Take a big breath – breathe in, breathe out.
Now try and do the same thing, only taking a breath through a straw.
Can’t get the same amount of air, can you?
Your HVAC system works in a similar fashion.
If your ducts are installed correctly and are clear from dirt and debris, air flow runs easily through the ventilation system every time your furnace or air conditioner turns on. 
But if something inhibits air flow, a sufficient amount of air can’t make it from your heating and cooling equipment out to each room in your home.
The HVAC system is just that – a complete system designed to work together. All of it is sized according to the structure and needs of your home. If any one piece in the system isn’t sized properly, or isn’t working at its optimal level, the system suffers. Air flow is constricted. Your entire system is put at risk.
The size of your heating and cooling equipment dictates the size of your duct work. When your home was initially built, that was the easiest time to ensure the ducts were sized and installed correctly. However, just because your duct work is “out of sight” doesn’t mean it should also be “out of mind.”
Have you noticed some rooms in your home are warmer or cooler than others?
That’s one of telltale signs a system isn’t operating properly. It’s also a sign your duct work might not be sized or installed correctly.
When your furnace or air conditioner operates, a blower sends conditioned air throughout the ducts. Think of it as an intricate navigation system designed to keep your home at its proper temperature. If it’s sized properly and working as it should, it’s similar to that big breath you took earlier. The conditioned air gets to where it’s supposed to go in a proper manner.
But if the ducts are blocked or are too narrow for the structure of your home, that air supply is strained. Your heating and cooling system tries to overcompensate, but it can’t keep up with demand.
It may take years, but eventually the problem will materialize in one way or another.
Whether you’re thinking of replacing your furnace or air conditioner because it doesn’t seem to be operating as efficiently as it once did, or you’re simply looking for ways to improve your home’s efficiency, an energy audit can help you determine if everything is working as it should, including your ducts.