Crawl space humidity control (home, to live in, low cost)

[Plinian]

Another "new to the area" question for those North Alabama residents lucky enough to live in a pier and beam crawl space structure...

Our home is several years old and is a "closed" crawl space--vapor barrier with a couple dehumidifiers draining to a sump pump which itself drains to the outside. For those of you with similar systems, how do you adjust the dehumidifier controls? (each dehumidifier has a rheostat probably numbered 1 - 10 which I'm guessing does not correspond to relative humidity)

At present, our system is completely manual, based on whether it feels musty down there or whether last month's electric bill was too high (we haven't seen an electric bill yet). I imagine there are automatic (humidistat) control systems, but I suspect most people around here use a more intuitive approach. Thanks for your input.

[Charles]

You could pick up a wireless temperature and relative humidity sensor and display that are generally used by weather geeks like me. They are probably around $50 or $60.

Stick the sensor in the crawl space and set the dehumidifier to 1, wait a while, look at the RH
set it for 10, wait a while, look at the RH. Now you know understand the operation of the control.

Now you can just use your weather station for normal use.

[harry chickpea]

I've been considering putting in a duct from the attic to the crawl space, with a continuously running small squirrel cage fan. Attic air is usually hot and dry, and pumping it down into the crawl space should serve to dehumidify at low cost.

[djmaxwell]

Originally Posted by harry chickpea

I've been considering putting in a duct from the attic to the crawl space, with a continuously running small squirrel cage fan. Attic air is usually hot and dry, and pumping it down into the crawl space should serve to dehumidify at low cost.

Are you looking at something like the flue on gas fireplaces where it both draws in the air and then exhausts it out? Otherwise, where is the air pumped into the crawlspace going to go?

[harry chickpea]

Metal flue with springloaded damper as firestop. 6" diameter. Air drawn through soffit vents in attic to the flue. Squirrel cage fan at bottom in crawl area. Hot air from attic pushed from flue into space puts positive pressure in crawl space. As the hot air enters, it meets the cold moist air of the crawl space, allowing it to carry more moisture. Since there is positive pressure, the combined air escapes through the vents of the crawlspace. If the space is completely sealed (doubtful) then a vent to the exterior would have to be added. The key concept is that the moist air is pushed out by the drier air from the attic. This avoids the tremendous losses that dehumidifiers have because of having to overcome the heat of fusion.

[HB2HSV]

Originally Posted by harry chickpea

Metal flue with springloaded damper as firestop. 6" diameter. Air drawn through soffit vents in attic to the flue. Squirrel cage fan at bottom in crawl area. Hot air from attic pushed from flue into space puts positive pressure in crawl space. As the hot air enters, it meets the cold moist air of the crawl space, allowing it to carry more moisture. Since there is positive pressure, the combined air escapes through the vents of the crawlspace. If the space is completely sealed (doubtful) then a vent to the exterior would have to be added. The key concept is that the moist air is pushed out by the drier air from the attic. This avoids the tremendous losses that dehumidifiers have because of having to overcome the heat of fusion.

Heat of fusion?

You mean the Heat of Vaporization? (the reverse is the Heat of Condensation)

[harry chickpea]

Sorry, term slippage. Had been recently discussing the issue of moisture in frozen wood used for heating. That has to go through two changes. Bottom line of that discussion - let your wood dry thoroughly.

[HB2HSV]

Originally Posted by harry chickpea

Sorry, term slippage. Had been recently discussing the issue of moisture in frozen wood used for heating. That has to go through two changes. Bottom line of that discussion - let your wood dry thoroughly.

It's okay. Only geeks like me notice terms as such.