Factors That May Impact the Performance of a Duct System

Many factors impact the performance of a duct system, which could result in poor heating and cooling, increased electricity bill, higher maintenance cost of air conditioners, or all of the above. To ensure these issues don’t happen, you need to consider some crucial elements before buying the right duct system.

As one of the most important components of HVAC systems, you need to take your time when choosing a duct system. Even if your HVAC installer recommends a specific system, it pays to remain vigilant and do your own research about it.

Sun City Air experts have lent us their expertise today and identified 10 critical factors you should consider when analysing the duct system performance and deciding whether it’s the right one for you.

Let’s look closely at these factors and how they determine duct system performance.

Factors That May Impact Duct System Performance

Fan Capacity

One of the first things you should look at is the indoor fan, also known as a blower. The blower’s capacity determines how much air it can blow into your rooms. It should be around 5 CFM (cubic feet per minute) for cooling and 5 CFM for heating (10 ft ceiling).

Hence, for every cubic foot, the blower will displace air at least 5 times per minute. However, the ideal CFM varies from room to room. Undersized blowers will cause your air conditioning unit to work much harder for cooling your room, thus increasing your electricity bill.

Cooling Coil/Air Filter

The coil is what truly helps an air conditioner cool the air since it has refrigerant in it. A duct system’s coils, however, are different. They are used to restrict or allow airflow when coupled with the filters and don’t do much in terms of cooling. This coil and air filter are the primary components you must check in your duct system.

Air filters tend to catch the dust coming in and out of your room. As more dust accumulates in the filters, resistance to airflow increases, directly impacting the duct system performance.

Consider checking National Comfort Institute’s (NCI’s) “Filter Sizing Procedure” guide to size your ducts better.

Duct Design

The duct design is key to ensuring proper performance. This is the blueprint that your duct system is built on. Even the slightest miscalculations here can lead to inconsistencies in the pieces, which, in turn, will impact the overall HVAC system performance.

You need to remember that proper duct design doesn’t automatically mean improved duct system performance. The design is something that ensures proper airflow and prevents leakage – not something that increases it.

Duct Fitting

The spider season in Australia means that any issues with the construction of duct or its fitting will invite several clusters to your home, which will be followed by other predatory insects, and so on. To ensure that this doesn’t happen, you will need to make sure that the ducts are fit properly without leaks.

One sign of poor duct fitting is excessive turbulence, which may eventually heat the whole system and damage something over time. Consider avoiding sharp and restrictive turns in your duct system. If there are any loose spots, reinstall the duct from there and make sure it isn’t wobbly.

Duct systems need to be secured in place and tight, which will facilitate the air circulation process. Not only will this help you reduce safety issues from the system, but it will also serve to increase the system capacity.

Ask a professional to cover up any mechanical connection in the duct system and insulate/seal all openings.

Make Sure There Are Volume Dampers

Some duct systems might not come with volume dampers. This is especially the case for second-hand or low-cost ducts. Volume dampers reduce how much air is flowing through the duct system. They may be remotely controlled or manually, each with its own pros and cons. You get to choose whether you are using the dampers to control the direction of airflow or the volume of air being displaced.

Unfortunately, many installers believe that the air will always find the path of least resistance without the dampers and improve the CFM of a duct system; this is not the case. The path of least resistance bit is true, but it doesn’t necessarily mean a better CFM.


When buying a duct system or getting one installed, you must look closely at the insulation you are provided with it. Not every new system comes with insulation and those that do, only come with insulation tape. This tape is not alone is NOT enough to keep your cool air cool.

The best insulation for ductworks is fibreglass. You can buy fibreglass in rigid or flexible form. You should consider at least R-6 insulation on ducts inside your house, and for the outside, consider at least R-8 insulation for climate zones 1-4 and R-12 for climate zones 5-8.


Duct systems need regular maintenance, especially in Australia, since rodents and insects have a way of finding their way into duct systems when the winter approaches. The performance will most likely degrade over time if you don’t maintain your duct system.

Measure the static pressure in your duct system and keep a close eye on any changes. If you ever feel like the airflow is starting to get restricted, pull the filters out and clean them. On average, a duct system needs to be serviced every 3-5 years and inspected before and after summer to ensure no rodents are hibernating within.

These factors should help you buy a high-performance duct system for your home or office, or if you already have one installed, it will help you understand what exactly you need to do to maintain the high performance.

If you have any questions that you would like to discuss with us or a specific problem you have, let us know down in the comments. We’d love to hear what you have to say!