Carbon Monoxide Warning Signs From a Furnace

Carbon monoxide (CO) is a colorless, odorless gas that a malfunctioning gas furnace can produce. Because you can’t see or smell it, knowing the warning signs is critical for every household in Greater Vancouver that heats with gas. This guide covers what to watch for, why it happens, and, most importantly, what to do.

Immediate Safety First

If your CO alarm sounds, or if anyone feels sick with the symptoms below, do not investigate. Get everyone, including pets, outside to fresh air immediately, then call 911 from outside. Leave the door open on your way out. Do not re-enter until emergency responders say it’s safe. This is the one situation where you act first and diagnose later. Never open windows and stay inside to “air it out,” and never re-enter to grab belongings, a phone, or a pet.

Physical Symptoms to Watch For

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• Headaches, especially dull or persistent ones
• Dizziness or light-headedness
• Nausea or vomiting
• Shortness of breath or chest tightness
• Confusion, drowsiness, or blurred vision
• Flu-like symptoms with no fever, especially if several household members feel it at once

A telltale clue: symptoms that improve when you leave the house and return when you come back. If multiple people or pets feel unwell at the same time, treat it as an emergency rather than assuming everyone caught the same bug.

Physical Signs Around the Furnace

Who Is Most at Risk

CO exposure affects everyone, but infants, older adults, people with heart or lung conditions, and pets are typically affected faster and more severely at lower concentrations. If anyone in the household falls into these groups, treat even mild, unexplained symptoms during heating season as a reason to check your CO detector and consider a professional inspection sooner rather than later.

What Causes CO From a Furnace

Common causes include a cracked heat exchanger, blocked or disconnected vent and flue pipes, incomplete combustion from a dirty or misadjusted burner, and inadequate combustion air supply to the furnace room or closet. Renovations that seal up a home tightly, block a vent terminal outside, or accidentally obstruct a fresh-air intake can also starve a furnace of the air it needs to burn cleanly. These are not homeowner repairs. Never attempt to open, adjust, or repair the furnace’s burner, heat exchanger, or venting yourself.

Prevention: Detectors and Maintenance

Install CO detectors on every level of your home and near sleeping areas, test them monthly, and replace them per the manufacturer’s date, most units need full replacement every five to ten years even if the alarm still sounds during a test. Just as important, have your gas furnace professionally inspected every year, ideally before heating season begins. A licensed technician checks the heat exchanger, combustion, and venting so problems are caught before they become dangerous. Our HVAC maintenance plans include annual safety inspections as part of scheduled visits.

Quick Home Safety Checklist

• CO detector on every level and near bedrooms, tested monthly
• Furnace flame is steady blue, not yellow or flickering
• No soot, rust, or unusual staining near the furnace or vent pipes
• Vent and flue pipes are connected, unobstructed, and slope correctly
• Annual professional inspection scheduled before heating season

ROMA Heating & Cooling is a TSBC-licensed gas contractor (Gas licence LGA0202903), serving Greater Vancouver since 1999. If your furnace is showing any warning signs, once everyone is safe, our furnace repair team can diagnose it, or an HVAC inspection can verify safe operation. We also service boilers and other gas appliances that share the same combustion and venting risks. To schedule, book a free estimate or contact us. When it comes to CO, never take chances.

Frequently Asked Questions

What should I do the moment my CO alarm goes off?

Get everyone and pets outside to fresh air immediately, then call 911 from outside. Do not stay inside to investigate, and do not re-enter until emergency responders confirm it is safe.

Can I smell carbon monoxide?

No. Carbon monoxide is colorless and odorless, which is why CO detectors are essential. You cannot rely on your senses to detect it, though a yellow burner flame or soot can be visible clues of a combustion problem.

How often should my gas furnace be inspected for CO risks?

Have a licensed technician inspect your gas furnace annually, ideally before heating season. The inspection checks the heat exchanger, combustion, and venting, which are the main sources of furnace-related CO.

Where should carbon monoxide detectors be placed?

Install CO detectors on every level of your home and near each sleeping area. Follow the manufacturer’s placement guidance, test them monthly, and replace units by their expiry date.

Reviewed by the ROMA Heating & Cooling team — TSBC-licensed gas contractor (Gas LGA0202903), serving Greater Vancouver since 1999. Updated June 2026.

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