HVAC
Heating, ventilation, and air conditioning. Furnace, AC, heat pump, thermostat, ductwork. What breaks, safe DIY diagnostics, and when to call a licensed HVAC tech.
Overview
Residential HVAC covers three functions: heating (furnace, heat pump, boiler), cooling (AC condenser, evaporator, or heat pump reverse cycle), and ventilation (ductwork, air exchange, humidity control). All three are increasingly interconnected in modern systems.
Most HVAC problems trace to two things: dirty filters and lack of annual maintenance. Both are cheap prevention. Real component failures (ignitors, capacitors, motors) are less common but not unusual after 8–10 years of service.
Gas furnaces and any gas appliance work require special caution — smell rotten eggs, evacuate immediately and call your gas utility. AC refrigerant work is EPA-regulated and cannot be DIY. See our safety disclaimer.
Most common fixes
The highest-search-volume issues in this system, each fully documented with safety-first framing, ranked causes, and cost estimates.
Sub-categories
Every corner of this system, organized by function. Click into any sub-category for the full fix and project inventory.
Furnace (gas & electric)
Startup issues, ignitor and flame sensor, filter changes, safety switch trips.
Air conditioning
Cooling issues, coil freeze, condenser cleaning, refrigerant (pro-only).
Heat pumps
Dual-function heating and cooling. Reversing valves, defrost cycles, backup heat.
Thermostats
Diagnosis, battery replacement, smart thermostat installation, wiring.
Ductwork & ventilation
Balancing, leaks, insulation, whole-house ventilation.
Filters & indoor air quality
MERV ratings, filter sizing, whole-house dehumidification.
Seasonal HVAC tasks
Spring and fall tune-up tasks, pre-season prep.
Materials used in this system
Tools you'll need
Project cost guides
What we do NOT teach as DIY
HVAC topics that are always licensed-tech only:
- Any refrigerant work (charging, leak repair, evacuation) — EPA 608 certification required by law
- Gas valve replacement or gas piping
- Heat exchanger inspection or replacement (cracked heat exchangers release CO)
- New system installation requiring load calculation and permits
- Boiler work (residential steam or hot water)
Frequently asked questions
Annually, ideally before the season starts (spring for AC, fall for furnace). $100–$200 per visit. Catches failing capacitors, weak ignitors, and cracked heat exchangers before they leave you without heat or cooling in an emergency.
No — EPA-regulated and requires certification. Also: if refrigerant is low, there's a leak. Adding without finding the leak means it'll be low again in weeks. Call a licensed HVAC tech.
MERV (Minimum Efficiency Reporting Value) rates how well a filter captures particles. MERV 8–11 is the sweet spot for most homes — filters well without restricting airflow. MERV 13+ improves air quality but can strain older systems. See MERV ratings explained.
For mild-to-moderate climates: often yes — one system handles both heating and cooling, and modern heat pumps run efficiently down to about 5°F. For very cold climates: dual-fuel system (heat pump + gas backup) is common. Sizing matters — get a Manual J load calculation from an HVAC pro.