What is the difference between net combustion efficiency and gross combustion efficiency?
Net Combustion Efficiency v Gross Combustion Efficiency
Net combustion efficiency calculations assume that the energy contained in the water vapour which is formed as a product of combustion is recovered and is not exhausted from the flue or stack.
Gross combustion efficiency calculations assume that the energy contained in the water vapour is not recovered.
Typically the difference between the value of net combustion efficiency and the value of gross combustion efficiency for a natural gas fuelled boiler is around 8% with the net value being higher than the gross value.
Most boiler manufacturers now quote their boiler efficiencies based on the net combustion efficiency.