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.

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 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….

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.