Is a gas stove dangerous for CO?

A well-tuned gas stove on simmer produces about 150 mg/min CO — similar to a candle. With kitchen ACH 0.5-1.0 + room volume 40-60 m³, steady-state CO stays under 10 ppm (below EPA NAAQS 9 ppm annual limit). Turn on an externally-vented range hood + ACH jumps to 15+, dropping CO under 2 ppm. POORLY-TUNED gas stove (yellow flame, not blue) produces 5-10x more CO (800+ mg/min) + can exceed 35 ppm within 30 minutes without venting. Rule: blue flame = good combustion; yellow/orange = service call. Critical distinction: RECIRCULATING hoods filter grease + odor but do NOT remove CO. EXTERNALLY-VENTED (ducted to outdoors) are the CO-protective ones. Many apartment kitchens have recirculating hoods; they provide zero CO benefit.

Why is running a portable generator in my garage so dangerous?

Portable generator emits ~400,000 mg/min CO — 2500x a gas stove. In a 60 m³ attached garage with ACH 0.5, steady-state CO exceeds 1000 ppm within 10 minutes — lethal range (death within 1 hour at 1600 ppm; unconsciousness within 2 hours at 800 ppm). Even with garage door open, CO reaches dangerous levels because ambient ACH is still 2-5 + generator emission overwhelms it. Reverse-infiltration to home above via shared walls, ducts, door gaps is also common + can kill sleeping occupants. CDC data: 70+ generator-related CO deaths per year in US, dominant cause of storm-season CO fatalities. NEVER run portable generator indoors, in garage even with door open, or within 20 ft of any window. Move it 20+ ft from structure with exhaust pointed AWAY. Tool flags generator + non-outdoor-location as CRITICAL lethal-within-minutes.

What is "cracked heat exchanger" and why is it an emergency?

Gas furnace heat exchanger is the metal barrier separating combustion gas (CO + CO2 + NO2 + water vapor) from your home circulation air. Metal fatigues over 15-20 years; cracks develop. Once cracked, combustion gas mixes with circulation air + every supply vent in your house emits CO. Tool models this as 3000 mg/min emission distributed throughout the house via HVAC ductwork — much larger effective room volume but also much larger ACH equivalent (forced-air circulation). Net effect: low-moderate CO levels throughout house, continuously, during heating season. Detection: annual HVAC inspection (flashlight test for visible cracks); family members experience chronic headaches peaking during winter heating season; CO detector chirping intermittently during furnace cycles. Emergency response: shut off furnace at circuit breaker immediately, open windows, call HVAC technician SAME-DAY, do NOT run until repaired or furnace replaced.

How often should I replace my CO detector?

Every 7-10 years regardless of battery. UL 2034 certification requires CO sensor lifespan of 7-10 years; after that, sensor degrades + may fail to activate even at dangerous levels. Battery vs sensor: battery-powered models chirp at low battery but the SENSOR itself has separate lifespan. "Replace unit" means buy a new UL 2034 alarm + swap in; do not just change the battery on a 10-year-old unit. Check manufacturer date printed on back — typical unit life 7 years from manufacture, some models 10. Hardwired units with 10-year sealed battery are set-and-forget for a decade. Test MONTHLY via test button; some states require it. CO detector unit costs US $20-40; split-incident cost calculus of $3-5/year is trivial.

Where exactly should I place CO detectors?

Per NFPA 720 Standard for Installation of Carbon Monoxide Detection: (1) EVERY LEVEL of home including basement + finished attic. Single-floor coverage misses CO accumulation on other floors. (2) WITHIN 10 FT OF EACH BEDROOM DOOR — critical for nighttime detection when occupants cannot consciously notice symptoms. (3) 15+ FT FROM COOKING APPLIANCES to reduce false alarms from brief cooking CO spikes (harmless 50-100 ppm during stove use). (4) NOT NEAR BATHROOMS — humidity damages sensor + causes false alarms. (5) PLACEMENT HEIGHT FLEXIBLE — CO density (28 g/mol) is nearly identical to air (29 g/mol), so both knee-height + ceiling work. Most alarms are wall-mounted 5 ft off floor or ceiling-mounted like smoke alarms. For homes with attached garage: put a unit in the garage too (some UL models are rated for garage temperature extremes).

I have headaches that improve when I leave the house — is that CO poisoning?

Potentially yes — headache + nausea + dizziness + confusion that improve when away from home are classic chronic-low-level CO exposure symptoms. Other signs: family members (including pets) also having symptoms, symptoms peaking during heating season, symptoms worsening after cooking with gas. Immediate action: leave the house + get fresh air + call 911 if symptoms are severe (confusion, chest pain, rapid heartbeat). Medical evaluation: ER can measure blood COHb level — over 2% in non-smokers is elevated, over 10% is significant exposure, over 25% is severe. Even if you leave + feel better, get inspected before returning — residual source is still there. Call fire department for CO inspection of home (they have portable meters); after clearance + before re-entry, install UL 2034 CO alarms if not already present. Never dismiss recurring headache-that-improves-outside as flu or stress; CO poisoning is the unlikely but high-consequence explanation worth ruling out.

Carbon Monoxide Room-Risk Calculator — CO ppm by combustion source + ventilation + room volume, with NFPA 720 detector placement

Name: Carbon Monoxide Room-Risk Calculator
Author: Kenny Tan

Carbon monoxide is the silent-killer class of indoor-air risk — colorless, odorless, and binds irreversibly to hemoglobin faster than your body can process. CDC records 400+ accidental CO deaths per year in the US, concentrated in predictable scenarios: generators run in garages during storms, cars idled in attached garages in winter, unvented combustion heaters in bedrooms, cracked furnace heat exchangers leaking combustion gas into circulation air. This calculator runs the mass-balance physics on YOUR configuration — 12 source categories with literature-validated emission rates, your room volume + ventilation + enclosure, EPA + OSHA + UL 2034 + ACGIH + CPSC threshold tiers, NFPA 720 detector placement guidance. Tool does not replace a CO detector; it sizes the risk so you know why detectors exist + where to place them.

Free Private Calculator

What this CO risk calculator delivers

12 combustion source presets with validated emission rates — gas stove tuned (~150 mg/min), gas stove poor (~800), gas water heater (~100), gas furnace healthy (~80) vs cracked-exchanger (~3000), wood stove EPA-certified (~500) vs leaking (~4000), unvented kerosene (~1500), indoor charcoal grill (~30K), portable generator (~400K), car idle (~15K), baseline. Sources: CPSC + EPA + Traynor/Apte LBNL-37414 + Jetter/Ebersviller EPA generator testing.
Mass-balance steady-state + transient math — CO_ss (mg/m³) = emission / (ACH × volume). Transient CO(t) = CO_ss × (1 - exp(-ACH × t)). Conversion 1 ppm CO ≈ 1.15 mg/m³ at 25°C 1 atm (ICAO). Both final concentration + time-to-threshold reported.
EPA + OSHA + UL 2034 + ACGIH + CPSC threshold tiers — 9 ppm (EPA NAAQS 8h limit), 35 ppm (OSHA PEL 8h + UL alarm 4-15h), 70 ppm (UL alarm 1-4h), 150 ppm (ACGIH ceiling; mild symptoms), 400 ppm (life-threatening within 1-2h), 800 ppm (unconsciousness within 2h + death 2-3h), 1600 ppm (death within 1h), 6400 ppm (death within 10-15 min).
Venting multiplier model — partial venting (open window) adds ~2 ACH; range hood at externally-vented 200-400 CFM adds ~12 ACH to typical kitchen; dedicated flue/chimney adds ~5 ACH for flue-vented equipment. Effective ACH = base + vent; appears in steady-state denominator.
NFPA 720 detector placement guidance — every level including basement; within 10 ft of each bedroom door; 15+ ft from cooking appliances; not near bathrooms; knee-height-or-ceiling both work; replace entire unit every 7-10 years per UL 2034 sensor lifespan.
8 warning classes covering common fatal-incident patterns — generator-in-enclosed-space (CDC 70+ deaths/year), indoor charcoal grill, car-idle attached-garage, cracked-heat-exchanger emergency, wood-stove-backdraft in tight houses, no-detector with combustion-source present, low-ACH amplifying every source, unvented kerosene state-regulation concerns.
3 demo scenarios — gas stove 30 min in kitchen hood-off, wood stove leaking in basement with low ACH cold winter, portable generator in attached garage (CRITICAL + lethal scenario). Shows how tier shifts across real incident patterns.
URL-state shareable — all inputs are parameters. Share URL with HVAC tech or public-safety partner for risk discussion.

Emission rates from Traynor G.W. + Apte M.G. + Chang G.M. (1996) "Pollutant Emission Factors from Residential Natural Gas Appliances" LBNL-37414 + Jetter J.J. + Ebersviller S. (2006) EPA residential generator emission testing + Lakewood Air Quality residential combustion source characterization. Health thresholds from EPA NAAQS 40 CFR 50, OSHA PEL 29 CFR 1910.1000 Table Z-1, ACGIH TLV Committee 2024, CPSC Publication 466, UL 2034 Standard for Single and Multiple Station Carbon Monoxide Alarms, NFPA 720 Standard for the Installation of Carbon Monoxide Detection and Warning Equipment. Mass-balance model is well-mixed-room approximation; real indoor air has stratification + incomplete mixing + transient gusts. Tool is a planning aid; CO detector is the primary safety device — install one on every level + test monthly.

Combustion sources (gas stove, wood stove, generator, idling car) emit carbon monoxide that accumulates in enclosed rooms at a rate set by emission source + room volume + ventilation. This calculator runs the mass-balance math using EPA + OSHA + UL thresholds to compute steady-state CO ppm, time-to-symptom-threshold, CO detector placement per NFPA 720, and 6 warning classes covering the common fatal-incident scenarios.

Privacy: inputs are combustion + room parameters — no personal data. Safe to persist + share via URL. Client-side only.

Combustion source 8 combustion source categories with literature-validated emission rates. Location / enclosure Affects default ACH + baseline risk framing. Room volume (m³) L × W × H. 3×4×2.5m bedroom = 30 m³; 5×8×2.5m open kitchen+living = 100 m³; 2-car garage ~60 m³. Ventilation (ACH) Air changes per hour. Modern tight house: 0.1-0.3. Older leaky house: 0.5-1.5. Window crack: +2-5. Exhaust hood running: +10-15. Open window: highly variable. Operation duration (min) How long the combustion source runs. Tool computes both time-to-exposure at target thresholds + final-state if run to steady-state. External venting Venting multiplies effective ACH. Hood 200-400 CFM adds ~10-20 ACH to a typical kitchen. CO detector status UL 2034 CO alarms have 7-10 year sensor lifespan regardless of battery. Replace on schedule.

Why carbon monoxide is the silent-killer class

Quick answer: CO is colorless, odorless, and binds to hemoglobin with 240x the affinity of oxygen. Once on a hemoglobin molecule, CO stays there for hours regardless of subsequent fresh-air exposure. Accumulation is fast: just 30 minutes in a 400 ppm environment saturates 20-30% of your blood hemoglobin (COHb), at which point headache + confusion + coordination loss begin. Sleeping through exposure means you never notice the symptoms because sleep suppresses the normal physiological responses that would wake you. CDC data: ~400 accidental CO deaths per year in US, concentrated in winter (heating + car idle + generator use during outages).

The counterintuitive part: CO poisoning scales with EXPOSURE TIME × CONCENTRATION, not just peak concentration. A bedroom at 50 ppm overnight (8 hours) produces roughly the same COHb saturation as an hour at 400 ppm. Most detector standards optimize for the 1-4 hour-to-alarm window at 70 ppm because that's the overnight-sleep scenario. Tool shows time-to-reach each threshold so you can size the risk across exposure durations.

The 3 common fatal-incident scenarios

Quick answer: CDC + CPSC fatal-CO-incident data clusters into three patterns. (1) PORTABLE GENERATOR IN GARAGE DURING POWER OUTAGE — dominates storm-season deaths. Lethal CO within minutes in a garage-sized space (60 m³); even with garage door open, reverse infiltration to home above can be fatal. Run generators 20+ ft from any structure with exhaust pointed AWAY. (2) CAR IDLING IN ATTACHED GARAGE — winter warm-up scenario. Catalytic converter reduces warm-engine CO but cold-start + idle produce high CO output. Garage-to-house CO transfer happens via shared walls, ducts, + door gaps. Even with garage door open, 10 minutes of idling can reach dangerous house levels. Never idle in attached garage. (3) CRACKED HEAT EXCHANGER IN GAS FURNACE — older furnace 15+ years old; metal fatigue cracks the exchanger barrier between combustion gas + circulation air. Every vent in the house becomes a CO emitter. Detected via annual HVAC inspection + flashlight test; if furnace is making unusual smell or family members experience chronic headaches peaking during winter heating, shut off at breaker + call HVAC technician same-day.

Tool flags all three scenarios as CRITICAL when inputs match: portable-generator source with non-outdoor location, car-idle with attached-garage, cracked-exchanger source regardless of venting.

Gas stove CO — real but usually manageable

Quick answer: a well-tuned gas stove on simmer produces ~150 mg/min CO — comparable to a candle. With kitchen ACH of 0.5-1.0 + room volume 40-60 m³, steady-state CO stays under 10 ppm (below EPA NAAQS 9 ppm annual average). Turn on the range hood (externally vented, not re-circulating) and effective ACH jumps to 15+, dropping steady-state CO to under 2 ppm. Poorly-tuned gas stove (yellow flame, not blue) produces 5-10x more CO — 800+ mg/min — and can exceed 35 ppm within 30 minutes without venting. Blue flame = good combustion; yellow or orange = service call.

Critical distinction: RECIRCULATING hoods filter grease + odor but do NOT remove CO (they vent back into kitchen). EXTERNALLY-VENTED hoods (ducted to outdoors) are the CO-protective ones. Many apartment kitchens have recirculating hoods; they are better than nothing for grease + smoke but provide zero CO benefit. Check your hood's venting path — some hoods are switchable.

Wood stove + fireplace — the backdraft hazard

Quick answer: EPA-certified wood stoves with good gaskets + proper flue operation emit minimal indoor CO — combustion products go up the chimney. Problems arise from three failure modes. (1) POOR GASKET — worn door seal leaks combustion gas into room. (2) CLOSED DAMPER WITH LIVE FIRE — common user error; combustion gas has nowhere to go except back into room. (3) BACKDRAFT IN TIGHT HOUSES — modern air-sealed house creates negative pressure; bath fan or range hood or dryer exhaust pulls chimney draft backward, pushing combustion gas into living space. Fix for #3: open a window while fire is lit + crack open in nearby room to equalize pressure; some homes need a dedicated makeup-air inlet for wood stoves.

Tool flags "wood-stove-leak + low ACH (under 0.3) + basement location" as high-probability-backdraft scenario. Inspect + service wood stove annually; replace door gasket every 2-3 years; never burn with damper closed.

Why ACH matters more than room volume

Quick answer: mass-balance math says steady-state CO = emission / (ACH × volume). Doubling room volume halves steady-state CO; doubling ACH also halves steady-state CO. But ACH has a bigger swing in practice. Room volumes vary 2-5x across home spaces (bedroom 30 m³, open kitchen 80 m³, basement 150 m³). ACH varies 20-100x (closed bedroom 0.1 → open window + hood on 20+). Getting CO below safe levels is usually easier via ventilation than via larger rooms — cracking a window + running a bath fan increases ACH by 3-5 more than moving to a larger room.

For emergency CO event: open EVERY window + door immediately, turn on EVERY fan (range hood, bath fans, whole-house fan), leave the house, call 911 from outside. Do not re-enter until CO drops below 9 ppm measured by a detector. Fire department has portable meters for clearance testing.

CO detector — the non-negotiable layer

Quick answer: calculator is a planning + understanding tool. CO detector is the primary safety device. NFPA 720 + most state building codes require CO alarms on every level + near sleeping areas in any home with combustion appliances OR attached garage. UL 2034 alarms cost $20-40 per unit + last 7-10 years (sensor degrades regardless of battery). Replace the ENTIRE unit at manufacturer end-of-life date printed on back — not just battery. Test monthly via the test button; swap battery annually if battery-powered model (hardwired + 10-year-sealed-battery models preferred for set-and-forget reliability).

Placement rules per NFPA 720: within 10 ft of each bedroom door (wakes sleepers); every level including basement (CO spreads but takes time to reach detectors on other floors); 15+ ft from cooking appliances (reduces false alarms from brief CO spikes); not in bathrooms (humidity damages sensor). CO density ≈ air density so knee-height + ceiling both work — placement is flexible. Hardwired with battery backup is ideal for permanent install; battery-powered for apartments / renters.

What this calculator does NOT do

Four things require different analysis. (1) ACUTE EXPOSURE DIAGNOSIS — if you or family members experience headache, dizziness, nausea, confusion (especially if improves when leaving house), that is potential CO poisoning. Leave immediately + call 911; ER can measure COHb via blood test. Do not use this calculator in lieu of medical assessment. (2) PROPERTY-SPECIFIC VENTILATION AUDIT — ACH is hard to measure without specialized equipment (blower door test, tracer gas). Tool uses typical-ACH estimates; actual value may differ 2x in either direction. For safety-critical scenarios, use a licensed HVAC technician to perform ventilation audit. (3) CO DETECTOR CERTIFICATION — tool does not replace a certified UL 2034 CO alarm. Install one on every level + near sleeping areas. (4) LONG-TERM LOW-LEVEL EXPOSURE — chronic exposure to 5-15 ppm CO (common indoor with combustion appliances in winter) has growing epidemiological evidence for cardiovascular + cognitive effects. Calculator flags above 9 ppm NAAQS; for chronic-exposure context consult EPA Integrated Science Assessment for Carbon Monoxide.

Sources + further reading

EPA NAAQS for CO (40 CFR 50) — regulatory 8-hour + 1-hour primary standards. OSHA PEL 29 CFR 1910.1000 Table Z-1 — occupational 8-hour PEL = 50 ppm (older) / 35 ppm (post-2020 revision in some jurisdictions). ACGIH TLV Committee 2024 — threshold limit values for workplace chemical exposure. CPSC Publication 466 "Carbon Monoxide Questions and Answers" (cpsc.gov) — consumer-focused overview + incident statistics. NFPA 720 Standard for the Installation of Carbon Monoxide Detection and Warning Equipment (nfpa.org) — detector placement + maintenance requirements. UL 2034 Standard for Single and Multiple Station Carbon Monoxide Alarms (ul.com) — alarm activation thresholds + sensor lifespan. Traynor G.W. + Apte M.G. + Chang G.M. (1996) "Pollutant Emission Factors from Residential Natural Gas Appliances" Lawrence Berkeley National Laboratory LBNL-37414 — canonical source for gas-appliance emission rates. Jetter J.J. + Ebersviller S. (2006) "Residential Carbon Monoxide (CO) Emissions from Portable Generators" US EPA Office of Research and Development — generator-specific emission data. CDC "Carbon Monoxide Poisoning" (cdc.gov/co) — epidemiology + seasonal incident patterns. EPA Integrated Science Assessment for Carbon Monoxide 2010 + updates — long-term exposure health evidence.

Kenny Tan Co-founder & Technical Lead

Ingredient Data Systems · Regulatory Content Architecture · Consumer Chemistry Research

Cross-domain expertise in software engineering, content systems, and infrastructure architecture.

Reviewed by Shanire — Co-founder & Creative Lead

21 April 2026 Also at: kennytan.net

Carbon Monoxide Room-Risk Calculator Tool v1 · canonical sources cited inline above · runs entirely client-side, no data transmitted

Tell us what could be better

Two questions. Takes 30 seconds. We read every reply.

More tools

Ingredient Checker Checker · Check ingredients

Indoor Air Quality Calculator Calculator · Analyze air quality

Tap Water Contaminant Decoder Decoder · Decode your water

Mold Risk Calculator Calculator · Assess mold growth risk

Informational & educational tool. Outputs are for educational purposes and do not constitute medical, legal, financial, tax, or professional advice, and are not a substitute for consultation with a qualified physician, attorney, accountant, or licensed professional. If a result indicates immediate danger — fire, carbon monoxide, acute exposure, or a life-threatening scenario — call emergency services (911 in the US, 995 in Singapore, or your local equivalent), evacuate if air quality is compromised, and ventilate affected areas immediately. For poisoning, contact your regional poison control center. Tool outputs should be verified against authoritative sources before relying on them for decisions with health, safety, legal, or financial consequences.