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Passive Annual Heat Storage

What is it? ....

     PAHS (Passive Annual Heat Storage) is an innovative, practical and simple technoloy of heat collection, storage and retrieval. The principle was developed by John Hait of the Rocky Mountain Research Center in 1983.

     PAHS is essentially placing an insulating and waterproof "umbrella" over and about 15-20 ft. beyond a typical earth sheltered home.

     With this umbrella keeping the earth dry, thermal energy will travel through the earth, allowing you to store the maximum amount of thermal energy under and around your foundation."

Cross Section of an Earth-Sheltered home using PAHS
Cross Section of an Earth-Sheltered home using PAHS

     The insulated umbrella also serves as a thermal break between the cold and wet top soil (top 2-3 feet), and the warm and dry soil below, thus increasing the amount of thermal mass available to you to store warmth.

     Conventional heating systems are unnecessary!

The ultimate year-round
energy conservation system should....

  • Be simple and straight forward.
  • Work on the natural annual heat cycle.
  • Collect and store free heat whenever it is available.
  • Automatically bring the heat out of storage when needed.
  • Provide ALL of a home's heating and cooling needs.
  • Provide a continuous supply of fresh air.
  • Provide a surplus of energy of other needs.
  • Not use mechanical equipment.
  • Never break down or wear out.
  • Work in climates all over the world.
  • Be inexpensive and easy to build.

First use of PAHS....

     An early version of passive annual heat storage was first used in a home called the Geodome in Missoula, Montana, built in 1981.

     Although the physics of underground heat flow is complex, PAHS can be easily applied by knowing a few easy-to-understand principles. Understanding the WAY things work, along with how things do NOT work, determines how well the house design will work.

The Geodome in Missoula, Montana
The Geodome
in Missoula, Montana

     All the development has been done, the mistakes have been made, sytems re-designed, and working models built proving the methods for over 25 years.

Earth Tube Ventilation....

Earth tube ventilation system
Earth tube ventilation system

     Earth tubes ventilate, store and retrieve heat automatically while providing year-round fresh air at ROOM TEMPERATURE.

     Without mechanical equipment or commercial power, Passive Annual Heat Storage inexpensively cools a home through blistering hot summers, saving those precious BTUs, and then returns them automatically when they are needed to keep the home comfortably warm through frigid northern winters.

     During the summer months, free solar heat naturally moves through convection-powered heat-exchanging earth tubes and is saved into a giant thermal storage mass of earth. All winter, the air flow naturally reverses, bringing warm air into the home.

     Natural air currents provide fresh air ventilation and purge the house of indoor pollution, even radon, without using mechanical equipment.

PAHS vs conventional solar power....

     Passive Annual Heat Storage works even in cold northern climates... or if it's cloudy all winter.

     It is all but impossible to collect a home's heating needs in the winter using solar power. But storing large quantities of excess summer heat in a natural, passively-operated reservoir... the earth, is easy!

Constant comfortable temperature....

     An earth-sheltered home using Passive Annual Heat Storage, controls the summer heat input and winter heat loss to establish a new average annual inside air temperature, which in turn, will produce a new constant temperature in the earth around the home.

     The home and the earth will work together to remain within just a few degrees of this average all year long. In this way the environment around the earth-sheltered home can be climatized to any suitable temperature needing neither air conditioners nor furnaces.

Insulation/watershed umbrella....

     Passive annual heat storage is a new approach to using the earth to store solar heat. This method treats the area of dirt surrounding a dwelling as a part of the structure's thermal mass by insulating it from the elements . . . but not from the walls.

cut-away view of the insulation/watershed umbrella
Cut-away view of the insulation/watershed umbrella

     For an earth-sheltered home to remain warm all winter from the heat gathered during the summer, the heat-storing earth must be kept both warm and dry. Cold rain water is not allowed to soak into the ground around the home, as it will causes waterproofing difficulties and cools off the earth.

     Through an insulated and watershed umbrella (extending 20 feet out around the house), rainwater is collected and controlled, making the earth into a warm dry blanket around your home. Walls and basements stay dry!

     The umbrella is carefully made with 3 layers of polyethylene plastic sheets laid just like shingles, with insulation in between and a layer of protective earth on top.


     Passive Annual Heat Storage using the earth tube ventilating methods is inherently inexpensive in comparison to the usual cost of building an earth-sheltered home. The insulation/watershed umbrella is made by laminating layers of rigid insulation with at least three layers of polyethylene sheeting. It is not only long lasting, but relatively inexpensive to buy and install. Also, waterproofing costs are reduced considerably because the home sets in a dry environment.

     After the initial cost of materials (insulation, plastic sheeting and plastic pipes), this natural climate-controlled method makes Passive Annual Heat Storage the least expensive energy management system anywhere!

Here is a wonderful book for more information....

Passive Annual Heat Storage,
improving the design of Earth Shelters

by John Hait and the Rocky Mountain Research Center

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