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Leave the house immediately with everyone in it. Do not turn lights or appliances on or off, do not use phones inside, and do not try to find the leak. From a safe distance outside, call 911 or your gas utility's emergency line. Do not go back in until you are told it is safe.
More on CO and gas safety checksMove everyone, including pets, outside into fresh air and call 911. Do not silence the alarm and stay inside. If anyone has headache, dizziness, nausea, or confusion, tell the dispatcher. After responders clear the home, have fuel-burning appliances inspected before normal use.
More on CO and gas safety checksUse only electric space heaters with tip-over and overheat protection, plugged directly into a wall outlet, with at least three feet of clearance from anything that can burn. Never use an oven, grill, or unvented fuel heater to heat the home.
Risk rises when indoor areas near exterior walls drop toward freezing. If heat will be out for a long time in very cold weather, open cabinet doors under sinks, let faucets on exterior walls drip slightly, and keep interior doors open to share heat.
The most common reasons are the thermostat fan set to ON instead of AUTO, burners that fail to light or stay lit, or an overheating safety lockout caused by a clogged filter. Set the fan to AUTO and check the filter. If air stays cold, a technician should test ignition and flame sensing.
More on the furnace symptom guideMost modern furnaces have a control board LED that blinks a fault code. The code chart is usually printed inside the access panel. Note the pattern before calling; it helps a technician narrow the cause quickly. Do not bypass switches to clear a code.
Many common repairs such as igniters, flame sensors, capacitors, and pressure switches are completed in one visit. Brand-specific boards or motors may require ordering parts. A safety finding may require the unit to stay off until resolved.
More on furnace repairMany gas furnaces last roughly 15 to 20 years with regular maintenance. Installation quality, airflow, and venting matter as much as climate. Age alone is not a reason to replace; age combined with a major repair or safety finding often is.
More on the repair-or-replace guideA common rule of thumb multiplies the furnace age by the repair cost; if the result exceeds about 5,000, replacement deserves a serious look. Treat it as a conversation starter, not a verdict. Safety findings and comfort problems can outweigh the math either way.
More on the repair-or-replace guideThe heat exchanger separates combustion gases from the air you breathe. A crack or hole can let combustion products into the airstream. A confirmed crack is usually a reason to stop using the furnace and replace it or the heat exchanger. Ask to see evidence such as photos or camera footage.
More on CO and gas safety checksQuotes often include different equipment efficiency, staging, venting changes, duct corrections, permits, and warranty terms. Two quotes for the same nameplate size may describe very different jobs. Compare scope line by line before comparing price.
More on furnace cost factorsA diagnostic fee pays for testing time and expertise. Many companies apply it toward the repair if you proceed. Ask how the fee works before the visit so there are no surprises.
More on furnace cost factorsYes. At about 5,280 feet there is less oxygen per cubic foot of air, which changes how gas burns. Manufacturers provide high-altitude instructions, often involving gas input adjustment or orifice changes. A furnace not set up for altitude can run hotter, trip safety limits, or burn less cleanly.
More on furnace tune-ups and maintenanceMany Denver homes are very dry in winter, and some homeowners add a whole-house humidifier for comfort. Humidifiers need seasonal cleaning, correct settings to avoid window condensation, and attention to drain lines.
Warm air rises, but in winter upper floors often lose more heat through roofs and have longer duct runs. Single-stage furnaces and undersized returns make it worse. Duct balancing, return air improvements, and two-stage equipment are common solutions.
More on the furnace symptom guideOnce a year, ideally in early fall before sustained cold weather. Heat pumps and dual-fuel systems benefit from both a fall and spring check because they operate year-round.
More on furnace tune-ups and maintenanceUse the size and type your system was designed for. A higher MERV rating captures more particles but can restrict airflow in systems with small returns. A thicker media filter usually allows better filtration with less restriction.
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