The Gross Calorific Value (GCV) measures the total heat of a fuel produced during combustion, and represents the maximum potential energy of that fuel.  The Net Calorific Value (NCV) represents the usable heat energy released when a fuel is burned. It accounts for the heat energy lost when water vapour from combustion escapes, making it a more practical measure of a fuel's energy content compared to GCV. When the moisture content of the fuel increases, the NCV typically decreases.

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The average moisture content of commercial firewood averages 15 - 20%. Under the Air Quality (Domestic Solid Fuels Standards) Regulations 2020 that now apply in England, wood fuel sold in volumes under 2m3 must be certified as Ready to Burn, (Ready to Burn is a certification scheme by The Department for Environment, Food & Rural Affairs - England), meaning that firewood must have a moisture content of 20% or less.​ Firewood sold in volumes of more than 2m3 does not need to be certified as  Ready to Burn,  

 

Most UK firewood are harvested from deciduous trees, such as beech, which has a GCV of 18,4MJ/kg. In order to calculate the NCV of a wood fuel with a specific moisture content (M), the following formula can be applied. NCV = [GCV x (100-M) - (2,44xM)] /100. (Wood Fuels Handbook. 2008. pg 25).

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Therefore we can determine that Beech firewood with a moisture content of 15%, has a NCV of 15,3MJ/kg, and if the moisture content was 20% (Highest permissible Ready-to-Burn wood) it would have a NCV of 14,2MJ/kg.

LOGGIs  have been tested and proven by SGS Laboratories (see Certificate of Analysis) to have a GCV of 21 MJ/kg and a moisture content of 3%, so if we apply the same formula we can conclude that LOGGI has a NCV of 20,3MJ/kg.

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Therefore the reality is that LOGGI's are 32% more efficient than common beech firewood with a moisture content of 15%.

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LOGGIs on average will burn 30% hotter, than most commercial firewood, so naturally you will need only 70% LOGGIs by mass compared firewood to heat the same home.

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