What causes a bathroom vent fan to drip water?
steve196
| Posted in Mechanicals on
A customer has a bathrrom exhaust fan which drips water. The pipe originally went up then turned horizontal and exited the bldg. I now goes straight up. He covered the aluminum duct- short run- maybe 18″ with spray foam to insulate. Do we need more insulation?
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Replies
Steve,
Q. "What causes a bathroom vent fan to drip water?"
A. Condensation (assuming that the phenomenon happens during cold weather). It's possible, but unlikely, that it's rain entry -- but that would only happen when it's raining.
If the duct is well insulated, this may be tough to fix. Switching back to a horizontal duct (sloping slightly to the exterior) that exits at a gable is one possible solution. I would certainly go up into the attic and make sure that the insulation job was carefully done. I would also verify that there is a backdraft damper to limit exfiltration through the duct when the fan isn't operating.
Thank you Martin.
Puzzling is that it has been dripping even when the weather is not cold. Another idea I read about was to increase the CFM of the fan. I will check both the insulation and for a backdraft damper.
Steve,
It's possible that the house (or specifically, the bathroom) is unusually humid. Running the fan more often might help lower the indoor relative humidity and reduce the condensation problem.