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  1. #1
    Join Date
    Jul 2006
    Posts
    21
    I'm seeing a lot of notes about the influence of relative humidity on comfort and some where the poster now has a new system that isn't doing as well as the old one - but has no information on what the relative humidity was earlier.

    Any reasonably accurate 'humidometers' ( ) available at a reasonable price?

    Thanks!

  2. #2
    Join Date
    Aug 2006
    Location
    Florida (some where) way-south
    Posts
    230
    Walmart or HomeDepot
    doing one call at a time.


  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,451
    Also Radio Shack. Really like the digital hygrometers. 15-30 dollars. Wal-Mart/Radio Shack have indoor outdoor with several radio remote transmitter. <50 dollars. TB

  4. #4
    Join Date
    Nov 2005
    Location
    Northern VA
    Posts
    512
    How is the response time on those Radio Shack models? I have a cheapo Walmart model right now, and it takes several minutes for the reading to stabilize. Doesn't work very well for walking around checking the temperature/humidity in various parts of the house. Getting several, and hoping the calibration doesn't drift too far out, is one option. I'd like to have one GOOD unit to go around and check with though, if that's practical.

  5. #5
    Join Date
    Jul 2006
    Location
    Staten Island NY
    Posts
    2

    Humidity

    I had the same concerns: price and response time. I finally chose to buy a Bacharach sling psychrometer for about $60 from Grainger. I paid more than I wanted, but I will never have to calibrate it, and it is portable.

  6. #6
    Join Date
    Feb 2006
    Posts
    468
    I have two of the radio shack units and I'm skeptical of both. One checked out okay with the salt paste test, the other 10 points too high. The one that checked out okay reads 44% now, which seems low.

  7. #7
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    reptile shop @ $10 -- put in baggie of salt water -- should read 75% overnight --
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  8. #8
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    The salt water test is fine as far as it goes, but it tests accuracy at one RH when you might want/need to know accuracy at a much lower one in your house. At least I *hope* you don't have 75% RH in your house!

    I have a half dozen cheap humidity meters, most from Walmart. One day with nothing else to do I put them all in the same place and recorded each reading after they had 20-30 minutes to stabilize. Repeated for 8 different readings as high and as low as could find, in the 40-70% range. Although it might have been of some value to know the temperature at each condition, at the time I did not suspect this and so did not record that.

    What I planned was to assume that the errors on the high side of correct %RH were random and equal to the errors on the low side. With that assumption one could average the readings and get pretty close to the objective, correct answer. My result was a set of calibration tables where I had a good estimate of error at 8 points along the RH scale.

    The surprise was that being accurate at one RH, did little to promise accuracy at the others. The error curve appeared to be random, in most cases was within 3% or 4%, with an outlier or two at 5% error measured on the RH scale.

    It seems the sensors in my thermostats and dehumidifiers are similarly imprecise. That matters little when you design to control RH over a +/- 5% band, which seems to be the norm. Not like temperature measurement, where we usually expect spot-on accuracy.

    So while I don't promise too great accuracy with these cheap little devices, I sure do like their ease of use. For real accuracy though I defer to the sling psychrometer, anyone traditional enough to use that earns my respect!

    Hope this helps -- Pstu


  9. #9
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    920

    Re: Humidity

    Originally posted by tomreichert
    I had the same concerns: price and response time. I finally chose to buy a Bacharach sling psychrometer for about $60 from Grainger. I paid more than I wanted, but I will never have to calibrate it, and it is portable.
    Hmmm, I started a "digital hygrometer response time" thread here, hardly got a hit!

    Even a high priced handheld digital hygrometer will take 15-20 minutes to adjust to a 5F change in temperature! If temperature is constant, humidity response is real fast!

    A sling psychrometer is much faster from what I hear.

    Can you even calibrate it? How accurate is the temperature?

    I returned a Fluke 971 which they deemed faulty to be replaced with a new one, tossed in calibration for free! It's just as slow as the old one but I find out now that's the way all handheld digital hygrometers are! Well, at least it's calibrated now.
    Bill

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Thumbs up Hygrometer +

    Oregon Scientific has seemed to be quite reliable,
    But do NOT look for a fast response.

    http://www.oregoninstruments.com/pro...p?itmky=256466

    Check outdoor thermometer section at Lowe's
    for $24.

    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  11. #11
    Join Date
    Aug 2006
    Location
    Panama City Beach, FL
    Posts
    17
    Originally posted by pstu
    The salt water test is fine as far as it goes, but it tests accuracy at one RH when you might want/need to know accuracy at a much lower one in your house. At least I *hope* you don't have 75% RH in your house!
    I found an interesting link on hygrometer calibration that includes a list of salts and the RH that they achieve in a closed environment. You could work out a complete calibration curve from 6 to 97% and work out all that randomness!
    http://www.kingofthehouse.com/hygrometer/

    Potassium carbonate gives a 43% environment. It's used in soaps and wine making and is available on ebay for very cheap. Any wine-making stores nearby? I have a 10 percentage point error between my thermostat RH reading and my Extech reading, so I'm looking forward to doing this.




  12. #12
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    the old Honeywell T87 round t-stat had 5/9F accuracy --

    probably the indicator is not accurate -- just the actuator of a t-stat is = what I want to work best --

    so, the RH% gage is off 5% --

    not much different than relying on the weatherman"s temp reading 5+ miles away & over a mountain -- which shifts our winds such that we do not agree with the weather station ~ 2miles away at "exec" airport --

    but, we are on a mountain, in woods -- 3- 10F cooler in summer!
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  13. #13
    Join Date
    Aug 2006
    Location
    Panama City Beach, FL
    Posts
    17
    I'm fortunate to have a friend two blocks away that has his weather station hooked up to wunderground.com.

    To clarify, I don't mean a 10% difference, 40% vs 44%, I'd be fine with that, I mean a 10 point difference, 40% vs 50%. And worse, I put a new battery in the Extech and now it's a 13 point difference. If the Extech is accurate, then I could be looking at at mid to high 50's RH.

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