The Air Up There: How Ducts Work

The Air Up There: How Ducts Work
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Earlier this month we unveiled our series looking at how your home HVAC works. Having explored thermostats (and their limitations), today we’re going to look at air ducts.

Babe Ruth and Irving Berlin

 1935: Babe Ruth retires, Irving Berlin is a pop genius and air ducts are introduced

First, let’s make something clear: as technology goes, ducts are ancient. The first forced hot air boilers with ductwork —replacing radiant steam heat— were introduced in 1935. To put this in perspective, in many ways we’re still heating and cooling our homes the same we did when Irving Berlin’s “Cheek to Cheek” was at the top of the charts and Babe Ruth was closing out his career with the Boston Braves. Eighty years later, only one of these three are still relevant (or alive, for that matter). While some improvements in materials have been made, fundamentally, ducts work the same way now as they did when Mutiny on the Bounty ruled the box office.

Ducts: Your HVAC’s circulatory system

If your furnace and central air unit functions as the heart of your home’s HVAC, ducts are the veins and arteries, transporting hot or cold air from a centralized location throughout the home—ending at a vent in each room. Some are solely focused on distributing air from the air handler across the home; others are supply vents, returning air from the home back to the handler to be reheated/re-cooled and redistributed.

But remember this: ducting is static and the air flows indiscriminately from the handler throughout the system (again, we’re talking about an idea that seemed big in 1935). The only way to change the flow of air is by opening or closing the vents in individual rooms – which when done manually is an HVAC disaster waiting to happen.

Critical for comfort—but imperfect

Ducts are an important, imperfect element of your comfort. Remember—air is moving indiscriminately throughout the ductwork. But the distance air has to travel throughout this circulatory system makes home comfort tricky. Basements that are right next to your air handler are going to get more air than an upstairs bedroom at the end of a long duct run.

As we said, you can try to manually adjust air flow by closing vents—which works, to an extent, but can also cause static pressure. To extend the circulatory analogy, think of static pressure like blood pressure. HVAC systems can handle a certain amount of static pressure, but too much, caused by air trying to get out of closed vents, can have the same catastrophic effect on HVAC systems as high blood pressure on the human body (and while not as catastrophic, we’ve all heard the whistling noise that comes with closed vents—let’s file that one under “annoying.”)

Air—it wants to escape, very badly

Additional challenges come in with heat loss and heat gain. Once heat is delivered from a duct through a vent into a room, it will find any way it can to escape—through cracks, unsealed windows, essentially any nook and cranny, hence the term “heat loss.” Conversely, heat gain happens when natural light enters through a window, further warming it. The fundamentals are the same for cooling.

That said, when installing ductwork at construction or renovation, calculations can be done to anticipate heat gain and loss to ensure proper ducting. The benefits are, in theory, significant: a more comfortable, energy-efficient home utilizing a smaller, less-expensive HVAC system can be used, one that will last longer before replacement.

But even taking the best planning into account, EPA studies show that 74 percent of homes have bad airflow throughout their duct systems.

Enter Ecovent

So how can you bring 1930s technology into the modern era? Check out Ecovent, the first complete system for room-by-room temperature control. It accounts for the imperfections of ducts and safely overcomes them by controlling the amount of hot and cold air going into each room. It does this without the need to constantly change the thermostat or run from room-to-room to open and close vents. The result? Unprecedented comfort—the kind that not even Babe Ruth or Irving Berlin could have imagined—that is also safe for your HVAC systems.

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