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How Does Custom Ductwork Help Your Air Conditioner Work Better ?

Custom ductwork refers to the design and fabrication of ducts tailored to meet the specifications of an A/C system installed or to be installed in a building or a home.

Unlike standard pre-made ducts, which are assembled on location, custom ductwork is cut by the HVAC contractor that installs the system; it fits exact dimensions and specifications to ensure unrestricted airflow and efficient heating and cooling.

For air conditioning specialists like Filan & Conner, having the in-house capability to design, cut, assemble, and weld ductwork is the only way we can address the complex challenges posed by buildings, homes, and the building codes in New Jersey.

Role of ductwork

Ductwork is a preponderant factor in the efficiency of an A/C unit. When custom-made, its

design must meet unique requirements in order and to maximize the airflow and control temperatures efficiently.

From all the experimentation we did over a 30+ year span in West Berlin and neighboring cities, custom ductwork delivers and returns conditioned air better than pre-assembled ducts.

Its 3 main benefits are improved indoor air quality (less elbows in a system mean less accumulation of dust and pollen), energy efficiency (due to less resistance to airflow) and lower power bills (speed of circulation enables thermostats to regulate temps more finely).

Custom ductwork also allows for stronger noise reduction, always a positive point in a home.

Design and Installation

Factors to consider

When designing custom ductwork, Filan & Conner takes into account several important factors:

  1. Size and layout of the space to heat up and cool off. The design of the ducts must distribute air throughout the space efficiently. Why? We need to ensure every room and common area receives adequate air flow. No dead spots.

  2. Type and size of the AC unit used or to be installed. What are its specifications? Is this a mini-split? A gas package? A heat pump? We take this into consideration because different systems require a different design for their ductwork if you want to optimize the energy performance of a system.

  3. Material used to build the ductwork. The main concerns of the builder is durability, resistance to corrosion (humidity), heat expansion characteristics (what % of metal expansion when the furnace is operating?).

  4. Finally, cost. In some situations, custom ductwork won’t fit the household’s budget. Financing can help, but banks don’t always lend. It’s a balancing exercise between what’s best for a home and what’s doable for a family.

Installation techniques

No one talks about it, but shoddy ductwork will shorten the lifespan of an air conditioning unit. People pay much attention to the specifications of the unit itself (which are important, make no mistake), and often not enough attention to how the ductwork will carry the air both ways: from the AC and back to the AC.

As mentioned earlier, custom ductwork aims at optimizing airflow and energy efficiency. When our ductwork department designs and cuts the ducts, their main concerns are simplifying the number of elbows to maximize air speed, and minimizing air leaks by ensuring perfect cuts at the seals.

Then our team of installers will focus on fastening the ducts securely to the structure (to minimize vibration and reduce noise), sealing all the ducts at their connection points (to minimize air loss), and wrapping the ductwork to insulate it against brutal temperature changes and to preserve the correct temperature inside the channel from the HVAC unit to the delivery vents (and minimizing temperature gain or loss).

When a technician uses proper installation techniques, the result will be less noise from vibrations (as internal pressure won’t make the ducts vibrate too much) and a better air quality (as infiltrations of dust, allergens, and contaminants are reduced).

Measure twice, cut once

This old saying couldn’t be truer insofar as AC ductwork is concerned. What determines the length and volume of the ducts?

  • Number of air vents and returns to serve

  • Shape (how many elbows and straights)

  • Tons of air conditioning (size of the HVAC unit itself)

Whenever the ductwork is improperly sized and cut, the overall system efficiency will suffer. If the volume is wrong, the airflow will be constrained and exert excessive back-pressure on the system. It may cause frequent start-stop cycles. This will accelerate wear & tear, and trigger critical component failures faster.

If the volume of the ducts is too big, the A/C unit has to work harder to push enough air pressure to get the right measurements. When the system pushes too much air too fast, the air can’t be properly dehumidified with resulting problems inside the home. On the contrary, when the airflow is too weak, the distribution of air becomes uneven with warmest and cooler zones.

It’s like a Goldilocks scenario: not too much, not too little, just right.

So the calculation of the size and volume of the ductwork requires good engineering skills. And cutting it precisely is also key to having good seals and not air leaks

Efficiency and Performance

Airflow and distribution

The overarching focus at Filan & Conner when our HVAC engineers design custom ductwork is airflow and air distribution. We seek to maximize airflow and optimize distribution throughout the house. Why? The triple answer is air quality, temperature regulation, and energy efficiency.

Because we design the ducts from scratch, we control both the direction and the speed of airflow, and we can reduce the risk of hot or cold spots within a home.

Energy consumption

With the rise in electricity rates since 2022, homeowners are very conscious that their utility bills are majorly impacted by air conditioning. HVAC manufacturers design their units to be very efficient, as defined by their S.E.E.R rating. The quality of the ductwork will either transfer this efficiency to the power bill, or waste energy and lose part of the efficiency of the air conditioner itself.

So, to reduce energy consumption, our engineers have to optimize energy usage and reduce the workload on the system.

Indoor air quality

For homeowners, this is not just a matter of controlling the cost of their utilities. It’s also about comfort. People usually define comfort as “the right temperature at an even level throughout our home”. Pockets of cool air during the winter and of warm air during the summer are signs that air pressure is not evenly distributed by the ductwork.

The other criterion that matters to homeowners is the quality of indoor air. How do you know your air isn’t good quality? You smell it. If it smells musky, that’s the symptom the air isn’t properly dehumidified, the filters don’t pull their weight, or the returns don’t work as planned.

Well-designed ductwork will push the right amount of air at the right airflow, allowing the filters to do their work. If you add UV filters in the design, we can even improve on air quality by getting rid of more allergens.

Customization choices


We referred to the metal expansion factor above. The 3 most common materials used in custom ductwork are galvanized steel, aluminum, and fiberglass.

  • Galvanized steel: known for its strength and resistance to corrosion, it is suitable for high-pressure systems.

  • Aluminum: lightweight and easy to install, it is a popular choice for residential applications.

  • Fiberglass: offers excellent thermal insulation properties, it is commonly used in commercial buildings.

Of these 3 materials, the first two offer excellent rigidity and the lowest resistance to airflow. This means less energy loss and a better overall efficiency for the AC system.

Fiberglass is not the best suited for this type of ducts because it increases airflow resistance due to its molecular structure.

Insulation & sealing

Insulation and sealing make a big difference in the performance and efficiency of an HVAC system. When the ductwork is properly insulated, its energy loss coefficient is reduced and the air pushed inside the ducts remains at a more constant temperature. Less energy loss also means less work for the AC unit and lower energy bills.

Good seals prevent air leaks and keep the integrity of the ductwork. Air leaks are a catastrophe for the energy efficiency of a system, and loose seals means the system vibrates more when pressurized with airflow and therefore makes more noise.

There again, materials and quality of workmanship make a big difference in the overall efficiency of the HVAC system.


This section of our article applies to pre-made ducts too, not just custom ductwork.

The efficiency of an HVAC system depends in part on the fact it is kept clean. All air conditioning companies will clean the AC unit itself, its evap coil, and the drainage system every time they inspect it. They will also change the filters or make sure the filters are clean.

But over time, dust, debris, and other contaminants will accumulate in the ductwork, and needs to be cleaned up in order to avoid reducing the airflow and creating potential health hazards.

Regular inspection & cleaning

Not all HAVC companies offer duct cleaning service because it is a specialty that falls slightly outside the scope of air conditioning repair and maintenance. This is why companies like Sears use to offer this service.

We discussed earlier the problem of internal airflow resistance: the more resistance in the system, the less efficient the system is. When dust and debris settle down in the system, they are “baked” on the inner side of the ducts, and clog the elbows. This constrains the volume of air pushed through, and increases airflow resistance. In turn, the AC unit has to work

harder to cool off or heat up the house and your utility bill increases.

The issue is compounded by the allergens that accumulate in the ductwork. Fine organic particles decompose and mold becomes airborne. A study published by the NIH on the mold from the crawl space of 238 homes in North Carolina found out that leakage in ductwork was a contributing factor to the concentration of mold spores inside these homes.

Another research study published by NIH found out that the 25 air handling units sampled were a site for mold growth (Clasporium). The study found mold in the blower wheel fan blades, the ductwork, and the cooling coil fins. Other types of mold spores were also collected in these systems.

Lastly, a study conducted in southern France found that blowing air on a piece of wallpaper contaminated with 3 common fungal toxins would release these toxins in the air, where they would then latch on fine dust particles considered easily breathable.

There is little doubt that indoor air quality depends in part on the cleanliness of the ductwork of a home, and that this system should be inspected and cleaned up appropriately regularly.

Repairing and replacing damaged ductwork

Because of vibrations, expansion on contraction of the metal due to temperature variations and to built-in air pressure, ductwork develops leaks and cracks leading to air leakage and reduced airflow.

As mentioned earlier, this decreases the comfort of the living space, increases the energy consumption of the system, and drives up utility costs.

Regular inspections of the ductwork and its insulation work to detect these leaks and prompt the necessary upkeep and repair.

Investing in custom ductwork

The bottom line is that custom ductwork enables an HVAC system to operate more efficiently, and decreases utility bills while slowing down wear & tear.

This requires precision work, a good choice of materials, careful installation, and regular inspection and upkeep.

There is no denying that getting custom ductwork installed in a home is an investment. This won't be recouped over a single year of use (unless the cost of energy skyrockets… in which case, people may just decide to use their air conditioning less and less).

So taking a long-term view, the rationale for investing a bit more money in the ductwork is to get a system that is tailored to the geometry of a home, built to oppose the least resistance to airflow, and precisely cut and assembled to minimize noise discomfort and air leakage.

Ultimately, it will also ensure an even temperature throughout the home. The dividends of the investment are measured in terms of comfort, quality of indoor air, lower energy bills, and for those who care, more protection of the environment.

About Filan & Conner:

Filan & Conner is an air conditioning repair company located in West Berlin, NJ. We have been serving South Jersey residents for several decades, and we are highly appreciated for our level of workmanship and service. Visit our website at

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