How to Check Your Home for Carbon Monoxide Risks

Carbon monoxide (CO) poisoning sends over 20,000 Americans to the emergency room each year, according to the CDC. This odorless gas forms when fuels don’t burn completely inside furnaces, water heaters, gas stoves, fireplaces, and even cars. A few simple checks and a professional combustion analysis can prevent tragedy. Here’s how to assess your home’s CO risk and what you should leave to licensed technicians.

Quick Answer: 5 Minutes to Safer Air

1. Make sure you have working CO alarms on every floor and outside sleeping areas. Test them monthly and replace units every 5–7 years.
2. Visually inspect furnace and water heater flames: they should be steady and blue, not yellow or flickering. Look for soot or stains around the appliance.
3. Keep vents and air intakes unblocked. Never run a car or generator inside an attached garage, even with the door open.
4. Know the symptoms of CO exposure: headache, dizziness, nausea, confusion—especially if they improve when you leave home.
5. Schedule a professional CO safety inspection if your equipment is older than 10 years or shows any warning signs.

Common CO Sources and Warning Signs

Safety Boundaries: Where You Must Call a Pro

Keep air moving: a clean duct system distributes fresh air and dilutes potential gas buildups. See our guide on ductwork maintenance.

When to Call a Professional: 4 Clear Decision Points

1. You see yellow or flickering burner flames. This indicates incomplete combustion—stop using the appliance and call a technician.
2. Your CO alarm reads any level above 0 ppm. Even low sustained readings (5–30 ppm) can cause health issues over time. Evacuate if anyone feels sick; otherwise ventilate and schedule an inspection.
3. Your furnace or water heater is more than 15 years old and hasn’t had a combustion test in the last 2 years. Age increases heat exchanger failure risk.
4. You notice soot, rust flakes, or water pooling around the base of a fuel-burning appliance. These often signal a venting or heat exchanger issue.

Use our repair or replace calculator if your aging furnace shows these symptoms—you may save money by upgrading to a sealed-combustion model.

Estimate Your Inspection Cost

A standard HVAC safety check including combustion analysis typically costs $150–$300, depending on your location and system type. Many contractors offer bundled maintenance plans that reduce the price. Use the HVAC cost estimator to see average inspection rates in your ZIP code. For emergency after-hours visits, expect $80–$200 extra; find emergency HVAC help here.

How Your Region Changes CO Risk

• Cold climates (Northeast, Midwest, Mountain West): Furnaces run heavily; cracked heat exchangers are more common after years of cycling. Annual fall inspections are critical.
• Humid climates (Southeast, Gulf Coast): Water heater backdrafting can worsen in muggy, low-pressure conditions. Ensure exhaust fans don’t compete with natural draft vents.
• Coastal homes: Salt air accelerates metal corrosion in flue pipes and heat exchangers. Inspect every year.
• Older homes (pre-1990): Venting may be undersized or uninsulated, leading to condensation and rust. Consider upgrading to direct-vent appliances.

12 Questions to Ask Before Hiring a CO Inspector

1. Are you licensed and insured for HVAC work in my state?
2. Do you use a calibrated electronic CO analyzer (not just a $30 alarm)?
3. Will you test CO levels at each exhaust flue and in living spaces?
4. Can you inspect the heat exchanger for cracks—what equipment do you use?
5. Do you check for proper draft and backdrafting under worst-case conditions (windows closed, exhaust fans on)?
6. Will you provide a written report of CO readings and any identified risks?
7. What is your total cost for a comprehensive CO safety audit, including any travel or diagnostic fees?
8. How long will the inspection take? (Should be at least 45 minutes for a thorough check.)
9. Do you offer a maintenance plan that includes annual combustion testing?
10. Can you show me proof of NCI (National Comfort Institute) or similar combustion analysis certification?
11. If you find a hazard, will you provide a written proposal with a breakdown of necessary repairs?
12. Are you able to pull permits if furnace or venting work is required?

Find vetted local professionals using our contractor search and compare profiles before booking.

How We Set These Recommendations

Carbon Monoxide Safety FAQs

1. How many CO alarms do I need?

Install at least one on every level of your home, including the basement, and outside each sleeping area. Interconnected alarms are best—when one sounds, they all do. Replace the entire alarm every 5–7 years, as sensors degrade.

2. My furnace flame is blue but my CO alarm occasionally shows a low reading. Is that dangerous?

Possibly. A blue flame usually means efficient combustion, but a reading over 0 ppm suggests a small leak or backdrafting. Start by checking for blocked vents or a faulty alarm (test it). If multiple alarms confirm low levels, call a professional for a combustion analysis. Chronic low-level exposure can cause flu-like symptoms.

3. How often should I have my furnace inspected for CO leaks?

Annual inspections are recommended, especially before heating season. During a maintenance visit, a technician should check the heat exchanger, burner, and flue draft, and take CO readings in the supply air and room.

4. What should I do if the CO alarm sounds and I feel fine?

Evacuate immediately. Open doors on your way out but don’t stop to open windows extensively—this can make it harder for firefighters to find the source. Call 911 from outside. Even if you feel fine, CO can overcome you quickly. Wait for the all-clear before re-entering.

5. Can I use a plug-in CO detector with a digital display instead of the ones with just an alarm?

Yes, a digital display can help you see low levels before they become hazardous. Look for units that meet UL 2034 standards. However, the alarm function is most critical—digital display is a bonus, not a replacement.