Carbon Monoxide and Your Furnace: What Every Arizona Homeowner Should Know
It has no smell, no color, and the early symptoms look like the flu. Here is what creates it, how detection works, and what to do if an alarm sounds.
Carbon monoxide is an odorless, colorless gas produced by incomplete combustion in gas furnaces, water heaters, and other fuel-burning appliances. Any home with gas appliances needs working CO detectors on every level and near sleeping areas. If a CO alarm sounds, leave the house immediately and call 911 from outside — do not investigate first.
Where it comes from
Complete combustion of natural gas produces carbon dioxide and water vapor, which vent safely up the flue. Incomplete combustion — insufficient air, a restricted burner, a blocked flue — produces carbon monoxide instead.
In a properly functioning furnace, combustion is contained inside the heat exchanger and its products vent outside. The air that circulates through your house passes over the outside of that heat exchanger and never mixes with the combustion gases.
A cracked heat exchanger breaks that separation. Combustion products can then mix with the air being circulated through every room in the house. This is why a cracked heat exchanger is not a repairable condition and why a furnace with one has to be shut down.
Other sources people forget
- Gas water heaters, especially with corroded or disconnected flues
- Gas ranges and ovens used for supplemental heat — never do this
- Blocked or bird-nested flues and chimneys
- A vehicle running in an attached garage, even briefly with the door open
- Portable generators used during a power outage — outdoors only, far from windows
- Gas fireplaces and space heaters that are unvented or improperly vented
Symptoms, and why they get missed
Early carbon monoxide exposure produces headache, dizziness, nausea, fatigue, and confusion. It looks exactly like the flu, which is precisely why it is dangerous in winter.
The pattern that should raise suspicion: symptoms that affect multiple people in the household at the same time, that improve when everyone leaves the house, and that return when they come back. Pets often show it first because of their smaller body mass.
Higher exposure produces confusion, loss of coordination, and loss of consciousness. At that stage people frequently cannot help themselves, which is why detection has to be automatic rather than dependent on anyone noticing.
Detectors: where and how many
- On every level of the home, including the basement if there is one
- Within about fifteen feet of every sleeping area
- Not directly beside a fuel-burning appliance, which produces brief normal spikes and causes nuisance alarms
- Not in a bathroom, not in direct sunlight, not within a few feet of a vent or window
- Replace the entire unit every five to seven years — the sensors have a service life and expire regardless of battery
- Test monthly. Press the button. It takes ten seconds.
A digital display model is worth the small extra cost. It shows the current reading, which lets a fire department or technician see whether there is a low-level chronic exposure rather than just a pass/fail alarm.
What a technician checks
Every gas heating service call we run includes combustion safety checks, whether or not that is what you called about.
- Visual heat exchanger inspection, with a camera where access allows
- Carbon monoxide measurement in the supply air stream
- Flue draft verification — confirming combustion products are actually leaving
- Burner flame quality, which tells you a great deal about combustion completeness
- Gas manifold pressure
- Combustion air availability, especially for furnaces in closets or small rooms
If we find a cracked heat exchanger, we red-tag the unit, shut off the gas to it, and show you the evidence. We do not expect anyone to take that on faith, and a legitimate finding comes with documentation — camera images and CO readings.
The Arizona-specific risk
Our particular risk profile comes from equipment that runs only a few months a year. Flues develop bird nests and debris over a long idle season. Water heater vents corrode without anyone looking at them. And because Valley homes are heated so little, a slowly developing problem has many months to progress unnoticed.
It is also easy to be complacent about heating equipment in a place defined by its summers. A gas furnace in Phoenix deserves the same annual attention as one in Chicago, even though it runs a fraction of the hours.
Frequently asked
Do I need a carbon monoxide detector in Arizona?
If you have any gas appliance — furnace, water heater, range, fireplace — or an attached garage, yes. Place them on every level and within about fifteen feet of sleeping areas, and replace the units every five to seven years because the sensors expire.
What are the symptoms of carbon monoxide poisoning?
Headache, dizziness, nausea, fatigue, and confusion — very similar to the flu. The distinguishing pattern is that symptoms affect multiple people at once, improve when everyone leaves the house, and return when they come back.
Can a cracked heat exchanger be repaired?
No. It has to be replaced, and on most furnaces the cost of a heat exchanger replacement approaches the cost of a new furnace. A furnace with a confirmed crack must be shut down until it is replaced, because combustion gases can mix with the air circulating through your home.