Quick Answer: What Produces Carbon Monoxide?
Carbon monoxide is produced by incomplete combustion of any fuel—gas, oil, wood, coal, gasoline, propane, or kerosene. When these fuels don't burn completely (due to poor ventilation, blocked vents, or malfunctioning equipment), they create CO instead of harmless CO₂.
Common household CO sources:
- • Furnaces (gas, oil, or propane) - #1 cause of CO deaths
- • Water heaters (gas or propane)
- • Gas ranges and ovens
- • Fireplaces and wood stoves (blocked chimneys)
- • Portable generators (NEVER run indoors)
- • Cars idling in attached garages
- • Space heaters (unvented propane or kerosene)
Appliances Ranked by CO Risk
Not all CO sources are equally dangerous. Here's the hierarchy based on fatality statistics, exposure duration, and malfunction frequency:
1. Furnaces (Gas, Oil, Propane)
HIGHEST RISK - Responsible for 60%+ of CO deaths
Why Furnaces Are So Dangerous:
They Run While You Sleep
Furnaces operate automatically, often overnight when you're unconscious and can't detect symptoms. A cracked heat exchanger can leak CO for hours while you're in bed, building lethal levels before morning.
High Volume, Continuous Output
A malfunctioning furnace produces far more CO than a gas stove or water heater because it burns more fuel continuously for 8-12 hours overnight. A cracked heat exchanger leaking just 100 ppm can fill your home to dangerous levels in 2-3 hours.
Silent Degradation Over Years
Heat exchangers don't crack overnight—they degrade slowly over 15-20 years. Tiny cracks develop, leak small amounts of CO initially (causing "flu-like" symptoms), then widen over months until they're lethal. Most victims had no idea their furnace was failing.
Located in Basement (CO Rises Through House)
Basements often have poor ventilation. CO accumulates there first, then seeps upward through ductwork, stairwells, and ceiling gaps into living spaces. By the time you smell/detect anything, the entire house is contaminated.
Warning Signs Your Furnace Is Leaking CO:
- • Yellow or orange flame (should be steady blue)
- • Soot or rust around furnace
- • Pilot light keeps going out
- • Excessive moisture on windows near furnace
- • Furnace cycles on/off frequently
- • Strange smells when furnace runs (rotten egg, burning)
- • Family develops headaches only in winter
- • Furnace is 15+ years old (high risk)
⚡ What You Must Do:
- • Annual professional inspection every fall before heating season (non-negotiable)
- • Replace furnaces older than 20 years—heat exchangers fail around this age
- • Install CO detector within 15 feet of furnace (basement + bedrooms)
- • Never ignore yellow flames or soot—shut down furnace and call HVAC tech immediately
- • Budget $100-200/year for professional furnace maintenance—it's life insurance
2. Water Heaters (Gas/Propane)
HIGH RISK - Often in poorly ventilated spaces
Why Water Heaters Are Dangerous:
Blocked or Disconnected Vents
Water heaters vent combustion gases through a flue pipe to the outside. If this pipe disconnects (from settling, corrosion, or DIY work), CO spills directly into your basement/utility room. Bird nests, debris, or collapsed sections block vents, causing backdrafting.
Often Located in Closets or Garages
Poor ventilation in these spaces means CO builds up quickly. If the water heater is in an attached garage, CO can seep into living spaces through shared walls and doors. Utility closets often lack fresh air intake, starving the burner of oxygen and creating incomplete combustion.
Ignored During Maintenance
Unlike furnaces (which people service because heating is critical), water heaters are often neglected. People don't notice problems until hot water runs out. By then, the unit may have been leaking CO for months. Most homeowners NEVER service their water heater.
Warning Signs Your Water Heater Is Leaking CO:
- • Rust or soot on top of water heater or on vent pipe
- • Vent pipe feels hot to touch (shouldn't be)
- • Vent pipe disconnected or damaged
- • Yellow pilot light flame (should be blue)
- • Excessive condensation on walls near water heater
- • Smell of exhaust or burning when water heater runs
What You Must Do:
- • Inspect vent pipe annually—look for disconnections, rust, holes
- • Ensure adequate ventilation in utility room/closet (fresh air intake)
- • Install CO detector near water heater (basement/utility room)
- • Replace water heaters older than 12 years—vents corrode, burners fail
- • Never store items on top of water heater—blocks venting
3. Gas Ranges and Ovens
MODERATE RISK - Mostly from misuse
Why Gas Stoves Cause CO Poisoning:
Used for Heating (Extremely Dangerous)
Desperate people use gas ovens to heat homes during winter (broken furnace, poverty, etc.). Running a gas oven continuously for hours creates massive CO buildup—CO levels can hit 200-400 ppm within 2-3 hours. Dozens of deaths annually from this practice.
Poor Ventilation During Normal Cooking
Gas stoves produce 5-30 ppm CO during normal operation (safe for short periods). But cooking for 3-4 hours (holiday meals, baking marathons) in a poorly ventilated kitchen can push levels to 50-100 ppm. Open windows or use range hood when cooking.
Malfunctioning Burners or Pilot Lights
Clogged burners (grease, food debris) cause incomplete combustion and yellow flames. Faulty pilot lights that don't fully ignite burners also create CO. Most people don't notice because exposure is brief—but chronic use adds up.
❌ NEVER DO THIS:
- • Never use gas oven to heat your home—deadly CO levels within hours
- • Never leave oven on overnight (even at low temp for bread proofing)
- • Never use all 4 burners + oven simultaneously for 3+ hours without ventilation
- • Never ignore yellow flames—sign of incomplete combustion (clean burners immediately)
What You Must Do:
- • Use range hood when cooking (vented to outside, not recirculating)
- • Open window during long cooking sessions (Thanksgiving, baking all day)
- • Clean burners monthly—grease and debris cause yellow flames
- • Inspect pilot lights and igniters—should light immediately with blue flame
- • Install CO detector 10-15 feet from stove (not directly above—false alarms)
4. Fireplaces & Wood Stoves
MODERATE RISK - Blocked chimneys are deadly
Why Fireplaces Cause CO Poisoning:
Blocked or Obstructed Chimneys
Bird nests, leaves, creosote buildup (tar-like substance from burning wood), or collapsed chimney sections block smoke and CO from venting outside. Result: CO backdrafts into your living room. This is especially common with chimneys that haven't been used in years—blockages develop over time.
Damper Left Closed
Starting a fire with the damper closed is a rookie mistake that happens more often than you'd think. All smoke and CO fills the room instantly. People realize their error within minutes (room fills with smoke), but if you're drunk, distracted, or in another room, CO can build to dangerous levels before you notice.
Negative Air Pressure (Modern Homes)
Modern airtight homes can create negative pressure when exhaust fans (bathroom, kitchen) run simultaneously with a fireplace. This sucks air down the chimney instead of up, pulling CO back into the room. Solution: crack a window when using fireplace to equalize pressure.
What You Must Do:
- • Chimney inspection and cleaning annually (before winter)—removes creosote, checks for blockages
- • Always open damper before lighting fire—check with flashlight if unsure
- • Crack window when using fireplace—prevents backdrafting
- • Install CO detector 15-20 feet from fireplace—close enough to detect, far enough to avoid false alarms
- • Never burn trash, treated wood, or glossy paper—creates toxic fumes and clogs chimney
5. Portable Generators
EXTREME RISK - #1 killer during power outages
Generators kill 50-100 people every year—mostly during winter storms and hurricanes when power is out for days. People run generators in garages, basements, or too close to windows, not realizing generators produce as much CO as 100 idling cars.
Why Generators Are So Deadly
A 5,000-watt generator produces 10,000+ ppm CO in its exhaust. Running one in a garage (even with door open) can fill the space with 1,000+ ppm in 10 minutes—lethal within 30 minutes. Deaths happen because people underestimate how much CO generators produce.
☠️ NEVER DO THIS (GUARANTEED DEATH):
- • Never run generator indoors—basement, garage, shed, crawl space (even with door/windows open)
- • Never run generator in attached garage—CO seeps through walls/doors into house
- • Never run generator within 20 feet of house—exhaust enters through windows/vents
- • Never run generator near bedroom windows—people die in sleep
Safe Generator Use:
- • 20+ feet from house, downwind—exhaust blows away from building
- • Point exhaust away from windows/doors
- • Never run overnight while sleeping (wind direction changes, CO drifts indoors)
- • Install CO detectors with battery backup—power outages disable hardwired units
- • Consider low-CO generators (newer models with automatic shutoff at 150 ppm)
6. Cars Idling in Attached Garages
HIGH RISK - Preventable but still kills dozens yearly
"I just warmed up my car for 5 minutes with the garage door open" is a sentence spoken by countless CO poisoning victims. Even with the garage door fully open, idling a car produces enough CO to seep into living spaces through shared walls and door gaps.
What You Must Do:
- • Never idle car in garage—not even "for a minute"
- • Push car out of garage to warm up (or just drive away immediately—modern cars don't need warming)
- • Install CO detector on house side of shared wall with garage
- • Check garage door closes fully—gaps allow CO to enter house
- • Never use remote start in garage—people forget car is running
Lesser-Known CO Sources (Still Dangerous)
🏕️ Camping Equipment Used Indoors
- • Charcoal grills (NEVER use indoors—even in garage)
- • Propane camp stoves
- • Catalytic heaters (unvented)
- • Lanterns (gas or kerosene)
Winter storms: Desperate people use these to heat homes during power outages. Dozens die annually from indoor charcoal grill use.
🛠️ Power Tools (Gas-Powered)
- • Pressure washers in closed garages
- • Chainsaws during indoor repairs
- • Concrete saws in basements
- • Snow blowers in garages
DIY hazard: Running gas tools indoors for even 10-15 minutes creates dangerous CO levels.
🚤 Boats with Enclosed Cabins
- • Generator exhaust entering cabin
- • Engine exhaust (swim platform deaths)
- • Propane stoves/heaters in cabin
Water hazard: 15-20 boaters die annually from CO poisoning—often while sleeping in cabin with generator running.
🏠 Nearby Sources Entering Your Home
- • Neighbor's generator (if too close to your house)
- • Cars idling in adjacent townhouse garage
- • Restaurant exhaust (if you live above commercial kitchen)
Shared walls: Row houses and townhouses share HVAC, walls, and attics—CO can migrate from neighbor's unit to yours.
Your Annual CO Prevention Checklist
Most CO deaths are preventable with basic maintenance. Here's your yearly checklist:
Every Fall (Before Heating Season):
Furnace professional inspection ($100-200)
HVAC technician checks heat exchanger for cracks, tests burner operation, inspects venting, measures CO output. Non-negotiable if furnace is 15+ years old.
Chimney sweep and inspection ($150-300)
Remove creosote, check for blockages (bird nests, debris), inspect chimney structure, verify damper operation.
Water heater inspection (DIY or $50-100 pro)
Check vent pipe for disconnections/rust, inspect burner flame (should be blue), test pressure relief valve, flush sediment.
Test all CO detectors
Press test button on each detector. Replace batteries if needed. If detector is 7+ years old, replace entire unit.
Clean gas stove burners
Remove grease and food debris. Check for yellow flames (sign of incomplete combustion). Clean or replace igniters.
Generator maintenance (if applicable)
Test generator before winter storms. Check exhaust system. Ensure you have 50+ feet of extension cord to place generator far from house.
💰 Annual Prevention Cost Breakdown:
Less than $2/day to protect your family from the #1 cause of accidental poisoning deaths in America.
Best CO Detectors for Multi-Appliance Homes
If your home has multiple CO sources (furnace + water heater + gas stove + fireplace), you need detectors strategically placed throughout the house:
Kidde 10-Year Sealed Battery (6-Pack)
Best for whole-home coverage
~$200
Buy on AmazonRecommended placement for typical home:
- • 1 near furnace (basement)
- • 1 near water heater (basement/utility room)
- • 1 in hallway outside bedrooms (upstairs)
- • 1 near kitchen (10-15 feet from stove)
- • 1 near fireplace (if applicable)
- • 1 near attached garage entrance
First Alert SC5 Smart Smoke & Carbon Monoxide Alarm
Best for large homes needing whole-home alerts
~$120/each
Buy on Amazon- ✓ All units alarm simultaneously when one detects CO
- ✓ Voice alerts tell you which room has CO
- ✓ Smartphone notifications (even when away)
- ✓ Worth it for homes over 2,500 sq ft or multi-story layouts
Common Questions About CO Sources
Do electric appliances produce carbon monoxide?
No. Electric heaters, stoves, ovens, and dryers do NOT produce carbon monoxide because they don't burn fuel. CO only comes from combustion of gas, oil, wood, coal, propane, kerosene, or gasoline. All-electric homes don't need CO detectors (unless you have an attached garage or generator).
How often should I service my furnace?
Annually, every fall before heating season. A professional HVAC inspection costs $100-200 and checks heat exchanger cracks, burner operation, venting, and CO output. Furnaces older than 15 years should be inspected twice yearly. Replace furnaces older than 20-25 years.
Can my neighbor's appliances leak CO into my home?
Yes, especially in townhouses, row houses, and apartments with shared walls/attics. CO from a neighbor's malfunctioning furnace can migrate through wall cavities, shared ductwork, or attic spaces. If you live in attached housing, install CO detectors even if you have all-electric appliances.
Is it safe to run a generator in my detached garage?
Only if the garage door is fully open and the generator is at the far end, pointing exhaust outside. Even then, it's risky—better to place generator outside, 20+ feet from any building. Never run generator in attached garage even with door open—CO seeps into house through walls.
Protect Your Family Today
Your furnace, water heater, and gas appliances could be leaking CO right now. Install detectors, schedule annual inspections, and never ignore warning signs.
Recommended: One detector per fuel-burning appliance + one per floor