Poor ventilation can impact your sleep, cognition, and overall health. Here’s why this matters and exactly what you can do about it.
CO₂ Levels and Ventilation
CO₂ levels are the most practical and reliable proxy to monitor how well your home is ventilated. Outdoors, CO₂ is naturally present at low levels, typically 400–500 ppm (parts per million). But indoors, especially in modern, energy-efficient homes where fresh air circulation is limited, CO₂ can accumulate quickly.
It’s not unusual for indoor CO₂ to exceed 1,000 ppm, and in some cases (such as bedrooms with doors and windows closed overnight) to reach 2,500–3,000 ppm or higher.
So what happens when CO₂ accumulates in your home?
Research shows some concerning effects on both your brain and your sleep:
- Multiple studies have found that cognitive performance drops at CO₂ levels around 1,000 ppm (Kajtar and Herczeg., 2012; Satish et al., 2012; Allen et al., 2016; Lee et al., 2022).
- Bedrooms with lower CO₂ levels (800–900 ppm or below) have been found to promote significantly better sleep (less next-day sleepiness, better logical thinking, shorter time to fall asleep) compared to rooms at c.2,400 ppm (Strøm-Tejsen., 2016).
However, it’s important to mention that some research suggests CO₂ itself may not be the actual culprit. In poorly ventilated spaces, other indoor pollutants (such as volatile organic compounds, body odors, and metabolic byproducts) accumulate alongside rising CO₂. Multiple studies indicate it’s these other pollutants that may be causing the issues attributed to elevated CO₂.
For example, in some studies where CO₂ levels are artificially increased with pure CO₂ (without other pollutants present), cognitive performance often remains stable. However, when high CO₂ results from poor ventilation, allowing other contaminants to build up, performance declines noticeably (Zhang et al., 2017; Du et al., 2020).
With that being said, improving ventilation always benefits your air quality, and measuring CO₂ is the most practical way to assess ventilation. So regularly monitoring your home’s levels and making adjustments is an effective strategy for healthier indoor air.
How Can You Improve Your Home’s Ventilation?
Step 1: Start monitoring
We recommend buying an indoor CO₂ monitor to track your levels. We like the Aranet4 Home because it’s very accurate (most cheap consumer devices aren’t) and has a long battery life. We suggest keeping one with you as you go about your day and making sure to leave it in your bedroom overnight. Just ensure you keep the monitor at least 1.5m away from people and away from doors, windows, or vents for reliable readings.
As a guideline, aim for CO₂ levels below 800 ppm, which is where problems can start to occur. Typically, the recommendation has been to keep levels under 1,000 ppm, but we’re more conservative based on the research we’ve seen.
Step 2: Actively ventilate
Open your windows daily, ideally for 15–30 minutes in the morning and evening, or whenever CO₂ exceeds 800 ppm. For best results, create a cross-breeze by opening windows on opposite sides of your home. If bedroom levels are high and noise or temperature allows, open a window for better ventilation overnight.
Step 3: Operate and maintain your ventilation system effectively
If you have central ventilation, regularly replace the filters and clean the ductwork according to the manufacturer’s recommended schedule to ensure a high flow rate. As long as you have sufficient in-room air purification, we also recommend using a MERV 8 HVAC filter rather than higher-efficacy MERV 13 or above filters, as higher-rated filters can significantly reduce airflow in most residential systems.
You can also consider changing the fan setting from “Auto” to “On” for continuous air circulation. However, this will increase energy consumption and filter replacement needs, and can introduce more humidity in humid climates, so consider the trade-offs specific to your system.
If you notice issues, have your system inspected and ensure the vents aren’t blocked.
Step 4: Add mechanical ventilation if CO₂ remains high
If levels are still elevated and the interventions above aren’t possible or effective, consider installing an Energy Recovery Ventilator (ERV) or Heat Recovery Ventilator (HRV), either a whole-home unit or a single-room model. This will bring in fresh, filtered outdoor air while transferring heat and moisture efficiently (which makes it energy efficient).