How do I get my Seattle home ready for the next heat wave?
The homes that suffer worst in Puget Sound heat events are the ones that try to solve cooling during the event itself — when every HVAC shop triages no-cool calls and install decisions get made from whatever is on the truck. Preparation splits into three layers: keeping heat out through shading and sealing, moving air smartly with night flushing, and mechanical cooling bought and serviced in the off-season when calendars are open.
The quick answer
- Book AC service or install decisions in spring/fall — heat-wave weeks are the industry's worst backlog
- Shade and night-flush first: block sun during the day, exhaust heat at night
- Existing AC? A pre-season tune-up catches weak capacitors and low charge before the stress test
- No ducts? Ductless heat pumps cool room-by-room and heat in winter too
The Seattle-specific problem
Our housing stock was designed for a climate that no longer quite exists — minimal insulation against heat, big west-facing glass, no cooling. When a multi-day heat event parks over Puget Sound, indoor temperatures in unconditioned homes climb daily because the house never fully sheds the previous day's heat.
The equipment market compounds it: when the forecast turns red, every HVAC shop's phone melts simultaneously. Decisions made that week are rushed, expensive, and picked from whatever's in stock. The best heat-wave decision is made in March or October.
Glendale's schedule follows the same curve every summer: tune-up and install slots fill in April and May, and by the first 95°F Puget Sound forecast we're triaging no-cool calls. Homeowners who booked in spring get capacitors checked before they fail; homeowners who waited get paid diagnostics in a queue.
Layer 1: keep heat out
Most heat enters through glass and the attic. Exterior shading (awnings, exterior shades) beats interior blinds because it stops heat before the glass; even cheap reflective window film on west windows makes a measurable difference. In the attic, insulation and ventilation slow the ceiling from becoming a radiant heater by evening.
Layer 2: move air on a schedule
The classic night-flush: when outdoor air drops below indoor temperature in the evening, open up and exhaust hot air (a window fan blowing OUT of the hottest upstairs room works better than one blowing in), then seal the house — windows, blinds, doors — before the morning sun. Homes run this way ride out moderate events surprisingly well.
Layer 3: mechanical cooling, chosen calmly
Ducted homes: central AC added to the furnace, or a heat pump that also replaces heating. No ducts: ductless mini-splits cool the rooms that matter (and heat all winter — in this climate, cooling-only equipment is usually the wrong buy). Either path starts with a load calculation so the system dehumidifies properly instead of short-cycling.
Already have AC? The pre-season tune-up is the cheap insurance: weak capacitors, marginal charge, and dirty coils all pass unnoticed in mild weather and fail in the first 95°F week — which is precisely when repair queues are longest.
No ducts? Ductless mini-splits cool the rooms that matter and heat all winter — in Puget Sound, cooling-only equipment is usually the wrong buy. SCL instant discounts ($300–$600 by efficiency tier) and PSE conversion rebates apply to heat pumps, not straight AC.
What goes wrong during the event
Setting the thermostat far below normal 'to cool faster' — it doesn't; it just runs the system past its design point. During extreme heat, a right-sized AC maintaining 15–20°F below outdoor temperature is performing correctly even if that's warmer than your usual setting.
Running the AC with a neglected filter through a smoke-plus-heat week (increasingly a combined event here) chokes airflow exactly when the system needs it most. And buying a portable unit in panic: fine as triage, but singularly inefficient — don't let a $500 panic purchase substitute for the real decision another year.
Another local pattern: west-facing glass with no shading turns living rooms into greenhouses by 4 PM. Mechanical cooling fights that load all evening — exterior shade or reflective film reduces the work your AC must do and often matters more than another half-ton of capacity.
Questions Seattle homeowners ask
When should I schedule AC work to beat the rush?
Install decisions: spring or fall, when estimates can be thorough and equipment choices aren't limited to what's on the truck. Tune-ups: before June. During an actual heat event, every shop in Puget Sound triages no-cool calls first — maintenance and installs wait. We're open Monday through Saturday 8–7 for scheduled work; Sunday is emergency on-call, not routine booking.
What indoor temperature should AC hold during extreme heat?
Residential systems are designed to hold roughly 15–20°F below outdoor temperature. At 100°F outside, an indoor 78–82°F means the system is doing its job, not failing. Close blinds, minimize oven use, and let it run steadily rather than chasing a low setpoint.
Is a heat pump or AC better if I'm adding cooling anyway?
If your furnace is past mid-life, a heat pump usually wins: same cooling, plus it takes over most heating, plus utility rebates apply (SCL instant discounts; PSE conversion rebates of $3,000–$4,000 for gas-to-heat-pump) — straight AC gets none. If your furnace is young, AC-only can be the budget-right call. We'll price both from one free estimate visit on new installs.
Do fans help in extreme heat?
Fans cool people (evaporation), not rooms — useful while occupied, pointless running in empty rooms. The exception is the night-flush exhaust fan, which genuinely removes heat from the house when outdoor air is cooler than indoor. In Puget Sound, that window often opens after 10 PM during heat events; seal the house again before morning sun hits west windows.
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How we know this
Guidance reflects Glendale's heat-event service experience across Greater Seattle and standard building-science practice for passive cooling; equipment design limits per manufacturer application data.
Reviewed by the Glendale Heating & Air Conditioning team · Last updated 2026-07-15
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