BUILD YOUR ENERGY INDEPENDENCE · ENERGY LADDER LEVEL 3
Passive heating and cooling. No power required.
A well-sealed, well-insulated home with the right shade, mass, and ventilation stays comfortable longer during any outage and cheaper to heat and cool every other day. These improvements cost less than a generator and last for decades.
By Dan Whelan, founder of New World Survival
Researched from government agencies, university extension services, and other published sources. See our sources
WHY THIS MATTERS
The cheapest energy is the energy you never use.
EVERY DAY
Space heating and air conditioning account for about 52% of a typical household's energy use.[1] The EPA estimates that air sealing and insulation alone can reduce heating and cooling costs by an average of 15%.[2]
Every passive improvement on this page pays back on every utility bill for the life of the house. Most of these changes cost less than a single HVAC service call and never need fuel, batteries, or maintenance.
DURING AN OUTAGE
When the HVAC stops, the envelope is all you have. A well-sealed home loses roughly 1-2 degrees per hour in winter. A poorly sealed older home can lose 5 or more. That difference determines whether your household has 6 hours of comfort or 24.
Passive improvements are the only energy investment that works during a power outage with zero additional equipment. A generator runs out of fuel. A battery runs out of charge. A tight envelope just keeps working.
FIRST PRIORITY
Air sealing. The best return in the house.
Before you add insulation, before you plant a shade tree, before you do anything else on this page: seal the air leaks. Air leakage is the single largest waste of conditioned air in most homes, and fixing it is the least expensive, highest-return improvement you can make.
Where air leaks
The biggest leaks are typically invisible. They live in the attic, around light fixtures, plumbing and electrical penetrations, the attic hatch, and where interior walls meet the attic floor. You cannot feel these leaks from the living space, but a blower door test reveals them immediately.
Secondary leak points: window and door framing (the framing gap, not the glass), the foundation sill plate where walls meet the foundation, fireplace dampers, recessed can lights, and electrical outlets on exterior walls.
A professional blower door test costs $200-$400 and produces a pressure map showing exactly where air is moving. It is worth doing before any major sealing project so you address the largest leaks first.
How to seal it
Most attic air sealing uses two products: caulk for gaps under a half inch and low-expansion spray foam for larger gaps around pipes, wires, and framing members. A homeowner with a Saturday and $100-$200 in materials can address the most significant leaks in a typical attic.
Around windows and doors: remove the interior trim, apply low-expansion foam in the gap between the frame and rough opening, and replace the trim. This is a half-day project per opening and meaningfully improves both draft comfort and energy performance.
Weatherstripping on exterior doors compresses and loses effectiveness over 5-7 years. Replace it when you can feel air movement around the door frame with your hand on a windy day.
Seal the attic hatch or pull-down stair with adhesive foam weatherstripping and a hook-and-latch closure. This single fix eliminates one of the largest air leaks in most homes.
The priority rule: Air sealing should be done before adding insulation. Insulation slows heat transfer, but air leaks bypass it entirely. Piling insulation over unsealed gaps is like putting a blanket over a window that is cracked open.
INSULATION
Attic first. Then work down.
Insulation resists heat transfer. R-value measures that resistance; higher is better. Where you add it and in what order determines your return on investment. A 2024 study by ICF Consulting found that 89% of U.S. single-family homes are under-insulated relative to 2012 energy code standards.[3]
PRIORITY 1
Attic floor
The largest surface area and the greatest temperature differential in most homes. Heat rises directly into an under-insulated attic in winter. In summer, attic temperatures above 140 degrees radiate heat downward into the living space.
DOE recommended: R-38 to R-60 depending on climate zone. Many older homes have R-11 or less. Blown-in cellulose or fiberglass is the most cost-effective upgrade for existing attics.
PRIORITY 2
Basement rim joists
The rim joist, where the floor framing meets the foundation wall, is often completely uninsulated and exposed to outdoor temperatures in older homes. Cutting rigid foam board to fit between joists and sealing the edges with caulk is a half-day project with outsized impact.
Target: R-15 minimum. Use 2-inch rigid XPS or polyiso foam board, cut to fit, sealed on all edges with acoustical caulk or foam.
PRIORITY 3
Exterior walls
Wall insulation is harder to add without opening walls. Blown-in insulation through small holes in the exterior siding is the least disruptive option for existing homes. Rigid foam board added during a siding replacement creates a continuous thermal break.
Homes built before 1980 often have little or no wall insulation. Verify with an outlet test or thermal camera before adding it to a priority list.
How to check your current insulation
In the attic, measure the depth of the existing insulation. Fiberglass batts are roughly R-3.2 per inch; blown-in cellulose is roughly R-3.7 per inch. If your attic insulation is at or below the top of the floor joists, you almost certainly need more.
For walls, remove an electrical outlet cover on an exterior wall (with the breaker off), shine a flashlight into the gap around the box, and look for insulation. If you see empty wall cavity, you have uninsulated walls. A thermal imaging camera (available as a smartphone accessory for $200-$400) reveals insulation gaps, thermal bridges, and air leaks through finished surfaces.
WINDOWS
The weakest link in the envelope.
Heat gain and loss through windows account for 25-30% of residential heating and cooling energy use, according to the DOE.[4] You do not need to replace your windows to improve them significantly.
Winter window management
Single-pane windows lose heat at roughly twice the rate of double-pane. For single-pane windows you are not ready to replace, apply interior window insulation film. These heat-shrink kits create a dead air space that mimics double glazing and reduce heat loss through that window by 25-50%. Cost: $5-$15 per window. Removable in spring.
Heavy thermal curtains (lined with insulating fabric) reduce heat loss through any window by an additional 10-25% when closed at night. Open them on south-facing windows during the day to admit solar heat, close them at dusk to trap it.
Check the weatherstripping and caulk around every window frame. Replace cracked or missing caulk on the exterior. Add V-strip weatherstripping to the sides of double-hung windows if they rattle in the wind.
Summer window management
Reflective window film applied to west- and south-facing windows reduces solar heat gain by 40-70%. Choose a film with a high visible light transmittance (VLT) rating if you want to preserve the view and natural light. Look for films with a solar heat gain coefficient (SHGC) of 0.30 or lower.
White-backed cellular (honeycomb) shades reduce solar heat gain by 50-60% when closed. They are more effective than standard blinds because the honeycomb structure traps insulating air. Close them on sun-exposed windows during peak heat hours.
The direction matters. West-facing windows receive the most intense solar heat in the afternoon when outdoor temperatures are already highest. South-facing windows get more total sun hours but at a higher angle that is easier to block with an overhang. East-facing windows get morning sun. Prioritize west and south for summer heat reduction.
When to replace windows: If your windows are single-pane, badly warped, or will not close properly, replacement pays for itself over time. But new windows are expensive ($300-$1,000+ per window installed) and the energy payback takes 10-20 years. Air sealing, insulation film, weatherstripping, and exterior shading often deliver 70% of the benefit at 10% of the cost. Do those first.
PASSIVE SOLAR HEATING
Let the sun heat the house. The house stores it.
Passive solar heating uses the building itself to collect, store, and distribute solar energy. No panels. No wiring. No fuel. The strategy relies on five elements: south-facing glass, thermal mass, insulation, distribution, and control.[5]
Orientation and glazing
In the Northern Hemisphere, the sun tracks low across the southern sky in winter and high overhead in summer. South-facing windows admit low winter sun deep into the room. The same sun, at a steep summer angle, is easily blocked by an overhang.
The building should face within 30 degrees of true south (not magnetic south) for effective passive solar performance.[5] South-facing glass should be maximized. North-facing windows should be minimized, since they lose heat all winter and gain little in return.
For existing homes, the orientation is fixed. But you can still optimize by enlarging south-facing windows during a renovation, adding glazed doors on the south wall, or building a sunroom or enclosed porch on the south side.
Thermal mass
Dense materials absorb heat slowly and release it slowly. A concrete, tile, or stone floor in a sunlit room absorbs solar heat during the day and radiates it back at night, smoothing temperature swings without any mechanical system.
For existing homes, the most practical additions are tile or stone flooring in sun-exposed rooms, an interior brick or stone accent wall that receives direct sunlight, and filled water containers (dark-colored 55-gallon drums in a sunspace, for example) that absorb solar energy during the day.
Thermal mass must be in the sun's path to work as intended. Mass that is permanently shaded absorbs heat from the room air rather than from the sun, which is counterproductive. Place mass where winter sunlight reaches it directly.
Overhangs and seasonal control
A properly sized overhang is the simplest passive solar control device. The geometry is straightforward: in winter, the sun sits low in the sky (20-30 degrees above the horizon at midday in northern states), so sunlight passes under the overhang and enters the room. In summer, the sun sits high (60-75 degrees at midday), and the overhang blocks it.
The exact overhang depth depends on your latitude and window height. For a window 6 feet tall at 36 degrees latitude (roughly the Carolinas to Oklahoma), an overhang projecting about 2 feet from the wall blocks summer sun while admitting winter sun. Your state Cooperative Extension service or a solar design calculator can provide the exact dimensions for your latitude.
What existing homeowners can do
You do not need a new house to benefit from passive solar principles. Start with what you have: open south-facing curtains during winter days to admit sunlight. Close them at dusk to trap the warmth. If a south-facing room has a dark tile, stone, or concrete floor, that floor is already acting as thermal mass.
If you are planning a renovation, adding south-facing glass and thermal mass flooring in the main living space delivers significant passive heating. A sunroom or enclosed south-facing porch extends the strategy further.
During a winter outage, passive solar gain through south-facing windows is free heat. Open curtains on south-facing windows during daylight. Close them at night. Close off rooms on the north side of the house. Concentrate the household in the rooms that receive the most sun.
PASSIVE COOLING
Block it, shade it, move it, flush it out.
Passive cooling follows a clear hierarchy: first, block heat before it enters the envelope. Second, shade the surfaces that would absorb it. Third, move air to create evaporative and convective cooling. Fourth, flush stored heat out overnight.
Exterior shading
Shade a window from outside and you block heat before it enters the glass. Shade it from inside with a curtain and you have already let the heat into the room.
Fixed overhangs block high-angle summer sun on south-facing walls. For east and west walls, where the sun hits at a low angle in the morning and afternoon, vertical shading is more effective: exterior shutters, louvered screens, or awnings with side panels.
Exterior roller shades or shade sails are the fastest retrofit. They mount to the exterior of the window frame and block solar heat before it reaches the glass. Effective on any window orientation.
Strategic landscaping
Deciduous trees planted on the south and west sides of the house provide natural, seasonal shading. They block summer sun with a full canopy and drop their leaves in winter to allow solar gain through. A mature deciduous tree on the west side of a house can reduce the summer cooling load by 10-25%.
Evergreen trees and shrubs on the north and northwest sides serve as a winter windbreak, reducing wind-driven heat loss. A well-placed windbreak can reduce winter heating costs by 10-30%, depending on wind exposure and the density of the planting.
Trees take years to mature, but they cost little to plant and do the work for decades. Plant them now even if the payoff is years away. It is one of the best long-term investments in household energy performance.
Cross-ventilation and stack effect
Cross-ventilation uses windows on opposite sides of the room or house. Wind creates higher pressure on the windward side and lower pressure on the leeward side, pulling air through the space. For best airflow, open the leeward window wider than the windward window.
Stack-effect ventilation works when there is no wind. Open low windows or vents on the cool side of the house and high windows, skylights, or vents on the warm side. Warm air rises out the top, pulling cooler air in from below. The greater the height difference between the low and high openings, the stronger the airflow.
During a summer outage: close all windows and curtains during the day to keep heat out. After sunset, when outdoor air drops below indoor temperature, open windows for cross-ventilation. A battery-powered box fan in one window accelerates the effect. This is the most important passive cooling technique for outage survival.
Night flushing
Night flushing is the most powerful passive cooling technique available in climates with a significant day-night temperature swing (15 degrees or more). The strategy uses the thermal mass of the building in reverse: open windows overnight to let cool air flush the heat stored in floors, walls, and furniture. By morning, the mass has been "recharged" with coolness and will absorb indoor heat gains throughout the next day, keeping the house noticeably cooler.
Night flushing works best in dry climates with wide temperature swings (the Mountain West, the Great Plains, much of California). It is less effective in humid climates where nighttime temperatures stay above 75 degrees, since the mass cannot cool enough to provide a useful buffer the next day.
A whole-house fan accelerates the process. These ceiling-mounted fans draw large volumes of outside air through the house and exhaust it through the attic. They use 200-700 watts, compared to 3,000-5,000 watts for central AC. During an outage, a whole-house fan on a battery station can cool a house in 15-20 minutes on a mild summer evening.
THE ROOF
Radiant barriers and cool roofs. Reflect it before it arrives.
The roof is the largest heat gain surface in most homes. In summer, a dark asphalt roof can reach 150-165 degrees. That heat radiates down through the attic and into the living space, even through insulation. Two strategies address it.
Radiant barriers
A radiant barrier is a reflective material (usually aluminum foil laminated to a backing) installed in the attic. It reflects radiant heat from the underside of the roof before it can conduct through the insulation. DOE research documents that radiant barriers reduce attic ceiling heat gain by 25-40% in hot climates.[6]
The benefit is greatest when ductwork and HVAC equipment are in the attic, which is common in Southern homes. A radiant barrier reduces the temperature of the air surrounding those ducts by 20-30 degrees, dramatically improving duct efficiency.
DIY installation (stapling foil sheets to the underside of the rafters) costs $150-$300 in materials for a typical attic. Professional installation runs $1,000-$1,500. In hot climates, the payback period is typically 2-5 years.
Cool roofs
A cool roof uses reflective materials or coatings to reflect solar energy rather than absorb it. A white or light-colored roof can be 50 degrees cooler at the surface than a dark roof on the same day.[7] That translates to less heat entering the attic and less heat reaching the living space.
Options range from reflective coatings applied to an existing roof ($0.50-$2.00 per square foot) to reflective metal roofing or light-colored shingles chosen when the roof is replaced. In hot climates, DOE estimates 10-25% cooling energy savings from a cool roof.[7]
In cold climates (IECC zones 5 and above), a cool roof may slightly increase winter heating costs because it reflects solar heat the house could use. In mixed climates, the summer cooling savings typically outweigh the winter heating penalty. Evaluate based on your climate zone.
The priority order for roof improvements: Insulation first (addresses conductive heat transfer). Air sealing second (addresses convective heat transfer). Radiant barrier or cool roof third (addresses radiant heat transfer). If your attic already has R-38 or more insulation and is well-sealed, a radiant barrier is the next logical improvement in hot climates.
INTERNAL GAINS
Stop heating the house from the inside.
Every appliance, light fixture, and warm body adds heat to the indoor environment. In summer, this internal heat forces your cooling system to work harder. Passive cooling works best when you reduce the heat you are generating inside the envelope.
Lighting
A 60W incandescent bulb produces 55 watts of heat and 5 watts of light. A 10W LED produces the same light with 8 watts of heat. Replacing all incandescent bulbs with LEDs reduces lighting-related heat gain by approximately 85%. In a house with 30 fixtures, the cumulative cooling benefit is meaningful.
Cooking
An oven at 350 degrees for an hour adds roughly 2,500-3,500 BTU to the kitchen. In summer, use a microwave, outdoor grill, slow cooker, or stovetop instead of the oven when possible. Run the range hood exhaust fan while cooking to vent heat and moisture outside. Cook during cooler hours.
Appliances
Run the dishwasher and clothes dryer after dark in summer to avoid adding heat during peak cooling hours. Insulate the hot water heater with a blanket if it is in a conditioned space. Use a clothesline instead of the dryer when practical. Each of these changes is small; together they meaningfully reduce the cooling load.
COMMON MISTAKES
Where people waste money and effort.
Insulating before sealing
Adding insulation over unsealed air leaks is the most common wasted investment. The air leaks bypass the insulation entirely. Always seal first, then insulate. This mistake costs hundreds of dollars and delivers disappointing results.
Replacing windows as the first step
New windows are expensive and their energy payback is slow. In most homes, $500 spent on attic air sealing and insulation saves more energy per year than $5,000 spent on window replacement. Windows should be addressed after the attic, rim joists, and wall insulation are handled.
Relying on interior shading in summer
Interior blinds and curtains block light but not heat. By the time sunlight passes through the glass, the heat is already inside the room. Exterior shading is 2-3 times more effective than interior shading at reducing solar heat gain. Prioritize exterior solutions on west and south windows.
Opening windows during the day in summer
When outdoor air is hotter than indoor air, opening windows lets heat in. During a summer outage, keep everything closed and curtained during the day. Open windows for ventilation only after outdoor temperatures drop below indoor temperatures, typically after dark.
Installing a radiant barrier in a cold climate
Radiant barriers are designed for hot climates with long cooling seasons. In northern states (IECC zones 5 and above), the savings from reduced summer cooling rarely justify the cost. Invest in more insulation instead.
Ignoring the attic hatch
An unsealed, uninsulated attic hatch or pull-down stair is one of the largest single air leaks in a typical home. Seal it with adhesive weatherstripping, add a rigid insulation cap, and install a latch to hold it tight. Cost: under $30. Time: one hour.
WHERE TO START
By housing situation. Prioritize what you can do.
Renters
Focus on reversible improvements: window insulation film in winter, reflective window film or exterior shade cloth in summer, heavy thermal curtains, removable weatherstripping on drafty doors and windows, LED bulbs in every fixture.
Learn your apartment's cross-ventilation options. Know which windows face which direction. Practice the summer outage protocol: closed and curtained during the day, open for cross-ventilation after dark. Total cost: under $100.
Suburban homeowners
Start with an attic air sealing project ($100-$200 in materials, one weekend). Add attic insulation to DOE recommended levels ($500-$2,000 depending on method). Seal rim joists in the basement ($100-$200). Weatherstrip exterior doors.
Second phase: add exterior shading on west-facing windows, plant deciduous trees on the south and west sides. Consider a whole-house fan if you are in a climate with cool summer nights. Consider a radiant barrier if you are in a hot climate with attic ductwork.
Rural homeowners
Everything above, plus: take advantage of land for strategic tree planting and windbreaks. If building new or renovating, orient the house and main living space to face within 30 degrees of true south. Add thermal mass flooring in south-facing rooms.
If you heat with wood, a tight envelope means you burn less fuel and the stove heats more effectively. Passive improvements and wood heat reinforce each other.
Sources
Government and research
- [1] EIA Residential Energy Consumption Survey (RECS), 2020. Heating and cooling account for approximately 52% of household energy use.
- [2] EPA Energy Star "Why Seal and Insulate." Homeowners can save an average of 15% on heating and cooling costs (11% of total energy costs) by air sealing and insulating.
- [3] ICF Consulting / NAIMA 2024 study: 89% of U.S. single-family homes are under-insulated relative to 2012 IECC standards.
- [4] DOE "Windows and Doors": heat gain and loss through windows account for 25-30% of residential heating and cooling energy use.
- [5] NREL "Passive Solar Design" (DOE/GO-102001-1105). Building orientation within 30 degrees of true south, five-element passive solar system design.
Radiant barriers and cool roofs
- [6] DOE / ORNL Radiant barrier research and RIMA International ASHRAE paper (2011): radiant barriers reduce ceiling heat gain 25-40% in attics with R-19 insulation.
- [7] LBNL Heat Island Group Cool roof research; DOE Cool Roof Calculator: cool roofs can reduce residential cooling costs 10-25% in IECC zones 1-3.
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