An HVAC system should be professionally serviced twice a year: once in the spring for the air conditioning and once in the fall for the heating system. Between those professional visits, the homeowner should replace the air filter every one to three months, keep the outdoor unit clear of debris, and listen for unusual sounds that indicate a problem is developing. The twice-yearly professional service is the minimum recommended by equipment manufacturers to maintain warranty coverage and by HVAC industry organizations to maintain efficiency and reliability. A system that is serviced on this schedule will last 15 to 20 years and operate at close to its original efficiency for most of that time. A system that is never serviced will fail years earlier and cost significantly more to operate while it is failing.
The professional service visits are not the same for cooling and heating equipment. The spring visit focuses on the air conditioning: cleaning the condenser and evaporator coils, checking the refrigerant charge, testing the capacitors and contactors, cleaning the condensate drain, and verifying the thermostat operation. The fall visit focuses on the heating system: cleaning the burners and the heat exchanger, checking the gas pressure, testing the ignition system and the flame sensor, inspecting the flue and the venting, and verifying the safety controls. A heat pump receives elements of both visits in each visit because it operates year-round.
EPA WaterSense advises that regular maintenance of home systems prevents waste and saves money. An HVAC system that is properly maintained uses less energy, delivers more consistent comfort, and is less likely to fail during the hottest or coldest weather when repair costs are highest.
The Twice-Yearly Service Schedule
Schedule the cooling service in early spring, March or April, before the first heat wave. HVAC contractors are least busy during the spring and fall shoulder seasons. The same service call in July, when the temperature is 95 degrees and every contractor in town has a backlog of no-cool calls, will cost more and will be harder to schedule. The spring service prepares the AC for the summer ahead. The technician cleans the outdoor condenser coil, checks the refrigerant pressures, tests the capacitors, and verifies that the system is ready to run for the next four or five months without interruption.
Schedule the heating service in early fall, September or October, before the first cold snap. The fall service prepares the furnace or heat pump for winter. The technician cleans the burners, inspects the heat exchanger for cracks, tests the ignition and the flame sensor, checks the gas pressure, and verifies that the safety controls are functioning correctly. A cracked heat exchanger is the most dangerous furnace failure because it can leak carbon monoxide into the house. The fall service is the annual check that the heat exchanger is intact.
For a heat pump, both visits are similar. The spring visit prepares the system for cooling. The fall visit prepares it for heating. The technician checks the reversing valve, the defrost cycle, and the auxiliary heat strips during the fall visit because those components are critical in heating mode.
DIY Maintenance Between Professional Visits
Replace the air filter every one to three months. The filter is the most important maintenance task that a homeowner performs. A dirty filter restricts airflow, reduces efficiency, causes the coil to freeze, and can lead to compressor failure. Check the filter monthly. Replace it when it is visibly dirty. A filter in a home with pets, in a dusty environment, or during heavy-use seasons may need replacement every month. A filter in a home with no pets and moderate use may last three months. The filter is not an annual task. It is a monthly check.
Keep the outdoor unit clear. Walk around the outdoor condenser or heat pump unit every few weeks during the operating season. Remove leaves, grass clippings, and debris that have accumulated against the coil. Trim back vegetation to maintain at least two feet of clearance around the unit. The condenser needs airflow to reject heat. A unit surrounded by shrubs or buried in leaves cannot operate efficiently and will eventually overheat.
Check the condensate drain if you have a central air conditioner or a high-efficiency furnace. Pour a cup of white vinegar into the drain line every three months during the cooling season to prevent algae and mold from clogging the line. A clogged drain causes water damage to the house and can trigger a safety float switch that shuts down the system.
Listen for changes in sound. An HVAC system that has been running smoothly for years will develop a distinctive sound profile that you become accustomed to. A new sound, a rattle, a squeal, a buzz, or a grind, is a problem developing. The earlier you catch it, the less expensive the repair. The noise diagnosis guides covered earlier in this series will help you identify the sound and its cause.
Common Mistakes in HVAC Maintenance
Mistake one: replacing the filter only when you remember, which is usually when the house is not cooling or heating properly. The filter does not have a reminder light. It relies on the homeowner to check it. Set a recurring calendar reminder. Check the filter on the first of every month. The filter costs $5 to $15. The compressor that fails because of a clogged filter costs $1,500 to $3,500.
Mistake two: skipping the heating service because the furnace worked fine last winter. A furnace that runs without problems can have a cracked heat exchanger that is invisible without a borescope inspection. The crack leaks carbon monoxide into the house. The furnace runs. The heat works. The CO detector never goes off because the crack is small. The fall service is the only time the heat exchanger gets inspected. Skip it at your own risk.
Mistake three: closing supply vents in unused rooms to save energy. Closing vents increases static pressure in the duct system, reduces airflow across the coil or heat exchanger, and can cause the coil to freeze or the heat exchanger to overheat and crack. The system was designed for a specific airflow. Closing vents changes that airflow in ways the system cannot compensate for. Keep all vents open.
Mistake four: using a filter with too high a MERV rating. A MERV 13 filter captures more particles than a MERV 8 filter. It also restricts airflow more. An older system or a system with undersized ductwork may not have enough blower capacity to pull air through a high-MERV filter. The restricted airflow causes the same problems as a dirty filter: reduced efficiency, coil freeze, and compressor damage. Use the MERV rating recommended by the equipment manufacturer. For most residential systems, MERV 8 is the appropriate balance of filtration and airflow.
Service Contracts: Are They Worth It?
An HVAC service contract, also called a maintenance agreement or a service plan, typically includes two annual service visits, one in the spring and one in the fall, plus priority scheduling and discounted repair rates. The contract costs $150 to $300 per year for a single system. The question is whether the contract costs less than paying for the two visits separately, which cost $100 to $200 each. At the low end, two visits at $100 each cost $200, the same as the average service contract. At the high end, two visits at $200 each cost $400, making the contract a better deal.
The value of a service contract is not just in the price of the visits. It is in the priority scheduling and the relationship with the contractor. A customer with a service contract gets priority when the temperature is 95 degrees and the contractor has 40 no-cool calls. A customer without a contract waits. The priority scheduling alone can be worth the cost of the contract if your system fails during extreme weather.
The contract is not a substitute for DIY maintenance. The contractor visits twice a year. The filter needs changing monthly. The outdoor unit needs clearing after every storm. The drain needs vinegar quarterly. The contract covers the professional tasks. The homeowner covers the intervals between visits. Both are necessary. Neither is sufficient alone.
Frequently Asked Questions
Does annual service keep my HVAC warranty valid?
Most HVAC equipment manufacturers require proof of annual professional maintenance to honor the warranty. A system that fails and has no service records may have the warranty claim denied. Keep the invoices from your service visits. The invoice should list the date, the services performed, and the technician’s name or license number. The warranty typically requires one professional service per year, not two, but two visits per year, one for cooling and one for heating, is the industry standard and provides better protection for the equipment.
Does a new HVAC system need to be serviced?
Yes. A new system needs the same maintenance as an old one. The first service visit should occur one year after installation. Some manufacturers require the first service within the first year to validate the warranty. The filter still needs changing monthly. The outdoor coil still collects debris. The drain still clogs. New equipment is not immune to the conditions that cause failures. It simply has more years of service life ahead of it to protect with regular maintenance.
What happens if I skip a year of service?
Nothing catastrophic happens immediately. The system runs. The house is comfortable. The filter may or may not be changed. The coil accumulates a year of dirt. The drain accumulates a year of algae. The capacitor degrades slightly without being tested. The system is a year closer to a failure that a service visit might have caught early. One skipped year will not destroy the system. Multiple skipped years will shorten its life significantly. The systems that fail at 10 years instead of 20 are the ones that were never serviced. The systems that last 20 years or more are the ones that saw a technician twice a year for their entire lives.
The Bottom Line
HVAC systems should be professionally serviced twice a year, spring for cooling and fall for heating. Between visits, the homeowner replaces the filter monthly, clears the outdoor unit, pours vinegar into the drain quarterly, and listens for unusual sounds. The professional service includes cleaning, testing, and adjusting components that require tools and training. The DIY maintenance includes the simple tasks that prevent the most common problems. Skipping service saves $200 to $400 per year and costs thousands in premature equipment failure. A service contract is worth it if the priority scheduling and the discounted repairs are valuable to you. The most important maintenance task is the one that gets done. The filter, the drain, and the outdoor coil are the parts that fail most often. Pay attention to them.
