What is pluming?

There are times when a white plume or discharge can be seen coming from the flue terminal on condensing boilers. This is due to the flue gases being cooler than in non-condensing boilers. With standard efficiency (non-condensing) boilers, flue gases are hotter and cool down further away from the flue's terminal and dissipate differently. The flue gases of condensing boilers exhaust at around 55 degrees C, cool quicker in the atmosphere and in certain outside temperatures cause a plume similar in effect to breath on a cold morning.