Understanding and Monitoring Basic Indoor Air Quality

Cam Allen L.I.W. NHI

August 28, 2026

In this weekly Q&A column, retired builder/building inspector Cam Allen answers readers’ home renovation questions. Have a question? Enter it in the form below.

It is no secret that the world’s air quality is declining, in some areas rapidly and this is certainly affecting the human race. I do not remember seeing so many children with respiratory issues when I went to public school as is documented today. In most studies they rank increased air pollution as the number one cause. Indoor air pollution is often worse than outdoor due to confined space, limited to no air ventilation which creates an enclosed area where pollutants accumulate over time.

Fully understanding indoor air quality would take completion of a major college course and even then there are variables, even within most homes. What I am going to try to cover in the space of this week’s column is some basic, usually present air quality issues. Also, what kind of testing a decent air quality monitor should display and type of filtration that should be in every air purifier.

There are a number of air quality terms that you will hear: PM2.5, PM1, C02, VOCs, HCHO and AQI. The first and most commonly known is particulate matter or PM for short. The rating most recognized is PM2.5. This means any pollutant that is made up of fine particles with a diameter of 2.5 micrometres or less. PM is not just one air pollutant, it’s a range of particles suspended in the air that comes from smoke, dust, pollen and liquids. Some you can see
like smoke, smog or soot. The most harmful are much smaller, hence the PM2.5 and PM1 measuring standard and how any filtration method is based upon its ability to reduce them in your indoor air. Finer airborne pollutants like the coronavirus and bacteria are measured in the PM1 scale. A good air quality
monitor should be able to detect and show this on their display.

CO2 is the short form for carbon dioxide. This is an odourless, colourless non-flammable gas. Outdoor CO2 is created in excess by forest fires, combustion of fossil fuels and organic decomposition. Inside your home it is produced by ordinary humans breathing, cigarette smoke and unvented or poorly vented fossil and wood burning appliances. Every home has some level of CO2 and if your monitor shows a number like 800PPM (parts per million) that is
accepted as a good level. If your air quality exceeds 1500PPM, this
means your air is quite stale and stuffy. You may notice drowsiness,
headaches and trouble focusing. A quick fix here is to open some windows and doors for an air exchange.

The next term on most air quality monitors is VOC (Volatile OrganicC ompounds). These are organic compounds with high vapour capabilities like paint, adhesives, cleaning sprays, disinfectants and air fresheners. Any furniture made with particleboard, plywood and most foam products will emit VOCs. It is a documented fact that VOCs inside a home are up to ten times higher than outside your home. VOCs have both short- and long-term health effects, starting with nose and throat irritation to long term liver and kidney
problems, to name a couple of major health concerns.

The last air quality issue that I prefer to see monitored is an offshoot of VOCs and its called HCHO which is the chemical formula for formaldehyde. It is a colourless, flammable chemical with a strong, sharp smell. It is used in nearly every household product including fabrics, pressed wood furniture, paint and household cleaners. It is caused by off-gassing from the product in use – even some emissions from kerosene space heaters, gas stoves and cigarette
smoke emit HCHO. The reason it’s used is that it’s an inexpensive binder as a resin or adhesive to create durable consumer products.

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The last display I think that should be on every air quality monitor is the Air Quality Index, which is the U.S. term, in Canada we call it the Air Quality Health Index. (AQHI) The short form is AQI. This level of monitoring bundles ground level ozone, PM 2.5 and PM 1, carbon monoxide, sulfur dioxide and nitrogen dioxide into a scale that ranks the air quality from 0 to 500+. Most quality air monitors use the green-yellow-orange-red colour scale for easier reading of the display about all of the pollutants I have described.

There are two other air quality issues, that being mould and radon and they both require specific testing and remedial action. Mould detected by visual patches of discolou ration, usually black or white with the white often appearing to be fluffy on the surface. A damp, musty smell is also a giveaway to the presence of mould. It can cause respiratory issues and should be removed as soon as possible from anywhere in a home.

Radon Gas in Canada is a bit regional, Ontario and Quebec are the provinces where most of the off gassing is present. This off-gassing is a by-product of uranium. You can buy radon home test kits for this and it’s best tested in the fall to the early spring. This allows you to seal off your crawl space or basement for testing. Professional remediation is recommended here. Radon is well documented as a cancer causing agent.

Lastly, how do you improve the air quality in your home? Some HRV (Heat Recovery Ventilation) and ERV (Energy Recovery Ventilation) installations are available with or can be retrofitted with a HEPA filter. This type of filtration is effective in removing PM 2.5 particles. HEPA is known as the world standard for air filtration. All effective air purifiers are equipped with this kind of filter which is known, in controlled testing, to capture 99 percent of indoor air pollutants.
While this is the advertised standard, in real life conditions, multiple tests have shown that the effectiveness is closer to 40 to 60 percent air purification. One study that I have on real life conditions is with a group of homes in Massachusetts that were tested. They started with no air purification, were tested and then 8 months later re-tested with a full HEPA/carbon air purifier operating. The indoor air PM 2.5 had dropped by an average of 45 percent. That is a significant improvement.

Lastly, on a personal note, like many of my colleagues we are recognizing the need for some manner of IAQ within our own homes. HRV systems have only been mandatory in Ontario since January 2025. Better home builders have installed them since the mid 2000s. Quebec mandated them in November 2000.

Other provinces came on line at intervals in between these time periods. That means, by a qualified guess, that less than 10 percent of homes in Canada have a full home ducted ventilation system like an HRV. This means the only effective way to improve and maintain some manner of purification is by portable purification. There are many on the market – we chose one made by Lorvyn as our home on the main level is an open concept style. It operates within its designed standard for a 510 square foot area. It came with an H13 HEPA filter core and a prefilter as part of the four-stage filtration. I am
monitoring it for another 6 months, it’s 2 months old. I have just installed an AQItech air quality monitor which monitors all of the impurities I have described.

Fortunately I have access to some commercial AQI testing equipment that allows me to see how effective the Lorvyn480 air purifier is and also how accurate the AQItech 16-in-1 monitor is. I will release my results sometime around Christmas this year.

Images from Depositphotos