crawl space condensation - http://www.hvacmechanic.com/ Forums
Original message
| talldavey
 |  "crawl space condensation"
, posted Tue 22 Jul 18:21  
I recently had flexible insulated 8" under floor ducts installed in a room addition.It has a plastic vapor barrier and gravel on top of dirt in a crawl space; the area is 22'x22' area with 5 vents in the block wall foundation.I am now getting a lot of condensation dripping off the flexible ducts causing the gravel and plastic to stay wet with some water accumilation on the plastic under the gravel.Should I install a dehumidifier or foundation vent fan?
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Replies:
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| theduke03
| "Re(1):crawl space condensation" , posted Tue 22 Jul 18:27
What is the R value of the sweaty flex? It should be R8.
Follow the water upwards, you may find that it's condensating on your floor boots which may be inadequately insulated.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | talldavey
| "Re(2):crawl space condensation" , posted Tue 22 Jul 18:47
I looked at the boots and water is dripping off the exposed metal directly under the floor.I will call the installer tomorrow.What is the proper way to fix this problem?Do I just wrap more insulation around the boot and staple it to the floor?Does it take a certain kind of insulation? I do not know what the r-value is.Will it be stamped on the flexible duct?
Thanks for the quick reply.
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| | theduke03
| "Re(3):crawl space condensation" , posted Tue 22 Jul 18:59
The flex will be labeled on the jacket, or may have stickers on the jacket that indicate the R value. The boots should be insulated with the same insulation as the ducts, they should be well wrapped, and seams taped with foil tape. If these connections are exposed to outdoor air it may always sweat some but this can be minimized. You should not be able to see any sheetmetal.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | talldavey
| "Re(4):crawl space condensation" , posted Tue 22 Jul 20:20
Thanks for the help-I went back under the house and wrapped insulation around the boot and used foil tape and also stapled insulation to the floor around the duct-It was r-4 insulation.
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| | theduke03
| "Re(5):crawl space condensation" , posted Tue 22 Jul 20:35
R-4? That's brutal, and probably against code. I would express my dissapointment to the installer and try to get some R-8, Otherwise your repairs to the boot will probably fix the condensation problem.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | Freon
| "Re(6):crawl space condensation" , posted Thu 24 Jul 15:46
Increase duct nsulation and seal all crawl space vents. Make sure no outside air can get into the crawl space. That will lover the relative humidity. have done this with a 3,000 sf ft crawl space in coastal GA (very humid and hot) and it works perfectly. Crawl space vents are not necessarily good.
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| | dwcaveney
| "Re(7):crawl space condensation" , posted Thu 24 Jul 17:37:
PG&E out here in California is telling us to do exactly what Freon says.
Similar to CRAC (computer room air conditioning) where the crawl space is the plenum.
They are also telling us to insulate the foundation walls.
Not a bad idea to rat proof (1.5" concrete) over the vapor barrier as well. (a fun job ha ha)
DW
[this message was edited by dwcaveney on Thu 24 Jul 17:46] |
| | talldavey
| "Re(8):crawl space condensation" , posted Thu 24 Jul 17:59
Is it a good idea to close the vents without completly sealing off the foundation and dirt floor with an air tight vapor barrier?
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| | dwcaveney
| "Re(9):crawl space condensation" , posted Fri 25 Jul 10:57
Oh, you mean the crawl space communicates with the main house crawl?
Might have to install a scuttle blocker (a piece of removable rigid insulation?)
Maybe re-check duke's post. (this is getting complicated and expensive)
I think you want adequate not perfect!
DW
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| | talldavey
| "Re(10):crawl space condensation" , posted Fri 25 Jul 12:07
The room addition was installed with a new foundation connected directly behind the old foundation.It has a seperate entrance to gain access to the crawl space.Holes have been knocked through for electrical service and the flexible ducts.There is also 4" of the blue board insulation on the foundation walls.
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| | dwcaveney
| "crawl space condensation" , posted Fri 25 Jul 16:26:
If duke's solution works, go with that.
What me and freon said, works well. But do you really want to rat proof and isolate new foundation from old? There is some work involved.
More insulation on the ducts might do the trick.
In the long run you might save a little energy doing it the hard way, how much I don't know. Comfort would most likely improve.
We are learning that many of these energy conservation measures do work well, but they are not really cost effective, mostly eco and comfort friendly. (the payback is more than 20 years)
You make a minor contribution to the environment, but at your cost!
When you figure cooking the cement, driving it to the job, etc, who knows, how much environment you save?
On the other hand, foundation vents are huge energy gobblers. Out here mild climate, virtually all new houses vapor barrier & rat proof the crawl space and insulate the foundation & underpinning, thereby requiring zero foundation vents.
EDIT: They don't let us block the foundation vents unless we VB 6 mil and rat proof with concrete.
DW
[this message was edited by dwcaveney on Sat 26 Jul 01:32] |
| | talldavey
| "Re(3):Re(10):crawl space condensation" , posted Fri 25 Jul 17:44
The temperature reading was the same at the floor vents in the addition and front room of the house.The only difference was the ducts in the original part of the house are un-insulated 6" galvanized pipes so I do not think using more insulation in the addition will help much unless I also insulate the galvanized pipes.Should the galvanized pipes be insulated or replaced with R-8 insulated flex.I would think the galvanized pipe would be less restictive to the air flow than the flex pipe at least that is what I have read or heard someplace.I think I will check the condensation problem in a few days since I put more insulation on the boots directly under the floor and then close the vents completly with insulated covers and see for myself what method works the best.I guess how long it will take for the floor to dyr up is anybodys guess unless I would put a de-humidifier down ther to help it dry up quicker.My funds are kind of limited right now since I just installed a new furnace.I just did not have the funds for ac also.Thanks for the ideas guys-much appreciated.I am open to any cheap suggestions.
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