Carbon Monoxide Testing in Kirkwood and West St. Louis County

Carbon monoxide is a colorless, odorless gas produced by incomplete combustion. It’s also one of the leading causes of accidental poisoning death in the United States, with over 400 deaths and 50,000 emergency room visits per year attributable to non-fire CO exposure. The risk in residential settings comes from gas-fired equipment producing more CO than properly vented combustion would allow, combined with depressurization or backdraft conditions that bring combustion gases into the living space rather than venting them outside. Tight modern construction and weatherized older homes have measurably elevated CO exposure risk compared to leakier construction, because reduced air infiltration means less dilution of any CO that enters the indoor air. This page documents the diagnostic services we provide for combustion safety verification and indoor CO monitoring — what we measure, when measurement is indicated, and what the readings mean.

How Carbon Monoxide Forms and Where It Comes From

Complete combustion of natural gas (methane) produces CO2 and water vapor. Incomplete combustion — from inadequate combustion air, improper gas/air mixture, cool flame quench against cold surfaces, or other combustion problems — produces CO along with the normal combustion products. Healthy gas-fired equipment produces under 100 ppm CO air-free in the flue gases; equipment producing above 400 ppm has combustion problems that warrant immediate service.

Residential CO sources include:

• Gas furnaces — especially equipment with combustion problems (dirty burners, restricted flue, inadequate combustion air) or cracked heat exchangers that allow combustion products to mix with supply air
• Gas water heaters — orphaned water heaters (water heater alone in basement after furnace upgrade) with oversized flues can experience backdrafting
• Gas ranges and ovens — particularly older equipment or units operated for extended periods without range hood ventilation
• Gas dryers — with venting problems
• Vehicles in attached garages — cars warming up with garage door closed produce significant CO that can migrate into the home through the door-to-garage interface
• Charcoal or gas grills — operated indoors or near intake vents (rare but serious risk)
• Portable generators — operated inside or near building openings during power outages
• Fireplaces and wood stoves — with venting problems or operated with closed dampers

Carbon Monoxide Exposure Effects

CO bonds to hemoglobin in red blood cells with affinity over 200 times greater than oxygen, forming carboxyhemoglobin (COHb) and reducing the blood’s oxygen-carrying capacity. Exposure effects scale with CO concentration and exposure duration:

• Up to 9 ppm — ASHRAE indoor air quality standard for residential occupied spaces. No measurable health effect at typical exposure.
• 10–35 ppm — mild headache and fatigue possible with prolonged exposure. Below standard CO alarm thresholds.
• 35–70 ppm — headache, fatigue, dizziness, nausea with prolonged exposure. UL 2034 residential CO alarm activation typically in this range with multi-hour exposure.
• 70–150 ppm — significant symptoms including severe headache, vomiting, confusion. Immediate UL 2034 alarm activation.
• 150–400 ppm — serious risk including loss of consciousness, particularly with extended exposure
• Above 400 ppm — potentially fatal exposure. Brain damage and death possible within hours.

The challenge with CO is that early-stage symptoms (headache, fatigue, flu-like) frequently get attributed to other causes — cold, flu, allergies, work stress — while exposure continues and accumulates. By the time symptoms are obvious enough to recognize as poisoning, exposure level is dangerous. CO alarms exist specifically because the human nose can’t detect CO and the early symptoms don’t reliably trigger evacuation.

What CO Testing Measures

Bacharach Fyrite Insight Plus Combustion Analysis

The Bacharach Fyrite Insight Plus is the industry-standard combustion analyzer for residential and commercial HVAC service. Inserted in the flue during equipment operation, it measures:

• CO air-free — carbon monoxide concentration in the flue gases adjusted for excess air dilution. The key measurement for combustion safety. Target under 100 ppm; investigation warranted above 100 ppm; immediate service required above 400 ppm.
• CO2 percentage — combustion efficiency indicator. Target 8–11% on natural gas residential.
• O2 percentage — excess combustion air indicator. Target 4–9% on residential equipment.
• Stack temperature — flue gas temperature compared to manufacturer specification
• Calculated combustion efficiency — matches the equipment’s AFUE rating within several percentage points on properly operating equipment
• Draft pressure — verifies flue draft adequate for safe venting

Combustion analysis is performed on every furnace tune-up and diagnostic visit. It’s the difference between “the furnace appears to be running” (visual observation) and “the furnace is producing safe combustion” (measurement).

Indoor Air CO Monitoring

For households with concerns about ambient indoor CO levels (separate from equipment combustion safety), portable CO monitors with data logging capability provide multi-hour measurement at specific locations:

• Living spaces during typical equipment operation
• Sleeping areas during overnight measurement
• Garage interior after vehicle operation
• Basement near combustion equipment during equipment cycling
• Areas with reported symptoms for time-correlated measurement

Indoor CO measurement at any sustained level above 10 ppm warrants investigation; sustained levels above 30 ppm warrant immediate action.

Backdraft and Spillage Testing

Some homes have venting configurations where combustion gases can backflow into the living space rather than venting properly outside. Backdraft and spillage testing involves:

• Worst-case depressurization testing — simulating maximum house depressurization (exhaust fans running, dryer operating, fireplace damper open) to verify combustion equipment can still vent properly
• Spillage detection at draft hoods and flues — using smoke or CO measurement to detect combustion gas escape from flue connections
• Pressure differential measurement — verifying adequate combustion air supply and proper venting

When CO Testing Is Indicated

• After CO alarm activation — verifying source and confirming safe levels after equipment service
• Annual furnace tune-up — included in standard tune-up service
• Symptoms suggesting CO exposure — flu-like symptoms that improve when leaving home and return when re-entering, especially during heating season
• Recent home weatherization — air sealing reduces ventilation and can affect combustion equipment performance
• Recent HVAC equipment change — verifying new equipment operates safely
• Tight new construction — verifying adequate combustion air supply in airtight envelope
• Orphaned water heater — after furnace upgrade where the water heater alone now occupies an oversized flue
• Real estate transactions — some inspection scopes include CO testing
• Health-sensitive occupants — elderly residents, infants, pregnant residents, people with cardiovascular or respiratory conditions where CO sensitivity is elevated

What to Do During a CO Alarm Event

If your CO alarm activates:

1. Evacuate immediately. Get all occupants outside to fresh air.
2. Call 911. Even if symptoms are mild or absent, professional response ensures safe re-entry verification.
3. Don’t re-enter the home until first responders verify CO levels are safe and the source has been identified or eliminated.
4. Contact your utility company (Spire Missouri at 800-887-4173 for natural gas emergencies) to shut off gas service if utility issue is suspected.
5. Contact a qualified HVAC contractor after the immediate emergency is resolved to diagnose the source. Purisync provides post-incident CO testing and equipment service.
6. Don’t ignore the alarm assuming it’s malfunctioning. CO alarms with low-battery warnings make different sounds than alarm activation; an actual alarm signal indicates CO is present.

Pricing

• Combustion analysis service visit (Bacharach Fyrite Insight Plus measurement on all gas-fired equipment): $129. Included in standard furnace tune-up at no additional cost.
• Indoor air CO monitoring service (24–72 hour data-logged measurement at multiple locations): $240–$420 depending on duration and number of locations.
• Backdraft and spillage testing (worst-case depressurization with measurement): $180–$340.
• Post-incident CO diagnostic (after CO alarm activation, includes combustion analysis, indoor monitoring, and venting verification): $280–$540 depending on scope.
• UL 2034 compliant CO alarm installation: $95–$180 per alarm including hardwired or battery-powered alarm and installation labor.

Frequently Asked Questions

How much does CO testing cost in Kirkwood?

Combustion analysis service visit (Bacharach Fyrite Insight Plus measurement on all gas-fired equipment) runs $129, included at no additional cost in standard furnace tune-up. Indoor air CO monitoring with 24-72 hour data-logged measurement at multiple locations runs $240-$420. Backdraft and spillage testing with worst-case depressurization runs $180-$340. Post-incident CO diagnostic after CO alarm activation runs $280-$540 depending on scope (combustion analysis, indoor monitoring, venting verification). UL 2034 compliant CO alarm installation runs $95-$180 per alarm. All pricing includes equipment, calibration, measurement, documentation, and Purisync recommendations for any required follow-up service.

How often should I have CO testing done?

Combustion analysis on gas-fired equipment is included in every fall furnace tune-up and every diagnostic service visit — annual testing is standard for any home with gas-fired heating. Additional CO testing is indicated after CO alarm activation, with symptoms suggesting CO exposure (flu-like symptoms that improve away from home and return upon re-entry during heating season), after home weatherization that reduced air infiltration, after HVAC equipment change, in tight new construction, with orphaned water heater situations, during real estate transactions, and for households with health-sensitive occupants. Standalone CO monitoring (multi-hour indoor air measurement) is typically a one-time service unless ongoing concerns warrant repeat testing.

What CO level is dangerous?

Effects scale with concentration and exposure duration. Under 9 ppm is the ASHRAE indoor air quality standard with no measurable health effect at typical exposure. 10-35 ppm produces mild headache and fatigue with prolonged exposure. 35-70 ppm produces headache, fatigue, dizziness, and nausea with prolonged exposure — UL 2034 residential CO alarm activation typically occurs in this range with multi-hour exposure. 70-150 ppm produces significant symptoms (severe headache, vomiting, confusion) with immediate alarm activation. 150-400 ppm presents serious risk including loss of consciousness. Above 400 ppm is potentially fatal — brain damage and death possible within hours. The challenge is that early-stage symptoms get attributed to cold, flu, or other causes while exposure continues. CO alarms exist because the human nose can’t detect CO and early symptoms don’t reliably trigger evacuation.

What should I do if my CO alarm goes off?

Evacuate immediately — get all occupants outside to fresh air. Call 911 even if symptoms are mild or absent (professional response ensures safe re-entry verification). Don’t re-enter the home until first responders verify CO levels are safe and the source has been identified or eliminated. Contact your utility company (Spire Missouri at 800-887-4173 for natural gas emergencies) to request gas service shut-off if utility issue is suspected. Contact a qualified HVAC contractor after the immediate emergency is resolved to diagnose the source — Purisync provides post-incident CO testing and equipment service. Don’t ignore the alarm assuming it’s malfunctioning; CO alarms with low-battery warnings make different sounds than alarm activation. An actual alarm signal indicates CO is present at concerning levels.

Are tight modern homes more at risk of CO exposure?

Yes, in two ways. First, reduced air infiltration means less natural dilution of any CO that enters the indoor air — the same CO source produces higher indoor concentration in a tight home than a leaky home. Second, depressurization from exhaust fans, range hoods, dryers, and other exhaust appliances can create conditions where combustion equipment can’t vent properly, drawing combustion gases including CO back into the living space (backdraft). Solutions for tight homes include verified combustion air supply (passive or active makeup air), direct-vent combustion equipment that uses outdoor combustion air via a separate pipe (immune to indoor depressurization), and mechanical ventilation systems (ERVs) that maintain net-zero pressure balance. Annual combustion analysis is particularly important in tight construction to catch developing issues before symptoms develop.

---

Contact Purisync Heating and Air

For carbon monoxide testing, post-incident CO diagnostic, or combustion safety verification, contact our 325 N Kirkwood Road office at (314) 338-5111. If your CO alarm has activated, evacuate immediately and call 911 before contacting us.

• Emergency Line (24/7): (314) 338-5111
• Address: 325 N Kirkwood Rd #245, Kirkwood, MO 63122
• Email: info@purisyncheatingairconditioning.xyz
• St. Louis County Mechanical Contractor License: #MC-2014-08439-STL
• Kirkwood Business Registration: #BL-2014-1187
• EPA Section 608 Universal: #608U-2014-385721

Contact Us →

Office Hours

• Emergency Service: 24 hours a day, 7 days a week
• Office Staff: Monday – Saturday, 9:00 AM – 5:00 PM
• Closed: Sundays and State/Federal Holidays (emergency line always active)