The following is based on my personal research:

A few thoughts about the use of Firewood in today's environmentally conscious atmosphere:

There are two types of energy: renewable and nonrenewable.

 Renewable energy = sun, wind, water, firewood, etc.

Nonrenewable energy = coal, crude oil and natural gas, etc.

The energy generated from the sun is known as solar energy,

that from water is hydel,

from firewood, animal dung, city biodegradable waste and agro-residue known as biomass,

and geothermal energy from hot dry rocks, magma, hot water springs, natural geysers, is called biogas, etc.

All the renewable sources of energy are fairly non-polluting and considered clean forms of energy.

Burning wood rather than gas or oil is good because the resource is renewable. It is essentially solar energy -- sunshine trapped by photosynthesis into the tree's tissue is released as heat in your home, so there's no net increase in heat at the earth's surface (discounting the time the energy is stored in the tree). An efficient fireplace releases mostly water vapor and carbon dioxide. The latter is a factor in global warming, but in the case of burning wood, no more so than if the tree had died in the forest and decomposed there. By contrast, burning coal, gas or oil releases CO2 that would otherwise have remained trapped underground.

While it is true that burning firewood can release particulates into our atmosphere, these particulates are for the most part organic, these in turn will bind with the “polluting” inorganic particulates already present in the atmosphere, making them heavy and making them fall to the earth faster, thus in effect, cleaning our air!

Renewable energy is derived from sources that never run out. The organic matter consumed is replaced as trees and other plants grow, without disruption to the natural carbon cycle. Fossil fuels, such as oil, coal and natural gas, release into the atmosphere vast amounts of additional carbon that would otherwise be stored below the earth, contributing to rising global temperatures through the greenhouse effect.