If you find yourself complaining that parts of your home are too hot in the summer and too cold in the winter, there’s a good chance you’re not using your furnace dampers correctly. Here’s how to balance your HVAC system for year-round comfort.
Most people are familiar with the registers and vents you see in the actual rooms (and with the concept of closing a vent in a particular room to slow or stop the flow of air through the heating and cooling system into that room). But closing the vents in rooms is nowhere near the most efficient way to control the flow of air through the system.
That’s where balancing dampers come into play. A balancing damper is just a simple mechanism inside the ductwork that closes off a given duct—they are called balancing dampers because you use them to balance the flow of air throughout the system. Below you can see an example of a manual balancing damper.
Unlike a register (which is located at the end of the duct run where the ducting meets the floor, wall, or ceiling of a room), however, the damper is located very close to the central unit. The benefit of this arrangement is that it closes down the duct closer to the source of the hot or cold air and helps more efficiently redirect the forced air somewhere else in your home.
So what does that mean in practical terms for you? It means more cold air from the AC in the summer, and more hot air from the furnace in the winter directed precisely where you want it.
Practically speaking, adjusting your dampers is as simple as turning the lever to open or close the damper. There’s a wee bit more to it than just that, however, especially if you’ve never done it before—so let’s dig into some practical tips and tricks. We’ll assume you’ve never fiddled with your dampers and will walk you through the entire process from start to finish.
First thing’s first. You can’t adjust anything until you find your dampers. This should be pretty straightforward for most folks, but there will be some situations for some readers in which adjusting the dampers isn’t an option.
In some homes (especially newer construction) there aren’t balancing dampers attached to the ductwork—a rather poor cost-cutting measure in our opinion. In other homes the dampers, if they exist, have been covered up by drywall during remodeling projects or when a basement was finished into a rec room or some such thing. (Conscientious contractors will often use “false” vents to provide access to the damper handles, so shine a flashlight in all the ceiling vents in your finished basement to check if what you thought was a functional vent is actually an access panel).
On the opposite (and more positive) side of things, if you have a premium system in place, you might have electronic dampers that are automatically controlled by your heating and cooling system and provide zone-controlled airflow. But let’s be real here—if you have this system, you’re probably not reading this article because your automatic system is already taking care of things. If you’re not sure whether you have such a system, you can figure it out pretty easily; instead of physical handles, your dampers will have little motors with wires attached.
Those two situations aside, locating your dampers should be pretty straightforward. Go to your furnace (be it in a utility room, crawl space, basement, etc.) and look at the main duct trunks radiating off the furnace. Dampers are almost always within 2-6 feet of the main trunk.
Here’s an example of dampers on our furnace located directly off the main truck and at the opening of the individual ducts the trunk splits into:
You may only have different style handles, the dampers might be located right off the main trunk or a few feet away, or they might even be rectangular, but you should see something like the image above, cobwebs and all.
Locating the dampers is one thing, and twisting the handle to open and close them is simple enough, but it doesn’t do you any good if you don’t know what damper goes where. Here’s where the real fun starts. If you can conscript a friend, spouse, or an older child to help out here, it’ll save you a whole bunch of running around your house trying to figure out which duct goes to which room.
Before you start, grab a permanent marker or grease pencil. Damper adjustment isn’t something you’ll be doing frequently and labeling them correctly now will make your life so much easier going forward.
First, go through your house and open all your registers/vents. You want maximum airflow as you’re testing each duct so that you don’t miss anything.
Next, return to the dampers. Select one damper to start. Follow the duct the damper is attached to as far as you can before it passes through a floor, wall, or is otherwise obscured. This will give you a rough idea where the duct goes. If you have an assistant, have them go to the area of the house you think the duct goes to.
Turn your furnace’s blower on by activating the fan mode using the thermostat. No fan mode? You can always run the heat or AC too.
Close the damper (remember, we’re doing this one at a time). Below you can see what a closed damper looks like. The handle should (unless you have a very fancy handle otherwise labeled) be perpendicular to the duct.
At this point either yell to your assistant to check the ducts in that room/area of the house or head back to the area to check them yourself. One or more of the vents in the area should be still with minimal to no airflow.
Confirm the damper in question is yielding the result you want by opening it and closing it again, just to be sure.
Return to the damper and using your marker, label the duct clearly with an easily understood name such as “Foyer,” “Kitchen,” or “Living Room.” For the sake of future homeowners, avoid names only you’ll understand (“Carl’s Room” only helps if you know who Carl is).
Finally, we’re going to label each damper for a Summer and Winter position. But, we’re not going to do so just yet because it requires we use the system for a little bit first to position our labels accurately. We’ll talk more about this in the next section.
Now that we know which damper goes where in the home, it’s merely a matter of making an initial adjustment based on the season and where we want the hot or cold air to flow.
We’re writing this at the start of summer, so let’s talk about AC-oriented adjustments first. Cold air sinks and, HVAC system or not, the lower levels of your home will stay cooler naturally—with no intervention at all the attic is always warmer than the basement. With that in mind, you want to start by closing dampers for ducts that distribute air to the basement and the first floor, forcing the bulk of the air up to the second floor. Don’t worry; we assure you the cold air does its best to flow downwards and the ground floor won’t be sweltering hot.
Even if there is no second floor, you can still adjust the dampers to send the maximum amount of cooled air to the primary living spaces like the bedrooms and the living room (or, if you’re like us, the home office).
As soon as it’s time to shut off the AC for the summer and think about firing up the furnace to keep the coming winter chill away, it’s time to revisit your dampers.
In summer, the goal is to force the chilled air upstairs. In winter, the goal is to force more air onto the main floor. Heat rises and adjusting the dampers for less airflow upstairs and more airflow downstairs will typically have a noticeable positive effect on heat distribution without resulting in chilly upstairs rooms.
Further people tend to sleep better when they are cooler so having bedrooms that are a little chillier in the winter is a net bonus. You get to sleep cooler without that summer AC bill! If chilly rooms aren’t your thing, however, and adjusting your dampers never seems to get the one room you want to warm up as warm as you would like, it’s really easy to heat a small space with a compact space heater.
You won’t know instantly if the tweaks you’ve made are ideal. While you will know if a particular vent has been dampened (because you checked them one by one in the previous section and labeled them), it might take a few days to get a sense as to whether or not the adjustments you made are yielding the effect you want.
Every day, check-in on the different rooms of your home to see how the adjustments are affecting the temperatures. Are rooms that were too cold warmer now? Are rooms that were too hot more comfortable? If so, you’ve dialed it in for the season. If not, adjust dampers as you see fit to get colder (or hotter) air where you need it.
While your personal comfort is the real metric you should use, it can also be helpful to have real data. Fortunately, temperature and humidity monitors are really inexpensive these days. We like the offerings from Govee: they’re cheap, accurate, and have both a visual display and Bluetooth connectivity to dump the data onto your phone for easy viewing and tracking.
Govee Indoor Temperature Gauge 2-Pack
It's easy to monitor temperatures around your home with these handy and inexpensive sensors.
Throw a few of these around your house in the rooms you’re monitoring and you’ll see exactly how warm or cool the room gets over the course of the day.
When you feel the system is pretty well balanced for the particular function (AC vs. heat), grab your marker again and label the duct with the appropriate season name where the handle should be during that season.
So, for example, if you just fine-tuned your system for summertime AC use, whenever the handles are pointing on the ducts is the spot you should write “Summer” as that indicates the position of the damper best suited for AC. Resist the urge to write the opposite season in the opposite position of the current one. You may find, when the seasons change over, that you don’t fully close a particular damper that was open and the “Winter” position might be 50% closed and not completely closed. Wait to label the opposite season until you’ve taken things for a spin.
All the hard work is behind you now. You located the dampers, you labeled and tested them, and you’ve got a much better-balanced HVAC system to show for it.
The only thing left to do is to set a reminder for yourself to jog your memory and remind you to change the dampers when the seasons change. You can put an alert in your phone calendar, or you can stick a big piece of paper with “Adjust dampers Spring and Fall!” right on the furnace, so you see it every time you change the filters—but whatever you do you need to remember to adjust them. Otherwise, come the season change, you’ll be too hot or too cold all over again.