Closing the Vents?

Does It Really Help to Close the Vent in an Unused Room?

Everyone wants to save money and in this article we are going to investigate the question: does it really help to close the vent in an unused room. You invested a great deal of money in your HVAC system and you have a couple of rooms that are not used every day. The tendency is to shut everything down in that room, close the vents, pull the curtains, and turn off the light.

But, does it really save money to do this? By preventing air from circulating into that room or rooms, are you causing your HVAC system to work less? What is actually happening when you close the vents and prevent air from circulating in that room?


Registers and Vents

First of all, let’s make sure we are talking about the same thing. In the field of HVAC, there are three kinds of words used to define where air flows in a house. There are registers, grilles, and returns. All of these come under the generic heading of “vents.”

Register: A register is a vent cover that covers the whole where the duct enters the room. They usually have adjustable slats that can open or close.

Grille: A grille is a vent cover wherever air goes into or out of a room and back into the HVAC system. They cannot be opened or closed.

Return: An air return is a vent grille that is often found in a hallway or a ceiling installed to extract air from a room. It does not have controls that allow one to adjust air flow.

In this scenario, we are working with a register. It is the only vent that can be adjusted with a dampener. A homeowner can move a roller or adjust a slide to control the amount of air flow. When the register is closed, it completely prevents air from flowing into the room.

The Blower Motor

At the very core of any HVAC system is the blower motor. It is the device that moves the air at a certain force throughout your house. This motor can be either a permanent split capacitor(PSC) or an electronically commutated motor(ECM). The goal of the blower is to keep air moving at so many pressurized feet per minute within a closed system.

So, when you seal up the register and shut down the air flow, you are creating a higher pressure within the total system. This higher pressure causes the motor to speed up to push against the pressure. The motor wants to provide the same air flow and will use up a more energy trying to provide it.

On the other hand, if it is a PSC motor, it will continue operation at lower speeds as the pressure goes up. This will produce less air flow and that is not a good thing.

Restricted Air Flow

Anytime you close an opening in the HVAC system of ducts, you are creating higher pressure. In addition to causing the motors to go into overtime, added pressure will be added to the duct system. This added pressure will go to work on the seals that hold the ducts together. Over time, the added pressure will cause leaks and that will, in turn cause the HVAC system to go to work even harder to provide the same air flow to areas of your home.

The more vents you close, the higher the pressure. The higher the pressure, the more potential for problems.

Here are some of the issues that can arise if you shut down air flow in rooms.

  • Comfort issues due to lower air flow
  • Frozen AC coil
  • Ruined compressor
  • Possibility of cracking the heat exchanger
  • Duct leaks
  • Lower air flow with PSC blower motors
  • Condensation and mold growth in the areas where there is not air flow

In the final analysis, it is not a good idea to shut off air flow to rooms. It may damage your HVAC system and cost you money.