Duct systems distribute air throughout your home — and can also spread dust, mold spores, and other contaminants. Understanding your duct system is key to maintaining clean, healthy indoor air.
Flexible duct (flex duct) is the most common material in Florida homes built since the 1990s. It consists of a flexible plastic inner liner, an insulation wrap, and an outer vapor barrier jacket. When properly installed — fully extended without sags or sharp bends — flex duct performs well. However, improper installation (kinked, compressed, or too-long runs) dramatically increases airflow resistance and can trap moisture.
Sheet metal (galvanized steel) ductwork is more rigid, more durable, and less prone to installation-related airflow issues. It’s the standard in commercial buildings and older Florida homes. Sheet metal is also easier to clean to NADCA standards when professional duct cleaning is warranted.
Fiberboard duct, made from compressed glass fibers with a foil facing, was common in Florida homes built in the 1970s and 1980s. The porous interior surface can trap debris and — critically — becomes a substrate for mold growth if it ever gets wet. Florida code now prohibits fiberboard duct in new construction. If your home has fiberboard ductwork, inspection and possible replacement should be on your radar.
NADCA (National Air Duct Cleaners Association) is the primary authority on residential and commercial duct cleaning standards. Their ACR (Assessment, Cleaning, and Restoration) standard defines what a thorough cleaning involves: physical removal of debris, inspection with video if warranted, and verification that components are clean post-service.
NADCA recommends considering duct cleaning after: visible mold growth inside ducts or on HVAC components, pest infestations within the duct system, ducts clogged with excessive debris that is actually being released into the living space, and after major construction or renovation that introduced drywall dust or debris into the system.
Routine duct cleaning on a fixed schedule (every X years) is not supported by current EPA or NADCA evidence unless one of the above conditions is present. Beware of low-cost duct cleaning offers — NADCA-certified cleaners must follow the ACR standard, which typically takes several hours and involves truck-mounted vacuum equipment, not a shop vac.
In South Florida, attic temperatures can exceed 140°F in summer. Supply ducts running through attics must be properly insulated to prevent two problems: energy loss (cold air warming up before it reaches the room) and condensation.
Condensation on ductwork occurs when the cold metal or plastic surface of an under-insulated duct meets the warm, humid attic air — the same principle as a cold glass sweating on a hot day. This moisture can drip onto ceilings or into wall cavities, creating ideal conditions for mold growth that may not be immediately visible from inside the home.
Florida Energy Code requires duct insulation to meet minimum R-value requirements in unconditioned spaces. If your ducts are wrapped in old, thin insulation, upgrading to R-8 flex duct or adding external insulation wrap is an IAQ and energy improvement in one step.
In South Florida’s humid subtropical climate, ductwork typically has a shorter lifespan than in drier regions. Here are the key signs that replacement — not just cleaning — may be the right call:
If you’re unsure whether cleaning or replacement is the right choice, a professional IAQ assessment can identify the condition of your duct system and recommend the most cost-effective solution.
Whether you’re tracking down a smell, dealing with allergy flare-ups, or managing a building — we publish plain-language guidance rooted in EPA, ASHRAE, and NADCA standards. Reach out anytime.