When a furnace is worth replacing
Age alone isn’t the reason. Houston winters are mild, so a furnace may run fewer hours here than in colder states, though its blower also moves air in summer if it’s part of your AC system. The signs that point toward replacing are a cracked heat exchanger, several repairs in a short time, a failed major part on an old unit, a furnace that can’t heat the house on a cold night, or rust and soot around the burners. We’ll show you what we find and price both options side by side.
A cracked heat exchanger is a safety problem
The heat exchanger keeps the burner’s exhaust (including carbon monoxide) out of the air that goes into your house. A crack in it is not something to run and watch. On most furnaces it means replacement. The U.S. Consumer Product Safety Commission recommends a yearly professional inspection of fuel-burning heating equipment and working carbon monoxide alarms on every level of the home. If your CO alarm sounds, get everyone outside and call 911.
Standard or high-efficiency: what changes in the install
Furnace efficiency is rated in AFUE, the share of the fuel that becomes heat for the house. Standard-efficiency gas furnaces are around 80% and vent through a metal flue. High-efficiency (condensing) models run 90% and up. They vent through plastic pipe and produce acidic condensate that has to drain away, so the vent route and a drain line become part of the job. Which one fits your home depends on where the furnace sits, how it can vent and how often you use it. We don’t quote savings percentages, because they vary too much from house to house.
Size it to the house, not to the old furnace
A furnace that’s too big heats the house in short bursts and shuts off, which wears parts and leaves some rooms uneven. The right size comes from a load calculation for your home, which is why the industry standard for it, ACCA Manual J, exists. Ask any contractor, including us, how the size was chosen. In Houston the ductwork and blower matter as much as the furnace, because they carry your cooling in summer too.
If your AC coil sits on the furnace
In many Houston attics and closets the AC’s indoor coil sits right on the furnace. A new furnace has to work with that coil, and your technician checks that it fits and tells you if the coil should be replaced too. Replacing the furnace and the AC together is a bigger project; see AC replacement and installation.
Gas, venting and safety checks
A furnace install is more than setting the new unit in place. The gas connection, the venting, the condensate drain on a high-efficiency model, the filter and return air, and the thermostat all have to be right. Your estimate lists what’s new and what’s reused, so there’s nothing left to guess.
Permits and inspections
In the City of Houston, installing or replacing HVAC equipment generally takes a mechanical permit and an inspection by the City. Outside the city limits the rules depend on where you live. We pull the permit ourselves. If you’re comparing quotes, ask each contractor who pulls theirs, and get the answer in writing.
Have a furnace that’s acting up but might be repairable? See heating and furnace repair.
Sources: U.S. CPSC, carbon monoxide safety · ACCA Manual J · U.S. DOE, Energy Saver: furnaces and boilers · City of Houston Permitting Center. Checked November 2026.
