Expert answers to your most important hvac questions
1-inch flat filters: every 30–60 days. 4-inch deep-pleated filters: every 3–6 months. MERV 8–11 is the sweet spot for most residential systems — effective filtration without airflow restriction. Check monthly and replace when visibly grey or clogged. A clogged filter is the single most common cause of HVAC problems: it causes frozen coils, overheated compressors, and system shutdowns.
SEER2 (the updated efficiency measurement standard) minimums vary: 13.4 in the North, 14.3 in the South and Southwest. For meaningful efficiency gains over baseline, look for SEER2 16–18 for split system AC. SEER2 18+ for inverter-driven variable speed systems. Higher SEER systems cost more upfront but reduce operating costs significantly — especially in climates where AC runs heavily. Calculate the payback period before making your decision.
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Find a ContractorBanging or clanking: likely a loose component or broken part inside the blower or compressor — shut off immediately and call a technician. Squealing or screaming: usually a bearing failure in the blower motor or inducer — can continue running briefly but schedule service same day. Clicking: normal on startup/shutdown; unusual clicking during operation indicates a relay or electrical issue. Humming: normal electrical sounds; loud humming may indicate a failing capacitor or contractor. Rattling: typically loose panels or debris near the outdoor unit.
Replace when: system is 15+ years old, uses R-22 refrigerant (no longer manufactured, very expensive), repair cost exceeds 30–40% of a new system's cost, or the system has had multiple failures in 2 years. The '5,000 rule': multiply repair cost by system age — if the result exceeds $5,000, replacement often makes more financial sense. Also consider: a new system's energy savings, available tax credits (up to 30% with the 25C credit for qualifying equipment), and whether your ductwork is in good condition.
A frozen coil results from insufficient airflow (clogged filter — check this first) or low refrigerant. The coil gets so cold it freezes the condensation. Symptoms: AC running but not cooling, ice visible on the refrigerant lines or indoor unit. Fix: turn off the AC (leave the fan on) to allow thaw — 24 hours. Then address the cause: replace the filter (if the filter was the cause, that may be all you need). If it freezes again, a refrigerant leak or airflow issue requires professional diagnosis.
For comfort and efficiency: summer cooling at 75–78°F while home, 82–85°F while away (or use a schedule/smart thermostat). Winter heating at 68–70°F while home and awake, 60–65°F while sleeping or away. Each degree of setback saves approximately 1% on energy costs. Thermostat programming or a smart thermostat consistently delivers 10–15% annual savings compared to manual operation.
Upgrade to a MERV 11–13 filter (if your system can handle the airflow restriction). Add a whole-house air purifier with UV-C or ionization (ask your HVAC contractor what integrates with your system). Maintain indoor humidity 30–50% — dehumidifiers prevent mold in summer, humidifiers prevent dry-air discomfort in winter. Schedule annual duct inspection for leaks and significant dust buildup. Ensure adequate fresh air ventilation, especially in tightly sealed newer homes.
A heat pump moves heat rather than generating it — in summer it moves heat out of your home (like a conventional AC); in winter it moves heat from outside air into your home. Modern cold-climate heat pumps work effectively down to -15°F. In mild to moderate climates, heat pumps are more efficient than gas heating for most of the heating season. In very cold climates, a dual-fuel system (heat pump + gas backup) provides efficient heating year-round. Heat pumps both heat and cool — one system, two seasons.
No — this is a common myth that actually increases HVAC operating costs and stress. Your duct system is designed for the total air volume of your home. Closing vents increases static pressure, which makes the system work harder, can freeze coils (AC mode), and increases duct leakage. If you want to reduce conditioning in certain rooms, look into zone control systems or ductless mini-splits for those spaces.
Signs of refrigerant leak: AC runs but doesn't cool effectively, ice forming on the refrigerant lines or indoor unit, hissing or bubbling sound near the unit, or higher-than-normal electric bills. A technician verifies with manifold gauge pressure readings. Note: simply adding refrigerant without finding and fixing the leak is wasteful and ineffective — EPA regulations require technicians to repair leaks before recharging systems with more than a certain refrigerant charge.
Emergency Heat is the backup electric resistance heating strip in a heat pump system — it activates when the heat pump cannot maintain temperature (typically below 35–40°F) or when the heat pump has failed. EM Heat is significantly more expensive to operate than the heat pump — about 3x the cost. Do not use EM Heat unless the heat pump has failed; if your heat pump is working, let it operate with its automatic backup. If EM Heat is your only functioning heating right now, call for service.
Program your thermostat to allow the home to warm while you're away. Use ceiling fans (counter-clockwise in summer) to create wind chill — allows thermostat setpoint 4°F higher with same comfort. Keep blinds and curtains closed on west and south-facing windows during peak afternoon heat. Ensure your outdoor unit has 2 feet of clearance and clean coils (hose it down annually). Run heat-producing appliances (dishwasher, oven, dryer) in the evening. Improve attic insulation and seal air leaks — the biggest long-term efficiency upgrade.