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<\/p>\nThe first smoke week we had, I did everything I was told.<\/p>\n
Windows down. Doors shut. Towel at the bottom of the front door, because someone on the internet said so.
\nThen I cooked dinner on the gas range, lit a candle because the house smelled like a campfire, and vacuumed the hallway.<\/p>\n
By nine at night I had a headache and I was blaming the smoke outside.<\/p>\n
I want to be honest about what I found when I actually went and read the evidence on indoor air quality: the part of the advice I had absorbed best was the part that was wrong, and the part I had ignored \u2014 source control inside the house \u2014 was the part that mattered most. Sealing up is the right call on a bad-air day. It just means the things your own house produces have nowhere to go.<\/p>\n
And one very widely repeated claim about what accumulates in there does not survive contact with the sources at all.<\/p>\n
<\/p>\n
This one circulates constantly, and I believed it for a while too.<\/p>\n
Radon is not a combustion product. It is not made by burning anything.<\/p>\n
Radon is a naturally occurring radioactive gas produced by the decay of uranium and radium in rock and soil.<\/strong> EPA puts it plainly: uranium “is essentially ubiquitous in the earth’s crust,” so radium-226 and radon-222 “are present in almost all rock and all soil and water.” WHO describes the same origin \u2014 decay of uranium “found in all rocks and soils” \u2014 and NCI adds a secondary contribution from some building materials and from well water.<\/p>\n So where does it come in? From below. WHO lists the entry points: cracks in floors, floor\u2013wall junctions, gaps around pipes or cables, pores in hollow-block walls, cavity walls, sumps and drains.<\/strong><\/p>\n No authoritative source \u2014 EPA, WHO or NCI \u2014 lists a stove, oven, furnace or any combustion appliance as a source of radon. Burning methane cannot create an element that comes from radioactive decay.<\/p>\n Here is the part of the original worry that is completely valid, though.<\/strong><\/p>\n A tightly sealed house can<\/em> end up with higher indoor radon. Not because it makes any, but because the soil gas that was already seeping in is now being diluted by much less outdoor air. EPA notes that how much radon reaches the house depends partly on “the suction within the house.”<\/p>\n So the concern was right. The mechanism was wrong. And the fix is different from what you would expect, because you cannot air your way out of a radon problem \u2014 that is a soil-gas issue solved by testing and mitigation, which I have put in its own section further down.<\/p>\n Not radon. A different and better-documented list: nitrogen dioxide, carbon monoxide, fine particles (PM2.5), formaldehyde and benzene.<\/strong><\/p>\n The benzene work is the one that changed how I think about my own kitchen. Kashtan and colleagues at Stanford measured 87 homes across California and Colorado (Environmental Science & Technology<\/em>, 2023) and found that gas and propane combustion “emitted detectable and repeatable levels of benzene that in some homes raised indoor benzene concentrations above well-established health benchmarks.”<\/p>\n The numbers:<\/p>\n Hours after. In a room where nobody cooked anything.<\/p>\n On nitrogen dioxide, the same group published in Science Advances<\/em> (2024) using measurements from more than 100 homes: gas and propane stoves increase long-term NO2 exposure by 4.0 parts per billion on average across the United States \u2014 75% of the WHO exposure guideline<\/strong>, from one appliance. Short-term NO2 during typical stove use “frequently exceeds both World Health Organization and U.S. Environmental Protection Agency benchmarks.” They estimate this exposure likely causes roughly 50,000 cases of current pediatric asthma<\/strong> from long-term NO2 alone.<\/p>\n Two findings from that paper deserve more attention than they get:<\/p>\n Carbon monoxide rides along too. EPA’s own figures: homes without gas stoves average 0.5 to 5 ppm<\/strong>; near a properly adjusted gas stove, levels “are often 5 to 15 ppm<\/strong>“; near a poorly adjusted one, 30 ppm or higher<\/strong>.<\/p>\n You have probably seen the headline: gas stoves cause about 13% of childhood asthma in the US. It deserves to be presented honestly, which means presenting the argument around it.<\/p>\n The estimate comes from Gruenwald and colleagues (IJERPH<\/em>, 2022): 12.7% (95% CI 6.3\u201319.3%)<\/strong> of current US childhood asthma attributable to gas stove use, from a meta-analytic odds ratio of 1.34 (1.12\u20131.57)<\/strong>, with 35%<\/strong> of US households cooking with gas. By state it ranges from Illinois at 21.1%<\/strong> down to Florida at 3.0%<\/strong>.<\/p>\n The criticism is substantive. Cox (Global Epidemiology<\/em>, 2023) argues the claim is “not supported by the data.” A 2024 paper by Li, Goodman and Long in the same journal asks “what was missed?” \u2014 and I have to disclose something there, because it matters when you weigh it: that paper’s record indicates American Gas Association funding.<\/strong> That does not make it wrong. It does mean it is not a neutral referee.<\/p>\n The real methodological objection is worth understanding, because it is not about gas stoves specifically. A population attributable fraction converts an observational association<\/strong> into a preventable fraction<\/strong>, which only holds if the association is causal, unconfounded and the exposure correctly specified. The original authors list their own limits too: aggregate rather than individual data, housing-survey data for only nine states, and an assumption that gas cooking is independent of other asthma risk factors. They also say ventilation “reduce[s], but not eliminate[s]” the risk.<\/p>\n For balance in the other direction: an independent Australian group (Knibbs et al., Med J Aust<\/em>, 2018) calculated the gas-stove PAF for Australian children at 12.3% (95% CI 8.9\u201315.8%)<\/strong> \u2014 a near-identical number, different country, different data.<\/p>\n Where I land, personally: treat 12.7% as a contested estimate, and treat the measured exposure<\/strong> work as the sturdier ground. Nobody is arguing about whether the benzene was in the bedroom. They measured it.<\/p>\n EPA’s first recommendation for both NO2 and CO is not a purifier and not a window. It is this: “Install and use an exhaust fan vented to outdoors over gas stoves.”<\/strong><\/p>\n Then there is what actually happens in kitchens. Zhao and colleagues monitored 54 single-family houses and 17 low-income apartments in California for a week each (IJERPH<\/em>, 2020):<\/p>\n Two practical things I had to fix in my own kitchen:<\/p>\n Check whether your hood actually vents outdoors.<\/strong> A recirculating hood \u2014 very common with over-the-range microwave units \u2014 pulls air through a charcoal filter and blows it back into the kitchen. It handles some grease and odor. It removes no<\/strong> NO2, no CO, no CO2. Go look for a duct that leaves the house; that is the only way to know which one you have.<\/p>\n Use it more, and earlier.<\/strong> Back burners capture better. Turn it on before you start and leave it running a few minutes after you finish. Run it for the oven too. And accept that it is imperfect even when used \u2014 one study measured a 26.4% drop<\/strong> in primary capture efficiency when cooking movement disturbed the airflow.<\/p>\n One caution on very powerful hoods.<\/strong> A high-capacity hood pulls a large volume of air out of a house, and in a tight home that air gets replaced through whatever leaks exist \u2014 potentially including the flue of a natural-draft furnace or water heater. EPA lists backdrafting from “furnaces, gas water heaters, wood stoves and fireplaces” as a carbon monoxide source. Depressurization can also pull more soil gas in. If you have a large hood in a tight house, have a licensed HVAC contractor assess whether you need dedicated makeup air.<\/p>\n<\/blockquote>\n This surprised me, and I had to rewrite my own mental model.<\/p>\n The headache and heavy-headedness in a closed-up room is well documented. But the best controlled evidence says the culprit is not the carbon dioxide molecule.<\/p>\n Zhang and colleagues (Indoor Air<\/em>, 2017) ran 255-minute blinded exposures on 25 subjects. Adding chemically pure CO2<\/strong> to clean air produced no<\/strong> significant effect on perceived air quality, acute symptoms or cognition. But exposure to bioeffluents<\/strong> \u2014 what human bodies off-gas \u2014 with CO2 at 3,000 ppm reduced perceived air quality and “increased the intensity of reported headache, fatigue, sleepiness, and difficulty in thinking clearly.<\/strong>“<\/p>\n Same CO2 number. Completely different result depending on what else was in the air.<\/p>\n And the famous CO2-and-cognition findings have not held up:<\/p>\n NIST’s Persily (Indoor Air<\/em>, 2022) is blunt about the number everyone quotes: a single concentration such as 1,000 ppm “is often used as a metric of IAQ and ventilation without an understanding of the significance” of that value, and he concludes “CO2 concentrations are of limited value as IAQ metrics.”<\/strong><\/p>\n So what do you do with a CO2 monitor? Read it as a ventilation proxy<\/strong>, not a toxicity meter. A rising number means air is not being exchanged \u2014 and unexchanged air carries the bioeffluents and VOCs that actually do the damage. EPA notes indoor levels of several organics average 2 to 5 times higher indoors than outdoors<\/strong>, and lists headaches, nausea, loss of coordination, fatigue and dizziness among VOC effects.<\/p>\n No US agency sets a binding residential indoor CO2 limit, and I am not going to give you a “safe ppm.” That is not how this works.<\/p>\n Here is the tension nobody resolves cleanly. Official US smoke guidance says keep the house closed. Common sense says stale air needs flushing. Both are right, at different times.<\/p>\n Let me deal with the specific instruction first, because it is everywhere: open two opposing windows about two inches, cross-ventilate for five minutes, once or twice a day.<\/strong><\/p>\n I went looking for the source. There isn’t one.<\/p>\n No EPA, CDC, WHO, AirNow or ASHRAE document I could find specifies a two-inch gap, a five-minute duration, or a once-or-twice-daily frequency. Those numbers appear to be folk guidance. The structure<\/em> of the advice is sound \u2014 brief, purposeful cross-ventilation moves more air per minute of exposure than one window cracked all day, and filtration afterward is the right order. But please do not treat the numbers as agency recommendations, because they are not.<\/p>\n What official guidance actually says is: time it by the air, not by the clock.<\/strong><\/p>\n EPA’s hinge sentence, from its wildfire guidance, is the permission slip: when conditions improve temporarily, “air out your home by opening windows or the fresh air intake on your HVAC system.” And from its ventilation guidance: “Avoid ventilation with outdoor air when outdoor air pollution or humidity are high.” Check AirNow first. AirNow itself notes that “smoke levels can change a lot during the day.”<\/p>\n This table is a practical framework, not an official cutoff.<\/strong> It is built from AirNow’s own category language plus EPA’s “air out when conditions improve” instruction. No source I could find publishes a crossover AQI number where “ventilate” flips to “don’t.” AirNow does note that an AQI of 100 “generally corresponds to the national ambient air quality standard.”<\/p>\n And the thing that decides a smoke day is not the window at all.<\/p>\n It’s source control.<\/strong> AirNow’s list of what to avoid indoors is exactly that: “frying foods, sweeping, vacuuming, and using gas, propane, or wood-burning stoves and furnaces.” Add candles and smoking. Not cooking on the gas range on a red-AQI day removes far more of your indoor load than a five-minute window ever adds.<\/p>\n![\"An](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-2.jpg\")
\nPhoto: Curtis Adams \/ Pexels<\/em><\/p>\n![\"Cutaway](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-3.png\")
<\/p>\n
\nWhat a gas stove actually emits<\/h2>\n
![\"Eggs](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-4.jpg\")
\nPhoto: Sarah Chai \/ Pexels<\/em><\/p>\n\n
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![\"Bar](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-5.png\")
<\/p>\nThe 12.7% asthma figure, and the fight over it<\/h3>\n
\nThe range hood is the first-line fix \u2014 and almost nobody uses it<\/h2>\n
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\nPhoto: Curtis Adams \/ Pexels<\/em><\/p>\n\n
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![\"Side-by-side](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-7.png\")
<\/p>\n
\nThe stuffy-room headache is real. CO2 is probably not the reason.<\/h2>\n
![\"A](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-8.jpg\")
\nPhoto: Tim Witzdam \/ Pexels<\/em><\/p>\n![\"Two-panel](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-9.png\")
<\/p>\n\n
\nSo do you open the windows, or not?<\/h2>\n
![\"Two](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-10.jpg\")
\nPhoto: Tito Zzzz \/ Pexels<\/em><\/p>\nA practical framework by AQI band<\/h3>\n
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\n \nAQI (PM2.5)<\/th>\n Category<\/th>\n What AirNow says<\/th>\n The window call<\/th>\n<\/tr>\n<\/thead>\n \n 0\u201350<\/td>\n Good<\/td>\n “Air quality is satisfactory, and air pollution poses little or no risk.”<\/td>\n Open up.<\/strong> This is your airing window \u2014 flush CO2, VOCs and cooking residue.<\/td>\n<\/tr>\n \n 51\u2013100<\/td>\n Moderate<\/td>\n “Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.”<\/td>\n Open up, briefly.<\/strong> For most households indoor accumulation is the bigger problem. Sensitive people keep it shorter.<\/td>\n<\/tr>\n \n 101\u2013150<\/td>\n Unhealthy for Sensitive Groups<\/td>\n “Members of sensitive groups may experience health effects. The general public is less likely to be affected.”<\/td>\n Judgment call.<\/strong> Short and purposeful if the house is stuffy or you have been cooking. Skip it if anyone at home has asthma, COPD or heart disease, is pregnant, a young child or an older adult.<\/td>\n<\/tr>\n \n 151\u2013200<\/td>\n Unhealthy<\/td>\n “Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.”<\/td>\n Keep closed, filter.<\/strong> Watch the curve \u2014 smoke often drops overnight or mid-morning. Take your airing then.<\/td>\n<\/tr>\n \n 201\u2013300<\/td>\n Very Unhealthy<\/td>\n “Health alert: The risk of health effects is increased for everyone.”<\/td>\n Closed.<\/strong> Recirculate, MERV-13, filtration, clean room. Do not open.<\/td>\n<\/tr>\n \n 301+<\/td>\n Hazardous<\/td>\n “Health warning of emergency conditions: everyone is more likely to be affected.”<\/td>\n Closed.<\/strong> Consider relocating if you cannot keep the house cool or filtered.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n ![\"AQI](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-11.png\")
<\/p>\nThe rest of the smoke-day setup<\/h3>\n
![\"A](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-12.jpg\")
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<\/p>\n![\"A](\"https:\/\/wewellinfo.com\/us\/wp-content\/uploads\/2026\/09\/body-14.jpg\")