IAQ Short Term Monitoring

Nov 23, 2021

If a building wants to evaluate its indoor air quality (IAQ), there are three main methods available. In this article, we will highlight a method that is rarely performed, yet is one of the most powerful tools for assessing IAQ.   It balances collecting high quality data with a lower price point and has a proven track record of finding indoor air quality problems. 

The Three Methods

The first method is professional assessment, where IAQ consultants, engineers, or industrial hygienists inspect a building and use advanced instruments to evaluate the indoor environment. The advantage of this method is that a thorough visual inspection can be performed to identify root causes of IAQ problems. Also, this method can utilize top-of-the-line equipment and sampling methods to identify exactly what is impacting the air quality. There is a key disadvantage, however. Professional assessments are performed over a few hours on a random day and are unlikely to identify issues not happening at the precise moment a particular room was being evaluated. A professional assessment is a snapshot in time rather than a full profile of how the building is performing.

The second method is continuous monitoring where IAQ sensors take minute-by-minute readings all day every day. By tracking the concentrations of key IAQ parameters continuously, conditions that would have otherwise been missed by a professional assessment may be discovered.  For example, a building might experience high humidity at night and over the weekends when the HVAC system sets back. A professional assessment would have missed that—but it would be identified by continuous monitoring.  IAQ sensors have come a long way in quality, cost, and selection.  A key disadvantage is that the sensors used in continuous monitors are typically low-cost and cannot be fully trusted to provide accurate results. There are security concerns related to connecting to the building’s WiFi network and safety concerns related to providing power to permanently mounted monitors. Despite these limitations, continuous monitoring has been growing at a rapid pace that no one expected a few years ago. 

The third method is short-term monitoring which is perhaps the most under-appreciated method for evaluating IAQ.

Why Short-Term Monitoring?

By short-term monitoring, we are referring to collecting continuous readings for a period of time ranging from 24 hours to 1 month. The longer the short-term monitoring, the better, so we recommend a minimum of 1-week. 

The advantage of this method is that you can use a high quality instruments, although that is not required.  Multiple high-end instruments can be rented for a week to collect the highest quality data possible, rather than relying on the typical low-cost monitor that uses $10 sensors.  Some buildings are more interested in extensive coverage rather than high-quality sensors. Short-term monitoring can be a great application for a building wanting to evaluate dozens of different areas without having the capital cost of buying all those sensors. 

Because short-term monitoring does not involve a permanent installation, it allays certain concerns related to continuous monitoring.  Instead of permanently mounting and powering these instruments on a wall which requires a licensed electrician, short-term monitoring can just use normal electrical outlets and command strips for wall mounting.  Or it can just be left on a table or desk because it will only be a short-term inconvenience. Also, with short-term monitoring there are no issues with data security related to connecting to the Wi-Fi. Over a short period of time, internal storage can handle the data collection to be downloaded later to produce graphs and charts. On a recent project, continuous monitoring was rejected due to these security concerns. The client didn’t want data in the cloud that could be used to pinpoint when a particular area was occupied or unoccupied by using CO2 data. 


Short-term monitoring has its disadvantages too.  As a stand-alone solution, it lacks a professional inspection that can more directly identify the underlying conditions causing problems. An IAQ monitor can’t identify the mold problem under a dripping sink. 

Another disadvantage is that there is variability over the entire year.  Some buildings predominantly experience IAQ problems in the winter, whereas others experience them in the summer. If doing short-term monitoring over a month in the winter will miss the problem that is only present in the summer. To combat this, a few weeks of short-term monitoring could be performed in the summer and winter. 


Each of the three methods is a tool that has advantages and disadvantages. When I first started in this field back in 1995, a professional assessment was really the only option available. I have been excited to see all the interest in continuous IAQ monitoring over the past decade, especially in response to COVID-19. But short term monitoring often neglected despite being a powerful tool in the tool-belt.  At Indoor Science we like to pair short-term or continuous monitoring with a professional assessment to provide the most comprehensive evaluation possible to our clients.