QUESTION: During a period of mild weather last February we noticed that the main-floor bathroom exhaust fan is dripping water. The water is not coming from within the exhaust duct, but rather around the casing of the exhaust fan.
We recently had an HRV unit installed in our house and do not run the bathroom fan anymore. Before the HRV was installed, we had no problems with any leaks, until now. The contractor that installed the HRV had mentioned to plug up the exhaust fan if we were not planning to use it anymore. I took that to mean putting a cloth in the duct at the exhaust fan. I did not do this as the exhaust duct in the attic appeared to be well-insulated. There is also about a foot of blown-in insulation covering the exhaust fan.
Would you have any idea why there would be leaking during the mild-weather snap? Should I have followed the contractor's advice and filled in the duct?
I have just now put some pink insulation in the opening of the exhaust fan leading to the exhaust duct. I am crossing my fingers that this will help.
Any feedback would be greatly appreciated.
Thanks, Gerald Teranishi, email
ANSWER: It is interesting to get questions about unforeseen problems arising after renovations, particularly related to energy-efficiency upgrades.
What is happening to cause the leakage you are seeing from the area around the bathroom exhaust fan is quite simple. You are getting frost building up around the older fan housing or in the ducting, which melts when the weather warms and drips back into the house around or through the fan housing. The older metal fan housing, which is connected to the ducting in the attic, is poorly sealed and insulated. There are probably significant gaps in the ceiling around the fan box that allows warm, moist air from the bathroom to leak into the attic.
Because the fan housing is likely metal, it will be much colder on the top and sides than it is on the underside, in the warm bathroom. The moist air that leaks into the attic will hit this cool surface and condense. When the weather drops significantly below freezing outside, the majority of the attic will also be near this temperature. The condensation on the outside of the metal fan box will freeze, often creating a thick layer of frost or ice from multiple days of air leakage.
The other item to explore is the older ducting attached to the fan housing. Even if this ducting is well-insulated, as you have noted, it will have a large surface area inside and warm air from the bathroom will surely fill this duct, even if the fan is not in service. This warm air will cool as it rises to the roof and will eventually come in contact with cool outside air that enters the ducting from the roof vent hood, above. Condensation inside, and often on the outside, of this pipe will be inevitable. This will also lead to leakage when the frost melts in the spring.
It may be difficult to differentiate between the water dripping from the ducting or from the housing, as this meltwater can run along the fan housing and leak into your ceiling in a different location than it originates.
There are two options to eliminating the leakage problem from your fan. The first approach is complete removal of the old fan assembly, ducting and vent hood. This may be the most labour-intensive approach, but will surely give you the most peace of mind that further problems won't occur.
This will require entering the attic, not only to remove the fan housing and ducts, but also to disconnect the power supply and safely remove the wiring or secure it in a properly covered junction box. It will also require a trip onto the roof to remove the vent hood and patch the hole, or seal the vent hood to prevent leakage.
The next step will be to patch the opening in the ceiling with drywall and install a properly sealed air/vapour barrier and insulation above. Taping and painting the ceiling patch will be the final requirement to finish the job.
A less labour-intensive approach is to block or remove the ducting and properly air-seal and insulate the fan without removing it. This will require entering the attic to remove the existing insulation from around the fan and the ducting, but will not require removal of the electrical wiring, as the fan can simply be unplugged and removed and the switch disconnected to render the wiring useless.
The main benefit to this method is the lack of repairs needed to the ceiling from removal of the fan housing. This becomes much less of a factor if the ceiling has become damaged from the leakage, and requires patching and painting anyway.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the president of the Canadian Association of Home & Property Inspectors -- Manitoba (www.cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca.
trainedeye@iname.com
