Water Heater Carbon Monoxide — Warning Signs and Prevention

Quick Answer

Carbon monoxide (CO) from a water heater is rare but deadly. It occurs when a gas heater’s venting is blocked, cracked, or improperly installed.

Symptoms:

• Headache
• Dizziness
• Nausea
• Confusion

These can feel like the flu.

If you suspect CO poisoning:

• Evacuate immediately
• Call 911
• Call Embridge: 1-800-333-4797

Prevention:

• Install a CO detector ($30–$50) near the heater
• Annual vent inspection: $100–$150

Do not assume your heater is safe just because it is working. Faulty venting is invisible.

Why Water Heaters Produce Carbon Monoxide

Gas water heaters burn fuel, producing CO as a byproduct.

Normally:

• Venting systems (chimney or sealed duct) remove CO outside

When venting fails:

• CO accumulates inside the home

Common Causes

• Blocked or damaged vent pipe
• Improper vent installation
• Backdrafting (air pressure pulls CO back inside)
• Older, non-sealed systems

Risk Factors

• Basement installations
• Unfinished or poorly ventilated basements
• Tight homes with limited airflow
• Older heaters
• High elevation (6,000+ ft)

Warning Signs of Carbon Monoxide Poisoning

Immediate Symptoms (Acute Exposure)

• Persistent headache
• Dizziness
• Nausea or vomiting
• Chest pain
• Confusion
• Loss of consciousness

Slow Symptoms (Chronic Exposure)

• Recurring headaches
• Fatigue
• Memory problems
• Difficulty concentrating
• Feeling “off” in a specific room

Red Flags

• Symptoms worsen in winter
• Symptoms improve outside
• Multiple people affected
• Pets acting lethargic

How to Tell CO Poisoning vs Flu

Rule: When in doubt, assume CO and evacuate.

Prevention: Actions You Can Take

1. Install a Carbon Monoxide Detector ($30–$50)

• Place near the heater (basement)
• Optional: one in each bedroom
• Test monthly
• Use a battery or hardwire with a backup
• Minimum 85 dB alarm

Brands: First Alert, Kidde, Nighthawk

2. Annual Vent Inspection ($100–$150)

A plumber will:

• Check for cracks or blockages
• Verify proper vent slope
• Inspect exterior vent
• Test for backdrafting

Recommended annually, especially before winter.

3. Maintain Basement Ventilation

• Avoid sealing basement completely
• Allow airflow from upper levels
• Use a fan if enclosed
• Open windows periodically

4. Check Exterior Vent

Inspect roof or wall exit:

• Blocked by snow or ice?
• Bird nests or debris?
• Too close to windows/doors?

Clear obstructions immediately.

5. Upgrade Older Heaters

• Older: B-vent systems (less safe)
• Newer: FVIR sealed combustion

If heater is 8+ years old and venting is questionable, consider replacement.

Safe Venting Checklist

Proper venting should:

• Rise upward from the heater
• Connect to the chimney or sealed duct
• Exit is above the roofline
• Maintain 1/4″ rise per 12″ horizontal run
• Use proper materials (Type B vent or sealed pipe)
• Have no gaps or cracks
• Terminate away from windows/doors

If any condition fails, call a plumber immediately.

When to Call 911

Call immediately if:

• Multiple people feel sick
• Loss of consciousness
• Severe chest pain
• Confusion or breathing difficulty
• Combined symptoms (headache + nausea + dizziness)

Emergency Procedure

1. Leave the home immediately
2. Go outside
3. Call 911 from outside
4. Report “possible carbon monoxide exposure at my home”
5. Do not re-enter until cleared by emergency services

Call Embridge (1-800-333-4797) if:

• You suspect gas + CO issue
• Venting is visibly damaged
• You need gas shutoff confirmation

What Happens If CO Detector Alarms

Immediate Actions

• Leave home immediately
• Open windows while exiting
• Call 911 or Embridge
• Do not re-enter

Optional: turn off the heater if safe

Professional Response

Fire department or Embridge will:

• Measure CO levels
• Inspect venting and heater
• Determine if a shutdown is required
• Recommend repairs

Find Local Help

Carbon monoxide is invisible and deadly. Annual inspection ($100–$150) is considered an essential prevention technique.

Embridge gas emergency: 1-800-333-4797

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Frequently Asked Questions

How common is CO from water heaters?

Rare, but extremely dangerous. Prevention is essential.

Is a CO detector enough?

No. It alerts after exposure begins. Inspection prevents exposure.

Is a finished basement safer?

Not necessarily. Venting must still be verified.

Can I inspect venting myself?

You can check visually, but professionals use CO meters and smoke tests.

My heater is 15 years old. Do I need an inspection?

Yes. Venting deteriorates over time. Annual checks are critical.

Sources and Update Policy

This article was last updated March 2026. CO safety guidance aligns with CDC recommendations.

Sources:

• CDC carbon monoxide poisoning guidance: https://www.cdc.gov/
• Embridge gas safety: 1-800-333-4797
• CPSC carbon monoxide detector standards
• International Fuel Gas Code (venting requirements)