How to Clean Air Ducts: A Step-By-Step Technician’s Guide

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Since air ducts should ideally be cleaned twice a year, technicians who learn the art of upselling during service calls and biannual maintenance visits can quickly expand their business, extending the life of HVAC systems and the quality of their performance. Asking homeowners about the state of their indoor air quality can be a good place to start:

When was the last time the air ducts were cleaned?
Have you recently remodeled your home?
Have you noticed any evidence of pests, such as nests or droppings?
Have you experienced excessive dust buildup around the home, especially near air vents?
Have you seen any mold and mildew around your HVAC system or ductwork?
Have you smelled any musty odors or experienced an increase in allergy symptoms?

From there, list the benefits of consistent air duct cleaning, such as improved air quality, increased HVAC system efficiency and the numerous health and respiratory advantages. Even taking a picture of the interior of vents during routine visits to show homeowners can go a long way to spurring them into action and landing you the sale.

This guide will act as a checklist and reminder for HVAC professionals on how to clean air ducts.

Supplies You’ll Need

Air compressor
Screwdriver
HEPA vacuum
Vacuum brush
Air filters
Reverse blasting ball
Duct whip
PPE
Ladder

How to Tell if Air Ducts Are Clogged?

Since the telltale signs and symptoms of a dirty ventilation system can mimic other problems within the HVAC system, it’s imperative to leave diagnosis and cleaning to the professionals. However, it can be helpful to both homeowner and technician to be aware of common indicators for the decision-making and diagnosis process:

Faster dust accumulation – In a typical home with a well-functioning HVAC system, you’d expect to see dust on surfaces every few days to a week. Accumulation faster than that could mean there’s a buildup within the vents.

Dirty air vent covers – Dust accumulation on and around air vents in a home or building means dust is being circulated through the ventilation system.

Increased energy bills – Property owners may have noticed an increase in their energy bills or that their energy bills are higher than neighbors.

Musty odors – If you notice an “old home” smell upon walking in, it may indicate poor ventilation conditions conducive for mold and mildew growth within the ducts.

Worsening allergies or respiratory issues – Homes and buildings with buildup in the vents can increase the risk of asthma attacks and pneumonia in susceptible people.

Signs of mold – Visible discoloration or stains around the ducts, registers and vents can appear as black, green or white spots or patches. If this is the case, you should recommend adding a chemical or botanical disinfection service.

Uneven heating and cooling – Temperature variances between rooms could mean a restriction in airflow caused by a blockage.

Frequent air filter changes – Ask the property owner how often they change their air filters. Negligence to routine maintenance or frequent replacements of clogged air filters might suggest a dirty ventilation system.

Reduced airflow – Although this symptom commonly presents as other HVAC issues, if the ducts are restricted, air is not going to flow.

Pest infestations – Mouse droppings, nesting materials, chew marks, dead pests and unusual noises coming from the ceilings and walls mean it’s time to check the ductwork for infestations.

How to Clean Air Ducts?

Whether you’re a seasoned technician thinking of starting your own business or a student wondering what the day-to-day is like, follow the steps below to learn how to clean air ducts:

Prepping the Ductwork for Cleaning

Step 1. Conduct an inspection – Inspect the ductwork for damage or loose sections and dust and mold buildup on vents, registers, and furnace and air handler components. Take pictures of your findings to show to the home or building owner.

Step 2. Conduct an airflow and leak detection test – To determine if there’s an airflow restriction, HVAC technicians should conduct a total external static pressure test.

Step 3. Turn off the HVAC system – Before beginning, turn off the HVAC system to protect internal components from an influx of dirt and debris.

Step 4. Create access points – If you’re using a truck-mounted vacuum vs a portable shop vac, you’ll need to cut access points in the ductwork to fit the vacuum and air compressor hoses.

Step 5. Remove vent covers and grilles – The next step is to remove the vent covers and grilles from the walls, ceilings and floors.

Step 6. Cover the supply vents – To prevent blowback, seal off the supply vents with either magnetic covers or plastic sheeting and tape.

Vacuuming the Ductwork

Step 7. Don the proper PPE – Put on your personal protective equipment, such as goggles, gloves and a respirator mask to protect your eyes, skin and lungs from potentially harmful contaminants.

Step 8. Vacuum the ducts and Agitate the dust and debris – Insert the vacuum hose into the access points and each of the vents, registers, duct runs, trunk lines, air return drop and plenum by turn. Use agitation tools, such as rotary brushes, air snakes, reverse/forward blasting balls, air rods or duct whips to loosen the dirt, dust and debris that’s accumulated within the vents.

Step 9. Take an after picture – Snap a picture of the fruits of your labor to show and send to the homeowners. It’s an excellent marketing and customer satisfaction technique that will build trust, enhance your professional reputation and provide proof of work.

Step 10. Clean the blower compartment and evaporator coil – It's common for the blower wheel to get caked in dust and the evaporator coil to house bacteria and mold. If it’s easily accessible, go ahead and clean the evaporator coil and blower wheel.

Step 11. Change the air filters – You wouldn’t put on dirty clothes after taking a shower, so you definitely shouldn’t leave an old air filter in after cleaning the vents. Remind homeowners and building managers that the best way to prevent future clogs and retain the health of their HVAC system is to regularly change the air filters.

Step 12. Disinfect the ductwork – Ductwork that shows evidence of mold and mildew will require a hose down. Use a fogger and an EPA-registered disinfectant solution to sanitize the entire system.

Sealing the Ductwork

Step 13. Reattach the vent covers and grilles – Return the vent and grille covers to their rightful place on the walls, ceilings and floors.

Step 14. Seal the access points – If you created any access points in the ductwork to perform the cleaning, patch the holes with duct plugs and sheet metal now.

Step 15. Tidy up – One of the last things to do is clean up and dispose of any dirt, dust and debris that might have escaped the vents while cleaning. Be sure to vacuum up any dust that might be clinging to the vents or registers.

Step 16. Turn on the HVAC system – Restore power to the HVAC unit, ensuring you reset the thermostat to either heating or cooling.

What Time of Year is Best for Duct Cleaning?

The best time of year for air duct cleaning is the end of spring or early fall, although cleaning can take place at any time during the year. Late spring after everything has bloomed is the ideal time for those with allergies. That way, pollen, pet shed and any other respiratory irritants can be removed from the home so residents can enjoy clean air for the rest of the year.

Fall is another HVAC off-season where homeowners may not be using their system as much as they would in summer and winter. Cleaning the ducts then can improve furnace efficiency just in time for the colder months without experiencing any gaps in heating and cooling.

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