HVAC replacement costs $5,000 to $11,000, including a new furnace and AC unit using the existing ductwork. Replacing an HVAC system and ductwork costs $7,000 to $16,000. Prices depend on the house size and the HVAC system size, type, brand, and fuel type.

• AC units with a higher SEER rating and high-efficiency furnaces cost 30% to 100% more up front but are more efficient and reduce your energy costs.
• Systems from popular brands like Carrier, Trane, and Lennox typically cost more to install and repair than other brands.

Adding optional features like an HVAC zoning system or new smart thermostat will increase your total installation costs but may reduce your energy costs in the long-term.

A service call for an HVAC system costs $75 to $200 to diagnose the problem. Small HVAC repairs cost $150 to $450, depending on the problem, which parts need replacing, and whether the system is still under warranty. Larger repairs like replacing the AC compressor or the furnace heat exchanger can cost $1,000 to $3,000+ if the system is no longer under warranty.

An annual HVAC service agreement or maintenance plan costs $120 to $360. Regular maintenance minimizes the need for repairs, reduces energy bills, and extends the system's life.

An HVAC system should be serviced at least once or twice per year, depending on the system's age, type, and usage. Most experts recommend servicing the air conditioning components in the spring and the heating components in the fall.

Look for these signs your HVAC system needs repairs or replacement:

• Rising energy bills
• Uneven home heating and cooling
• Weak or limited airflow from the vents
• Furnace or AC unit cycles on and often frequently
• Excessive humidity in the home
• Stale or musty odors from the vents
• Knocking, clicking, or gurgling noises from the system

HVAC systems last 15 to 25 years on average, depending on the brand, climate, and usage. Each component has its own lifespan:

• A furnace lasts 15 to 30 years.
• An AC unit lasts 15 to 20 years.
• A heat pump lasts 10 to 20 years.

HVAC service techs typically don't expect a tip, but they appreciate a $10 to $20 tip for outstanding service. Consider offering the technicians a beverage and use of your restroom, send positive feedback to their manager, and post a positive review online.

Use these helpful tips to choose the best local HVAC service company:

• Get at least three estimates to compare. Confirm the estimates include equipment of the same size and quality.
• Look for a company with certifications from North American Technician Excellence (NATE), the American Society of Heating, Refrigeration, & Air-Conditioning Engineers (ASHRAE), or HVAC Excellence.
• Choose companies that are licensed, insured, bonded, and have been in business for 5+ years.
• Check out their reviews and previous work on HomeGuide and Google.
• Be wary of selecting the lowest quote as it may indicate low-quality workmanship or equipment.
• Get a detailed contract and warranty in writing before the work begins.
• Never pay in full before the project starts.

Ask these questions to ensure you hire the best HVAC repair service:

• How long have you been in business?
• Are you licensed, bonded, and insured?
• Which certifications do you have?
• Can you provide references?
• Can my HVAC system be repaired or does it need replacing?
• How long will the repairs take?
• What extra costs should I expect?
• Are the new parts covered by a manufacturer's warranty?
• Do you warranty the labor?
• Will you inspect my existing ductwork for leaks, mold, and asbestos?
• Do you offer an HVAC maintenance or service plan?