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How to Improve Indoor Air Quality in Single-Family Homes

Priority areas to address and budget-friendly actions to take for healthier indoor air

The Corentium Continuous Radon Monitor provides an average reading over several months for a more accurate picture of radon levels. Image credit: courtesy of manufacturer.

COVID19 has put a spotlight on indoor air quality (IAQ), and homeowners are looking for ways to improve the health of their interior environments. I recommend the following as an actionable, cost-effective plan for improving IAQ in single-family homes.

Part 1: Evaluate the existing conditions


A home is a system of systems, meaning everything is connected. The goal is to reduce the potential for harmful feedback loops, such as tightening the building enclosure without upgrading the ventilation system.


People are a part of the system of systems. People are the main source of carbon dioxide (CO2) in a building. If CO2 is high, it means other pollutants along with infectious viruses and bacteria are also building up. This can occur where people gather and can be exacerbated by tight buildings without good ventilation.

Outdoor and indoor air

Outdoor air pollutants can concentrate inside. This can happen if your home is tight or leaky. Outdoor air quality is defined and measured by the Environmental Protection Agency (EPA) but indoor air, where we spend 90% of our time, is not. It’s up to you to identify the sources of indoor-generated pollutants.

Radon levels

Radon is the second leading cause of lung cancer. It is a radioactive soil gas and, depending on the radon zone you are in, can be present inside your home. There is no way to know without measuring.

Fuel source/s

Open-combustion appliances or equipment that uses fossil gases or solid fuel include cook stoves, water heaters, and furnaces with “open vents,” ventless fireplaces and wood stoves. All can release a wide range of indoor air pollutants. If carbon monoxide (CO) is present, it is likely several other pollutants are also present. Use CO as a proxy for combustion appliance–related bad air. Such equipment also emits surprisingly large amounts of particulate matter.

Shared boundaries 

Unconditioned attached garages, basements/crawlspaces, and attics often communicate with conditioned spaces. When there are unsealed openings between these areas, polluted air can make its way into the living spaces. Think: dust, mold or other biologicals, water vapor, and exhaust fumes.

Sources of chemicals

Disinfectants, cleaning agents, cosmetics, lotions, paints/stains, and like products, as well as new furnishings and items that off-gas when new can combine to form other dangerous chemicals that pollute the air. Many such chemicals can also interact with chemicals on our skin.

Part 2: Set priorities and take action

Here is a list of 11 priority areas with advice on addressing them and the associated costs:

Priority 1: Know outdoor air quality to control indoor air quality

  • Action: Check daily. Understand that bad outdoor air is a source of bad indoor air, so close and ventilate the house accordingly.
  • Budget: $0

Priority 2: Use open-combustion appliances wisely (and infrequently, if possible)

  • Action: Service these appliances and equipment regularly.
  • Budget: Varies, depending on your home. Sometimes fire stations or local gas companies will service equipment for free.

Priority 3: Control radon

  • Action: Determine your radon zone using the EPA’s map. Get a continuous radon monitor that provides an average reading over several months extending over a summer and a winter. If long-term levels are more than 2 pC/l, call a radon mitigation company to install an active radon mitigation system. Keep the monitor running to verify that the mitigation system is working. (High radon solutions may involve some building enclosure upgrades like sealing a crawlspace or basement that can only be ascertained by a building scientist.)
  • Budget: Corentium Continuous Radon Monitor: $180

Priority 4: Monitor CO

  • Action: Get a carbon monoxide monitor that provides the actual levels of CO so you can do something about it before things get dangerous. If levels begin to rise (even as low as 5 to 10 ppm), turn off the culprit appliance and open a window.
  • Budget: $25 for a basic CO monitor

Priority 5: Exhaust cooking gases

  • Action: Use your stove exhaust vent while cooking and for several minutes afterward. If your stove exhaust does not vent to the exterior, then open a window while you are using gas stoves or fireplaces. (I was shocked to learn that cooking generates more particulate matter than the worst outdoor air levels do).
  • Budget: $0

Priority 6: Exhaust water vapor

  • Action: Humidity levels of 60% or more encourage mites, mildew, and mold. Use your bathroom exhaust vent while bathing or showering for at least 10 minutes. Like the stove exhaust advice, if you don’t have an exhaust fan, then open a window to release water vapor to the exterior.
  • Budget: $0

Priority 7: Monitor CO2

  • Action: Get a carbon dioxide monitor. The best ones are easy to set up and read. If CO2 readings go above 800 ppm, do the following: Turn on air filtration or, if it is pleasant outside, open windows and doors on opposite sides of the house for cross-ventilation. If you have an energy recovery ventilator (ERV), turn it on. If CO2 levels are above 1200 and the above recommendations are not possible or not working, consider leaving the room or building. Return when levels go below 600 ppm.
  • Budget: Aranet 4 CO2 monitor: $250

Priority 8: Reduce air leakage

  • Action: To the extent possible, seal openings/penetrations between conditioned and unconditioned spaces to prevent the mixing of air streams. This may require professional assessment via an energy audit.
  • Budget: Dependent on air-sealing method/s and product/s

Priority 9: Minimize exposure to chemicals

  • Action: Reduce the use of oxidizing cleansers like bleach, and reliance on chemicals in general. Less is more. Store any paints or strong chemicals outside of the home in an area that is well separated from indoor air. Responsibly dispose of any chemicals that are no longer useful.
  • Budget: $0

Priority 10: Filter indoor air

  • Action: Here is an excellent DIY filter fan that anyone can make. It’s as good as or better than most of the air purifiers on the market.
  • Budget: $0 to $120

Priority 11: Get an energy audit

  • Action: You’ve done a lot already, but you may still have questions or problems that require professional help. This is where a certified energy audit, completed by a professional building scientist, comes in. Look for Building Performance Institute (BPI)–certified professionals—ideally with several years of experience.
  • Budget: $500 to $1000 for a comprehensive energy audit. (Beware of “free” energy audits performed by companies that sell things like photovoltaic systems or HVAC equipment.)

I consider these areas to be the low-hanging fruit when it comes to improving IAQ. In general, they are listed in order of what to consider and act on first, second, third, etc. to ensure an orderly and consistent approach. It approximates the order I would use as a building scientist when doing an energy audit, but at a client-friendly “DIY-but-do-no-harm” level. For an energy or home performance audit, I would do a deeper dive and get more into the math and physics; I would also use blower-door, infrared, and various other testing equipment. My hope here is to demonstrate that you don’t necessarily need to invest in an entirely new HVAC system to better your indoor environment.


Monica Rokicki is a BPI Analyst, Healthy Home Evaluator, and founder/CEO of Better Building Works LLC in Roanoke, Virginia.


  1. nickdefabrizio | | #1

    Thanks for this informative article...

    One underestimated risk in the home is the mixing of otherwise mild chemicals ( directly, as residual surface films or in the air) in a manner which creates dangerous or noxious compounds. Most folks know that mixing bleach with ammonia is dangerous, but there are many products that contain traces of bleach or ammonia (or close derivatives) that are not well labeled, increasing the risk of an accidental mixing. Also, there are many other chemical combinations that we know very little about because they typically occur in the open environment where controlled testing is difficult. In addition, people can develop sensitivities to common household chemicals making them far more sensitive to adverse reactions. I was someone who was skeptical of chemical sensitivity until I was exposed to an inadvertent mix of several mold cleaners. Years later I still get a mild allergic reaction when I go into the basement room where this occurred.

    Overall, I think in general the fewer chemicals we use as cleaning agents, pesticides or as feedstock for plastics, paint and other manmade materials, the better.

    1. Monica_Rokicki | | #3

      Thanks, Nick. Yes you are 100% correct about that. Most of us don't realize the oxidizing power of things like bleach and ozone-generators. These interact (and accelerate interactions) with other chemicals like those found in Lysol, terpenes, foam cushions in furniture, etc. Some interactions can also create mystery odors that can persist for months. Fewer chemicals is always better. Proper ventilation of spaces is also critical to make sure they don't concentrate and keep mixing.

      1. nickdefabrizio | | #7

        Yes. Many of these substances are very common. In my case I think that it was a combination of Phenol (in Sporicidin mold cleaner) and bleach. Phenol is a very common chemical used in cleaners and also in many types of plastics (e.g., autos).

        1. Monica_Rokicki | | #21

          Oh yes - we had a similar issue with a client who hired someone to do "mold remediation". The combination of the disinfectant / mold cleaner and overkill with ozone generators wreaked havoc in their home. It took us a while to figure out. Secondary and tertiary reactions ended up creating chemicals that were very unusual and not easy to explain for a residence. TLDR: just don't ever ever use ozone generators and use bleach or other oxidizers sparingly, if at all.

      2. PBP1 | | #10

        As to ozone, there's a recent article on the impact of ozone on human chemical emissions, the presence of ozone causes reactions, whether on skin or exhaled chemicals. Emission Rates of Volatile Organic Compounds from Humans (

        Humans emit many things, indications of diabetes can be detected by smell of ketones (diabetic ketoacidosis), a smell similar to nail polish remover (acetone) or overly ripe fruit.

  2. Deleted | | #2


  3. Expert Member
    ARMANDO COBO | | #4

    Good advice in this article. You could add to Part 1 smoke habits (cigarette, pipe, and cannabis) and room deodorizers with chemicals we can’t pronounce, pot pourris, candles, but the biggest of all in terms of allergens at home is pet dander. Avoid carpets if possible.
    You could add to Part 2 to seal, seal and seal the building envelope and include a good moisture management.
    Hire a true HVAC Professional to design, install and commission a good system, with an ERV and dehumidifier if needed.
    Some cultural cooking also require additional MUA equipment in the kitchens. I’ve done it many times and it’s always appreciated.

    1. Monica_Rokicki | | #5

      You are right, Armando! Doing things in the right order is critical and a systems approach that takes into account building enclosure, HVAC systems, appliances, and occupant habits is the only way to avoid negative feedback loops. I'm always surprised by what I learn with this data-driven approach and how many of my own assumptions get busted when applying 'general' rules to 'specific' instances.

    2. Expert Member
      MALCOLM TAYLOR | | #6


      Just say the word and I will send you my cat - and pay the shipping.

  4. vpc2 | | #8

    Lots of good information, not discussed nearly enough. Thanks.
    I would add:
    Central Vacuum: venting to outside. Great effect on removing lots of nasty stuff.
    PFOS/PFOA in carpet, furniture,... Dangerous in PPTs.
    Flame Retardants in padding in furniture and bedding.
    Insect prevention treatments inside and around foundations.
    Keeping the house closed all year with heat and AC and no open windows.
    Floor mats at exterior entries.
    Unfortunately, lots of chemicals are in/on home products and no warnings are given.
    Deregulation, ain't it wonderful.

  5. PBP1 | | #9

    Thanks for the thoughtful post.

    Dr. Poppendieck at NIST posts regularly to Twitter as to IAQ, including a post as to "Development and Application of an Indoor Carbon Dioxide Metric" (

    I believe the recommendation as to "If CO2 levels are above 1200 and the above recommendations are not possible or not working, consider leaving the room or building. Return when levels go below 600 ppm" may not be supported by science.

    Not that I can vouch for OSHA, but it has 8 hour standards of less than 5000 ppm. People work in elevated CO2 environments day in and day out (especially where "dry ice" is involved). OSHA also states: "CO2 levels in outdoor air typically range from 300 to 400 ppm (0.03% to 0.04%) but can be as high as 600-900 ppm in metropolitan areas." And: "10,000 ppm (1.0%) Typically no effects, possible drowsiness".

    If outdoor, street level is 600-900 ppm, then you need an indoor CO2 sink (sequestration) to maintain 600 ppm.

    A relatively recent review article reaches no health concerning conclusions for 1000 ppm or even 1500 ppm. As reducing indoor CO2 means expending energy (particularly in hot/cold conditions), the green building movement needs to strike a science-informed balance. I believe 1500 ppm is acceptable for periods of time, perhaps a peak/max level for a day (24 hour period). The more energy spent on airing out indoor environments to reach a target of 600 ppm, the more CO2 into the environment (whether through mfg of equipment, energy spent running the equipment, transfer of CO2 into the environment, etc.).

    A target of 600 ppm CO2 may very well be anti-green and without provable health benefits. That said, other measures of IAQ (other than CO2) can be concerning. CO2 can give a hint as to what other things may be collecting indoors.

    From Dr. Poppendieck: "Healthy" is hard to define. But it would be interesting if we just set ventilation standards based on re-breathing fraction (say 1% or 1.5%). That would be the first health-link ventilation standard.

  6. Expert Member
    MALCOLM TAYLOR | | #11


    The 600ppm may be too low, but OSHA's claim that "CO2 levels in outdoor air typically range from 300 to 400 ppm (0.03% to 0.04%) but can be as high as 600-900 ppm in metropolitan areas." And: "10,000 ppm (1.0%) Typically no effects, possible drowsiness" misses that drowsiness may be another way of describing lowered cognitive functioning.

    1. PBP1 | | #12

      Thanks Malcolm, I've been looking around and at details of various studies, including Satish et al. and Allen et al. Here's another study that cites Satish et al. and Allen et al.: "Human Responses to Carbon Dioxide, a Follow-up Study at Recommended Exposure Limits in Non-industrial Environments" (

      "Other results indicate additionally that a 2.5-hour exposure to CO2 up to 5,000 ppm did not increase intensity of health symptoms reported by healthy young individuals and their performance of simple or moderately difficult cognitive tests and some tasks resembling office work. These results accord well with the current occupational exposure limit recommendation for CO2 and with many other reports published in the literature."

      What I see is a lack of agreement as to study techniques and metrics, along with small sample size studies, such as 10 people, 24 people, or 30 people. These pale in comparison to the gold standard, such as the Framingham Heart Study (began in 1948 with 5,209 adult subjects from Framingham, and is now on its third generation of participants). The small, unharmonized studies on CO2 are hard to compare. Let's hope this important issue gets addressed sometime soon.

      Prepandemic, I was a fan of "hot" yoga, typically in relatively small rooms packed with people dripping sweat for 1.5 hours. I wish I had brought in my CO2 meter and perhaps a VOC meter. I speculate that levels reached 5000 ppm or more. Maybe the "good" feeling after "hot" yoga comes from getting out of the room to greatly reduced CO2 levels? I also competed in ergometer competitions, where ergs were closely spaced and everyone breathing really (really) hard. We have the "bad" scenarios at hand, if we can just instrument them to get the data.

      1. Monica_Rokicki | | #15

        Thank you for the science-based approach - yes, I think this deserves a lot more research. Since outdoor levels are in the low 400's these days, I'm curious about any area less than that. My recommendation for the CO2 level is not just informed by articles like the one you mentioned, but also as a proxy (imperfect as it is) for other chemicals in the air and as a way to estimate 'rebreathed fraction of air' for the purposes of infection control - very big topic that I learned about from Dr. Richard Corsi (@CorsIAQ on Twitter). That one deserves another post, ideally by Dr. Corsi! In any case, keeping things as low as possible is a good approach, and learning trends through frequent use of monitors helps a lot.

        Another thing concern is that the OSHA levels are typically for 8 hour work periods for able, usually male adults who are sitting or standing. These levels are not necessarily the right ones for people indoors for longer, sustained periods, for children, infirm or older adults, etc. These levels may also be influenced by industry lobby groups whose metric is productivity rather than overall well-being.

        There was a Harvard article not too long ago that spoke of the affect on cognitive performance beginning at lower than assumed levels. This study, again, measures for able adults.

        In any case, I too - like you - have forgone yoga in enclosed spaces (and have measured with disturbing results that reinforce that decision).

        1. PBP1 | | #19

          Thanks Monica, the Harvard study is Allen et al., which is cited and brought into question by Zhang et al. Satish et al. and Allen et al. are often cited for lower levels, however, the findings do not fully square with other studies and sample sizes are small. I've done consumer research, including in-lab and in-home studies for P&G, I've seen what people do and say, things like the "halo" effect. We need more and better research, your post helps to highlight that point.

          Also, Allen et al. is often misinterpreted, there was no significant difference between 700 ppm and 1500 ppm for the 30 pilots on the 21 maneuvers. Though there was a greater probability of passing some of the more difficult maneuvers at 700 ppm than 1500 ppm - but again, no significant difference between 700 ppm and 1500 ppm. Look at Fig. 2 in Allen et al., for level of difficulty "A", the data show that the pilots passed "better" at 1500 ppm than at 700 ppm.

          Further, right from Allen et al.: "the difference between the medium and low CO2 conditions was not significant" and "In multivariate models controlling for maneuver order, we did not see any statistically significant impacts on flight performance as measured by the simulator data at either 700 ppm or 1500 ppm, relative to 2500 ppm".

          My training in biology, knowledge of how humans breath (I use PowerBreathe), the levels of CO2 in human breath, how humans have lived, divers, mask wearing surgeons, etc., (and even Allen et al.) lead me to speculate that 1500 ppm CO2 is not a health issue. A goal of 600 ppm indoors will be costly and likely inequitable. We need research.

          1. Monica_Rokicki | | #20

            Thanks for this information! It's a work in progress, for sure. Scientists like you are so important. The increased visibility of this fascinating field of study brings healthier indoor environments into better focus.

          2. JC72 | | #22

            This is a great example of why certain studies will be highlighted in order to pursue an unrelated policy goal. Scaremongering over CO2 levels in order to encourage the banning of NatGas for residential use.

      2. Expert Member
        MALCOLM TAYLOR | | #17


        If you are ever up this way, our community hall offers an alternative to indoor yoga that features great quality outdoor air - and some friends thrown in for entertainment:

        1. PBP1 | | #18

          Thank you Malcolm, I'll check out the website.

  7. BirchwoodBill | | #13

    Great post, it helps to illustrate how poor todays residential HVAC / IEQ systems are put together. One system to monitor and other systems to actually control. Need to start thinking of whole house environmental control and using predictive or adaptive machine learning software. The home PLC should be able to turn on a radon fan when a sensor goes high, or modulate the fan for an ERV when CO2 goes over a threshold. After a while the system should learn that the machine (house) performs in a cyclic fashion and start adjusting air flow, heat pump based on predictive behavior.

    1. Monica_Rokicki | | #16

      Thanks, William. Absolutely we need integrated monitor and control systems that are simple, easy to understand, that can learn, and that can be easily maintained / replaced. There is so much potential for the many systems and appliances in our homes to be integrated with efficiency and indoor air quality gains!

  8. Expert Member
    ARMANDO COBO | | #14

    Actually, there are a few folks that have develop products and tools to monitor and manage IEQ through the emergence of big data technologies and Internet of Things (IoT) solutions. Sensor integration, wireless information and cloud services are combined to help deliver IEQ information to the residents, and I think sky is the limit in this new technology.
    What is also cool is that some of these devises have learning capabilities, which can inform homeowners when and where IEQ performances are deficient.
    EEBA recently has done a good job in their webinar series to showcase a couple of them. To see those webinars go to:
    Sendal, is an IoT software program that helps control the whole house systems, designed for new homes.
    Panasonic and Swidget have joined forces to monitor, asses and optimize IEQ in homes, new and existing.
    Broan/NuTone has developed Overture to integrate IAQ with the HVAC system with three modules. Their sensors monitor pollutants that contribute to poor IAQ.

  9. trigonman3 | | #23

    The EPA's radon zone map lists zones 1 to 3, but doesn't actually say what those zones mean. A google search gave me this info:

    (darkest) Highest Risk – Zone 1: Counties with predicted average indoor radon screening levels greater than 4 pCi/L

    (medium) Medium Risk – Zone 2: Counties with predicted average indoor radon screening levels from 2 to 4 pCi/L

    (lightest) Little Risk – Zone 3: Counties with predicted average indoor radon screening levels less than 2 pCi/L

    1. Monica_Rokicki | | #24

      Yes, Scott ALKB - it can be tricky to understand. Radon is generally the radioactive byproduct of old rocks (think mountains). In most building codes, it is required to at least do what is called a 'passive' radon mitigation system for new homes in Radon Zone 1. Older homes are just left on their own. And don't just assume because a neighbor - or a short term reading - was low that you're good to go. We've observed, for example, levels of 35 and even 50 pCi/l in the SW VA region, while nearby readings were below 2. Only continuous readings are accurate because, as a soil gas, levels can rise inside a home as a result of stack effect forces and other conditions.

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