Almost every week a homeowner calls and says, "My bill jumped. What is wrong with my AC?" Sometimes it is the AC. Often it is not. Here is how I sort it out.
First, compare the right months
June is always higher than May because the AC runs far more. Compare this June to last June. If usage (kWh, not dollars) is about the same, the difference is the rate, not your house. If usage is clearly higher, keep reading.
HVAC causes, most common first
1. A clogged filter
A filter you cannot see light through makes the blower work harder and the system run longer. Change it today.
2. Thermostat settings
Every degree cooler in summer adds run time. Try 76 to 78 when home in summer and 68 in winter, with ceiling fans in occupied rooms.
3. A dirty outdoor coil
Pollen, grass and dirt on the outdoor coil keep the system from getting rid of heat, so it runs longer. Turn the power off and gently rinse it with a garden hose, or have it cleaned during a tune-up.
4. Low refrigerant
A slow leak makes the system run longer for less cooling. Signs: air that is cool rather than cold, a house that will not get below 78, ice on the copper lines. The leak needs to be found and repaired.
5. Leaky ducts
Ducts in an attic that leak are cooling the attic. Disconnected or crushed runs are common in older homes and quick builds.
6. An oversized system
A system that is too big cools fast, shuts off before it removes humidity, and the house feels clammy, so people turn the thermostat down. The fix is correct sizing at replacement time.
7. An aging system
Equipment past 12 to 15 years has usually lost efficiency. When repairs and bills both climb, it is worth comparing a repair with a replacement.
Non-HVAC causes worth ruling out
- Thin attic insulation and air leaks around attic stairs, recessed lights and old windows.
- A new appliance: a garage freezer, pool pump or EV charger.
- An aging water heater.
Myths I hear constantly
- "Setting it to 65 cools faster." It does not. It just runs longer.
- "Close vents in unused rooms to save energy." It usually upsets airflow rather than saving money. Ask us before closing more than one or two.
- "A new system does not need maintenance." It does, and most manufacturers expect yearly maintenance records.
Do these four things this week
- Change the filter.
- Set the thermostat to 76 to 78 in summer, 68 in winter.
- Rinse the outdoor coil and clear 2 to 3 feet around the unit.
- Open supply vents and move furniture off returns.
If the bill still makes no sense, a tune-up ($135 for one system) checks refrigerant, coils, electrical parts and airflow and ends with a written report. Plan members ($229 a year, $189 the first year) get that in spring and fall.