High levels of carbon dioxide (CO₂) in your home can make you feel tired, foggy-headed, and uncomfortable.
If you’ve noticed your CO₂ monitor consistently showing readings above 1,000 parts per million (ppm), you’re likely wondering what’s causing it and how to fix it.
In this guide, we’ll explore the common sources of indoor CO₂, why levels might remain high even with good ventilation, and provide you with a step-by-step approach to diagnose and solve your high CO₂ problem.
Understanding Indoor CO₂: Why It Matters
Carbon dioxide (CO₂) is a colorless, odorless gas that’s a natural byproduct of human respiration and many household activities. While low levels of CO₂ are normal, concentrations above 1,000 ppm can lead to symptoms like headaches, drowsiness, and difficulty concentrating. Prolonged exposure to high CO₂ can even impact your overall health and comfort.
Is my CO₂ monitor accurate?
Yes, if you’ve purchased a reputable CO₂ monitor from a trusted brand, it should provide accurate readings.
Look for monitors that are certified by recognized organizations like the International Society of Automation (ISA) or the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). Regular calibration and proper placement (away from direct CO₂ sources) will ensure your readings are reliable.
Common Sources of Indoor CO₂
Understanding where CO₂ comes from in your home is the first step to addressing high levels. Here are some common sources to consider:
Human Respiration
Even in small households, human respiration can contribute significantly to indoor CO₂. Each person exhales about 2.3 pounds of CO₂ per day, which can quickly build up in poorly ventilated spaces.
Pets and Indoor Plants
Your furry friends and houseplants also produce CO₂ through respiration. While the impact is usually small, it can add up in a closed environment.
Cooking, Burning Candles/Incense, Gas Appliances
Any combustion process, whether it’s cooking on a gas stove, burning candles, or using a fireplace, produces CO₂. Gas appliances like furnaces and water heaters can also leak small amounts of CO₂ into your home.
Building Materials and Aging Insulation
Some building materials, especially those containing urea-formaldehyde foam insulation, can off-gas CO₂ over time. This is typically a minor source but can contribute to overall indoor levels.
Can AC or HVAC systems increase CO₂?
While air conditioning (AC) and heating, ventilation, and air conditioning (HVAC) systems don’t directly produce CO₂, they can recirculate indoor air, potentially trapping CO₂ inside. If your system doesn’t have a fresh air intake, it may not be effectively diluting indoor CO₂.
Can mold or musty smells signal hidden CO₂ problems?
Mold growth itself doesn’t directly produce CO₂, but it can be an indicator of poor ventilation, which may also lead to high CO₂ levels. Musty smells often suggest moisture issues that could contribute to a stagnant indoor environment.
Why Do CO₂ Levels Stay High Even With Good Ventilation?
It’s frustrating to have high CO₂ levels even when you think your home is well-ventilated. Here’s why this might be happening:
Air Exchange Rate vs. Temporary Venting
Opening a window temporarily can help lower CO₂ levels, but the key is having a consistent air exchange rate. If your home doesn’t have a continuous ventilation system, CO₂ can build up between venting sessions.
Hidden Air Leaks, Closed Doors Between Rooms, Two-Story House Airflow
Air leaks and closed doors can disrupt proper airflow, trapping CO₂ in certain areas. In two-story homes, CO₂ can accumulate on the lower level if the upper level is not properly ventilated.
AC Use and Recirculation: How They Work For/Against CO₂
While AC can help circulate air, it often recirculates indoor air rather than bringing in fresh outdoor air. This can lead to a buildup of CO₂ over time, especially in systems without a dedicated fresh air intake.
Nighttime CO₂ Build-Up: Stack Effect, HVAC Cycling, Window Closure
At night, CO₂ can accumulate due to the stack effect (warm air rising), HVAC systems cycling off, and windows being closed. This can result in higher morning CO₂ levels, even if daytime ventilation seems sufficient.
Diagnosing Your High CO₂ Problem: Step-by-Step
To pinpoint the cause of your high CO₂ levels, follow these steps:
Regular Monitoring (How, Where, When)
Place your CO₂ monitor in the room where you spend the most time. Take readings throughout the day, noting any patterns or spikes. Monitor during different activities and times of day to get a comprehensive picture.
Stepwise Isolation (Turn Off AC, Change Filters, Open vs Closed Techniques)
Start by turning off your AC and opening windows to see if CO₂ levels drop.
If they do, it suggests your AC system may be recirculating CO₂. Try changing your HVAC filters and see if that improves the situation.
Experiment with keeping doors open or closed to assess airflow within your home.
Smell and Moisture: Investigating for Mold or Mildew
Check for musty smells or visible signs of mold or mildew, especially in bathrooms, kitchens, and basements. These areas may have poor ventilation, contributing to high CO₂ levels.
Appliances and Gas Leaks: Basic Checks
Inspect your gas appliances for any signs of leaks or improper venting. Check your stove, furnace, water heater, and fireplace for proper operation.
If you suspect a gas leak, contact a professional immediately.
Checklist: How to Diagnose High CO₂ at Home
1. Place CO₂ monitor in main living area
2. Take regular readings throughout the day
3. Turn off AC and open windows to test ventilation
4. Change HVAC filters and reassess
5. Check for mold or mildew in damp areas
6. Inspect gas appliances for leaks or issues
7. Experiment with door positions to optimize airflow
Solving Persistent CO₂ Issues: Proven Solutions
Once you’ve identified the likely causes of your high CO₂ levels, it’s time to implement solutions:
Improving and Automating Ventilation (Trickle Vents, HRVs, ERVs)
Install trickle vents in your windows to provide a constant trickle of fresh air. Consider a heat recovery ventilation (HRV) or energy recovery ventilation (ERV) system to bring in fresh air while maintaining energy efficiency.
Upgrading HVAC with Fresh Air Intake
If your HVAC system doesn’t have a fresh air intake, consider upgrading to one that does. This will help dilute indoor CO₂ by bringing in outdoor air.
Removing Potential Sources (Mold Remediation, Gas Appliance Checks)
Address any mold or mildew issues through professional remediation. Have a certified technician inspect and service your gas appliances to ensure they’re not leaking CO₂.
Smart Ventilation Controls for Energy/Air Quality Balance
Use smart ventilation controls to optimize your home’s ventilation based on CO₂ levels, occupancy, and outdoor air quality. This can help maintain a healthy indoor environment while minimizing energy waste.
When to Consult Professionals (Indoor Air Quality Specialists, HVAC Pros)
If you’ve tried these solutions and still have high CO₂ levels, it’s time to call in the experts. An indoor air quality specialist can conduct a comprehensive assessment and recommend targeted solutions. An HVAC professional can diagnose and fix any issues with your heating and cooling system.
FAQ: Uncommon Causes and Expert Answers
Sometimes, high CO₂ levels can have less obvious causes. Here are some expert answers to common questions:
Can new furniture or renovations increase CO₂?
Yes, new furniture and building materials can off-gas volatile organic compounds (VOCs), which can contribute to indoor CO₂ levels. This effect is usually temporary but can be significant in a new or recently renovated home.
Is airtight construction to blame?
Airtight construction can lead to high CO₂ levels if not properly ventilated. While energy-efficient, these homes require mechanical ventilation to maintain healthy indoor air quality.
Can certain houseplants raise or lower CO₂?
Houseplants do produce CO₂ through respiration, but they also absorb CO₂ during photosynthesis. The net effect is usually minimal, but certain plants like snake plants and spider plants are known to be particularly effective at CO₂ absorption.
What about nearby garages, basements, or crawl spaces?
Attached garages, basements, and crawl spaces can be sources of CO₂, especially if they contain gas-powered equipment or have poor ventilation. Ensure these areas are properly ventilated and that any potential sources of CO₂ are addressed.
Resources and References
For more information on indoor air quality, check out these trusted resources:
EPA Indoor Air Quality
CDC Indoor Environmental Quality
ASHRAE Indoor Air Quality Guide
Remember, if you’ve tried these steps and still have concerns, don’t hesitate to reach out to indoor air quality specialists or HVAC professionals for expert guidance.
Take control of your indoor air quality today and enjoy the benefits of a fresh, healthy home.
