Efflorescence around the furnace exhaust pipe

[ambrosia]

Hi,

I have visited a house recently. The house was built in 1963. The house use a oil furnace with forced air. I've noticed that the furnace has two exhaust pipes that are exiting through the basement wall. Around one of the exhaust pipe there is a fair amount of efflorescence.

Do you have some idea what could be the cause of this? I didn't find any other efflorescence except at this specific spot.

Thanks for your help!

[jon_ran]

A damaged or non-existant crown at the chimney?

Damaged masonry on the chase?

[Mark P]

Is it venting vertically or horizontally?

We don’t have oil furnaces in my neck of the woods, but I’ll give this a shot. If it is venting horizontally it is supposed to be a high efficiency (92%+) furnace and one pipe brings in combustion air and the other is the exhaust vent. If it is truly efflorescence it is caused from water coming through the wall leaving the mineral deposits behind, which is the definition of efflorescence. So the real question is where is the water coming from?

Now if it is venting vertically and the white deposits are on the exhaust pipe itself it is not efflorescence at all. One of the byproducts of combustion is water vapor, if the water vapor is not making it outside and runs back down the exhaust pipe, it leaves a white residue when it dries. This is a sign of a problem with the furnace exhaust because not only is the condensate corrosive and will damage the equipment, but the other exhaust byproducts are not making it outside too.