If my CO detector hasn't alarmed, can my home still have a CO problem?

Yes, in three scenarios. First, UL 2034 detectors are designed to alarm at 70 ppm for 60–240 minutes — chronic exposure to lower levels (10–50 ppm) can still produce health effects but won't trigger standard alarms. Low-level CO detectors (NSI 3000, Defender LL6070) alarm at 15–25 ppm and are appropriate for households with sensitivity concerns. Second, the detector itself might be past its service life (most detectors are designed for 5–7 years) and the electrochemical sensor has degraded. Third, detector placement matters — a single detector at one location doesn't measure CO in other parts of the home. Multiple detectors per the recommended density catches CO issues that single-detector placements miss.

How long do CO detectors last?

Most residential CO detectors have a 5–7 year service life; some premium models reach 10 years. The electrochemical sensor degrades over time regardless of whether the detector has been used. Manufacture date is printed on the back of every detector; detectors past their service life should be replaced regardless of apparent functionality. The LED indicators and test button can still function after the sensor has degraded, which gives false confidence that the detector is working when it actually isn't. Annual battery replacement on battery-powered detectors and periodic detector replacement per the manufacture date are both important.

What's the difference between CO testing and combustion analysis during a tune-up?

Different measurement target. Combustion analysis during a tune-up measures CO at the appliance — what the burner is producing at the heat exchanger, draft inducer, or vent termination. The question being answered is 'is this specific appliance operating with normal combustion?' Whole-house CO testing measures CO in the ambient air people breathe — in living spaces, near sleeping areas, near suspected migration points. The question being answered is 'is your family being exposed to elevated CO from any source?' The two measurements complement each other but answer different questions.

What CO level is dangerous?

Depends on exposure duration. Acute exposure to high levels: 800–1,000 ppm can cause unconsciousness within hours and death within longer exposure. 1,500–3,000 ppm can cause death within 30 minutes to an hour. Chronic exposure to low levels: 9 ppm sustained for 8 hours is the EPA NAAQS limit. 30–50 ppm sustained for hours produces measurable cognitive effects, fatigue, and headaches especially in sensitive individuals. The danger isn't always immediately obvious because low-level CO produces symptoms similar to flu or general fatigue. Persistent unexplained headaches improving when leaving the home is a classic chronic CO exposure pattern.

If my CO detector is alarming, should I call 911 or your office?

Both, in this order. First, evacuate the home immediately and call 911 from outside the home. Fire department response is the safety-first dispatch — they have CO measurement equipment, can identify acute hazards, and can determine when the home is safe to re-enter. Once the fire department has secured the situation, call our office for follow-up diagnostic testing and source identification. Don't try to investigate the source yourself while CO is potentially still elevated in the home — CO is colorless, odorless, and impairs judgment. Evacuate, call 911, then call us.

Carbon Monoxide Testing — Omaha Heating and Air Conditioning

Carbon monoxide testing as a standalone service is distinct from the combustion analysis we perform during furnace tune-ups and heat-exchanger diagnostic visits. Combustion analysis measures CO production at the appliance — what the burner is emitting at the heat exchanger or vent termination. CO testing as a whole-house service measures CO in the air people breathe — what’s actually present in occupied spaces, regardless of which appliance or source produced it. The two measurements answer different questions. Combustion analysis answers “is this appliance operating properly?” Whole-house CO testing answers “is your family being exposed to elevated CO from any source in or around the home?” The relevant action levels, testing equipment, and source-identification methodology differ. This page covers when whole-house CO testing is worth scheduling, what the action levels actually mean (UL 2034 alarm thresholds vs. OSHA workplace limits vs. EPA NAAQS limits, which differ substantially), the source identification process when elevated CO is detected, and CO detector replacement guidance because most homes have detectors past their service life.

When CO Testing as a Service Is Worth Scheduling

Specific situations where dedicated CO testing delivers real value:

CO detector alarming intermittently with no clear source — first-generation low-level CO detectors and well-maintained current detectors alarm at specific PPM thresholds. Intermittent alarms (alarming once, resetting, alarming again days later) often indicate a real low-level CO source that’s hard to identify without dedicated testing equipment. We deploy professional CO meters at multiple locations to identify when and where elevated CO is occurring.
Family symptoms suggesting low-level CO exposure — persistent headaches that improve when family members leave the home, flu-like symptoms with no infection, fatigue and confusion that don’t have other clear causes, especially during heating-season-only patterns. Symptom-driven testing identifies whether CO is actually a factor or rule out CO and direct attention to other potential causes.
Suspected heat exchanger compromise on existing equipment — covered in detail on the heat exchanger repair page, but ambient CO measurement at supply registers and in living spaces is part of confirming heat exchanger leakage diagnosis.
After CO-producing appliance installation — new gas water heater, gas range, gas fireplace, generator, or other combustion appliance installation. Baseline CO testing post-installation confirms the new appliance is operating properly and not creating exposure.
Pre-purchase home inspection — some homebuyers schedule CO testing as part of inspection due diligence, especially when buying older homes with multiple combustion appliances. Provides objective measurement to supplement visual inspection.
Post-CO-incident verification — after a CO alarm event where MUD or fire department secured the situation, follow-up testing confirms the source has been addressed and the home is safe for re-occupancy.
Workplace and commercial environments — auto repair shops, commercial kitchens, parking structures with attached spaces, and other commercial environments where CO exposure compliance with OSHA standards needs documentation.

When CO Testing Probably Isn’t Necessary

Routine annual checkups absent symptoms or alarms — combustion analysis on combustion appliances during annual tune-ups catches developing CO production issues at the source. Standalone whole-house CO testing on top of routine appliance combustion analysis usually doesn’t add information.
“Preventive” testing sold without specific diagnostic question — contractors offering routine CO testing visits without specific concerns aren’t typically delivering value. The combustion analysis during tune-ups is the high-impact intervention.
Single CO detector alarm with obvious cause — alarms with clear obvious causes (vehicle left running in attached garage, fireplace recently lit with closed damper, range left on accidentally) usually don’t need diagnostic testing. The cause is identifiable; addressing the cause is the action.

Action Levels — What the Numbers Actually Mean

CO action levels vary substantially between authorities, which causes confusion. The relevant standards:

UL 2034 (Residential CO Alarms)

The standard governing residential CO detector alarm thresholds. UL 2034 requires alarms to sound at:

70 ppm sustained for 60–240 minutes — the lowest threshold; designed to alarm before sustained low-level exposure causes harm.
150 ppm sustained for 10–50 minutes — intermediate threshold for higher exposures.
400 ppm sustained for 4–15 minutes — rapid response threshold for high-concentration events.

The implication: UL 2034 detectors are designed for emergency notification, not for low-level chronic exposure detection. CO levels below 70 ppm won’t trigger UL 2034 alarms but can still cause health effects with sustained exposure. Some “low-level” CO detectors (NSI 3000, Defender LL6070) alarm at lower thresholds (15–25 ppm) and are appropriate for households with sensitivity concerns or where UL 2034 alarms have proven insufficient.

OSHA Workplace Limits

Occupational Safety and Health Administration sets workplace exposure limits:

50 ppm 8-hour time-weighted average — the OSHA permissible exposure limit (PEL) for general industry.
200 ppm ceiling — the maximum momentary exposure allowed in workplace environments.

Workplace limits are based on healthy adult tolerances during 8-hour exposure periods. They’re not appropriate residential exposure targets, especially for children, elderly residents, pregnant women, or anyone with cardiovascular or respiratory conditions.

EPA National Ambient Air Quality Standard (NAAQS)

The EPA sets stricter limits for residential ambient air:

9 ppm 8-hour average — the NAAQS limit for outdoor ambient CO. Indoor levels in residential spaces should not exceed this benchmark for sustained periods.
35 ppm 1-hour average — the short-duration NAAQS limit.

EPA NAAQS reflects health-protective ambient air targets for the general population including sensitive subgroups. The 9 ppm 8-hour target is dramatically below UL 2034 alarm thresholds, which is why standard CO detectors won’t alarm on chronic low-level exposure that still produces health effects.

What These Differences Mean in Practice

A residential space with CO levels of 30–50 ppm is:

Well below the UL 2034 70 ppm alarm threshold (so standard detectors won’t alarm).
Approaching OSHA workplace 50 ppm 8-hour limit (concerning even for working-age adults).
Substantially above EPA NAAQS 9 ppm 8-hour limit (concerning for general population including children, elderly, pregnant women).
Producing measurable cognitive effects, fatigue, headache symptoms during sustained exposure.

This is the gap that whole-house CO testing addresses: detecting chronic low-level exposure that’s below detector alarm thresholds but above health-protective limits. Our professional CO meters measure down to single-digit PPM with documented calibration, providing measurement evidence of exposure levels that consumer alarms miss entirely.

Professional Testing Equipment

Our CO testing equipment includes:

Bacharach Monoxor III / Monoxor Plus — portable CO meter calibrated to 1 ppm resolution. The dominant professional CO measurement instrument in HVAC service work. Logs measurements with timestamps for documentation.
BW Gas Alert Extreme / GasAlertMicroClip — personal CO monitors worn by technicians during diagnostic work. Records cumulative exposure data over the service visit.
Bacharach Fyrite InTech — combustion analyzer with CO measurement that complements ambient measurement during combustion-side appliance diagnosis.
TPI 9035 / TPI 770 — combustion analyzer alternatives.
UEi C155 / C165 — specialized combustion analyzers for high-output commercial applications.

All measurement equipment is factory-calibrated annually with documented calibration records. Field-zero calibration is performed at the start of every diagnostic visit to verify equipment readiness.

Source Identification — What We Look For

When elevated ambient CO is detected, source identification follows a structured workflow:

Gas Combustion Appliances

Each gas combustion appliance in the home receives combustion analysis to determine if it’s a CO source:

Gas furnace — combustion analysis at the heat exchanger, draft inducer, and vent termination. CO production above 100 ppm air-free or trending up from prior baselines indicates heat exchanger compromise or combustion problems.
Gas water heater — atmospheric water heaters are a common CO source, especially in basements with marginal venting or when other appliances are causing back-drafting. Sealed-combustion water heaters less commonly produce CO issues.
Gas range and oven — ranges without proper exhaust ventilation can produce CO during high-fire operation. Many ranges produce some CO as a normal byproduct; the concern is sustained elevated CO from improper combustion or extended operation without ventilation.
Gas dryer — gas dryers occasionally produce CO from improper venting or restricted exhaust. Confirmed by exhaust path verification.
Gas fireplace — vented gas fireplaces depend on flue draft to remove combustion products. Draft problems can dump CO into living spaces. Unvented (vent-free) gas fireplaces and decorative log sets are designed to vent combustion products into the room and are inherently CO sources; their use should be limited per manufacturer specification.
Wood-burning fireplace — wood combustion produces CO. Properly-functioning draft removes combustion products through the chimney; draft failures or back-drafting from competing exhaust appliances can produce indoor CO.

Attached Garage CO Migration

Attached garages are a frequent residential CO source. Vehicle warm-up periods, gasoline-powered equipment operation in the garage, or vehicles left running with garage doors open but doors to the home open or air-leak pathways present can produce substantial CO migration into living spaces. The pattern: CO levels spike during morning vehicle warm-up, decline through the day, spike again on evening return. Detection requires testing during vehicle-active periods.

Generator and Outdoor Equipment

Whole-home standby generators (Generac, Kohler, similar) produce combustion products that are normally vented away from the home. Generator placement too close to operable windows, fresh-air intakes, or HVAC intakes can produce CO migration during generator operation. Particularly relevant during power outages when generators run for extended periods.

Neighboring Properties

In some Omaha neighborhoods with attached or townhouse-style construction, CO from neighboring properties can migrate through shared walls or attic spaces. Less common but documented in specific construction types.

CO Detector Replacement — Most Homes Have Outdated Detectors

Residential CO detectors have a defined service life because the electrochemical sensor inside the detector degrades over time. Most detectors are designed for 5–7 year service life; some premium models reach 10 years. After service life expiration, the detector may still appear to function (the LED indicators light, the test button produces an alarm) but the actual CO-sensing capability degrades, sometimes to the point of complete loss of sensitivity.

Specific recommendations:

Check manufacture dates — every CO detector has a manufacture date printed on the back. Detectors past their service life should be replaced regardless of apparent functionality.
Multiple detectors recommended — one detector per sleeping area and one on each floor, minimum. Detectors near combustion appliances (basements with furnaces and water heaters, kitchens with gas ranges) supplement the primary detectors.
Combination smoke/CO detectors — popular convenience option. Verify both functions are tested separately because either can fail independently of the other.
Low-level CO detectors — for households with sensitivity concerns, NSI 3000 / Defender LL6070 and similar low-level alarms (15–25 ppm threshold) supplement UL 2034 alarms with earlier warning.
Hardwired vs. battery — hardwired detectors with battery backup are required by code on new construction in most Omaha-area municipalities. Existing homes with battery-only detectors should verify battery replacement annually.

Pricing

Typical CO-related service pricing in 2026:

Standalone whole-house ambient CO testing visit (1.5–3 hour assessment): $185–$385.
CO testing as part of a tune-up or service visit: typically no additional charge above the visit cost.
Suspected heat exchanger combustion analysis (already covered in heat exchanger diagnostic workflow): $145–$285.
Multi-appliance source identification (testing all combustion appliances during one visit): $285–$485.
Post-CO-incident verification (after CO event resolved): $185–$285.
CO detector replacement (single detector, including unit cost): $85–$165 standard UL 2034.
Low-level CO detector (NSI 3000 or Defender): $185–$285 installed.

Frequently Asked Questions

If my CO detector hasn’t alarmed, can my home still have a CO problem?: Yes, in three scenarios. First, UL 2034 detectors are designed to alarm at 70 ppm for 60–240 minutes — chronic exposure to lower levels (10–50 ppm) can still produce health effects but won’t trigger standard alarms. Low-level CO detectors (NSI 3000, Defender LL6070) alarm at 15–25 ppm and are appropriate for households with sensitivity concerns. Second, the detector itself might be past its service life (most detectors are designed for 5–7 years) and the electrochemical sensor has degraded. Third, detector placement matters — a single detector at one location doesn’t measure CO in other parts of the home. Multiple detectors per the recommended density catches CO issues that single-detector placements miss.
How long do CO detectors last?: Most residential CO detectors have a 5–7 year service life; some premium models reach 10 years. The electrochemical sensor degrades over time regardless of whether the detector has been used. Manufacture date is printed on the back of every detector; detectors past their service life should be replaced regardless of apparent functionality. The LED indicators and test button can still function after the sensor has degraded, which gives false confidence that the detector is working when it actually isn’t. Annual battery replacement on battery-powered detectors and periodic detector replacement per the manufacture date are both important.
What’s the difference between CO testing and combustion analysis during a tune-up?: Different measurement target. Combustion analysis during a tune-up measures CO at the appliance — what the burner is producing at the heat exchanger, draft inducer, or vent termination. The question being answered is “is this specific appliance operating with normal combustion?” Whole-house CO testing measures CO in the ambient air people breathe — in living spaces, near sleeping areas, near suspected migration points. The question being answered is “is your family being exposed to elevated CO from any source?” The two measurements complement each other but answer different questions. Tune-up combustion analysis catches developing CO production at the appliance level; whole-house CO testing catches exposure that’s reaching occupants regardless of source.
What CO level is dangerous?: Depends on exposure duration. Acute exposure to high levels: 800–1,000 ppm can cause unconsciousness within hours and death within longer exposure. 1,500–3,000 ppm can cause death within 30 minutes to an hour. Chronic exposure to low levels: 9 ppm sustained for 8 hours is the EPA NAAQS limit and represents the upper threshold for health-protective indoor air. 30–50 ppm sustained for hours produces measurable cognitive effects, fatigue, and headaches especially in sensitive individuals. The danger isn’t always immediately obvious because low-level CO produces symptoms similar to flu or general fatigue. Persistent unexplained headaches improving when leaving the home is a classic chronic CO exposure pattern. Higher acute levels produce confusion, nausea, and loss of consciousness more rapidly. If symptoms suggest CO exposure, evacuate first and investigate after.
If my CO detector is alarming, should I call 911 or your office?: Both, in this order. First, evacuate the home immediately and call 911 from outside the home. Fire department response is the safety-first dispatch — they have CO measurement equipment, can identify acute hazards, and can determine when the home is safe to re-enter. Once the fire department has secured the situation, call our office for follow-up diagnostic testing and source identification. We work with the fire department’s initial findings to identify and address the underlying cause. Don’t try to investigate the source yourself while CO is potentially still elevated in the home — CO is colorless, odorless, and impairs judgment, so testing CO exposure on yourself is exactly the wrong approach. Evacuate, call 911, then call us.

Contact Omaha Heating and Air Conditioning

Our Regency Parkway office is in west Omaha at the I-680 and West Dodge Road interchange. For CO testing consultations, suspected exposure investigations, or post-incident follow-up after a CO alarm event, call during business hours. For active CO alarms or suspected acute CO exposure, evacuate and call 911 first; call us after the fire department has secured the situation.

Emergency Line (24/7): (402) 258-6703
911: for active CO alarms or suspected acute CO exposure — evacuate first and call 911 from outside the home
MUD Gas Emergency: 402-554-7777 for suspected natural gas leaks (distinct from CO; gas leaks have a mercaptan odor, CO has no odor)
Address: Lake Regency Building, 450 Regency Pkwy #370, Omaha, NE 68114
Email: info@omahaheatingairconditioning.xyz
City of Omaha Mechanical Contractor License: #MC-2014-08847
Iowa Plumbing & Mechanical Systems Board License: #B-027841
EPA Section 608 Universal: #608U-2014-227841

Office Hours

Emergency Service: 24 hours a day, 7 days a week
Office Staff: Monday – Saturday, 8:00 AM – 5:00 PM
Closed: Sundays and State/Federal Holidays (emergency line always active)

CO Testing Omaha | Ambient Detection, Source Identification