By Jared White
Most Pacific Northwest homes were built for rain, not heat. They have the thermal mass, the limited insulation, and the no-AC floor plan of a region that assumed summer evenings would always cool things off. That assumption no longer holds, and the gap between how these homes were built and the heat they now face is exactly what makes a plan worth having. This guide covers how to keep a PNW home safe and livable during a heat wave when you do not have central air conditioning: the free tactics to do first, the equipment that actually works here, how to size it, and the smoke-season twist that makes mechanical cooling more important than it used to be.
Why PNW Heat Is Now Dangerous
The June 2021 heat dome made the risk concrete. Portland reached an official high of 116°F on June 28, 2021, and the multi-day event caused hundreds of excess deaths across Oregon, Washington, and British Columbia. The pattern in those deaths is the part worth sitting with: many victims were found in homes and apartments without air conditioning. A historically mild climate with low AC penetration turned out to be uniquely vulnerable when extreme heat arrived, because neither the housing nor the habits were built for it.
Two structural facts make PNW homes slow to shed heat. First, compared with hotter US regions, Seattle and Portland have historically low rates of residential air conditioning, especially central AC, and many homes were designed to be cooled by opening windows rather than by ducted equipment. Second, a lot of the housing stock is older, with significant thermal mass and limited insulation, so once the structure soaks up heat during a multi-day event it holds that heat overnight, and indoor temperatures stay dangerous even after the outdoor air cools. The risk falls hardest on older adults, people with chronic illness, lower-income residents, and anyone in a top-floor or poorly insulated unit. With climate projections pointing toward more frequent and more intense heat waves, cooling has moved from a comfort question to a resilience one. See how it fits the broader plan in the PNW resilience stack.
Start With Passive Tactics
Before buying any equipment, use the free and cheap tactics, because they reduce how much cooling you need to buy and run.
Flush the house at night. PNW nights still tend to cool down, so when the outdoor temperature drops below the indoor temperature and the air quality allows it, open windows and use fans to push hot indoor air out and pull cooler air in. This cools the home's thermal mass so it starts the next day lower. The catch, covered below, is that smoke can take this option away.
Block daytime solar gain. Sunlight through windows is one of the largest sources of indoor heat. Exterior shading like awnings and exterior blinds is most effective because it stops the heat before it reaches the glass, but interior blackout curtains and cellular shades help too. Shade the east and west windows that catch low morning and evening sun.
Use fans correctly, and know their limit. Fans cool people, not rooms. They make you feel cooler through air movement and evaporation, but they do not lower the air temperature. They help in moderate heat, but in very high heat, especially with higher humidity, their benefit drops and they can stop being protective. Treat fans as supportive, not sufficient, during an extreme event, and never rely on a fan alone as the cooling plan for a vulnerable person.
Manage behavior and bodies. Stay hydrated, avoid heavy exertion during peak heat, take cool showers, and wear light clothing. These sound minor and are not; behavior is a large part of heat safety.
Designate a cool room. Just as smoke season calls for a clean room, a heat wave calls for a cool room: one space you keep cooler with shading, fans, and ideally air conditioning, used as a refuge during the worst hours, especially for anyone vulnerable. In the PNW this should usually be the same room as your clean room.
Cooling Equipment Compared
For a home without central AC, four options cover most situations, and they differ a lot in efficiency.
Window AC is generally the most efficient of the plug-in options because it sits in the window and keeps the compressor and condenser outside, exhausting heat directly outdoors. It needs a compatible window and secure installation to avoid air leaks and the genuine safety risk of a unit falling. Single-hose portable AC is the convenient but least efficient choice: it exhausts hot air through one hose while drawing replacement air from the room, which creates negative pressure that pulls warm air in from elsewhere in the house or outside, undercutting its own cooling. Dual-hose portable AC fixes much of this by using one hose to bring in outdoor air for the condenser and another to exhaust, reducing the negative-pressure problem and improving efficiency, at the cost of a bit more bulk. Ductless mini-split heat pumps are the high-efficiency, permanent option: a wall-mounted indoor unit paired with an outdoor compressor, no ductwork required, quieter than window or portable units, and able to both cool and heat. Evaporative or swamp coolers deserve a caution in the PNW: they cool by evaporating water and work best in hot, dry climates. PNW summer humidity is moderate, so they can offer some relief in drier inland areas but are less effective near the coast or on humid days, and they add moisture indoors, which can create comfort or dampness problems.
Sizing: How Many BTU You Need
Air conditioner and heat pump cooling capacity is measured in BTU per hour. A common starting rule is roughly 20 to 25 BTU per square foot, then adjusted up for high ceilings, heavy sun exposure, more occupants, or heat-producing appliances.
| Room size | Target capacity | Notes |
|---|---|---|
| 100-150 sq ft | 5,000-6,000 BTU | Small bedroom; adjust for sun and occupants. |
| 150-250 sq ft | 6,000-8,000 BTU | Larger bedroom or small living room. |
| 250-350 sq ft | 8,000-10,000 BTU | Medium living room. |
| 350-450 sq ft | 10,000-12,000 BTU | Larger living room or open area. |
| 450-550 sq ft | 12,000-14,000 BTU | Very large room or small open plan. |
Guidelines as of mid-2026; actual needs vary with insulation, window area, and occupancy. Confirm against current ENERGY STAR sizing guidance. Resist the urge to buy far bigger than you need. An oversized unit short-cycles, cools unevenly, dehumidifies poorly, and wastes energy. Sizing close to the room is better than sizing way over it.
Cooling Options at a Glance
| Type | Upfront cost | Efficiency | Works with windows closed for smoke? | Rebate-eligible? |
|---|---|---|---|---|
| Fans only | ~$20-200 | Comfort only, no cooling | Yes, but provides no real cooling | No |
| Window AC | ~$300-800 | Moderate | Yes, if sealed well | Rarely |
| Portable AC (single-hose) | ~$300-700 | Lower | Yes, but less efficient | Rarely |
| Portable AC (dual-hose) | ~$400-900 | Better than single-hose | Yes | Rarely |
| Ductless mini-split heat pump | ~$3,000-10,000+ installed | High | Yes | Often, via IRA/utility |
| Central heat pump retrofit | ~$8,000-20,000+ | High | Yes | Often, via IRA/utility |
| Evaporative cooler | ~$200-700 | Dry climates only | Needs venting; adds humidity | Rarely |
Prices are approximate and swing with summer demand and local install costs. Verify before buying.
Why a Heat Pump Is Often the PNW Answer
For owners who can invest, a heat pump is frequently the smartest cooling purchase in the Pacific Northwest, for three reasons. It is efficient: a heat pump moves far more heating and cooling per unit of electricity than resistance heat or older AC, and modern cold-climate models hold performance well into low outdoor temperatures. It is year-round: the same ductless or central heat pump that cools you in a July heat wave heats you efficiently through the shoulder seasons and winter, which means it earns its keep all year rather than sitting idle ten months of the time. And it is incentivized: heat pumps commonly qualify for federal tax credits, state programs, and utility rebates that can substantially cut the upfront cost. The details and amounts change, so plan the purchase alongside the rebates and incentives guide rather than assuming a number. One distinction to keep straight: permanently installed ductless mini-splits give you efficient, multi-room cooling and heating, while the newer portable heat-pump units are closer to an advanced portable AC and do not match a mini-split's efficiency.
The Smoke and Heat Overlap
This is the PNW-specific trap that makes mechanical cooling matter more than it would in a drier, smoke-free climate. During wildfire smoke the guidance is to keep windows closed, because open-window cooling means breathing high levels of PM2.5. But open windows and night flushing are exactly how many PNW homes have always cooled themselves. When smoke and heat overlap, that traditional strategy becomes unsafe, and the only durable answer is mechanical cooling paired with filtration: an AC unit or mini-split to hold the temperature, and a HEPA purifier or DIY box to hold the air quality, in a sealed room. That is the clean and cool room, and it is why cooling and smoke defense should be planned together rather than as separate projects. If outages are also a risk in your area, plan how you would run that cooling on backup power.
Common Mistakes
- Relying only on fans in extreme heat. Fans help people feel cooler but do not lower temperature, and in severe heat they can stop being protective. A vulnerable person needs actual cooling or access to a cool space, not just airflow.
- Buying a single-hose portable AC without understanding the tradeoff. It is the convenient choice and the least efficient one, because it pulls warm replacement air in as it works. A window unit or dual-hose portable cools better for the energy used.
- Sizing poorly. Too small never keeps up; far too large short-cycles and dehumidifies badly. Size close to the room, adjusting for sun and occupants.
- Ignoring shading and the envelope. Trying to cool a sun-baked, leaky room is fighting uphill. Block solar gain and seal obvious leaks first; the sealing guide covers the envelope side.
How Hot Is Too Hot Indoors?
There is no single number that is dangerous for everyone, but a useful guideline is to keep indoor temperatures below roughly 80 to 82°F for most people during a heat wave, and cooler than that for anyone who is older, pregnant, chronically ill, or otherwise vulnerable. The risk is not only the daytime peak; it is sustained heat that never lets up, especially overnight, because the body needs cooler hours to recover. This is exactly where an older PNW home's thermal mass works against you, holding heat into the night. If you cannot keep the whole home under that range, concentrate your cooling on the one cool room and make sure vulnerable household members spend the hottest hours there. Watch how people feel, not just the thermostat: confusion, dizziness, a pounding heart, or stopping sweating are signs to cool down and hydrate immediately.
Frequently Asked Questions
Do I really need air conditioning in the Pacific Northwest now?
For most homes, some form of mechanical cooling has become a safety measure rather than a luxury, because the 2021 heat dome showed that fans and night cooling are not enough in extreme heat, especially for vulnerable people. You do not necessarily need whole-home AC; one properly cooled room can serve as a refuge.
Window or portable AC for an older home without ducts?
A window unit is usually the more efficient choice if your window suits one and it can be installed securely. If a window unit is not practical, choose a dual-hose portable over a single-hose model for noticeably better efficiency.
What size AC or heat pump do I need?
Start at roughly 20 to 25 BTU per square foot and adjust up for sun, ceiling height, and occupants. A small bedroom typically wants 5,000 to 6,000 BTU; a medium living room around 8,000 to 10,000. Avoid drastically oversizing, which causes short-cycling.
Are heat pumps good for cooling, or mainly for heating?
Both. A heat pump is an efficient air conditioner in summer and an efficient heater the rest of the year, which is what makes it such a strong PNW choice, along with its eligibility for rebates and tax credits.
Can I keep windows closed for smoke and still stay cool in a heat wave?
Only with mechanical cooling. When smoke forces the windows shut, an AC unit or mini-split plus filtration lets you hold both temperature and air quality in a clean, cool room. That pairing is the core of PNW resilience.
Do the free things first, size your cooling to the room, and lean toward a heat pump if you can invest, because it cools, heats, and qualifies for incentives. Plan cooling alongside smoke defense and your eligible rebates, see how it fits the whole stack, or get a tailored plan from the Resilient Home Stack Builder.