How does the Radiant Firegrate work?

In studying the challenges of burning wood in an open fireplace, pressure is constant and can be ignored for now, temperature will change and increase as the exothermic reaction gets going and the trick is to capture and contain as much of the heat as possible within the combustion zone, and transfer that heat into the room, not the chimney.

By positioning the wood as shown (left), and minimizing underfire air, a great deal of the heat generated in the combustion zone is retained. The surfaces of the logs glow and radiate heat, also burning up particulates as in an "after-burner".

The comwbustion heat converts itself to the infrared end of the spectrum of light, the same spectrum that heats the earth from the sun. Due to the concave arrangement of the stacked wood, heat is thrown out into the room, much as a concave mirror magnifies the image it reflects.

On the surface of the earth, we are all dependent on the heat energy from the Sun for our existence. It takes about one million years for this heat to reach us after it is formed.

To a large extent the Sun is a ball of Hydrogen formed some 5 billion years ago. Heat is developed when Hydrogen fuses with Helium. The temperature increases outwards in the Sun's upper atmosphere reaching temperatures of around 1 million degrees Kelvin.
Fossil fuels contain solar energy stored from bygone ages. Wood is dependent on the sun for growth and trees belong to seed bearing plants, coniferous or softwoods (Gymnospermae) and hardwoods (Angiospermae).

Wood is composed of elongated cells, most of which are oriented in the longitudinal direction of the stem, which is why wood seasons from the ends regardless of size, and at the same rate. Wood will not season any faster if split into smaller pieces, wood is split for sizing not seasoning. These cells consist mainly of cellulose, hemicellulose and lignin, all of which are organic and combustible.

Inorganic constituents exist in the bark of trees amounting to 2-5% of dry bark weight (determined as ash). It is from this bark that dioxins, furans and other undesirable emissions originate.

Heating wood in the absence of oxygen is called pyrolysis and in the 19th century the process was used to produce methanol, turpentine, acetic acid, phenols and wood tar, all of which are organic or carbonaceous and combustible. Heating wood to just above 100 degrees Centigrade initiates some thermal decomposition, above 250 degrees it becomes more active and above 270 degrees it is exothermic, producing more and more heat.
During this heat increase, the process produces a mixture of Carbon Monoxide, Hydrogen, Methane and other gasses which can be burned to produce heat, or flashed off with other unburned bi-products.

The trick in a home heating appliance is to burn all of these bi-products and waste nothing, cutting back on harmful emissions in the process. For all practical purposes, we human beings live at the bottom of an ocean of air comprising 79.1% nitrogen and 20.9% oxygen, requiring oxygen to breathe and survive and burn wood, fossil fuels and operate vehicles.

Trees and vegetation convert Carbon Dioxide back to oxygen in a process known as photosynthesis, contributing to the life cycle. When burning wood or fossil fuels, specific chemical reactions have been established and the behaviour of the bi-product gasses defined.
For example, burning 1 lb of carbon in wood will require 11.5 lbs of air, resulting in 31.4 cubic feet of Carbon Dioxide and 119 cubic feet of Nitrogen.

From the 17th century onwards, work has been done by Boyle, Gay-Lussac, Avogadro, Dalton, Graham, Van der Waals and others to determine the behaviour of gasses under temperature and pressure changes and these factors all exist in open fireplaces and woodstoves when wood is burned.

G.R. Telfer/RONJAN Inc/FIREGRATES 'R Us Inc.
24 January 2002.