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HVAC Tech Says to Block Off Crawl Space's Return Vent #5069375
04/09/19 02:25 PM
04/09/19 02:25 PM
Joined: Jul 2007
Posts: 4,690
Midwest USA
LoneRanger Offline OP
LoneRanger  Offline OP

Joined: Jul 2007
Posts: 4,690
Midwest USA
Conditioned crawl space, no foundation vents. One supply duct blows heat or cool into crawl space, open ended w/ no register grill. Approx. 6 - 8 ft from this single duct that supplies conditioned air to crawl space, there is a return opening that draws crawl space air into the system, intermixing it with return air from the living space above.

Yesterday, an HVAC technician recommended blocking off that crawl space return. Said when their company does new construction rough-ins they never put returns in conditioned crawl spaces, only supply registers, and if you *are* going to have a return in there that intermixes crawl space air with living space air then you should consider having a UV light treatment system installed on the return plenum (in a serviceable area, usually on return plenum near where it connects to furnace) as well as a dehumidifier installed in crawl space.

I tend to agree with this guy. I don't think the rough-in contractor back in 2003 when house was built should've put a return opening in the crawl space. I am going to take the advice of yesterday's technician (from company that installed the new Amana system in February) and block off the crawl space return vent. May also install dehumidifier in crawl space as well, could be plumbed into sump pump's drain pipe with relative ease.




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Re: HVAC Tech Says to Block Off Crawl Space's Return Vent [Re: LoneRanger] #5069407
04/09/19 02:52 PM
04/09/19 02:52 PM
Joined: Mar 2004
Posts: 22,489
Upstate NY
Donald Offline
Donald  Offline

Joined: Mar 2004
Posts: 22,489
Upstate NY
Why even supply air from the HVAC into crawl space? Does it ever need heat? Dehumidifier is a good idea. As is a remove RH gauge in living area. They typically use expensive basement or crawl space dehumidifiers in crawl space. Aprilaire is a good brand.

I have home in DE. No freezing issues in crawl space. The home HVAC is not doing anything with the air in the crawl space. The dehumidifier is. Keep it 45 to 50 RH.


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Re: HVAC Tech Says to Block Off Crawl Space's Return Vent [Re: LoneRanger] #5069440
04/09/19 03:23 PM
04/09/19 03:23 PM
Joined: Apr 2010
Posts: 3,579
Atlanta,GA
BMWTurboDzl Offline
BMWTurboDzl  Offline

Joined: Apr 2010
Posts: 3,579
Atlanta,GA
There's nothing wrong with putting a return in a conditioned crawlspace. There's no need for a dedicated UV filter for the crawl either. If you want a UV filter have it installed near the filter for the furnace so that all of the return air is sanitized.


Last edited by BMWTurboDzl; 04/09/19 03:49 PM.

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Re: HVAC Tech Says to Block Off Crawl Space's Return Vent [Re: LoneRanger] #5069637
04/09/19 06:35 PM
04/09/19 06:35 PM
Joined: May 2013
Posts: 278
Peace valley, Missouri
Fitter30 Offline
Fitter30  Offline

Joined: May 2013
Posts: 278
Peace valley, Missouri
What type of floor is in the crawl space?

Re: HVAC Tech Says to Block Off Crawl Space's Return Vent [Re: Fitter30] #5075886
04/15/19 03:27 PM
04/15/19 03:27 PM
Joined: Jul 2007
Posts: 4,690
Midwest USA
LoneRanger Offline OP
LoneRanger  Offline OP

Joined: Jul 2007
Posts: 4,690
Midwest USA
Originally Posted by Fitter30
What type of floor is in the crawl space?


Plastic vapor barrier laid over pea gravel.



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Re: HVAC Tech Says to Block Off Crawl Space's Return Vent [Re: LoneRanger] #5076021
04/15/19 05:32 PM
04/15/19 05:32 PM
Joined: Mar 2004
Posts: 22,489
Upstate NY
Donald Offline
Donald  Offline

Joined: Mar 2004
Posts: 22,489
Upstate NY
Originally Posted by LoneRanger
Originally Posted by Fitter30
What type of floor is in the crawl space?


Plastic vapor barrier laid over pea gravel.


If you want to really do the crawl space properly you need to redo the plastic sheeting with a proper vapor barrier for the floor and walls with everything taped and sealed. A lot of work. Not cheap to hire a pro. In my crawl space in my DE home the height is between crawling on my belly and crawling on my hands and knees.

Once done properly then a dehumidifier can easily bring down the RH to 45% to 50%.


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Re: HVAC Tech Says to Block Off Crawl Space's Return Vent [Re: LoneRanger] #5076145
04/15/19 08:17 PM
04/15/19 08:17 PM
Joined: May 2012
Posts: 4,822
Baltimore, Maryland, USA
zzyzzx Offline
zzyzzx  Offline

Joined: May 2012
Posts: 4,822
Baltimore, Maryland, USA
No basement in Delaware?

Re: HVAC Tech Says to Block Off Crawl Space's Return Vent [Re: Donald] #5084070
04/23/19 06:57 PM
04/23/19 06:57 PM
Joined: Dec 2016
Posts: 471
Indiana
5AcresAndAFool Offline
5AcresAndAFool  Offline

Joined: Dec 2016
Posts: 471
Indiana
Originally Posted by Donald
Originally Posted by LoneRanger
Originally Posted by Fitter30
What type of floor is in the crawl space?


Plastic vapor barrier laid over pea gravel.


If you want to really do the crawl space properly you need to redo the plastic sheeting with a proper vapor barrier for the floor and walls with everything taped and sealed. A lot of work. Not cheap to hire a pro. In my crawl space in my DE home the height is between crawling on my belly and crawling on my hands and knees.

Once done properly then a dehumidifier can easily bring down the RH to 45% to 50%.


And if you do all this you might as well have a basement. Here in our part of Indiana basements can be fairly rare, Many crawl spaces I have been in, which numbers at least 200, have had moisture issues and a shoddily installed vapor barrier with pea gravel on it. My favorite one had a sump pit in it which was in the higher part of the crawl so water ran away from it and it had no drain tiles running into it so it was effectively useless.

I have been in one that was completely sealed with a pool liner like material, it was clean, dry and conditioned. Once you factor in the expense of doing this plus the expense of conditioning it, I figure you might as well have a basement, even if just for storage.

In the heat of the summer most crawl spaces here have moisture condensing on almost everything it can. IMHO here it is just to cold and damp and hot and humid most of the time to have a crawl space vented to the outside and not expect moisture in there. It gets so ungodly humid here its ridiculous.

What aggravates me is the work is a lot easier and cheaper to do if its done right after the block is laid. but its seems like out of sight out of mind when they build these homes and someone 15 or 30 years later has to deal with the problems the poor preparation creates.

Last edited by 5AcresAndAFool; 04/23/19 06:58 PM.
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