Fuel-burning heat in a Tucson house is usually a gas furnace. Carbon monoxide is a risk when combustion or venting is wrong. The gas has no odor. The alarm, or people getting sick while the heater runs, is the signal. Sabino Creek’s role on this page is the order of operations and a link to the agencies that publish the guidance. We are not a medical office and we are not the gas utility.
Read CDC: about carbon monoxide. The CDC describes carbon monoxide as a colorless, odorless gas and lists symptoms that include headache, dizziness, weakness, nausea, chest pain, and confusion. Read EPA: carbon monoxide’s impact on indoor air quality for how appliances and attached garages show up in indoor air. If those pages and this one disagree, the agency page wins.
Symptoms and how they’re checked
The price column is omitted. Safety steps are not a quoted repair.
| Symptom | Likely cause | How it’s checked |
|---|---|---|
| CO alarm sounds | The alarm is doing its job. Cause is not known from the hallway. | Everyone out, including pets. Call 911 from outside. Do not silence the alarm and stay. |
| Rotten-egg smell at the furnace | That odor is gas, which is not the same gas as carbon monoxide | Leave. Call 911 or Southwest Gas. Do not hunt for the leak. |
| People feel sick only while the heater runs, and better in fresh air | A pattern the CDC tells you not to ignore | Leave and call 911. Do not wait to see if a second cycle is milder. |
| Dusty smell on the first fire, no alarm, no one sick | Often dust on a cold heat exchanger | Not a CO event by itself. See the burning-smell page. If an alarm is added to the story, treat it as an alarm. |
| You want the furnace checked after the house is cleared | Combustion, venting, and the heat exchanger are the repair-side questions | Send the form only after the fire department or gas utility has said the house is safe. |
A heating visit can look at ignition, venting, and the heat exchanger. It does not replace an alarm and it does not clear a house. After the emergency is over, furnace repair and burning smell are the service pages. The seasonal reminder to test the alarm is on the checklist.
A gas water heater in the same closet is a second combustion appliance. If the alarm or the gas smell is the water heater rather than the furnace, the order of operations is the same: leave first. The repair conversation, after the house is clear, is water heater repair. Sabino Creek refers that visit. We do not service the heater.