OT-basement venting help please

I know, no metalworking really but there is a lot of varied experience here. I need to vent a basement room. It's about 20 x 12. What happens
now is moisture laden air goes down the stairs and then drops the moisture in the basement room. I want to keep the room cool so heating to get rid of the moisture is out. So I have been looking at vent fans and pretty much all I see are fans for venting crawl spaces and attics. So what kind of fan should I use? Thewre must be some sort of shutter and a screen but I think those can be added to the outside. And do I need two fans? One at each end of the room? So that fresh air comes in and old air goes out. Or just an exhaust fan? The room is aligned lenghtways sort of north to south. The southern fan would be the exhaust fan and would vent under the front porch. The northern fan, if there is one, would draw air in from the north facing end of the house. I live about 30 miles north of Seattle so I guess weather should be taken into account too. Thanks, Eric
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On Thu, 14 Nov 2019 09:10:49 -0800 snipped-for-privacy@whidbey.com wrote:

You need a dehumidifier. But they aren't all that cheap to run and they also produce heat. Fans will do nothing to help the problem unless they have a source of drier air to move in...
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Leon Fisk
Grand Rapids MI
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wrote:

A temperature and humidity weather station with remotes outdoors and in the basement would be a great help to recognize problems and test solutions. Unfortunately the nice Oregon Scientific one I have was discontinued, or I'd suggest it.
A datalogger like this is useful if you become serious about monitoring and controlling home energy. (Amazon.com product link shortened)40520815&sr=1-2
We could be one election away from strict energy conservation mandates. I hope the rest of us aren't forced to follow California into the darkness.
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On Thu, 14 Nov 2019 15:12:06 -0500
<snip>

<snip>
I have a couple cheap humidity stations placed downstairs. This one is my favorite:
(Amazon.com product link shortened)
I don't think its readings are all that accurate but consistent. After years of looking at it, along with the time of the year, I got a feel for what causes problems and needs knocking back down. Have a 60 pint dehumidifier that I wheel into the room and let run for several hours or what I feel is necessary...
Right now with the dropping temps outside and forced air running inside upstairs the humidity level isn't a problem. Next spring when the reverse happens I'll have to run the dehumidifier while the basement temp rises along with the rising outside temp plus high humidity...
--
Leon Fisk
Grand Rapids MI
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wrote:

I've been making industrial, scientific and home project temperature measurements since the 1960's and learned to compensate for inaccuracy, though not inconsistency. Lining up all the instruments on the bench and writing down their readings of room temperature is a good start that gives offsets, repeating in an ice bath or boiling kettle shows if there's also a gain error term or a gross inaccuracy. Usually I cared about rates of temperature change more than absolute values. The 0.1 degree digit is good for that even though the absolute accuracy may be +/- 2 degrees.
Logged data from multiple sensors can be corrected in a spreadsheet by inserting columns that add or subtract the individual offsets.
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On 14/11/2019 20:12, Jim Wilkins wrote:

A guy I know built a straw bale garden room and while it was drying out after it was rendered with lime mortar inside and out he monitored it with a Rasberry Pi with a simple humidity sensor add on, as the room had internet access he was able to monitor the readings from his house which was a few hundred meters away.
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wrote:

I see that wattle and daub is making a comeback too. https://www.lowimpact.org/lowimpact-topic/wattle-daub/
Personally I use pallets for the floors and walls of sheds framed with tree trunks.
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Here in New England we can have Hudson's Bay cold or Gulf of Mexico heat and humidity or anything between. Right now it's record cold.
I sealed the living space doors and windows until the indoor humidity began to rise, leaving the basement doors and windows as-is to leak in air for the wood stove. As a result the basement humidity rises above 80% during humid periods in summer, when the outdoor dew point is above 70F. One of these has been enough to remove enough humidity that my machine tools don't rust. It fills in 3 days and uses about 25 Watts. Two can dry the bathroom after a shower when outdoor air is too cold or humid to blow in. (Amazon.com product link shortened) I it isn't enough you can try a larger compressor dehumidifier.
In summer I watch the indoor and outdoor temperature and humidity and cool the house with night air whenever practical, which isn't too often. I'd say you want an exhaust fan on the downwind (suction) side and maybe not a basement intake fan that could blow ground-level humid night air and mold spores upstairs, let upstairs leakage be the air source to remove cooking odors.
You can see air flow within the house with a Mylar helium balloon ballasted weightless. Rubber balloons leak too fast.
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On 11/14/2019 9:10 AM, snipped-for-privacy@whidbey.com wrote:

Venting is the wrong thing to do. You need to have higher air pressure in the basement to keep the moist air out. I know Whidbey outside air is moist, but you need to find a source of dryer air to force into the basement.
For temperature, you just need to keep the temp above the dewpoint for the humidity level in the basement air. So a fan with a bit of heat to circulate in the basement might work.
What do your neighbors do?
Paul
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wrote:

I don't know anybody with a basement. When we built our house I found that basements, even half ones like we have, aren't very common. Thanks for the advice. I was starting to think that vent fans were a bad idea. I was told by a contractor that i should have them but now I think he didn't know what he was talking about. Thanks, Eric
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On 15/11/19 10:27 am, snipped-for-privacy@whidbey.com wrote:

I mostly disagree with the other respondents in this thread.
Ventilation helps here in Sydney. Humid but non-condensing air starts to condense on changes in temperature or pressure. So if you have airflow, you only get condensation inside if there is also condensation outside, because the airflow keeps the inside conditions similar to outside. When it stops condensing outside and starts evaporating, any condensation inside also dries off.
Without airflow you get a big lag in the equalisation of temperature and moisture content, but *pressure changes are instantaneous*, causing more condensation inside, and delayed drying of any condensation that has occurred (because the air gets saturated and evaporation stops).
All that means that ventilation (passive or active) is an advantage.
If you have significant cooling (heat flow into the soil) coming from the sub-soil (other than caused by evaporation of moisture already in the basement), or significant sub-soil sources of moisture so your basement has a higher relative humidity than outdoors, ventilation won't help. You should use a moisture barrier and thermal insulation, then ventilation will work as described above.
Clifford Heath.
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On Fri, 15 Nov 2019 11:57:31 +1100, Clifford Heath

I have no personal experience but have heard that a dct booster fan installed to pick up at floor level and exhaust to the outside will help. In my case, SWMBO insists that the air conditioner must run from June first to the end of September.
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wrote:

Air conditioners remove humidity very well. A 5000 BTU unit placed in my bathroom window after taking a shower clears the fogged mirror in 5 minutes and dries the air to the level of the rest of the house in 15, costing $0.03 in electricity.
I made a shelf for the A/C that rests on the window sill and clear panels that fill the gaps on either side, so it's quick and easy to install or remove, though it usually stays in the window through the tropical months of summer. When removed it goes on a stool (=seat) in the shower to drain.
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I'd start simple and cheap, a window fan or the minimal dehumidifier I mentioned, and watch what happens with a temperature & humidity meter.
Perhaps you could solve the problem by venting the bathroom outdoors after baths or showers. I squeegee and sponge the walls dry after a shower to help control humidity in my tightly sealed house with antique machine tools in the basement.
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On Thu, 14 Nov 2019 15:27:02 -0800, snipped-for-privacy@whidbey.com wrote:

I had a full basement in Midland, Michigan. I erected a "paint booth" of sticks and plastic and used one of these https://www.mcmaster.com/1963K13 to keep a negative pressure and keep paint odors out of the house.
I mounted it on a homemade concrete pad in the crawl space under an addition, and piped the vent outside under the deck. The installation was a pain in the ass, but the fan worked well. I let it run during cleaning and painting of my old hardinge mill. Never had a complaint about odors.
It would only work to dehumidify if the source air was relatively dry, like from the rest of the house. I think the dehumidifier suggestions are spot on for your need.
Good luck.
Pete Keillor
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On Fri, 15 Nov 2019 06:38:52 -0600, Pete Keillor

If I need to do a small rattle can paint job in my basement shop, I turn on the clothes drier to air dry (no heat) and use that as an exhaust fan.
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snipped-for-privacy@whidbey.com on Thu, 14 Nov 2019 09:10:49 -0800 typed in rec.crafts.metalworking the following:

    Step 1: stop this air flow.      Door, curtain, whatever, the problem is the cooler "damp air" going down where it will be further cooled below the dew point, and drop all the water.          Other option, you will need to confine the cooling air to one area until it reaches "room temp" and drops any excess humidity. A door at the bottom would accomplish this.
    Because if you can't stop the damp air, you're going to have to remove the water somehow. Dehumidifiers to extract it, or heaters to raise the dew point of the air. Fans are just going to move air from one place to another, and around the Puget Sound from Oct to June, you can bet on it being damp outside.

    The advantage of this is that you'll be drawing "cooler" air (a bit "drier", or at least more saturated) in from the north side, which can mix with the warm damp air coming down into the basement, and ah, hmmm. Cool off the warm damp air, condense some of the water out, and blow the rest out under the porch.
    Stopping the airflow with doors or other barriers seems a better idea.
tschus pyotr
I had a house which needed the "cross connect duct" replaced. I had no heat in the front half of the house, like it my office. I hung a curtain in the doorway to about six inches off the floor (this also let the cat come and go without my having to get up all the time.) and that trapped the heat from the space heater. My office would be toasty, but the rest of the house was ... "Brisk"? Nippy? Down right fridged? Well, for Snoho county, anyway.     That was on the list to get done after I got work again.
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pyotr filipivich
"With Age comes Wisdom. Although far too often, Age travels alone."
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