Passive heating and cooling in a house

September 16, 2026
5 minute read
By Betsy Hines

A thermal barrier in an external wall slows the movement of heat between inside and outside, so the house loses less warmth in winter and takes in less heat in summer. Earth tubes and ground heat storage use the steady temperature of the soil, roughly 50 to 55 F at depth in New England, to pre-condition incoming air or to store heat for later. A roof can act as a solar collector, but only if it is built as one: an ordinary shingled roof sheds water and does not gather heat. The useful work begins by looking closely, naming the trade-offs, and keeping the next decision visible. This guide is a starting point for a conversation, not a substitute for a site visit or qualified professional advice where the work requires it.

How does a thermal barrier work in an external wall?

A wall separates two bodies of air that are usually at different temperatures. Heat moves across that separation in three ways: conduction through solid material, convection through air that circulates inside cavities, and radiation between surfaces. A thermal barrier is the layer or assembly that interrupts all three. In practice, the barrier is not one product. It is a sequence. The exterior cladding sheds rain and blocks direct sun. A vented cavity behind the cladding lets moisture escape and breaks the path for conducted heat. The insulation layer, whether mineral wool, cellulose, wood fiber or rigid foam, provides the resistance to heat flow, measured as R-value per inch. An air barrier, often a membrane or a taped sheathing joint, stops the movement of air itself, because a wall that leaks air loses far more heat than its R-value suggests. Inside, a vapor control layer and the finish complete the assembly. The order matters. In a cold climate, the insulation belongs on the cold side of the structural frame or in a continuous layer outside it, so that the framing does not become a thermal bridge. A stud is a poor insulator compared with the cavity beside it, and each stud conducts heat straight through the wall. Continuous exterior insulation covers the studs and reduces that path. What the barrier is meant to do, then, is not to stop heat entirely. It is to make the rate of heat loss slow enough that a small heat source can keep the house comfortable, and to keep interior surface temperatures high enough that moisture does not condense on them. A more detailed explanation of how such a barrier is planned and measured appears in the Passive Climate Journal's account of the thermal barrier exterior wall, which treats the wall as one part of a whole-house energy balance rather than as a single product.

How do earth tubes and ground heat storage work?

Both use the same fact: below the frost line, soil temperature stays close to the annual average air temperature of the region. In southern New England that is around 50 F. It changes slowly with the seasons and hardly at all with the weather of a given week. An earth tube, also called an earth-to-air heat exchanger, is a buried pipe, usually 6 to 10 inches in diameter and 50 to 150 feet long, laid below the frost line with a slight slope for drainage. Outside air is drawn through it before entering the ventilation system. In summer, the soil is cooler than the incoming air, so the air is cooled and some of its moisture condenses in the pipe. In winter, the soil is warmer than the outside air, so the air is preheated. The effect is modest, typically a shift of several degrees, but it reduces the load on whatever system does the final heating or cooling. Three details decide whether an earth tube works. It must drain, because standing water breeds mold. It must be smooth inside and accessible for cleaning. And its intake must be placed away from exhaust vents, radon paths and standing water. Ground heat storage is a larger proposition. Instead of passing air through a pipe once, the system stores heat in a mass of soil or in a water tank and draws on it later. Heat collected in summer, from a solar roof or from the cooling demand of the house, is pushed into the ground through a loop of pipes. In winter the same loop extracts it. The storage volume has to be large, insulated at its edges and separated from groundwater, or the heat simply disperses. A single house can rarely justify the excavation; the economics improve when several buildings share one store. A ground-source heat pump is not the same thing. It extracts heat from the ground continuously and returns it at a lower temperature, but it does not store summer heat for winter. Storage is a deliberate design choice, not a byproduct.

Can a roof act as a solar collector?

Yes, and it does so in three distinct ways, which are often confused. The first is a solar thermal collector: a panel or a set of tubes through which a fluid is pumped, absorbing heat that is then used for domestic hot water or, less often, for space heating. The roof is only the mounting surface. The collector is a manufactured component with a selective coating and, in cold climates, a freeze-protected circuit. The second is a photovoltaic array, which converts sunlight to electricity. It produces no heat for the house directly, though the panels themselves get warm and lose efficiency as they do. The third is the roof itself as an integral collector, sometimes called a solar roof or a thermo-active roof. Here the roof structure contains channels or a metal deck through which air or fluid is circulated, and the roof surface absorbs solar radiation and transfers it. This is the oldest of the three ideas and the one with the longest documented history in low-energy building. It works best on a dark, unshaded, steeply pitched roof, and it needs a place to put the heat: a storage mass, a ground loop or a ventilation system that can use preheated air. An ordinary asphalt shingle roof over a vented attic is not a collector in any useful sense. It is designed to shed heat, and the attic ventilation that keeps the shingles cool also throws away whatever the sun delivered. Turning a roof into a collector means changing the assembly: closing the cavity, adding a transfer layer, and connecting the roof to storage.

What ties the three together

A thermal barrier, an earth tube and a solar roof are not three separate purchases. They are three answers to the same question: where does the heat come from, where does it go, and how slowly does it move. A well-insulated, airtight wall reduces the amount of heat the house needs. An earth tube reduces the extremes the ventilation system has to handle. A solar roof or a ground store shifts the supply of heat from winter to summer or from day to night. Sizing them separately produces a house that is over-equipped in one place and under-equipped in another. The order of work is usually the reverse of the order of interest: airtightness and insulation first, ventilation second, collection and storage last. A house that loses heat quickly cannot be fixed by adding collectors.

What to check before committing

Ask for the heat load calculation, not a rule of thumb. It should state the design outdoor temperature, the indoor target, the air change rate at test pressure and the assumed internal gains. Without those numbers, any claim about the wall or the roof is a guess. Ask how the earth tube drains and how it is cleaned. Ask where the ground storage boundary is and what separates it from groundwater. Ask what happens in a week of heavy cloud in January, when the roof collects little and the store is drawn down. Standards help here. Passivhaus sets a limit on heating demand and on airtightness. NZEB sets a near-zero energy target without prescribing the route. LEED scores a broader set of categories, of which energy is one. None of them tells you whether a thermal barrier, an earth tube or a solar roof is right for a particular house. That depends on the site, the soil, the shading and the budget, and it is settled by calculation rather than by principle. Orientation decides how much of that work is needed, and reading the sun path before the plan is the step that comes first.

Close detail showing passive heating and cooling in context — Details are easier to judge when context and next steps stay together.

Second detail showing a practical New England home decision — Details are easier to judge when context and next steps stay together.