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Old 07-16-2020, 07:50 AM   #16
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Re: Duct Condensation


So cutting a hole for a return in the blue box area would be OK?
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Old 07-16-2020, 08:27 AM   #17
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Re: Duct Condensation


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So cutting a hole for a return in the blue box area would be OK?
If there are gas fired flue connected devices in the unfinished area that depend on a gravity vent, then you need to be mindful of not creating a negative pressure in the area. That's especially concerning if that area is closed off and without any supply air from the hvac. Infiltration is reduced in a basement so attention to supply versus return balance is especially important. That can be mitigated somewhat if the basement is always open to the upstairs and by providing high/low wall venting from enclosed areas to balanced areas but even so it's best to shoot for a perfect balance in individual areas to the extent that it's possible and practical based on the size of the area.

With the preceeding as the caveat, the cut-in you propose will be worth a shot for a quick test if it's upstream of your existing filter. You can leave the door ajar to the finished area, if such there be, for the test. Air movement through the crack at the door with the hvac running will be a good indicator of a possible imbalance issue.
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Old 07-17-2020, 07:58 AM   #18
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Re: Duct Condensation


Actually, I figured out maybe it's better to swap that elbow from the existing lower return for a tee, and slap a register box on the end of the tee. That way if things don't work out, I can just put the elbow back in and everything is the way it was before. No need to cut anything.
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Old 07-17-2020, 08:24 AM   #19
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Re: Duct Condensation


It is absolutely unsafe and illegal to draw return air close to gas fired equipment unless everything draws combustion air from outside.
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Old 07-18-2020, 08:02 AM   #20
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Re: Duct Condensation


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It is absolutely unsafe and illegal to draw return air close to gas fired equipment unless everything draws combustion air from outside.
So how close is too close? Can you quote a code section I can parse?
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Old 07-18-2020, 12:25 PM   #21
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Re: Duct Condensation


For consideration, mine is 6' away and the furnace area is not closed off from the finished basement area. I hope and expect you wouldn't block off the furnace area and put a return air register in there without proper consideration.

I know you can find any number of Google sources that will advise against ever providing return air registers in a basement. What they don't tell you is that if the basement is fully developed into a space for human occupancy, that's a whole new consideration. As is usually the case, you have to regard the source and under what conditions the advice applies.
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Old 07-19-2020, 12:31 AM   #22
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Re: Duct Condensation


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Perhaps I will experimentally run a fan down there to get some circulation going, just to see what happens.

If I end up insulating, what's the proper stuff?
I am no expert in these matters, just another person trying to sort through similar issues in my crawlspace. That said I think running a fan will just move the problem, that the condensation will move to another place based on the airflow (unless you have some high airflow exchange between the inside and outside). That the real cure is to fix the source of moisture in the air; whether that means fixing overflowing gutters, a clogged footer tile drain, missing french drain, sealing foundation walls, etc. So that the humidity level will drop.
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Old 07-19-2020, 01:56 AM   #23
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Re: Duct Condensation


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So how close is too close? Can you quote a code section I can parse?
i don't know where you're located - anything you do has to comply with codes in your particular area.
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