# Dehumidifier question

**URL:** <https://boards.straightdope.com/t/dehumidifier-question/632876>\
**Category:** Factual Questions\
**Created:** [August 28, 2012, 12:11am UTC](https://boards.straightdope.com/t/dehumidifier-question/632876 "2012-08-28T00:11:52Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![sundog66](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@sundog66](https://boards.straightdope.com/u/sundog66)\
**Post date:** [August 28, 2012, 12:11am UTC](https://boards.straightdope.com/t/dehumidifier-question/632876/1 "2012-08-28T00:11:52Z")

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I just received a used Maytag dehumidifier (Model # M3DH30B2A) without a manual. It has a knob labeled “Humidistat” with settings ranging from 1 through 8, plus “Continuous Run”, and “Off”. But relative humidity is expressed as a percentage. Does anyone know (or know how I would figure out) what the mapping is between Maytag’s scale of 1-8 and the standard way of measuring humidity? With this cryptic scale I have no idea how to ensure that I keep my home at the recommended humidity level.

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**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\
**Post date:** [August 28, 2012, 12:49am UTC](https://boards.straightdope.com/t/dehumidifier-question/632876/2 "2012-08-28T00:49:14Z")

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there may have been some correspondence given though maybe not. it would be very crude and may change over the years anyway. get a hygrometer (humidity meter), you can find these paired with thermometers and barometers, plentiful used at thrift stores and rummage sales.

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**Author:** ![j666](https://avatars.discourse-cdn.com/v4/letter/j/9de0a6/32.png) [@j666](https://boards.straightdope.com/u/j666)\
**Post date:** [August 28, 2012, 1:02am UTC](https://boards.straightdope.com/t/dehumidifier-question/632876/3 "2012-08-28T01:02:55Z")

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If you want a good, accurate hygrometer, ask a friend who works in (a company that runs) a testing lab. Some companies don’t think it’s worth the cost to recalibrate them every year.

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**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\
**Post date:** [August 28, 2012, 1:34am UTC](https://boards.straightdope.com/t/dehumidifier-question/632876/4 "2012-08-28T01:34:14Z")

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I think 1-8 are just its power settings, like a heater with no thermostat. So it runs at a fixed rate and your RH will depend on the weather.

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**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\
**Post date:** [August 28, 2012, 4:01am UTC](https://boards.straightdope.com/t/dehumidifier-question/632876/5 "2012-08-28T04:01:12Z")

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From the manual : - “Automatic Humidity Control  
The humidistat control automatically turns your dehumidifier on or  
off to maintain the humidity level you select. Allow dehumidifier  
to reach room temperature, then turn control knob to number 5  
(normal average setting). The fan and compressor will run together,  
dehumidifying the room. If unit does not turn on at this setting, this  
generally means that the relative humidity is already low and  
dehumidification may not be needed at this time.  
After operating several days at this setting with doors and windows  
closed, you may readjust this control to a slightly higher number  
for lower humidity (drier air) or to a slightly lower number for  
higher humidity (moist air).  
If knob is turned to “Continuous Run” then the compressor will run  
regardless of actual room humidity. If not properly monitored, this  
setting could cause excess energy usage.”

You can download the manual here : [click](http://data.manualslib.com/pdf/6/511/51029-fedders/a3dh30b2a.pdf?743bba788a5b0c1e62c0b2f171a4e56f)

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**Author:** ![sundog66](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@sundog66](https://boards.straightdope.com/u/sundog66)\
**Post date:** [August 28, 2012, 7:00pm UTC](https://boards.straightdope.com/t/dehumidifier-question/632876/6 "2012-08-28T19:00:43Z")

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Thanks everyone for your suggestions, and thanks to **am77494** in particular for finding the manual. That’s great!