Reverse-process stove

Reverse-process stove

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The reverse-process indoor wood burning stove is a non-catalytic airtight heater. Employing a unique reverse process whereby it not only draws exterior air in to the wood stove for combustion, thus eliminating interior drafts, it also releases fresh outside air into the room through a rear-mounted plenum, where it is heated before entering the premises. This initiates a healthy fresh air exchange system, by introducing oxygen-rich air in to the building. The innovation by Jan Steen started as the Chinook, but later became known as the Sunrise wood stove.


The reverse-process stove is a wood-burning stove
Wood-burning stove
For a list of stove types see Stove .A wood-burning stove is a heating appliance capable of burning wood fuel and wood-derived biomass fuel. Generally the appliance consists of a solid metal closed fire chamber, a grate and an adjustable air control...

 based on two simple principles. One: It draws in fresh, cooler air from outside the building, then sends that air through interior steel pipes, before releasing it near the rear of the stove for combustion. This prevents cold air being drawn in to the premises. Two: Additional exterior drawn cold, fresh air is released to flow gently up the stove's outside rear plenum
Plenum may refer to:* Plenum chamber, a chamber intended to contain air, gas, or liquid at positive pressure* Plenism, or Horror vacui...

, where it is heated and released in to the room at the top of the plenum. This now hot, moist, oxygen-rich air creates a slight positive air pressure within the building. Since this positive air pressure is minimal, there is need for a corresponding exit
Ventilation (architecture)
Ventilating is the process of "changing" or replacing air in any space to provide high indoor air quality...

 somewhere up high in the building, to allow the subtle air pressure differential to continue.

This double effect, i.e. drawing air for combustion from the exterior as well as introducing fresh air in to the dwelling, makes this unit the 'reverse-process' wood-burning stove. Present day wood heating stoves are "95% more efficient than in earlier times" according to Carol Forsloff.

Additionally, the stove's very large cast iron baffle, when closed, forces the combustion gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

ses up to the bottom of the baffle, where (temperature allowing) they hopefully ignite. Remnant gasses and air then travel forwards and over the opening at the front of the baffle to be finally released up the rear positioned chimney/pipe.

It must be understood that the potential British thermal unit (BTU)
British thermal unit
The British thermal unit is a traditional unit of energy equal to about 1055 joules. It is approximately the amount of energy needed to heat of water, which is exactly one tenth of a UK gallon or about 0.1198 US gallons, from 39°F to 40°F...

 output allowed by wood-fuel comes mainly from its inherent combustible gasses which are released upon heating. About 70% of these potential heat-releasing BTUs are created by these gasses upon combustion. Many stoves' temperatures do not reach the required 700 plus degrees Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...

 to allow these volatile gasses to combust within the confines of the stove. For wood to become optimum fuel, it must have as little moisture content as possible. Differing wood types, i.e. the faster growing, Softwood
The term softwood is used to describe wood from trees that are known as gymnosperms.Conifers are an example. It may also be used to describe trees, which tend to be evergreen, notable exceptions being bald cypress and the larches....

 trees such as cedar and alder
Alder is the common name of a genus of flowering plants belonging to the birch family . The genus comprises about 30 species of monoecious trees and shrubs, few reaching large size, distributed throughout the North Temperate Zone and in the Americas along the Andes southwards to...

, will at best have half the potential BTUs, when compared to the harder
Hardwood is wood from angiosperm trees . It may also be used for those trees themselves: these are usually broad-leaved; in temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen.Hardwood contrasts with softwood...

, denser growing trees, such as fir
Firs are a genus of 48–55 species of evergreen conifers in the family Pinaceae. They are found through much of North and Central America, Europe, Asia, and North Africa, occurring in mountains over most of the range...

 and oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...

, etc.

Additional features, such as a water jacket, can be installed inside the stove. Although the most solid are cast-iron, experience teaches that water heated through a copper coil is better on the skin. Iron in the water makes a skin quite itchy. However, it must be realized that anything that hinders the process of combustion, by drawing away degrees of heat from the chamber, interferes with the potential of complete combustion.


Jan Steen is the innovator of the Chinook (later named 'Sunrise') reverse-process wood burning stove. After settling on an island in the Salish Sea
Salish Sea
The name Salish Sea was coined only in the late 20th century, and was officially recognized by the United States in 2009 and by Canada in 2010, to describe the coastal waterways surrounding southern Vancouver Island and Puget Sound between Canada and the United States of America...

 on British Columbia's west coast in 1976, the Franklin stove
Franklin stove
The Franklin stove is a metal-lined fireplace named after its inventor, Benjamin Franklin. It was invented in 1741.L.W. Labaree, W. Bell, W.B. Willcox, et al., eds., The Papers of Benjamin Franklin , vol. 2, page 419...

 installed in the rented farm house was far from satisfactory. Air leakage through badly fitting doors, a broad and narrow depth combustion chamber and an insatiable need for small pieces of wood because of its short, uncontrolled burns, led Jan to begin his experiments towards the creation of a more efficient stove. After 12 prototype models and refining the double airflow configuration, the reverse-process wood-burning stove was born as a far more efficient, time saving, low-tech device. Sadly, with the need for his own foundry, and the industry's costly new safety requirements, the stove never went in to production. The Sunrise 'reverse-process Stove' is a non-catalytic stove which, as a forerunner to the re-introduction of Wood-burning Stoves in the late seventies, was never certified by the United States, or Canada. It was an improvement, created by an entrepreneur at the time. Steen managed to deliver some 75 stoves across Canada with several ending up in Oregon.


With its large firebox design, and extended cast-iron baffle, this barrel shaped stove works as a highly efficient heat producer. However, its uniqueness continues to lie in its reverse-process air flow of releasing hot, moist oxygen air in to the house. Baffles radiate wood gasses back into the heat, allowing for a more complete, secondary combustion. Additionally, the preheated fresh air supply helps keep the primary and secondary combustion temperatures high. As Matthew Stein notes, "the most efficient wood stoves allow for ducting the air intake to draw air directly from outside your home." Open fireplaces are essentially totally in-efficient. While they do radiate heat, giving a sense of immediate comfort to those sitting in front of it, the fact they draw air directly from the room, sending hot air up the chimney, ultimately results in lowering the overall temperature of the premises. This can be verified by reading a temperature gauge located away from the fireplace.


Any indoor closed heating appliance used to heat up a building requires the oxygen in fresh air for burning the wood. Upon combustion there is an output of carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 (CO). Carbon monoxide is a poisonous, odorless gas which exits via the chimney. During the cold winter months, wood stoves are employed for heat. In the 1970s building codes were adopted introducing new construction standards. These required tighter sealed windows and doors, and plastic vapor barriers in walls and ceilings. While this created a tighter sealed barrier to the exterior of the building, it stopped fresh air from entering. This increased the build up of indoor pollution by creating stale air. That in turn led to condensation, with the result of the formation of highly toxic molds and mildews. So with all good intentions, while improving in one area, it created problems in another.

A wood stove employing indoor air for combustion creates problems, since cold air is sucked in to the premise, while on its way to the stove to ultimately disappear up the chimney. The reverse process wood burning stove provides a means of fresh warm air entering the home, rather than creating constant drafts of cold air being drawn in from small openings around windows and doors. By releasing fresh air into the room, the building breathes outwards rather than inwards, allowing for a slight positive air pressure to flow gently through the inside of the building.

A passive solar building design
Passive solar building design
In passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer...

 maximizes heating efficiency and due to its tight heat conserving principles and seals must consider adequate air exchange. The building codes for solar homes necessitate a back up heating system. In this regards the highly insulated solar home will also benefit from preheated fresh air entering the home from a back up wood burning stove such as the reverse-process stove.

The National Building Code of Canada
National Building Code of Canada
The National Building Code of Canada is the model building code of Canada. It is issued by the Institute for Research In Construction ], a part of the National Research Council of Canada...

 mandates new sealed airtight homes with improved air and vapour barriers, including a ventilation system which can replace one-third of the volume of interior air each hour. Similarly, the American Society of Heating, Refrigerating and Air Conditioning Engineers, recommend that air in a dwelling should be replaced totally every three hours. Fresh air intake is needed to reduce the dangers of indoor pollutants such as particle board
Particle board
Particle board, or particleboard , is an engineered wood product manufactured from wood particles, such as wood chips, sawmill shavings, or even saw dust, and a synthetic resin or other suitable binder, which is pressed and extruded...

Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...

 releases and radon gas infiltration. With a reverse-process wood burning stove, or fireplace, fresh air is drawn into the home directly, eliminating cold air draft while conserving costs by creating heating efficiency. A reverse-process stove reduces indoor air pollution with its constant intake of fresh air from outdoors.

See also

  • Space heater
  • Angithi
    An angithi is a traditional brazier used for space-heating and cooking in the northern areas of the Indian subcontinent, mainly in North India, Pakistan and Nepal...

  • Air-tight stove
  • Franklin stove
    Franklin stove
    The Franklin stove is a metal-lined fireplace named after its inventor, Benjamin Franklin. It was invented in 1741.L.W. Labaree, W. Bell, W.B. Willcox, et al., eds., The Papers of Benjamin Franklin , vol. 2, page 419...

  • Rocket stove
    Rocket stove
    A rocket stove is an innovative clean and efficient cooking stove using small diameter wood fuel which is burned in simple high-temperature combustion chamber containing an insulated vertical chimney which ensures complete combustion prior to the flames reaching the cooking surface. The principles...

  • Bukhari (heater)
    Bukhari (heater)
    A bukhāri is a traditional space heater from the northern areas of the Indian subcontinent, which is typically a wood-burning stove. Bukharis consist of a wide cylindrical fire-chamber at the base in which wood, charcoal or other fuel is burned and a narrower cylinder on the top that helps in...

    , traditional Indian wood stove
  • Wood-burning stove
    Wood-burning stove
    For a list of stove types see Stove .A wood-burning stove is a heating appliance capable of burning wood fuel and wood-derived biomass fuel. Generally the appliance consists of a solid metal closed fire chamber, a grate and an adjustable air control...