Home Ducts Sealing & Insulation Basics
Leaks in the ductwork for heating and cooling systems (forced air furnaces, central air conditioners and heat pumps) are big energy wasters. Many homeowners’ complaints about the energy bills and discomfort in their houses are due to problems with ductwork.

Energy losses
The US DOE estimates that in older homes with forced-air furnaces, 20% of the home's heated air is lost due to leaky ducts. But something alike happens in many modern homes, or in southern climates, where AC duct leaks also accounts for a significant amount of the total cooling costs….
See also: Duct Leaks & Health and Safety issues
Duct leakage impact on heating and cooling systems
Many complaints about high energy bills and discomfort are due to poor ductwork. Leaks involving 20% of the total air flow will cause a 50% drop in the efficiency - and a shorter lifespan - of the cooling or heating equipments.
Where to look for duct leaks and What to Air Seal
See:
Ducts sealing
Sealing the Duct Air Handler, Boots and elbows
Duct insulation
If your ducts are installed in basements or other unconditioned spaces of the your house, insulating them can be highly advantageous.
See: Duct Insulation
ductwork Installation
Improper duct installation, involving numerous bends and turns, will lead to poor air flow rates and incorrect air velocities, causing inefficient operation and energy waste. In other words: if you are installing a new air distribution system, or remodeling the existing one, pay attention to the design and the details concerning the duct installation and size.
See: Duct design, sizing and installation
Mastic and tapes
Sealing duct leaks is a highly effective conservation measure. Just make sure that you use proper mastic or foil tape. 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 questions.
In fact, 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, supply duct leakage may create different zone pressures inside the home, drawing in contaminants and posing safety hazards (caused by back-drafting of furnace or other combustion equipment gases). These problems aren't exactly frequent, but can happen in leaky and poorly installed duct systems.
See also:
Pipe insulation
Duct Insulation
Duct sealing
Sealing the Duct Air Handler, Boots and elbows
Duct design, sizing and installation
Duct Mastic
Duct Tapes
Duct fasteners
Insulation basics
Insulation materials
Spray-on foam insulation
Cellulose insulation
Fiberglass and mineral wool insulation
Reflective insulation: Radiant barriers
Insulation performance
Roof Insulation
Home Attic Insulation
Walls Insulation
Floor Insulation
Slab Insulation
Moisture and insulation
How to deal with Insulation contractors and home builders
Insulation in your climate zone
