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What Does a Fresh Air Damper Do?

Dampers may be found in various parts of an HVAC system. A fresh air damper is one of them. It works similarly to dampers elsewhere in ductwork but allows air in from outside. It is located in the duct leading to the air handler (before the fan), at a point where air can enter the system. We’ll now answer the question, “What does a fresh air damper do?” in more detail.

How a Fresh Air Damper Works

A damper is a device that opens or closes. It should be closed when your HVAC system is off so conditioned air doesn’t escape your home. The damper should be open when the AC or heater is on, so fresh air can be allowed in.

When the damper is open, outside air can enter the structure through a vent inlet on the roof or sidewall. This air passes through a filter before passing through a duct and into the return plenum. It then mixes with the return air. The supply ducts then disperse the mixture of air throughout the building.

Not every fresh air damper is created equal. Aside from having volume dampers to control the amount of airflow in fresh air ducts, and shutoff dampers that seal off the duct from outside when the blower motor shuts off, there are three basic types of fresh air dampers. They are:

  • Motorized Dampers: An electric motor controls the damper; this is the most commonly used type in HVAC systems.
  • Manual Dampers: Are operated with a handle or knob, so you can essentially open and close one by hand.
  • Automatic Dampers: Are modulated based on feedback from a sensor that monitors the amount of fresh air required.

Benefits of a Fresh Air Damper

Many people may ask, “What does a fresh air damper do to improve indoor air quality?” There are two main benefits of a fresh air damper. The first is that it pressurizes a building; more air is delivered inside than is pulled from the structure, creating positive pressure while the fan is running. This positive pressure helps prevent pollutants from getting pulled in from outside.

By controlling air infiltration, it’s also possible to reduce heat loss or gain. So, in addition to diluting polluted or stale indoor air, a fresh air damper can contribute to improved energy efficiency. The source of air intake must be in a clean location to see any of these benefits. Generally, having 5% to 10% outdoor air by volume can maintain a fresh indoor air supply.

Fresh air dampers are also beneficial to combustion appliances. They can provide increased oxygen to enable more efficient burning of fuels. Flue draft pressure can be increased as well, so fumes and fuel by-products are well-ventilated.

Fresh Air Inlets Can Increase Heating or Cooling Load

An important consideration is the intake’s effect on the system’s heating or cooling load. To calculate the increase in load, in British Thermal Units (BTUs):

  • Measure how much fresh air is pulled into the building, in cubic feet per minute (cfm).
  • Determine the difference between the temperature inside your home and outside.
  • Subtract the outdoor temperature from the indoor temperature for a season.
  • Multiply the cfm value by the temperature difference (to determine how many BTUs are added).
  • Use this formula: Fresh Air Sensible BTU = (Fresh Air cfm x Temperature Difference) x 1.08.

Should I Install a Fresh Air Damper?

First, determine if your HVAC system already has one. If not, it can have many benefits; but there are a few considerations when designing and installing a damper. An HVAC professional can determine whether a fresh air damper is present, meets your needs, or install one with the important considerations in mind. Black Hills can help with fresh air damper installation, air duct cleaning, and other air quality services. For assistance in the Olympia area, schedule an appointment online or call 888-402-3514 today.

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