A vent is a vent is a vent, right? If you’re like most homeowners, you probably think a lot more about the efficiency of your HVAC units, and not the performance of your air supply and return systems. But your unit’s air supply and return does a lot of behind-the-scenes work to keep your system working efficiently—and your home comfortable. It maintains air pressure, air quality, and air circulation through your home, and also helps your system work more efficiently. And that helps you save money. Here’s the skinny on supply and return registers, and the best place to put them for great HVAC efficiency.
The Difference Between Air Supply and Return Ducts and Registers
Your home actually has two different kinds of air vents: supply registers and return registers. To understand why, you need to know a little bit about how HVAC units work. Your unit’s ducts push heated or cooled air into a room—that’s the “supply” part. But they can’t just keep pumping your home’s interiors with conditioned air. That would cause air pressure to build up to uncomfortable levels, for one thing.
To solve that problem, your duct work also contains a “return” system, which pulls conditioned air from your home and draws it back into your unit. From there, it can be reheated or re-cooled and pumped back into your home’s interiors. Not only does that improve air pressure, it also helps circulate air, keeping it fresh and filtering out dust and other particles. In fact, it even helps your unit work more effectively—as long as return registers are properly placed around your home.
Return Systems Make HVAC Systems More Efficient, Too
Before we get into the mechanics of return register placement, however, let’s talk about how a return system impacts your unit’s overall efficiency. Obviously, when there’s a big difference between the temperature on the thermostat and the temperature of the air in your home, your unit’s going to work harder to stabilize the actual temperature until it matches your settings. And when your unit is on full blast, it sucks down more energy. That’s why drafts and air leaks drive up your energy expenses.
A well-placed return system pulls conditioned air from your home’s rooms and cycles it back into your unit. If your heater or air conditioner has been on for a while, then, there might not be that much of a difference between that air’s temperature and the thermostat dial. So your unit can take a load off by recycling air through your system again.
Return Registers Boost Efficiency When They’re Placed Properly
HVAC professionals spend a ton of time learning about the scientific principles of air flow, currents, and pressure—so generally, they’re the ones you should turn to in order to diagnose duct flaws. Air moves in mysterious ways, so it’s possible you could completely circumvent the efficacy of your system if you try to fix your ducting system yourself.
That being said, there’s a couple of factors you should know that do play into the efficiency of your return system—and your unit as a whole. Most systems work a lot more effectively when there’s both a return line and a supply duct in the same room. Unfortunately, that’s not how every home was designed. A lot of spaces simply have a main return line located in a central hallway.
If that’s how your home was built, you basically have two options: you can simply live with the inefficiency, or you can have an HVAC professional out to extend the line into each room. It depends on how much the return register placement affects your comfort—in some homes, you can just sense that the air feels stale and unhealthy. If you decide to stay with a limited supply line, make sure that your interior doors have large gaps beneath them so that air can flow out of the room even when the door is shut.
Other design items that can affect return system performance? The registers’ placement on each wall. Because heated air rises, it’s a good idea to have return registers installed high up on the wall. That way, when you run your air conditioning in the summertime, the return registers will be well positioned to pull the hottest air out of a room. However, if you don’t run your A/C all that much or don’t even have a cooling unit in your home, low-to-the-ground registers may be the best way to go.
Return registers also perform best on an interior wall—not one adjacent with the outdoors. Instead, that’s where your supply registers should be, ideally under a window. Lastly, make sure the return registers aren’t too close to the supply registers, because that could cause your system to work harder. The return registers could funnel off conditioned air before it has had a chance to circulate around the room.
How to Tell a Supply Register from a Return Register
Now that you know everything you probably need to about return registers, you’re probably asking yourself, “how do I tell my return registers and supply vents apart?” It’s actually pretty easy. Supply vents have some identifying—namely, they’re usually smaller. If you look inside a supply vent, you’ll see slats behind the vent cover running perpendicular to the fins on the grill. They also don’t need a filter—that’s only for return vents.
You can also tell them apart by performing a paper test. If you place a piece of paper in front of the vent, and it blows outward, you’re looking at a supply register. If it does the opposite, it’s a return register.
Now that you know the difference between the two, you’ll never look at your vents the same way again!