You switched the thermostat over to heat for the first time since spring, caught a whiff of something burning, and now you are wondering whether that furnace is safe to run all winter. Booking a gas furnace safety inspection is the right instinct. Riley Plumbing, Heating, and Air has been crawling into Carson Valley crawlspaces, Reno attics, and Tahoe-basin garages since 1999, and the furnace that quietly worked all last winter is not automatically the furnace that is safe this one. Combustion equipment fails slowly and quietly. Here is what our technicians actually put a meter on when we open your furnace up, and what we do about what we find.
The Heat Exchanger Is the Whole Point
Your furnace burns gas inside a sealed steel chamber. The combustion gases, carbon monoxide among them, go up the flue. The air that heats your house passes over the outside of that chamber and never touches the flame. That separation is the entire safety design of a forced-air gas furnace, and it depends on the heat exchanger staying intact.
Steel that heats and cools several times an hour fatigues, usually at the welds and the tightest bends. Restricted airflow speeds it up, because a furnace that cannot move enough air across the exchanger runs hotter than it was built to run. That is why a clogged filter is a safety issue and not only an efficiency one.
We inspect the exchanger with a mirror and a camera through the burner compartment and the collector box, then watch the burner flames at the moment the blower starts. If a flame pulls sideways, flutters, or changes color when the fan engages, air is getting somewhere it should not be. That tells us more than a visual pass alone.
What a Gas Furnace Safety Inspection Covers, Step by Step
A gas furnace safety inspection is a sequence of measurements, not a look-over.
Our technicians put a combustion analyzer in the flue and read oxygen, carbon monoxide, and stack temperature through a full cycle. We check inlet and manifold gas pressure against what the data plate calls for. We read the flame signal in microamps, because a weak signal is the most common reason a furnace quits on the coldest night of the year. And we measure temperature rise between return and supply against the range stamped on the unit, which says immediately whether the blower is moving the air the furnace needs.
Then the safety circuit: rollout switches, high limit, pressure switch, draft inducer. Every one exists to shut the furnace down when something has already gone wrong, so we test that they still work instead of assuming.
Last, the venting, where we find more than homeowners expect. On one call this fall a home inspection had flagged corrosion on the flue elbows and standing water in the ductwork, and it was all real. On another we set a new four-inch B-vent elbow in an attic for the furnace and corrected five feet of three-inch B-vent on the water heater flue in the same visit. Nobody had looked at either in years, because nobody goes in the attic.
Elevation Changes the Math on Gas Appliances Here
This is the part homeowners moving in from sea level are surprised by. Gardnerville sits around 4,750 feet. Carson City is close behind, Reno is near 4,500, and South Lake Tahoe is above 6,200. The national fuel gas code requires gas appliances to be derated above 2,000 feet of elevation, and manufacturers publish specific high-altitude orifice sizes and manifold pressures for installations up here.
A furnace running sea-level orifices at 6,000 feet is overfired. There is not enough oxygen in a cubic foot of air up here to burn all that gas cleanly, so you get soot on the burners, higher carbon monoxide, and an exchanger running past its design temperature. The fix is not a repair. It is the orifice and pressure change the installer skipped.
It is also why our installs include the unglamorous items: a hard-piped gas line with a sediment trap at the cabinet, a non-combustible base under downflow units, sheet metal insulated where code calls for it. None of it shows up in a brochure. All of it matters up here.
Carbon Monoxide: What We Measure, and Where
A carbon monoxide alarm in your hallway is important and you should have one on every level. It is not a furnace test. Those alarms warn you after room air has been dangerous for a while. They cannot tell you your combustion is drifting.
We measure carbon monoxide in the flue stream, in the exhaust itself, where a problem shows up long before a room alarm reacts. A clean-burning furnace reads low and holds steady. Numbers that climb as the unit heats up, or spike the moment the blower starts, point us at the heat exchanger or the combustion air supply. We also check for spillage at the draft hood and make sure a bath fan is not pulling the flue backward.
We took a call this fall from an owner whose thermostat was throwing a carbon monoxide warning on a boiler system, tenants in the house, nobody able to say what had changed. That is a same-day call every time. If an alarm or a thermostat says there is carbon monoxide in the building, get everyone outside first, then call us.
When We Shut a Furnace Down, and When We Do Not
Here is the honest part. We do not condemn a furnace for being old, and a gas furnace safety inspection is not a sales appointment. Two of the heating maintenance calls we ran last month were on eighteen-year-old gas furnaces, one under the house in a crawlspace and one in a garage, and both were burning clean with years left in them.
We shut a furnace down for a confirmed breach in the heat exchanger, for unsafe venting, for flame rollout, or for combustion readings we cannot bring into range. Those are not judgment calls and we will show you what we found.
But when we suspect a crack and cannot prove one, we say so in those words, show you the readings, and let you decide. What we will not do is sell you a system on a maybe. If any technician tells you your heat exchanger is cracked, ask to see it and ask for the combustion numbers. Anyone doing the job right will have both.
A Few Things Worth Checking Before You Call
- The filter. If you cannot remember changing it, that is your answer.
- Supply and return registers, including the ones behind the couch. Closing registers to save money raises exchanger temperature.
- The flue termination outside. Sidewall vents on Tahoe-area homes get buried in snow and blocked by rodent nests.
- Combustion air openings in a furnace closet. Storage stacked against a louvered door starves the burners.
- Your carbon monoxide alarms. Press the test button, and replace any unit more than ten years old.
If the house is already cold, skip the checklist. We ran a no-heat call this fall with the house down to 58 degrees. At that point you are not troubleshooting a filter.
Call Riley Plumbing, Heating, and Air
Riley Plumbing, Heating, and Air is locally owned and operated, and we have been working on Northern Nevada and Tahoe-basin homes since 1999. Our technicians are factory trained, our trucks are stocked, and we answer the phone for heating emergencies 24 hours a day. We are licensed in both states: CA License #774078, NV License #85622 C-1, and NV License #85623 C-21B.
We serve Gardnerville, Minden, Carson City, Reno, Zephyr Cove, Indian Hills, and South Lake Tahoe. Call us at 775-293-8855 in Nevada or 530-564-8855 in California, email service@rileypha.com, or schedule online.
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