A cogeneration power plant for producing steam and electricity, comprising: A. a boiler for producing steam, said boiler operating under variable boiler load, B. a boiler burner for receiving boiler combustion air and fuel to produce hot gases for said boiler, C. an internal combustion engine, for receiving fuel and air for combustion, said internal combustion engine comprising: 1. an engine block, and 2. engine oil, D. an electrical generator driven by said internal combustion energy, said electrical generator for producing electricity, E. a internal combustion engine exhaust output line for capturing engine exhaust from said internal combustion engine, F. an engine jacket and oil cooler connected to said internal combustion engine, said engine jacket and oil cooler for cooling said engine block and engine oil, G. a water circuit for removing heat from said engine jacket and oil cooler, H. a water-to-air heat exchanger connected to said water circuit, said water-to-air heat exchanger for transferring heat to ambient air to produce heated boiler combustion air, I. a boiler combustion air fan for receiving said heated boiler combustion air from said water-to-air heat exchanger and said engine exhaust from said internal combustion engine, said boiler combustion air fan for producing boiler combustion air mixture for said boiler burner, J. a boiler exhaust duct for directing boiler exhaust away from said boiler K. a boiler combustion control system for automatically monitoring said boiler load and said combustion air and engine exhaust mixture oxygen level and temperature and for adjusting the speed of said boiler combustion air fan accordingly to provide a near stoichiometric mixture so as to provide for a high burner temperature causing the reduction of NO x emissions in said boiler exhaust. A. a boiler for producing steam, said boiler operating under variable boiler load, B. a boiler burner for receiving boiler combustion air and fuel to produce hot gases for said boiler, C. an internal combustion engine, for receiving fuel and air for combustion, said internal combustion engine comprising: 1. an engine block, and 2. engine oil, 1. an engine block, and 2. engine oil, D. an electrical generator driven by said internal combustion energy, said electrical generator for producing electricity, E. a internal combustion engine exhaust output line for capturing engine exhaust from said internal combustion engine, F. an engine jacket and oil cooler connected to said internal combustion engine, said engine jacket and oil cooler for cooling said engine block and engine oil, G. a water circuit for removing heat from said engine jacket and oil cooler, H. a water-to-air heat exchanger connected to said water circuit, said water-to-air heat exchanger for transferring heat to ambient air to produce heated boiler combustion air, I. a boiler combustion air fan for receiving said heated boiler combustion air from said water-to-air heat exchanger and said engine exhaust from said internal combustion engine, said boiler combustion air fan for producing boiler combustion air mixture for said boiler burner, J. a boiler exhaust duct for directing boiler exhaust away from said boiler K. a boiler combustion control system for automatically monitoring said boiler load and said combustion air and engine exhaust mixture oxygen level and temperature and for adjusting the speed of said boiler combustion air fan accordingly to provide a near stoichiometric mixture so as to provide for a high burner temperature causing the reduction of NO x emissions in said boiler exhaust.