The air from inside your home is sucked in through that “return” duct and passes over a filter to catch dust particles. The air is then blown over a coil that is made of copper and aluminum, and looks similar to a giant radiator. That coil has refrigerant inside of it that cools the coil ice cold in the summer. The air gets sucked through that coil and cooled down. After the air gets sucked through the coil and is cold, it gets pushed out the other side of your unit into the “supply” ductwork. The ductwork is either made of metal tubes or rectangular boxes that are connected together in sections, or it can be flex tubes that are like a giant slinky wrapped in insulation, or sometimes a combination of both. The air travels through the “supply” ductwork and is spit out of all the different registers in your home.
You also have a return duct that connects to a filter box and grill. Some houses have multiple return ducts, each connecting to a box with a filter grill. In many cases, those “return” boxes are leaking at the seams and at the main collar connection where the ductwork is attached to the box. The return ducts may also be leaking at various connections in the ductwork, and at the main connection at the unit. The unit should pull air from the inside of your home over the filter to remove particles, and blow it over the coil to be cooled and distributed throughout the home. If the return ducts have leakage it causes some of the air to bypass the filter. That means that the unit is sucking in some air from your home and the filter is catching the particles, and some of the air is sucking in through all of the seams, gaps, and holes in the “return” ducts from the attic.
That attic air is full of dust and debris, as well as fiberglass insulation that you don’t want to breathe. Also, the attic air is usually between 120-170 degrees in the summer, much hotter than the 75-85 degree air inside your home. So the unit has to work much harder to cool down 120-170 degree air, rather than 75-85 degree air. That reduces the lifespan of the system and increases your energy bills. The system is also affected by the particles that bypassed the filter. You don’t want to breathe the attic air full of dust and fiberglass, but it also hurts the unit. The air from the attic gets blown over the coil to be cooled, and that causes the coil to sweat condensation. Some of the dust and fiberglass particles from the attic air end up sticking to the wet coil, and it creates build up, sort of like a lint trap in a dryer. Most manufacturers recommend that you clean the indoor coil every 2-3 years, and APS and Energy Star recommend cleaning it every 2-4 years. Cleaning the coil is difficult and costly, so sealing the ductwork will help keep that coil cleaner. When the coil gets residue and build up, it causes the motor to run harder in order to suck the air through that coil because it’s impacted with debris so the airflow is restricted. When the motor runs harder, the amp draw increases, and so does your energy bill, not to mention the fact that it reduces the lifespan of the motor. The dust and fiberglass particles that make it through the coil are pushed through the “supply” ducts and distributed in the air throughout your home. Those particles also build up in both your “return” and “supply” ducts as well. So if you have leakage in your “return” ductwork, it creates poor indoor air quality, an increase in dust throughout the home, an increase in your utility bills, and it reduces the efficiency and lifespan of the unit.
There can also be leakage from the “supply” ductwork. The leaks are usually also found at connections, as well as the seams and gaps inside the trunkline, distribution boxes, or the “supply” boxes that have the registers attached to them. After the air is sucked through the unit and cooled from the coil, it travels into the supply ductwork and some air just blows into the attic. Besides cooling down your home, you’re also cooling down your attic, which is a waste of money.
The other issue is that the leakage from the supply ductwork will cause a vacuum effect on the home. A five ton unit is made to suck in 2,000 cfm of air through the filter, and spit out 2,000 cfm through the registers. So if that five ton system has 10% air leakage from the “supply” ducts, it’s sucking in 2,000 cfm, but it’s only blowing about 1,800 cfm into the home, and 200 cfm into the attic. The unit still needs to suck in 2,000 cfm, and since it can’t get all of the air back that it spit out because 200 cfm went in the attic, it causes a vacuum in the home. That vacuum pulls in warm outside air from doors and windows, and it also pulls in dusty and polluted air from behind electrical outlets and switches, as well as from any gaps at plumbing penetrations, light fixtures, ceiling fans, recessed can lights, and so on. So once again, the leakage is affecting your indoor air quality and inviting allergies and bronchial health ailments.
How To Repair A Duct System Leak?
Sealing air duct leaks in your duct system is usually an all day job, and in some cases it may take 2 or 3 days. The total cost to make the necessary repairs depends on the size of the home, the type of ductwork used in the system, the amount of air leakage detected during the negative pressure test, and the overall condition of the duct system. Hey, don’t worry though, the good news is that both Phoenix utility giants APS and SRP offer rebates to homeowners who have their duct system properly sealed by a certified contractor. APS will refund up to $325.00 towards repairs and SRP will refund up to $400.00 towards repairs. That’s a pretty smoking deal.
In many cases, customers who seal their air duct system see a reduction in their monthly energy costs and a return in their investment in just a few years. Our home comfort tech seals all of the supply and return ductwork in the attic at all seams, connections, and collars using a high temperature fiberglass reinforced elastomeric sealer. We also seal any distribution boxes at the seams, collars, and end caps using the same sealer. We’ll then remove all supply registers and seal the ductwork from the inside at seams, joints, collars, and connections with a high temperature fiberglass reinforced elastomeric sealer. Then we fill up any gaps in the drywall behind the registers using a silicone latex caulk, and reattach the registers. In some circumstances it will require additional sealing. Air duct systems that use return air platforms may require plating off areas using duct board or sheet metal and sealing over the plates. Systems with fresh air return ductwork also usually require plating off areas and sealing over the capped section with sealer. Sometimes leaks in the duct system are located at torn or deteriorated flex duct runs, or damaged hard duct runs or distribution boxes that cannot be properly sealed. In those cases we replace or repair the ductwork as needed, and proceed with sealing the ductwork after making the repairs.
Some Phoenix homeowners have conditioned air loss from the shell of the home, referred to as the home envelope. In some cases, customers request that Morehart Air and Heating make the necessary repairs to reduce the conditioned air loss as well as seal the duct system. Our technician can explain the benefits of sealing the home envelope after performing the negative pressure test, and inform you of the priority of the repairs, depending on the issues (allergies, asthma, dust, warm or cold rooms, energy consumption, etc.) each customer is concerned about the most. There are a variety of repairs that can be made to a Phoenix home to help reduce conditioned air loss, ranging from replacing leaky lights with air tight lights and sealing around plumbing pipe penetrations and installing weather stripping around door frames, to sealing inside electrical outlets and switches and sealing around speakers, sky lights, and light fixtures. In some circumstances we’ll be unable to repair the issues we locate, such as replacing a leaky window. In these special cases, our tech will inform you of the problem, and recommend a company that can perform the repairs.
Once our team has completed all of the necessary repairs to your ductwork and eliminated the air loss, we’ll perform the air duct leak test again to ensure that the duct system is properly sealed. Morehart Air and Heating uses only high quality products when sealing your duct system, so the seal should last decades, and you will most likely never need to seal your ductwork again in the future.