Crawlspace - Vent Fan vs Encapsulation

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Reelsix

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I recently had an indoor air quality expert advise that I install a Crawlspace vent vs Encapsulating the space. They advised this would be cost-effective approach. Vent would be humidity controlled and would turn on if crawlspace humidity was higher than outdoor humidity. Crawlspace would be sealed as best possible using weather stripping on the access door (inside) and any gaps and cracks around pipes sealed with foam. Duct worked to be sealed if any leaks.

I live in the South and furnace/ac is in the crawlspace.

My concern is that fan would not run as it would be rare that outside humidity would be lower than in crawlspace so it would remain a "wet" space. Also, that limited sealing approach recommended would be ineffective in my 1950s home (hardwood floors in kitchen above crawl are cupped due to excess moisture). Are my concerns valid?

FYI - Expert was not pushing approach to gain any additional business.
 

Snoonyb

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My 1st question would be, is the required make-up air for you your comfort heating appliance ducted from the exterior of the building envelope, or is it taken from the crawlspace?

If your proposal is to exhaust, you also need an equal volume of replacement air, and while you are being advised to weatherstrip and seal, what about the required foundation venting?
 

Reelsix

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I believe it is taken from the crawlspace (is this different from the air it pulls from returns in livable space?)

The crawlspace does have "passive" vents in place that ventilate to the outside and they would remain open. Is that what you are asking about?

Novice so trying to answer to the best of my ability.
 

Snoonyb

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I believe it is taken from the crawlspace (is this different from the air it pulls from returns in livable space?)
Yes, the recirculated air within the building envelope, is conditioned air and cannot be used as combustion air.
Combustion air is drawn into the combustion chamber as fresh or natural air, and is exhausted as a product of that combustion.

The crawlspace does have "passive" vents in place that ventilate to the outside and they would remain open. Is that what you are asking about?
Those are the source of the combustion air and as required cross ventilation of the crawlspace.

I would ask the volume of the exhaust fans. The concern being robbing the comfort heating appliance of needed combustion air, thereby affecting its efficiency.

Novice so trying to answer to the best of my ability.
Life's a dance, and you learn as you go. It's what we are hear for.
 

nealtw

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Sealing the crawl space seams to high on the list of places for people spend money.
If you seal the craw space you also need a duct to bring air to the fire in the furnace as noted above, of cause nothing works if you have water laying in there.
I would bet that you do not have a perimeter drain at the depth of the footing either inside or out. Encapsulating will not work until you have the drain to keep the water out and if you have the drain, there would be a good chance passive would work just fine. Did they also mention that if you encapsulate you would have to condition the space as in heat and air condition.
 

Snoonyb

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Just another question, is there insulation in the floor joists?
 

Reelsix

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Hi. There is no insulation in the floor joist. I have read that it is not a great idea in a vented crawl bc moisture can build in the insulation and create mold.
 

Snoonyb

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The purpose of the ventilation is the circumvent that.

You can connect the fan on a timer or controlled by relative humidity.

You could also use closed cell rigid insulation.
 
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