The risks of carbon dioxide (CO2) accumulation.
Carbon Dioxide or CO2 is an invisible, odorless, greenhouse gas that is mostly generated by burning fossil fuels, decomposition of organic matter, and as by-product of the respiration of living organisms.
A relatively small amount of CO2 is present in our atmosphere (outside air), this is approximately 420ppm (parts per million) or 0.042%. Higher concentrations can cause drowsiness, headaches, high blood pressure, fatigue, confusion, and even death by suffocation.
Levels above 1,000ppm (0.1%) could impact the cognitive function (think of brain fog), particularly for complex cognitive tasks, and continuous exposure may not be doing you any favors, especially if you spend significant time indoors. Levels above 40,000ppm (4.0%) are deemed immediately dangerous to life or health.
The pursuit of more energy efficient homes and the appeal of a controlled temperature is effectively transforming American homes into enclosed vessels in which harmful substances, including CO2, buildup over time.
The average American, single-family home is about 2,300 square feet; Assuming 8-foot-tall ceiling and ignoring the volumetric impact of furniture, space between walls, attic space, etc. the volume of such dwelling would be somewhere around 18,400 cubic feet or 521m3.
An average adult male with moderate activity for 16 hours and rest for the remaining 8 hours consumes approximately 22.8m3 of air per day. For simplicity, let’s assume that the average consumption is 24.0m3 per day or 1.0m3 per hour; About 5% of the inhaled air, equivalent to 1.2m3 per day, is exhaled as metabolic CO2.
Imagine a scenario where you have a total of 10 adults inside an average home to enjoy dinner. Over the course of 4 hours, the CO2 concentration could be over 3,800 ppm, which is above the threshold known as detrimental for cognitive tasks. Perhaps the term ‘stuffy’ air rings a bell.
After six hours the party is over, you tide up the kitchen and then go to bed. By then, the CO2 concentration could be above 5,500 ppm; Not surprisingly, you may end up with a headache, a poor night’s sleep and more than likely feeling a bit fuzzy the next morning.
In this example, most people are unlikely to stick around for more than a few hours, but for the sake of the conversation, imagine a situation where people remain inside for 12, 24, or 48 hours. Within a couple of days, the air quality inside this dwelling moved from poor to dangerous to life and health.
Here are few alternatives to prevent CO2 (and perhaps other contaminants) from building up inside your home.
Beginner: The easiest way to allow outside air into your home is to open a couple of windows on opposite sides of the dwelling (weather permitting) to help with air circulation.
Intermediate: Use the kitchen extraction fan (assuming you have it routed outside, as suggested in the sick building syndrome post) or a bathroom exhaust in combination with an open window to exchange air more effectively.
Pro: Have a make-up air system installed and set up to allow outside air into your HVAC system for a few hours every day. An advantage of a properly designed make-up system is that outside air will be filtered prior to reaching the living areas, which could be huge for allergy-sensitive people and when outside air quality is not great (remember the wildfires?).
Super Pro: Have a make-up and extraction system combination installed and tied to an air quality measuring device. Using this approach, one could maintain indoor CO2 within a desired range and even dynamically increase the air exchange process when CO2 levels are increasing at higher rates, for instance, when entertaining guests.
Final note on air exchange: CO2 is likely the mildest threat when it comes to indoor air quality (Carbon Monoxide or CO can be deadly at much lower concentrations), hence having a healthy air exchange process in place will also help to dilute other contaminants and pollutants.