Bay Area Summer Heatwave Preparation: Your HVAC Checklist

Why Bay Area Heatwaves Are Different Now

Bay Area summers historically meant 75-85°F daytime highs with strong marine influence keeping things mild. That pattern has shifted. Since 2017, the Bay Area has experienced regular September "heat dome" events with 95-105°F afternoon temperatures lasting 3-7 days. The September 2022 event hit 116°F in some interior valley locations.

The shift has implications for HVAC. Equipment installed in the 2000s-2010s was sized for the older, milder climate pattern. Many older AC systems can't maintain set point during current heatwave events because they're actually undersized for the conditions, even though they were correctly sized at installation. Equipment age also matters — units 15+ years old have degraded capacity even relative to nameplate spec.

Spring Pre-Season Checklist (March-May)

Complete these before peak season starts in mid-June:

• •Replace air filter (or clean if reusable). Pleated 1-inch every 1-3 months; 4-5-inch media every 6-12 months
• •Clear vegetation from around outdoor unit — minimum 2-foot clearance on all sides
• •Hose off the outdoor condenser coil with a garden hose (gentle stream, not pressure washer) to remove pollen and debris from the past winter
• •Inspect refrigerant lines for visible oil residue (indicates a leak)
• •Test the AC by setting thermostat 5°F below room temperature; verify cold air at supply registers within 10 minutes
• •Check that condensate drain line is clear (look for water near the indoor unit)
• •Schedule professional tune-up if overdue (more than 12 months since last service)
• •Confirm smart thermostat is operating correctly and Eco mode schedules are reasonable

During-Heatwave Operating Strategies

When forecasts call for 95°F+ temperatures, follow these strategies to maximize comfort while protecting your equipment:

Start cooling early. Don't wait until the house is already hot. Set the thermostat at 75-78°F starting in the morning — running the AC at moderate output for many hours is more efficient than maxing it out for a few hours after temperatures spike.

Close blinds on south and west-facing windows during the hottest part of the day (typically noon-7pm). Solar heat gain through unshaded windows can match or exceed heat from outdoor air infiltration.

Run ceiling fans in occupied rooms — they don't lower temperature, but the air movement makes the perceived temperature 3-4°F cooler, allowing you to set the thermostat higher and reduce AC runtime.

Don't aggressively lower the thermostat. Setting 68°F when it's 105°F outside doesn't cool faster — it just runs your system at full capacity for longer, increasing wear and energy cost. 75-78°F is a sustainable indoor target.

Avoid running heat-generating appliances during peak heat. Defer dishwashing, laundry drying, and oven use to early morning or late evening.

When to Call for Service

Don't wait if you notice these issues during a heatwave:

• •AC running but not cooling (warm air at registers): could be low refrigerant, frozen evaporator coil, failed compressor, or stuck reversing valve. Turn off the system to prevent compressor damage and call.
• •AC running constantly without reaching set point: could be undersized (need bigger unit), low refrigerant, dirty coils, or duct leakage. Doesn't require emergency response but worth diagnosing.
• •Ice or frost on refrigerant lines or evaporator coil: turn off the system, wait for thaw, and call. Continuing to run with iced-up coil damages the compressor.
• •Strange noises: rattling (loose mounting, debris in fan), grinding (failing motor bearings), screeching (worn fan belt — older units), buzzing (capacitor or contactor). Some are urgent, some can wait — describe over the phone for triage.
• •Smell of burning or hot electrical: turn off at the disconnect immediately and call. Possible motor or capacitor overheating.
• •Water leaking from indoor unit or air handler: clogged condensate drain, failed condensate pump, or possibly frozen coil thawing. Catch the water if possible and call.