How To Fix It

Should an HVAC Zone Damper Bleed Air?

Have you recently noticed that your zone damper is bleeding air? This might be a sign that there’s something wrong with the element. 

In a properly installed HVAC system with a bypass duct, the zone dampers should not be bleeding air – when the element is closed, it has to be tightly sealed. Some zoned systems might not have a bypass duct, in such a case, dampers can be adjusted to never fully close.

Should an HVAC Zone Damper Bleed Air?

You might think that leaving the dampers slightly open is a good idea as static pressure won’t be able to build in the HVAC system. However, if your heating and cooling equipment was installed correctly, you wouldn’t have to make the dampers bleed air.

A lot of zoned HVAC systems include a bypass damper that opens whenever there is a need to maintain the appropriate pressure within the system. Such a solution has a few benefits:

  • It eliminates the need to bleed air in every zone
  • It promotes better dehumidification
  • It circulates the air across the evaporator coil multiple times which contributes to more effective cooling

If your system does not have a bypass damper, then the dampers in the supply zones can be adjusted to allow air to bleed. 

Read: How To Adjust HVAC Automatic Dampers?

How Do You Tell If an HVAC Damper Is Working?

If your damper is bleeding air and you know that your zoned HVAC system has a bypass duct, then there might be an issue with the damper.

  • Low-quality dampers might bleed air simply because they don’t seal well
  • The rubber or foam gasket that seals the dampers where they close might have gone bad
  • There is an issue with the damper motor
  • The damper’s position has not been adjusted correctly (some elements allow you to adjust the damper to be more open or closed when power is applied in order to regulate the temperature more effectively)

If you turn your HVAC system on in one zone and the other zones do not receive any conditioned air, then your dampers are working perfectly fine. 

Read: How To Know If HVAC Zone Damper Is Bad?

How Do You Check a Damper?

Usually, all you would have to do to check if the damper is working properly is turn on the HVAC system and take note of the airflow in the registers. There should be a normal amount of airflow and the room should be able to maintain the set temperature.

How Do I Adjust My HVAC Dampers?

Some dampers can be adjusted to bleed 10%, 20%, or more of their air. If your system has 2 zones and every zone is able to handle about 75% of the total CFM, then you can adjust the largest damper to bleed 20% of air (such a configuration might not require a bypass damper).

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Manual dampers can be easily adjusted with the help of a lever. Automatic dampers with electric actuators can typically be individually configured from the controller

How Do You Manually Close a Damper?

You need to have access to the ducts, in order to be able to manually adjust the dampers. Find the lever responsible for the damper that you want to tackle and turn it in the opposite direction of the duct (if the lever is parallel to the duct, then the damper is open). 

Read: How To Locate HVAC Dampers In Ductwork?

How Do You Manually Open a Damper?

In case you have automatic dampers that are normally closed and you can’t open the element from the controller, then you might have to disconnect the damper.

Some motors have a manual release button. If you push it, you’ll be able to turn the shaft by hand.

Remember to turn the power to the system off before attempting to manually open or close an automatic damper. 

Read: How To Troubleshoot A Honeywell Zone Damper?

How Do I Know If My Damper Motor Is Bad?

You can always test the actual motor with a multimeter to find out if it’s faulty or not. But there are also ways to tell that the damper had gone bad without accessing the ducts.

  • There is no air coming from the registers when the heating or cooling in this zone is supposed to be on
  • You can hear or feel air coming from the registers in a zone that is supposed to be turned off
  • The room feels drafty

Read: Can Zone Damper System Save You Money And Is It Really Worth It?


Are Zone Damper Normally Closed?

Dampers can be either normally open or closed when power is not applied.

When the elements are fully closed, they shouldn’t be bleeding any air at all, unless you choose to slightly open the damper.

What Does a Zone Damper Do?

In a word, a zone damper controls the flow of air in a heating and cooling system. It is an essential part of a zoned HVAC system.

Dampers operate together with thermostats and the zone control panel.

Why Is There Barely Any Air Coming Out of Vents?

If you have a zoned system, the first thing that you need to check is whether the dampers are open or closed (there will be no air coming from the vents, if the damper is closed).

A few other reasons for airflow problems include:

Is It OK to Close HVAC Dampers?

In a zoned HVAC system, the only way to control the temperature in the different parts of the house is by opening or closing the dampers. 

If the system has been installed correctly, then you should not worry about closing off some dampers as the excess air is going to travel through the bypass duct. In case the latter was not installed, dampers in the supply ducts should be left slightly open.

What Are the Two Methods of Controlling Zone Dampers?

The two types of zone damper control include pressure-dependent and pressure-independent damper control.

  • Pressure-dependent damper control includes a controllable damper that can be either open or closed or a modulating damper that can be adjusted to be not fully open or closed.The thermostat would send an open/closed signal to the dampers whenever the zone temperature becomes different from the set temperature. With such control, the zone system has no idea how much air is being supplied to the zone.
  • Pressure-independent damper control includes not only a damper but also an airflow measuring device. The damper does not just open or close, it controls the airflow to the zone.

How Do You Increase Airflow in Air Ducts?

To increase the airflow, you would have to open the damper and the registers. Cleaning the filter and ducts will also help. 

When Should You Adjust a Balancing Damper?

As the seasons change, you would want to either open or close the upstairs dampers. In the winter, for example, you can keep the upper floor dampers closed as warm air naturally rises. 

How Much Air Should Be Coming Out of Vents?

Measuring the amount of air coming out of the vents can be challenging for a regular homeowner. Moreover, the strength of the airflow will vary from one system to another.

However, you have to make sure that the airflow from the vents is roughly equal throughout the whole house (where the dampers are open, of course).

Is It OK to Close Vents in Unused Rooms?

Closing air vents is not a great idea as this can lead to equipment damage. Closing off some zone dampers, however, is totally acceptable.