Brown ceiling, extractor fan issue.

Smithy99

Does anyone know what's likely to be causing these brown marks on the ceiling and our shower extractor fan?  I've read it may be because the ducting isn't insulated so condensation is forming on the outside of the ducting and running back down to the ceiling? But it also looks like water/condensation is coming down from inside the fan too.  Would lack of insulation cause condensation inside and outside the ducting? 

The ducting runs along the top of the attic insulation and I'm pretty sure the vent at the side of the side of the house is a cowl vent although will double check tomorrow.   I've also noticed the bathroom feels colder than usual the last few days but that may be coincidental as it's been very cold this week anyway.  We checked the attic when a small stain appeared and all the vent ducting connections looked fine but it's suddenly got worse over the last couple of days.  Thanks.

tacpot12

Smithy99 said:

Does anyone know what's likely to be causing these brown marks on the ceiling and our shower extractor fan?  I've read it may be because the ducting isn't insulated so condensation is forming on the outside of the ducting and running back down to the ceiling? But it also looks like water/condensation is coming down from inside the fan too.  Would lack of insulation cause condensation inside and outside the ducting? 

The ducting runs along the top of the attic insulation and I'm pretty sure the vent at the side of the side of the house is a cowl vent although will double check tomorrow.   I've also noticed the bathroom feels colder than usual the last few days but that may be coincidental as it's been very cold this week anyway.  We checked the attic when a small stain appeared and all the vent ducting connections looked fine but it's suddenly got worse over the last couple of days.  Thanks.

It's caused by condensation. Water droplets rolling down the inside of the ducting pickup microscopic particles of dirt and dust, and when the water evaporates when it reaches the warmth of the bathroom, it leaves the dirt on the ceiling as brown spots. I don't think you have a problem with condensation on the outside of the duct; it's be sure that it is the warm, wet, air travelling up the duct that is condensing because the duct isn't insulated. I would try insulting the duct first, and it this doesn't work, fit a condensation trap at the bottom of the duct. 

Smithy99

Thank you. So does the fact it's been very cold this week mean there may have more condensation hence it suddenly getting worse? 

grumbler

Yes, this is a likely reason.

Did you see this recent thread here? - Bathroom Extractor Fan Dripping

Smithy99

No I didn't!  Thanks

tacpot12

Smithy99 said:

Thank you. So does the fact it's been very cold this week mean there may have more condensation hence it suddenly getting worse? 

Yes, colder temperatures outside will mean the loft and therefore the duct is colder. The amount of water in the air going up the duct won't have changed, but the colder temperatures mean that this water will condense more readily. 

coffeehound

The brown may be due to the condensate rusting the soft iron bits inside the fan motor; this does not bode well for the life expectancy of the fan