Maintain the Cleanliness of the Air

Jeffrey Parsons

2300 North Yellowstone Highway, Idaho Falls, ID, United States

Office: (208) 535-3289

Cell: (208) 360-7892 


Primary Goals of crawlspace ducting

Maintain the Warmth of the Air

Crawl space ducting is presented with an interesting challenge.  It is tasked with taking clean, filtered air and delivering it through a very unclean environment (the crawl space).  When the ducting fails to achieve this goal, the consequences can be significant.  In this article, we’ll discuss the common problems and solutions for crawl space duct issues.


This goal is achieved by maintaining properly sealed ducts.  Back in the day, this was accomplished with duct tape.  Initially, this worked well and provided a tightly sealed air delivery mechanism.  However, over the years contractors began to find evidence of material failure.  In short, with enough time, duct tape loses its super sticky sealing ability and allows air to pass through.  Unfortunately, many HVAC companies still use duct tape because this problem comes along after they're gone.

Fast forward a few decades and now many municipalities require mastic instead of duct tape.  Though much messier to work with, mastic offers far more durability.  Even in areas that don’t formally require mastic, any proactive HVAC contractor uses the material.  Any home trying to reach a high degree of energy efficiency will use mastic.  Once applied, it looks like a thick, goopy, gray paint.  You’ll find it on all major joints and seams.

Broadly speaking, HVAC contractors use three primary techniques to maintain the warmth of the air.  The first two are far more common and comprise 90% of homes using crawlspace ducting.

  • Insulation applied to rigid ducting.
  • Insulated flexible ducting.
  • Sealed/heated crawl space.

Until recently, crawlspace ducting was composed of rigid galvanized steel sheet metal. After installation, the insulation contractor wrapped the ducting with fiberglass. This technique has several advantages.  First, the rigid ducting is far more durable than flex ducting and if kept dry will last many decades.  Second, rigid ducting can be easily cleaned, while flex ducting cannot.  Duct cleaning is rarely recommended, however, so this attribute is not especially important.

Flex ducting has dramatic advantages as well.  Because the line of ducting comes from the factory in one continuous piece, the number of air leakage points is minimal.  The only potential air leakage points and heat loss pointsType your paragraph here.

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