By Robert Patterson
The short answer: a gas furnace burns fuel to heat air, then blows it through your ducts. The number that matters is AFUE (how much fuel becomes heat), and the step that matters most is a combustion and carbon-monoxide check on every visit.
How does a gas furnace work?
Burners ignite gas in a sealed heat exchanger; the blower pushes household air across that hot exchanger and into your ducts; exhaust gases vent safely outside. If the heat exchanger cracks, exhaust can mix with your air — which is exactly why safety testing isn't optional.
What is AFUE and how much should you care?
AFUE is the furnace's seasonal efficiency. In our mild-winter climate a furnace runs far fewer hours than your AC, so chasing the very top AFUE tier pays back slower here than up north. If you heat a lot or want one system for both seasons, weigh a furnace vs. a heat pump instead.
The failure mode we watch for
Short-cycling, a cracked heat exchanger, a failing igniter, or a clogged flue. These are safety issues, not just comfort ones. Our TDLR-licensed technicians end every furnace repair and tune-up with a combustion + CO test.
Your next step
Get ahead of the first cold snap — see our mild-winter heating guide, explore heating services, or keep it on schedule with the $159/yr maintenance plan. Book a heating check or visit the Learning Center.