Before we begin on the cleaning do’s & don’ts of cleaning flex duct let’s discuss some basic information about flexible duct work….
Anatomy: Flexible ducts, known as flex, for HVAC applications typically have three components. First, an outer polyethylene protective liner. Second, fiberglass insulation beneath the outer liner. Third, an inner polyethylene liner with embedded round metal wire giving the duct its round shape.
Upsides: First, flex duct is very convenient and cost efficient for builders/installers in terms of ‘hanging’ and routing around obstacles residing in crawlspaces or attics. Second, flex duct can only have air leakage at the attachment points which are collars and/or transitions versus rigid where air leakage can occur at all union points. Lastly, flex duct is insulated.
Downsides: First, builders/installers should keep their installed lengths (runs) short, e.g., less than 15 feet or so and minimize turns. However, many times, excessively long runs are used. The round, metal wire embedded in the inner liner creates a corrigated surface which increases static pressure as air travels away from the furnace/air handler. Static pressure reduces air flow as it travels from the furnace/air handler. Second, when installed, kinks or sags in flex must be avoided or minimzed to avoid restricted air flow. Third, rodents can easily chew through the outer liner, fiberglass insulation and inner liner thus entering the duct work where conditioned air travels and enters the occupied space. Obviously, this creates health issues on a number of levels. Lastly, polyethylene liners can breakdown over time allowing splits and holes to develop compromising the integrity of the duct.
Cleaning flexible duct work must be done carefully to prevent punctures/breaches of the inner liner. Once the inner liner is compromised, fiberglass fibers infiltrate the duct creating potential health hazard to occupants.
Air Medic, specifically, considers two critical elements; condition of inner liner & type of agitation device.
- Inner Liner quality & condition. It’s not unusual the inner liner is made of low grade plastic and/or has become brittle through the years making puncture or breach more likely. Air Medic uses skipper balls and/or mild aggressive air whips in these cases or, in some cases, recommend the flex duct itself be replaced completely.
- Air Medic almost exclusively uses air whips (light to medium aggressive) and/or skipper ball agitation equipment instead of rotating brushes to minimize risk of puncturing/breaching the inner liner during the cleaning process.
Once we’ve inspected the inner liner and decided which agitation or combination of agitation devices will be used Air Medic will zone off the supply and return sides of the system, set up our commercial grade negative air machine using a 12″, 10″ or 8″ hose to generate high air flow to depressurize the duct work. With the negative air source at the furnace/air handler we then begin cleaning with air whips and/or skipper balls at the other end which are at the vents. The agitation tools are inserted into the vents and through the length of the duct or as far as the duct will allow the tool to be inserted without too much force.
We hope this information is educational and helpful to you.