Duct Sealing and Insulation

Leaks in the heating and cooling ductwork systems (forced air furnaces, central air conditioners, heat pumps...) are big energy wasters. Complaints about energy bills and discomfort are often due to problems involving the home ductwork.

Image Credit: Energy Star; A= Leaky connections; B= Leaky return; C= Furniture blocking registers D=Leaks at furnace and air filter slot and duct tape failures E=Fallen duct insulation; F=Leaky Supply Ducts G= Kinks restricting airflow.

Energy losses

The US DOE estimates that in older homes with forced-air furnaces, 20% of the home's heated air is lost through leaky ducts. But AC duct leaks are also responsible for a significant part of cooling costs….

Duct leakage impact on heating and cooling systems

Many complaints about high energy bills and discomfort are due to poor ductwork sealing and insulation. Leaks involving 20% of the total air flow will cause a 50% drop in the efficiency of the cooling or heating equipments, and a shorter lifespan.

Where to look for duct leaks and What to Air Seal

See:
Ducts sealing
Sealing the Duct Air Handler, Boots and elbows

Duct insulation

Ducts in an insulated ceiling (with Icynene) You should insulate ducts installed in basements or other unconditioned spaces to get higher energy savings.

See: Duct Insulation

ductwork Installation

Improper duct installation - namely designs involving numerous bends and turns - are also a cause of poor air-flow rates and unbalanced air velocity, causing inefficient operation and higher energy bills.

If you are installing a new air distribution system, or remodeling the existing one, pay attention to the design and the details concerning the size and the installation of your duct system.

See: Duct design, sizing and installation

Mastic and tapes

Sealing duct leaks requires proper mastic or foil tape. Be aware: most duct tapes are highly ineffective. Pay also attention to mechanical fasteners: mastic and tapes don’t hold ducts together.

See:
Duct Mastic
Duct Tapes
Duct fasteners

Ducts & Safety and Health issues

Leaky ducts pose safety and health issues. Leaky return ducts will draw contaminated air - with mold, dust, moisture or even toxins, radon or gases - from spaces where they are located (crawl spaces, basement and attics...) directly into the living rooms...

On the other hand, leaky supply and poorly installed ducts may create different indoor pressures, which may drawn in contaminants or pose safety hazards (due to back-drafting).