Ducting

Okay, So How Important Are the Ducts in My Home?

While you may not pay a lot of attention to the ducts in your home, airflow is one of the most important parts of HVAC system design. Since your ducts carry all of the air circulated through your HVAC system, if they are poorly designed, undersized, dirty or poorly insulated, they can cause a lot of problems in your home. We regularly see situations when customers have replaced certain parts of their HVAC system, multiple times (and spending thousands of dollars), before we show them an airflow issue that is the root cause of their issues. 

Efficiency

Efficiency is highly influenced by your ductwork. You might be wondering why that matters. There are really two reasons, and the combination of both issues can make a HUGE difference in your energy bills.

First, because ductwork carries air that is warmer or cooler than the ambient air in your home, and the outside of the ductwork needs to be well insulated to prevent the loss of heat or cooling. In the 70’s and before, most ductwork was what we call “hard” duct. Hard duct is rectangular (or sometimes round) metal duct that is insulated inside or outside. The problem with hard duct is that it has a high heat capacity, which is its ability to hold and retain heat (or cool). If you insulate hard duct internally, it causes more drag on the air, which in turn increases the static pressure (and ultimately lowers efficiency). If you insulate hard duct on the outside, that allows the duct to absorb heat (remember that high heat capacity?), which robs your system of BTU’s of heating or cooling that could otherwise be delivered to the conditioned spaces of your home.

Regardless of where it is insulated, hard duct has a low R-value (a measure of efficiency in insulation), and over time that R-value tends to go down as the insulating materials degrade. So the upshot is that if your ductwork is old, you are spending lots of money conditioning your crawl space, attic, or other area your ductwork traverses. Any poorly sealed duct connections only make the efficiency worse.

Recently built or upgraded homes will primarily have flexible (“flex”) duct that does a much better job of getting the conditioned air to where it needs to go without losing nearly so much energy on the way.

Health

In most cases the stuff you imagine lurking in your ducts is just a figment, but there are definitely situations when we find some pretty nasty stuff. The conditions are often right for pretty scary stuff to grow if the insulation breaks down or wasn’t properly installed. Your ducts will “sweat” in summer as condensation forms on surfaces cooler than the ambient air. The presence of dust, which is a mixture of organic and inorganic compounds, provides food for tiny organisms, and before you know it, you have a full-blown science experiment in your attic or crawlspace. You certainly don’t want your HVAC system spreading this marvel of science around your home (and into your lungs), which is exactly what happens if stuff is living inside your ducts when the system is running. 

System Longevity

There are lots of ways that poor airflow can lead to a reduced life for your HVAC system.

The heart of your HVAC system is your blower motor. The blower motor converts electricity to kinetic energy (the rotation of the fan) that pulls air through your returns and delivers it through your ducts. This blower motor is designed for a specific RPM (rotations per minute) and a specific range of resistance, and the efficiency of your system is actually measured under these conditions. When your duct system is restricted, either by design or clogged filters or something else, the blower motor has to work extra hard– which then increases the energy use, makes it overheat, and generally reduces its life. In some cases we have seen brand-new blower motors that haven’t even lasted 6 months because the duct restriction was so high.

Another example involves the electric heat strips used as auxiliary heat in a heat pump system. Poor airflow doesn’t transfer enough heat from the strips to the air in the ducts, causing the temperature to exceed the design conditions they were built for. When this continues, ultimately the heat strips burn out and need to be replaced.

There are many other examples, but the basic idea is that HVAC systems are engineered for certain design conditions which include a range of acceptable “static pressures” (the simplified definition is the measure of the ability of air to flow through the system/ductwork). When your home causes this static pressure to exceed design conditions, nothing good will come of it.

Noise

While it may not be the highest consideration on your list, ductwork can be responsible for all kinds of noise in your home. From hard duct that “bangs” when it fills with air to the whistling of air through your registers and returns, if you are hearing noises from your HVAC system it might be a good idea to have someone take a look. Ductwork shouldn’t be that noticeable in your home.

Comfort

The ductwork in your home is responsible for the delivery of comfort. Since all of the heated or conditioned air in your home flows through your ductwork, if your ductwork isn’t designed well, you will have hot or cold spots and other problems in your home — maybe even water stains on your ceiling. If you suspect your ductwork may be to blame for the loss of comfort in your home, let us take a look and we’ll tell you what we think.

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