Bathroom Vent Close to AC Register Causing Condensation
I live in the south and have been in a newly constructed home for 2 years. In the summer, I’ve had a problem with condensation buildup on the AC register which is inches away from the bathroom vent fan. This problem is in two upstairs bathrooms that are hardly used.
I’ve had an AC guy come in and he states the way to fix this is with a backflow preventer on the bathroom vent duct. The charge is over $400.
Before I spend this money, I’d like to know if he is telling me the correct info. Also, I’ve researched backflow preventers and none seem to cost more than $50. If I installed this myself, where would I place it? Inline or near outside exhaust?
Thanks
Rob
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Replies
You could confirm the theory by taping up the exhaust vent when it isn't being used.
Be sure to leave the bathroom door open when it isn't being used.
Great idea
If you only see that condensation during or after taking a shower, and it's forming ON the vent, it's probably because your A/C came on, the metal the vent is made of got cold enough to drop below the dew point of the humid air in the bathroom, and condensation formed. If that's the case, a "back flow preventer" (damper) on the bathroom fan exhaust duct isn't going to do anything.
If the condensation is dripping out of the vent and is forming IN the vent (more specifically, it's forming in the ductwork supplying air to the vent), then I'd say "maybe" a damper would help, since it would keep humid bathroom air from flowing back up into the supply duct when the A/C shuts off. You might still have some condensation forming on the vent itself (for the reasons I described earlier), but at least it would be less.
Bill
Thank you for answering. The bathrooms are not used much and so showers are vary rarely used. So it’s not the ac coming on while taking a shower. There isn’t condensation inside the registers. I believe the tech was trying to tell me moist air is coming from bath vent ducting.
I also live in the south. Humidity is at 90 percent as I type this and there's condensation on all my windows.
I have serious doubts about the diagnosis and would say that the issue is that the supply register is simply too close to the fan. When the fan is operating it's going to continuously pull moist air across the register. I know you're probably out of warranty but that supply register needs to be moved. Is your home is a tract-house? If so you could ask your neighbors if they have the same issue with their bathrooms and then the community can go after the builder.
Thank you for answering. It’s not air being “pulled” across the vent because we hardly use the bathrooms or turn on the vent fan. Rather just static air in the vent ducting.
If you have multiple bathroom fans sharing a common exhaust duct, then I could see potential issues with fans in one bathroom pushing moist air into the others. If each bathroom has it's own, seperate, exhaust vent run to the outdoors, then I don't really see how a damper is going to help here.
I would experiment a bit by taping some paper over the A/C vent or the bathroom fan and see if anything changes. If there are no changes with the bathroom fan sealed, then the damper isn't going to do anything, either.
Bill