Frequently Asked Questions (FAQs)

What is a blower door?

The blower door is a diagnostic tool which helps locate air leaks in buildings and measures how leaky they are.  Originally developed over 30 years ago by scientists researching building energy losses, it is now used by hundreds of HVAC contractors to find a host of problems related to home comfort, dust and allergy problems and high utility bills.

Can a blower door find duct leakage?

The blower door was originally used to find over all building infiltration, it is common practice to use a blower door in conjunction with a air capture hood to measure duct leakage.

What actually is duct leakage?

This is the expensive conditioned air leaking out of supply ducts to the outside, and outdoor air leaking into return ducts and plenums.

I can see how disconnected ducts can be a problem, but do the small cracks and gaps really amount to much?

Until recently the extent of duct leakage was largely overlooked.  But research as found that unsealed joints and loose connections in the typical system adds up to between 30 and 80 square inches of combined leakage area.

What can duct leakage do to a systems performance?

Duct leaks can dramatically reduce the capacity of an otherwise well installed HVAC system.  In fact in a study done by the EPA they state that typical duct systems lose 25-40 % of the heating or cooling energy put out by the central furnace heat pump or air conditioner.

Can duct leakage attribute to indoor air quality problems?

Duct leakage often worsens building indoor air quality by bringing in outdoor contaminants from garages, crawl spaces, and attics.  In some cases duct leakage causes combustion and fire hazards due to backdrafting of appliances.

Air infiltration in a home, is this a serious problem?

Uncontrolled air infiltration represents a sizeable portion of the cooling dehumidification and heating loads, typically between 20% and 30%.  Many homes have Equivalent Leakage Areas of between three and eight square feet.

I have heard of a Thermal Bypass, but what actually is one?

Most homes have hidden or "Thermal Bypasses" which cause significant conductive energy loss.  Typically these area are dropped ceiling (fur downs) over kitchen cabinets, bath tubs or closets.  Open wall cavities around fireplace chimneys or plumbing/duct chases, and of course insulated attic hatches, pull down stairs and bare sheetrock.  Heat gain or loss is often greater through these areas than through the rest of the attic floor.

Can a poor thermal envelope cause any other problems?

Thermal envelope problems contribute to discomfort of all kinds.  They add to the cooling and dehumidification load in the summer.  They cause cold drafts and dryness in the winter.  They bring in dust, noise and insects from outside.  Fixing these problems have more benefits than simply energy savings.

If you have a question that was not answered, contact us to ask Comfort Institute your specific question.