Understanding Indoor Air Quality

Indoor air quality (IAQ) is a critical aspect of home health that often goes unnoticed. It refers to many airborne compounds and pollutants inside our homes and buildings. Poor IAQ can lead to multiple health issues, from minor irritations to severe respiratory problems. Proper ventilation and IAQ management have become more relevant as homes have become more energy-efficient and airtight.

In this guide and the video above, This Old House experts Ross and Richard Trethewey highlight the significance of indoor air quality and review several air quality monitoring solutions to help homeowners maintain a healthy living environment.

Common Indoor Air Pollutants

Several pollutants are to blame for the majority of indoor air issues. Below are the biggest indoor air quality offenders, according to the U.S. Environmental Protection Agency (EPA):

• Carbon dioxide (CO2): A byproduct of gas appliances, boilers, clothes dryers, and human respiration
• Mold and mildew: Spores and bacteria that thrive in excess moisture and standing water
• Particulate matter: Tiny airborne particles that result from cooking, dust, or outdoor pollution
• Radon: A naturally occurring radioactive gas that can seep into homes from the ground
• Volatile organic compounds (VOCs): Compounds emitted from various household products, including paints, cleaning supplies, and furniture

Measuring Indoor Air Quality

You can monitor your IAQ by tracking and measuring certain pollutants with various IAQ monitoring devices. We’ll go over the kinds of monitors available and how to choose one that suits your needs.

Types of IAQ Monitors

Several categories of IAQ monitors are available, and each type is engineered to detect and measure specific pollutants. Here are the four most common IAQ monitors:

Pro Tip: Ross Trethewey, This Old House home technology expert, advises: “Knowledge is power. A monitor will let you know if your air quality is not that great, so you can do something about it.” Many modern monitors can alert you via smartphone to changes in air quality, or communicate with your smart thermostat to activate the ventilation system automatically.

• CO2 monitors: These track carbon dioxide levels and can show you how effective your ventilation is.
• Particulate matter monitors: These measure the concentration of tiny particles in the air.
• Temperature and humidity sensors: While not pollutants, these factors can affect overall air quality and comfort.
• VOC sensors: These detect the presence of VOCs in the air.

Choosing the Right IAQ Monitor

As the Tretheweys discuss, there are no universal IAQ monitors—you need different devices to measure different pollutants. Weigh these factors when purchasing an IAQ monitor:

• Accuracy and reliability of the device, including any certifications
• Price point and long-term value
• Types of pollutants you want to measure
• User-friendly features, such as smartphone connectivity

We recommend reading reviews before purchasing an IAQ monitor, as the quality of sensors can vary significantly between models. 

Must-Do Monitoring: While most IAQ monitors use carbon dioxide (CO2) as a general indicator of air quality, few track carbon monoxide (CO) or radon. Carbon monoxide is the leading cause of accidental poisoning deaths in the U.S., so all homes should have a dedicated CO detector installed on each level. Radon, a carcinogenic gas, can be detected with an at-home test kit; if levels are high, a dedicated mitigation system that vents the gas outside should be installed.

Smart Home Integration for IAQ Management

Smart home systems are increasingly incorporating IAQ management features. They offer a modern solution for optimizing air quality.

IAQ Monitors with Smart Home Connectivity

Many modern IAQ monitors can connect to smartphones or home automation systems. These features allow homeowners to improve their IAQ in several ways:

• Automatically trigger ventilation systems when pollutant levels rise
• Receive real-time alerts about air quality issues
• Track air quality trends over time

Automated Ventilation Systems

Smart ventilation systems synchronize with IAQ monitors to automatically adjust ventilation rates based on current air quality. This advantage saves you from constantly adjusting your systems manually.

Improving Indoor Air Quality

Once you’ve identified air quality issues in your home, there are several steps you can take to improve the situation.

Ventilation Solutions

Proper ventilation is key to good indoor air quality. Mechanical ventilation systems are especially important in modern, airtight homes.

Pro Tip: Richard Trethewey, This Old House heating and plumbing expert, sums up the importance of ventilation in tight homes: “If you’re going to insulate, you’ve got to ventilate.”

Energy Recovery Ventilators (ERVs)

ERVs are an excellent solution for maintaining good air quality without sacrificing energy efficiency.

A quality ERV device offers the following benefits:

• Acts as “lungs” for the building, bringing in fresh air while expelling stale air
• Helps maintain consistent temperature and humidity levels
• Transfers heat and moisture between incoming and outgoing air 

Here’s how an ERV works: Two fans draw air into the unit—one brings fresh air in from outside the house, while the other draws stale air from inside. The two airstreams are channeled past each other—but do not mix—in an exchange core made of a conductive material such as aluminum or plastic that allows the heat and moisture from one stream to transfer to the other. The ERV may be programmed to run periodically on its own, or may be activated along with a furnace blower.

Simple Steps To Improve IAQ

Homeowners can take the following steps to improve indoor air quality:

• Choose low-VOC paints and cleaning products
• Open windows regularly to allow fresh air circulation
• Regularly clean and maintain HVAC systems
• Use air purifiers with HEPA filters
• Use exhaust fans when cooking or showering

Regular HVAC maintenance also prevents pollutant buildup.

Indoor Air Strategies Beyond the Basics

Maintaining good IAQ requires a combination of strategies beyond basic monitoring and ventilation.

Houseplants for Natural Air Purification

Certain houseplants are known to help purify the air naturally:

• Aloe vera: Reduces benzene and formaldehyde
• Snake plant: Converts CO2 into oxygen at night, which is beneficial for bedrooms
• Spider plant: Removes carbon monoxide and xylene

Reality Check: As This Old House Magazine noted in its indoor air quality coverage, “while laboratory experiments have shown plants can reduce levels of some airborne chemicals, there’s no evidence that a few houseplants can significantly improve household air.” A balanced system of mechanical ventilation remains the most effective way to improve indoor air quality — houseplants are a lovely complement, not a replacement.

Limiting Pollutant Sources

Reducing indoor pollution sources can significantly improve IAQ. Here are a few ways that you can limit your indoor pollution directly:

• Avoid smoking indoors
• Opt for natural or eco-friendly products
• Store chemical and cleaning products properly

Implementing Comprehensive IAQ Solutions

Combining different IAQ solutions can lead to more effective results. For example, using mechanical ventilation systems alongside simple steps such as exhaust fans and houseplants can create a multi-layered strategy for better indoor air quality.

Resources

In the video, the Tretheways tested several different IAQ monitors, including one made by Foobot, Airthings Wave Plus by Airthings, Awair, and Hobo by Onset.

Most homeowner-friendly IAQ monitors have similar price points, but Ross Tretheway suggests carefully reading reviews before investing in one. They have different sensor quality levels, and some are more accurate than others.