Ducts/ Duct Sealing

Get Rebates,
Incentives & Services

Introduction

The duct system in your home or building circulates warm and cool air supplied by your space conditioning unit (air conditioning and/or heating). Space conditioning accounts for as much as 40% of your energy bill, according to the California Energy Commission (CEC). Duct losses can account for more than 30% of energy consumption for space conditioning, especially if the ducts are in an unconditioned space such as an attic. A duct system that has been properly sealed and insulated can safely and efficiently keep your home or office feeling fresh and comfortable year-round — and save you money too.

Technology Options

Ducts are the network that connects your furnace, air-conditioner, or heat pump to the air vents throughout your home or building, delivering heated or cooled air to make you more comfortable. Small holes or gaps in your duct system are common and can make your system inefficient by leaking this conditioned air to the outside and forcing your system to work harder to provide the desired temperature.

An enormous waste of energy occurs when cooled air escapes from supply ducts or when hot attic air leaks into return ducts. Recent studies indicate that 10 to 30% of the conditioned air in an average central air conditioning system escapes from the ducts.

For central air conditioning to be efficient, ducts must be airtight. Hiring a competent professional service technician to detect and correct duct leaks is a good investment, since leaky ducts may be difficult to find without experience and test equipment. Ducts must be sealed with duct "mastic," metal-backed tape or aerosol sealant. The old standby of duct tape is ineffective for sealing ducts; it cannot withstand the heat and will fail.

In places that are hard to reach or cannot be seen, Aerosol sealant, or Aeroseal, might be an option. This patented technology utilizes tiny particles of sticky material that are blown through your duct system and attach themselves to the edges of leaks. Though more expensive, it might be a good solution for special situations.

Obstructions can impair the efficiency of a duct system almost as much as leaks. You should be careful not to obstruct the flow of air from supply or return registers with furniture, drapes or tightly fitted interior doors. Dirty filters and clogged evaporator coils also can be major obstructions to air flow.

For optimum efficiency, insulate your ducts. The large temperature difference between attics and ducts makes heat conduction through ducts almost as big a problem as air leakage and obstructions. Ducts in attics should be insulated heavily in addition to being made airtight. Duct insulation should be rated at least R-6. See the Insulation Guide for information about R-ratings.

Efficiency Benefits

In a typical house, about 20 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts. The California Energy Commission (CEC) standard for duct leakage is less than 6 percent of system airflow. Visit ENERGY STAR for more information on the benefits of duct sealing.

Safety
During normal operation, gas appliances such as water heaters, clothes dryers, and furnaces release combustion gases (like carbon monoxide) through their ventilation systems. Leaky ductwork in your heating and cooling system may cause “backdrafting,” where these gases are drawn back into the living space, rather than expelled to the outdoors. Sealing leaks can minimize this risk.

Savings
Duct sealing increases efficiency and lowers your energy bills. The typical home could save up to $150 annually. Commercial buildings could save even more. And, many utilities provide rebates for upgrading your duct system. Payback periods range anywhere from two to four years based on the cost of diagnostics and repair.

Environmental Benefits
Energy generation and use is the single largest contributor to air pollution. If you are wasting 20% of your heating and cooling systems' performance through leaky ducts, you are using more energy to get the same job done. By sealing your ducts and reducing the amount of energy necessary to comfortably heat and/or cool your home or building, you will reduce the amount of air pollution created from generating the energy.

Purchasing Tips

  • Hire a good contractor. A knowledgeable contractor can perform tests on your duct system to determine if duct sealing will make you more comfortable and efficient. When improving your duct work, your contractor should:
    • Identify any leaks with diagnostic equipment.
    • Seal ducts with mastic, metal-backed tape or aerosol sealant - not duct tape.
    • Test airflow out of the registers after ducts are sealed.
    • Insulate your ducts to keep air at the desired temperature.
    • Conduct a combustion safety test after ducts are sealed to be sure all gas- or oil-burning appliances are working properly.
  • When hiring a contractor:
    • Focus on local companies.
    • Look for licensed, insured contractors.
    • Get three bids with details in writing.
    • Ask about previous experience.
    • Check references.
    • Check the status of their license at the Contractor's State License Board.

For more information about reducing energy loss in your ducts or to get a referral to a qualified Home Performance contractor, visit the California Building Performance Contractors Association.