Furnace Smells and Carbon Monoxide Safety
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A rotten-egg smell means a possible gas leak: leave the house and call 911 or Southwest Gas from outside. A dusty burning smell at the first cold snap is usually normal. A sharp electrical or plastic smell means shut the furnace off. If a carbon monoxide alarm sounds, get everyone outside and call 911.
Last reviewed October 19, 2026.
What does each furnace smell usually mean?
- Rotten eggs or sulfur: natural gas and propane are given this odor so leaks can be detected. Leave immediately; don’t use switches, phones, or flames inside. Call 911 or Southwest Gas (or your propane supplier) from outside.
- Dusty burning smell for the first hour of the season: dust burning off the heat exchanger. Usually normal if it fades.
- Electrical burning or melting plastic: an overheating motor or wiring. Turn the furnace off and call.
- Exhaust smell: possible venting problem. Turn the furnace off, ventilate, and call.
What should you do if the carbon monoxide alarm goes off?
Carbon monoxide has no smell. According to the CDC, symptoms include headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. If the alarm sounds, get everyone, including pets, into fresh air and call 911. Don’t go back in until responders say it’s safe, and have the furnace and any other fuel-burning appliance inspected before using them again.
Do California homes need CO alarms?
Yes. California’s Carbon Monoxide Poisoning Prevention Act requires carbon monoxide alarms in dwelling units that have a fossil-fuel-burning appliance, a fireplace, or an attached garage. Put alarms outside sleeping areas and on each level, and test them monthly.
Why does a furnace produce carbon monoxide?
Any fuel-burning appliance can produce CO if combustion is poor or the exhaust can’t escape. Causes include a cracked heat exchanger, a blocked flue or vent (including snow and ice), and burners that need adjustment. An annual inspection includes these checks.
When should you call an emergency furnace pro in Big Bear?
Call for urgent help, and leave the house first where noted, if any of these apply:
- You smell gas (a rotten-egg odor): leave right away without flipping switches, then call 911 or your gas utility (Southwest Gas in the Big Bear Valley) from outside.
- A carbon monoxide alarm sounds, or people feel headache, dizziness, or nausea that eases outdoors: get everyone into fresh air and call 911.
- There is no heat and indoor temperatures are dropping toward freezing, especially with infants, older adults, someone with a medical condition, or water pipes at risk.
- The furnace trips the breaker repeatedly, smells like burning wiring, or shows scorch marks.
- You see flames outside the burner area, heavy soot, or a lazy yellow flame instead of a steady blue one.
- A vacant cabin's thermostat or smart sensor reports the house is losing heat during a cold spell.
If you smell gas or a carbon monoxide alarm goes off, leave the building first and call 911 or your gas utility from outside. Don't wait for a contractor.
Where is furnace smells & co safety help available near Big Bear?
Requests are taken from Big Bear Lake and these nearby communities:
What do people ask about furnace repair in Big Bear?
Is a burning smell normal when I first turn on the heat?
A dusty smell that fades within an hour or so is common at the start of the season. A smell that keeps coming back, or smells like wiring or plastic, is not normal.
Can a cracked heat exchanger cause carbon monoxide?
It can allow combustion gases to mix with your home's air. HomeGuide notes that technicians usually replace rather than repair heat exchangers for this reason, at a typical cost of $1,000 to $3,000.
Where should CO alarms go?
The CPSC recommends alarms on each level of the home and outside sleeping areas. Follow the manufacturer's instructions and replace alarms at the end of their rated life.
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