Ductwork FAQs: 12 Questions Answered

Is duct cleaning worth it?
How do you install ductwork?
How do you size ductwork?
How do you tap into existing ductwork?
How do you clean ductwork?
How do you clean mold out of ductwork?
How much does air duct cleaning cost?
How do you seal ductwork?
How do you repair flexible ductwork?
How do you repair ductwork in the attic?
How do you reduce static pressure in ductwork?
How can I tell if my air ducts are leaking?

Is duct cleaning worth it?

Duct cleaning is sometimes worth it, but not as a routine every-year service for most homes. It makes sense after a remodel with heavy dust, when there is visible mold, after a rodent or pest problem, or when vents are clogged with debris.

In the dusty West Valley, a filter that is changed often and ducts that are sealed tightly will keep most of the dirt out. If your real issue is weak airflow, uneven rooms or high bills, leaky or crushed ducts and a dirty coil are more likely causes than dust in the ducts. A technician can inspect and tell you whether a cleaning would help.

How do you install ductwork?

Ductwork installation starts with a design, because duct size, length and layout determine airflow. A contractor sizes the ducts using a load calculation for each room, then runs a trunk line from the air handler with branches to the registers, using proper supports, sealed joints and attic insulation.

Connections are sealed with mastic or approved tape, not standard duct tape, and the work is often done under a permit. Poor design causes noisy, weak or uneven airflow that no equipment can fix. Because it affects the whole system, ductwork is a job for a licensed HVAC contractor.

How do you size ductwork?

Ducts are sized by the airflow each room needs, measured in cubic feet per minute, along with the length of the run, the number of bends, and the resistance the duct and registers add. The airflow comes from a load calculation for each room.

The duct diameter or dimensions are then chosen to deliver it at a reasonable speed without whistling. Duct calculators and friction charts are used by professionals. A duct that is too small makes noise and starves the room. One that is too large may not move air well. For a new or modified system, have a licensed contractor do the design.

How do you tap into existing ductwork?

To tap into existing ductwork, a technician checks the system's size, the available static pressure and the duct layout, then cuts a collar into the trunk or plenum, attaches a takeoff, and seals every joint. It is possible but easy to do badly.

The main issue is whether the system has the capacity to serve the additional room, since adding a run without enough airflow takes air from the other rooms. The technician also balances the airflow after. If the system is already stretched, the new room may stay uncomfortable, and a separate system such as a mini split can be a better choice.

How do you clean ductwork?

Professional duct cleaning uses a powerful vacuum connected to the duct system and agitation tools, like brushes or compressed air, to loosen dust and debris from the inside. The technician cleans the registers, the main trunk and the branches, and often inspects the coil and blower.

A homeowner can vacuum the visible register openings and wash the grilles, and should change the filter on schedule. Do not run a vacuum hose into ducts that you cannot see. Avoid any service that promises miracle results or sprays chemicals without explaining them. If the ducts have damage or leaks, repair them first.

How do you clean mold out of ductwork?

Do not try to clean mold out of ductwork yourself. Visible mold in ducts usually points to a moisture problem, such as a dirty or leaking coil, a clogged condensate drain, or poor insulation causing condensation, and it will come back unless the source is fixed.

In the West Valley, it is less common than in humid climates but does happen, especially around the air handler. A technician finds the source, repairs it, and decides whether the ducts can be cleaned or must be replaced, especially for porous flex duct and duct board. If you suspect mold, turn off the system and call a professional.

How much does air duct cleaning cost?

The cost of air duct cleaning depends on the size of the home, the number of vents and returns, the number of systems, how dirty the ducts are, and how easy they are to reach. A home with an attic air handler and long flex runs takes more time than a small one.

Add-ons like coil cleaning, blower cleaning, sanitizing or mold remediation change the total. Be careful with very low advertised prices, which may lead to add-ons. Ask what is included, how many vents and returns are covered, and whether the work includes the air handler. A written quote protects you.

How do you seal ductwork?

You seal ductwork at every joint, seam and connection using duct mastic, a paste applied with a brush or gloved hand, or approved foil tape. Regular cloth duct tape is not suitable, since it dries out and fails in a hot attic.

Start with the connections at the air handler, the plenum, the boots at each register and the trunk joints. Repair any torn flex duct and secure the inner liner properly before sealing. Many Arizona attic ducts leak a lot of cooled air outside the home. A technician can test the system to find where the air is escaping.

How do you repair flexible ductwork?

To repair flexible ductwork, replace the damaged section if the inner liner is torn, crushed or disconnected, since the liner carries the air. Small tears in the outer jacket can be patched, but a damaged liner needs a cut out and a new section with a proper connector.

Technicians secure the new section with a strap and seal it with mastic. They also fix sags and sharp bends that restrict airflow. Flex duct in a hot Arizona attic ages, so if it is brittle, crumbling or sagging in many places, replacing the run may be a better use of money than repeated patches.

How do you repair ductwork in the attic?

Attic duct repair starts with finding the problem: disconnected joints, torn flex, crushed sections, missing insulation or sagging runs. The technician then reconnects the ducts, replaces damaged sections, supports them properly, seals joints with mastic and adds insulation where needed.

The attic is extremely hot in the summer, so the work is usually done in the cooler part of the day and with care for safety. Do not enter a hot attic alone or walk off the joists, as you can fall through the ceiling. A professional has the tools, protective gear and knowledge to do the repair safely.

How do you reduce static pressure in ductwork?

To reduce static pressure in ductwork, find what is restricting airflow. High static pressure means the blower is working against too much resistance. Start by changing the filter and making sure the registers are open, then have a technician check the coil and ducts if it stays high.

Common causes are a dirty filter, a clogged evaporator coil, closed or blocked registers, undersized ducts, too many sharp bends or crushed flex duct, and a filter that is too restrictive. If it is still high, a technician measures the pressure across the system with a manometer and finds the restriction. The fix may be cleaning the coil, adding a return or resizing a duct. High static shortens blower life and reduces comfort.

How can I tell if my air ducts are leaking?

You can tell your air ducts are leaking if some rooms never get comfortable, registers have weak airflow, the system runs constantly, cooling bills are high, or the house has excess dust. In the attic, disconnected ducts, torn insulation or dirty streaks around joints show where air escapes.

A technician can confirm a leak with a duct pressure test or a smoke test, which shows how much air is lost and where. In the West Valley, leaks in an attic push cooled air into a space that can be very hot, so repairs often make a noticeable difference.

Ductwork: 12 Duct Questions Answered for Arizona Homes