Home
Well-sealed home with gas furnace, gas water heater, gas stove
Symptoms
Persistent headaches, fatigue, difficulty concentrating (weekdays)
Root Cause
Cracked heat exchanger leaking CO below alarm threshold
Resolution
Headaches gone within one week of furnace repair
What Was Happening?
A homeowner who worked remotely started experiencing persistent headaches and fatigue in October. The headaches appeared by mid-morning and worsened through the afternoon. They improved on weekends when the homeowner spent more time outdoors and away from the house. A doctor's visit found no medical explanation. The homeowner tried adjusting sleep habits, diet, and screen time without improvement.
The timing mattered: symptoms started in October, which was when the furnace kicked on for heating season. But nobody connected the two until the EezyAir assessment flagged the correlation between symptom onset, heating season, and the home's combustion appliance configuration.
What Did the Assessment Find?
The assessment identified a combination of factors that created the conditions for chronic low-level CO exposure without triggering the home's CO alarm.
Three gas combustion appliances in a well-sealed home
The home had a gas furnace, gas water heater, and gas stove. The house had been weatherized for energy efficiency, which reduced fresh air infiltration. In a well-sealed home, combustion byproducts that would be diluted by natural air exchange in a drafty home can accumulate to higher concentrations. The tighter the envelope, the less margin for error if any combustion appliance malfunctions.
Home office adjacent to the utility closet
The
home office where the homeowner spent 8+ hours per day was next to the utility closet containing the gas water heater. Any CO leaking from the furnace or water heater would reach the office at higher concentrations than other rooms simply because of proximity. The homeowner was accumulating the highest exposure of anyone in the household because of where they spent their working hours.
CO detectors with expired batteries
The home had CO detectors installed, but the batteries had expired. Even with functioning batteries, standard residential CO alarms are designed to alert at 70 ppm sustained for one to four hours. A cracked heat exchanger producing 10 to 25 ppm would never trigger the alarm, but those levels sustained over an 8-hour workday are sufficient to produce headaches, fatigue, and cognitive difficulty.
Symptoms correlated with the start of heating season
The assessment specifically asks about when symptoms started and what changed around that time. October was when the furnace began running regularly. The weekday-weekend pattern further narrowed the investigation: the homeowner spent more consecutive hours in the home on workdays than weekends, producing higher cumulative CO exposure during the work week.
What Actions Were Taken?
✓
Immediate: replaced CO detector batteries and added a detector near the home office door. The new detector did not alarm, confirming levels were below the standard threshold, but a low-level CO monitor placed in the office showed readings between 12 and 18 ppm during furnace operation.
✓
An HVAC technician inspected the furnace and identified a cracked heat exchanger. The crack was allowing combustion gases, including CO, to leak from the combustion chamber into the air supply distributed through the ductwork.
✓
The heat exchanger was repaired. Post-repair monitoring showed CO levels in the office dropped to background levels (0 to 2 ppm).
✓
The homeowner began opening a window in the home office during work hours and using the range hood consistently when cooking, as additional ventilation measures for the remaining gas appliances.
What Happened?
Headaches resolved within one week of the furnace repair. The fatigue and concentration difficulty cleared around the same time. The homeowner had spent months attributing the symptoms to stress, screen time, and sleep quality. The doctor had found no medical cause. The answer was in the furnace, 10 feet from the desk.
The total cost of investigation and repair was significantly less than the ongoing medical appointments that had not identified the cause. The cracked heat exchanger was also a safety risk that would have worsened over time if left undetected.
What Does This Case Illustrate?
This case demonstrates the danger of low-level CO exposure that sits below the alarm threshold. The homeowner had CO detectors, which is the standard safety recommendation. But the detectors are designed for acute, life-threatening events, not for chronic, sub-threshold exposure that produces real symptoms over hours of daily exposure. The weekday-weekend pattern was the critical clue: symptoms that track with time spent in the home, not with any medical variable, point to the environment.
It also shows why symptom timing matters more than a single measurement. A technician visiting for a standard furnace checkup might not have identified the cracked heat exchanger without specifically looking for it. The assessment connected the symptom timeline (started in October, worse on weekdays, improved away from home) to the heating system startup and flagged combustion exposure as the most probable cause. The timeline was the diagnostic tool that the CO alarm could not provide.
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