A condensing boiler differs from a non-condensing boiler in that it uses the heat from the flue gases to pre-heat the cold water returning to the boiler, increasing efficiency. Condensing boilers can achieve efficiencies of 90% or higher, compared to non-condensing boilers which typically have efficiencies around 80%. The benefits of condensing boilers include reduced energy consumption, lower emissions, and cost savings. However, condensing boilers require proper installation, maintenance, and operation to achieve these benefits.