HVAC FAQ: Answers to Common AC, Heating and Ductwork Questions

The most common causes are an outdoor unit that is not running (tripped breaker, failed capacitor or contactor), a clogged filter, a dirty or frozen coil, or low refrigerant from a leak. Check the thermostat, filter and breakers first. Full guide: AC not blowing cold air.

Signs include ice on the larger copper line or indoor coil, a hissing sound, long run times with lukewarm air, and higher bills. Refrigerant does not get used up, so low refrigerant means a leak. A technician has to confirm it with gauges and find the leak.

Usually not enough air moving across the indoor coil (a dirty filter, closed vents, a dirty coil or blower problem) or low refrigerant. Turn cooling off, set the fan to On to thaw it, and replace the filter. See why an AC freezes up.

Most often the condensate drain line is clogged, so water backs up out of the drain pan. A cracked pan, failed condensate pump or melting ice can also cause it. Turn the system off and see AC leaking water inside.

On 95-degree afternoons, long run times are normal. It is not normal if it never shuts off in mild weather, the house keeps getting warmer, or it feels humid inside. Those point to low refrigerant, dirty coils, leaky ducts or a system that is too small.

The U.S. Department of Energy suggests setting it as high as is comfortable while you are home. Many households are comfortable at 76 to 78 degrees with ceiling fans. Raising it while you are away saves the most. See thermostat settings.

Once a year, ideally in spring before the heat arrives. A heat pump heats and cools, so it should be serviced twice a year. Learn about AC maintenance.

About 12 to 15 years is typical in North Alabama. Heat pumps, which run year-round, often last about 10 to 15 years. See how long HVAC systems last.

A rough rule of thumb in the South is 1 ton for every 500 to 600 square feet, but insulation, windows and ducts change the answer. A Manual J load calculation is the right way to size a system. See what size AC you need.

Buzzing often comes from an electrical part like a contactor, capacitor or motor. Hissing can mean a refrigerant leak. Both should be checked by a technician. Turn the system off if the noise is loud or you smell burning.

Common causes are the thermostat fan set to On, a clogged filter, a dirty flame sensor, a failed ignitor, the gas supply being off, or a clogged drain on a high-efficiency furnace. See furnace blowing cold air.

Set the thermostat to Off, turn off the furnace power switch (it looks like a light switch) for about a minute, turn it back on, then set the thermostat to Heat. If it fails again, leave it off and call. If you smell gas, leave the house and call your gas utility from outside.

Banging at startup, grinding or scraping metal, and rumbling after the burners shut off all need a technician. A click, a whoosh and a steady hum are normal. See furnace noises explained.

Yes, if the heat exchanger is cracked or the vent pipe is blocked or disconnected. Put CO alarms on every level and outside sleeping areas, and have the furnace checked every year. See carbon monoxide and furnace safety.

A light burning dust smell for the first few minutes of the season is normal. A burning plastic or electrical smell is not. Turn the system off and call. See HVAC smells explained.

When it is near or below freezing, yes. A heat pump runs long, steady cycles in cold weather. It is not normal if it runs nonstop in mild weather or cannot reach the set temperature. See heat pumps in winter.

That is a normal defrost cycle. The heat pump melts frost off the outdoor coil for about 5 to 15 minutes, and the melting frost turns to steam. Thick ice that does not clear is not normal.

Only when the heat pump itself is not working, such as an outdoor unit frozen solid. Emergency heat runs the electric heat strips alone, which costs much more. Call for repair and switch back once it is fixed.

It may be in defrost (normal, a few minutes), or there may be a thermostat setting, tripped breaker, ice, low refrigerant or failed part. See heat pump not heating.

Both work well here. Heat pumps are efficient through most of our mild winter and also cool. Gas furnaces deliver hotter air on the coldest nights. The right choice depends on your home and fuel. See heat pump vs. gas furnace.

Every 1 to 3 months for most 1-inch filters. Change it more often if you have pets, allergies or a dusty house. Thicker media filters can last longer; follow the filter maker’s guidance.

Twice a year is ideal: the AC in spring and the heat in fall. Heat pumps should be serviced twice a year because they run in both seasons. See our fall HVAC checklist.

A good tune-up typically includes cleaning and checking coils, checking refrigerant and electrical parts, testing safety controls, flushing the condensate drain, checking the blower, and on gas furnaces, inspecting burners, flame and venting. Learn about HVAC maintenance.

Yes for most homes. Yearly service catches small problems, like a weak capacitor or clogged drain, before they cause a breakdown, and keeps the system running efficiently.

Multiply the system’s age by the repair cost. Over 5,000, lean toward replacing. Under 5,000, repairing usually makes sense. See the $5,000 rule explained.

About 12 to 15 years for an AC, 10 to 15 for a heat pump, and 15 to 20 for a gas furnace. See how long HVAC systems last.

SEER2 is the cooling efficiency rating under the test method that began in 2023. Higher is more efficient. In the Southeast, including Alabama, new central air conditioners under 45,000 BTU and heat pumps must be at least 14.3 SEER2, according to the U.S. Department of Energy.

Hot or cold spells raise bills, but jumps often come from a dirty filter, low refrigerant, leaky ducts, an aging system, or heat pump backup heat running too much. See thermostat settings and high bills.

Repair if the system is fairly young and the repair is modest. Consider replacing if it is 12 or more years old, uses R-22 refrigerant, needs a major part, or keeps breaking down. See repair or replace.

It depends on the size of the system, the type (AC, heat pump or furnace), efficiency, and whether ductwork needs work. We give free estimates on new systems and can talk through financing options. Call (256) 534-2941.

Usually only when there is visible mold in hard ducts or system parts, rodents or insects in the ducts, or debris blowing out of the vents. Those are the cases the EPA lists. See is duct cleaning worth it.

There is no set schedule. The EPA advises cleaning only when needed, not as routine maintenance.

Rooms that never get comfortable, high bills, weak airflow, extra dust, ceiling stains, musty smells, and crushed or torn ducts are common signs. See signs your ductwork needs replacing.

Metal ducts can last for decades if they stay dry and sealed. Flexible duct in a hot attic often shows wear after 15 to 25 years.

Cold air in the duct meets hot, humid attic air, and moisture condenses where insulation is thin or joints leak. Sealing and re-insulating or replacing the duct fixes it and prevents ceiling stains and mold.

Ducts in unconditioned spaces, such as attics, crawlspaces and garages, should be insulated. In our climate, that keeps cool air cool and helps prevent sweating.

ENERGY STAR says about 20 to 30% of the air moving through a typical home’s ducts is lost to leaks, holes and poorly connected ducts.

No. ENERGY STAR says never use duct tape on ducts because it does not last. Use mastic sealant or metal tape.

Common causes are a leaky or crushed duct to that room, a duct run that is too long or too small, a closed damper, a missing return, or extra heat from sunny windows. A duct check usually finds it. See duct repair.

Not always, but check. If the ducts are old, leaky, crushed or undersized, the new system will not perform as rated. Replacing the worst sections, or all of it, at the same time is often the best timing. See duct replacement.