Crawl space dehumidifier without vapor barrier?

[Scoobie]

I did a “poor man” crawl space seal under my house about five years ago.

House is about fifty years old. Vapor barrier on the crawl floor was in bad shape. Vents all open and everything sweating.

I just laid fairly thick plastic on the floor. Didn’t tape seams just overlapped a few feet. Went to the masonry foundation walls, not up the walls. I had vents that automatically opened when it was warm. I just put a piece of light ga metal over them. Started out with a Lowe’s el cheapo dehumidifier someone gave me. It really worked great, solved the problem. After a year I bought a better dehum like the ones tb reps.

Sealing up the foundation walls would save a little power as the unit would run less. The floor plan of my house juts around and it was going to be a pita to really do a good job on the walls.

I wish I had used plexy glass to seal the vents instead of metal, to let a little natural light in.

[brock125]

UPDATE:

I was able to get my crawl space encapsulated (foundation vents sealed and vapor barrier installed) and dehumidifier (Aprilaire 1830) installed. The dehumidifier read 78% when I started in on the morning of 4/6. It currently read 52% but it's been running nonstop for over 2 days. The crawl space is around 1200 sq ft with a height of 18-24". Should I be concerned that it's been running for over 2 days now? It went from 78% to 58% after 1 day. It went from 58% on 4/7 to 52% this afternoon on 4/8. I'm using an Aprilaire 76 control unit with it and I have it set to 5 (if that means anything to any of you). It looks like this setting relies on the temp and %RH to determine when it will start/stop running. The temp in the crawl space has been between 65 and 70 degrees for the past few days according to another sensor I have down there. I was mostly curious if running for this long is the norm or not.

[Poodle Head Mikey]

It's not something that I would worry about. Don't forget - that reading you are seeing is the RH % of the AIR in the crawlspace - not the floor. The now drier air is still drawing the moisture out of the floor and walls and ceiling of the space.

I would let it run for a week or two before I would look into judging the results.

PHM
----------

UPDATE:

I was able to get my crawl space encapsulated (foundation vents sealed and vapor barrier installed) and dehumidifier (Aprilaire 1830) installed. The dehumidifier read 78% when I started in on the morning of 4/6. It currently read 52% but it's been running nonstop for over 2 days. The crawl space is around 1200 sq ft with a height of 18-24". Should I be concerned that it's been running for over 2 days now? It went from 78% to 58% after 1 day. It went from 58% on 4/7 to 52% this afternoon on 4/8. I'm using an Aprilaire 76 control unit with it and I have it set to 5 (if that means anything to any of you). It looks like this setting relies on the temp and %RH to determine when it will start/stop running. The temp in the crawl space has been between 65 and 70 degrees for the past few days according to another sensor I have down there. I was mostly curious if running for this long is the norm or not.

[servicefitter]

How sealed is the floor of the house ?

[teddy bear]

To confirm that the dehu is functioning, measure the condensate from the dehu for an hour. Your unit should remove 2-3 lbs./pints per hour.
Also measure the temp/%RH of the dehu supply verses the air going into the return. This will confirm the amount of moisture being removed by comparing the dew point in and out.
As others pointed out, any air from the home passing through the crawlspace will benefit from the dehumidifier.
It takes a couple weeks to dry down the materials in the crawlspace. During windy damp weather, the dehu may run 50%-75% of the time. After dry down and when the outdoor dew points are below the dew point desired in the crawlspace, the dehu should run much less.
A 68^F, 50%RH crawlspace is 49^F. Consider that outside vary from 60^F-75^F. During cold weather, the outdoor dew is much lower, usually equal to the evening low temperatures, but the crawlspace is cooler and may still have a small dehumidifier load.
Someday when the dehu fails consider the Santa Fe Compact, my favorite. The unit you have should be large enough to do the job. Keeping your crawlspace dry will help keep your home dry!

Keep us posted.
Regards Teddy Bear

[brock125]

How sealed is the floor of the house ?

I’m not exactly sure. It has the original hardwood floors or at least that’s how it appears.

[brock125]

To confirm that the dehu is functioning, measure the condensate from the dehu for an hour. Your unit should remove 2-3 lbs./pints per hour.
Also measure the temp/%RH of the dehu supply verses the air going into the return. This will confirm the amount of moisture being removed by comparing the dew point in and out.
As others pointed out, any air from the home passing through the crawlspace will benefit from the dehumidifier.
It takes a couple weeks to dry down the materials in the crawlspace. During windy damp weather, the dehu may run 50%-75% of the time. After dry down and when the outdoor dew points are below the dew point desired in the crawlspace, the dehu should run much less.
A 68^F, 50%RH crawlspace is 49^F. Consider that outside vary from 60^F-75^F. During cold weather, the outdoor dew is much lower, usually equal to the evening low temperatures, but the crawlspace is cooler and may still have a small dehumidifier load.
Someday when the dehu fails consider the Santa Fe Compact, my favorite. The unit you have should be large enough to do the job. Keeping your crawlspace dry will help keep your home dry!

Keep us posted.
Regards Teddy Bear

Thanks for all of this info. You mention the Santa Fe Compact but do you have any experience with the Aprilaire units? If so? What do you think of them?

[ga-hvac-tech]

The SanteFe's are more like Mercedes...
Other brands are Fords and Chevy's...
Grin!

One gets what they pay for.

Above all... avoid the big box store portables... they are junk, do not work well, use too much electricity, and rarely last more than 2-3-4 years.

[teddy bear]

The dehu you have should do the job if it is functioning properly. Measure the condensate output for an hour along with the temp/%RH of input and output. Expect 2- 3 lbs. per hour of condensate. If less, the unit may need service.
As long as it functions, I would use it. When it comes time for replacement, consider the Santa Fe.
Keep us posted.
Regards Teddy Bear

[Wolff]

Are santa fe dehumidifiers really that good? Mine Crane was working for 5 years but I accidentally broke it one week ago, but it seemed sometimes that it's not that warm as it could be

[teddy bear]

The Santa Fe may be more dehumidifier than you need. Tell us about what you are trying to do and in what part of God's Green Earth you are in>
Regards Teddy Bear

[Wolff]

I am a retired engineer visiting a friend of mine in Siberia. We are building a blockhouse of solid wood so I am looking for a powerful dehumidifier to keep the construction dry. For sure we will insulate the walls, floor etc. I still feel something like fust, though, and would like to help him avoid this in future