The Environmental Protection Agency (EPA) warns that indoor air pollution is a top health concern for Americans. Air purifiers are a solution for trapping dangerous pollutants and contaminants so you can breathe cleaner air. Portable air purifiers are a relatively inexpensive option, but they only clean a small area and can be noisy.
Whole-house air purifiers are a more effective solution and have proven to be of better value for many homeowners in the long term. There are a variety of whole-home air purification configurations. Among the most popular is the in-duct air purifier. Let’s explore how these systems function.
Active Return-Side Air Purification
In-duct air purifiers are air cleaning systems that integrate into and take advantage of your central HVAC system. An in-duct configuration has two benefits. One is that the air purifier provides clean air throughout your entire home as part of your forced air system. This is a notable contrast to a room purifier that only provides cleaned air within its coverage zone.
The other benefit is that whole-house air purifiers have their own fans and motors. Passive filtration, such as your HVAC air filter, is usually limited to a minimum efficiency reporting value (MERV) of 13. Unfortunately, this level of air filtration may not be adequate for your home. The higher the MERV rating, the more restricted airflow is, and most residential climate control systems can’t handle more than MERV 13.
An active air cleaning configuration eliminates this concern. An HVAC professional usually installs a whole-home system on the return side of your system. They pull conditioned air from your heater or air conditioner through the air purifier. This process allows you to opt for powerful mechanical filtration, such as a high-efficiency particulate air (HEPA) filter.
When considering whole-home air purification, there are several measurements to be aware of. We’ll explain them below.
Cubic Feet Per Minute
The size of the fan motor in an air purifier dictates how much air it can draw. The industry measures this airflow in cubic feet per minute (CFM). However, CFM only tells you part of the story when sizing an in-duct air purifier. There must be a balance between the CFM and the total square footage of your house. You must also factor in the air resistance and overall size of the filter media. An HVAC professional can help you determine the size of the motor you need in your air purifier to meet the needs of your household.
Air Changes Per Hour
Many in-duct air purifier manufacturers provide air change per hour (ACH) information along with CFM to help you decide on a system. This measurement tells you how often all the air in a given space will be filtered per hour. For instance, a product that a manufacturer has rated for 4 ACH at 2,500 square feet means that in a 2,500-square-foot home, it would filter all the air in the house completely four times an hour.
The U.S. Centers for Disease Control and Prevention (CDC) recommends 4 ACH as a minimum for the average American home. Many in-duct air purifiers on the market provide 5 ACH. You may want to go higher than that if someone in the home has severe respiratory issues.
Clean Air Delivery Rate
Some manufacturers also provide clean air delivery rates (CADR). It indicates the amount of clean air the system delivers per minute. Experts recommend that the CADR be two-thirds of a home’s square footage. An air purifier with a CADR of 1200 would be good for homes up to 1,800 sq. ft.
Filter Media
An integrated air purification system forces your home’s air through a series of filter stages. Stages vary from one product to another, but the common steps are prefiltration, activated charcoal, and mechanical filtration.
Prefiltration
The role of the prefilter is to prevent premature clogging of the other, often more expensive, filter media. Prefilters generally trap particles sized 5 microns and larger. They’re typically inexpensive relative to the other filter media, which saves you the expense of replacing expensive filters more often than necessary.
Activated Charcoal
Activated charcoal, also known as activated carbon, can serve as the prefilter in air purifiers without a dedicated prefilter. Its main role is to perform absorptive filtration. Manufacturers create it by processing carbon to have many minuscule pores. That gives the substance a substantial surface area through which it can bond to pollutants and contaminants.
This filter is effective at eliminating odors. It also traps:
- Gases
- Smoke and fumes
- Airborne chemicals
- Volatile organic compounds
Mechanical Filtration
The mechanical filtration stage removes particulate matter (PM) from the air you breathe. It’s similar to the intake filter that can remove dust, pollen, and pet dander. Most in-duct air purifier manufacturers use HEPA filters. True HEPA filters remove the same particles but at a much higher level of efficiency. HEPA filters trap most particles down to 3.0 microns small and also a significant amount of fine particulate matter. Fine particulate matter comprises particles that are 2.5 microns or smaller.
If you want to trap even higher levels of PM, you can opt for medical-grade HEPA filters. Note that not every in-duct air purifier will support the added air resistance. It’s also worth noting that medical-grade HEPA filters are more expensive. If you’re interested, look for H13 and H14. Both trap particles down to 2.0 microns. An H13 filter does so at 99.95% efficiency, and an H14 filter does so at 99.995%.
Ultraviolet Radiation
Some in-duct air purifiers also have an ultraviolet (UV) radiation stage. It has a UV lamp that gives off a germicidal light. That light kills bacteria, viruses, microbes, and so forth. There is some debate about whether you should have a UV lamp in an air purifier because air moves quickly through the system. Some experts assert it reduces the efficiency of the UV light. An alternative is a separate UV lamp, which you can install in the duct outside the air purifier. The slower air movement in the duct allows contaminants to be exposed to the light for more extended time periods.
Ion Air Purifiers
Ion air purifiers incorporate an electrostatic plate in their design. This plate emits negatively charged ions into the air. These ions attach to airborne particles traveling through the unit, such as dust, pollen, smoke, and allergens, causing them to become negatively charged. Next, they are pulled into a filter with a positive charge. The ions on the filter are then treated with an electric field, rendering them harmless and enhancing air quality throughout your living spaces.
In-Duct Air Purifiers in Tigard
At Specialty Heating & Cooling LLC, we have been serving the residents of Portland, OR, and the surrounding areas since 1985. We install, maintain, and repair heating and cooling systems. We also specialize in indoor air quality services, including whole-home air purification systems and duct cleaning. Contact us today to schedule an appointment with one of our experienced team members.
