445815

We have two and have used them for years to measure both dryness and moisture. The readings differ by just a little bit. I think I returned a third one for being much further off calibration, so it may take a couple rounds when you purchase these. The device allows detach the sensor from the base and thus some ability to measure into places slightly distant from the base. Mostly, though, they reside on furniture and measure ambient air humidity. It does a good job of supplementing my dehumidifier readings as well, as those dehumidifier readings can be way off.

Purchased this instrument to monitor the humidity in our closets and walk-in closet in our home. Some of the rooms within our house have more mildew than others. Took comparison readings of the different rooms and closets. Tried the heating rods in the closets to determine whether these rods help in lowering the relative humidity. Tried running the central A/C system on DRY mode in one of the bedrooms to see whether the A/C works in lowering the RH (relative humidity) and it does. Love the large digital readout and simplicity of use. Moved the instrument among the closets in different rooms of the house to get an idea of the humidity in these areas and to confirm the likelihood and severity of moisture, possibility of mildew development. It's only been about a week of using this meter, but I think it is essential in attempting to control the RH and mildew within your home. Concerned about the electrical consumption of whatever mildew device I utilize, so trying various other processes to see if these work before resorting to a dehumidifier. The hanging Damp Rid fragance free collects a lot of liquid in its pouch, but the RH in the closet has not decreased noticeably at all. The heating rods do not lower the RH quickly and I may need to give this more time. If you want to systematically work towards getting rid of your mildew/mold problems, you should seriously consider getting this instrument.

I set mine up for my T room. With the nice large LCD readout at a quick glance I can see what each enclosure's humidity and temperature is. I don't use the alarm features since I have a room humidifier control system that has alerts for the overall room humidity. Overall, this is a nice, easy to ready, humidity and Temperature display + options with audible alarms for Max and Minimum thresholds. I have one sitting on each of my enclosures with the probe inserted to measure humidity. Works Great. Would like to have seen included a probe attachment; such as a suction cup for glass and or a hook for wire enclosures.

From my testing, the calibration pots on the Extech 445815 model DO NOT WORK. I’ve owned 5 of these units over the past 10 years. All these units except one could not be adjusted or calibrated as advertised. The only unit of the 5 that had a functioning calibration pot is my NIST-certified, Extech 445815 unit that retails for over $200.00. The non-NIST units were all between 6 to 9 percent off (higher and lower). I’ve returned several od these units for replacement and those units failed as well. I contacted Extech numerous times and explained the non-adjustability problem. I suspect the 445815 models are not defective, but that all non-NIST-certified Extech 445815 models are likely non-adjustable from the factory by design, i.e., either the calibration pot is disabled or not present. Numerous reviews on Amazon and elsewhere report the exact same non-adjustability problem with the 445815 model. Extech's follow-up responses went as I expected. They ignored the main issue at every step: First, they claimed that my NIST-certified Extech 445815 unit was out of calibration, and the new units were likely more accurate. I explained why that was not true (see #1 below). Second, they claimed that I didn't conduct the test properly. I explained why that was not true (see #2 below). Third, they claimed that only their proprietary RH300-CAL kits could properly test their hygrometers, and again I explained why that was not true (see #3 below). #1) I tested each of the units twice (older NIST-certified Extech 445815-unit, older non-certified Extech 445815 unit, and the new non-certified Extech 445815 units). The older NIST-certified Extech 445815 unit was within 1% accuracy (74% RH with the Sodium Chloride solution). I adjusted the unit in accordance with the Extech instructions, and the unit then measured accurately at 75% RH -- the test threshold for a Sodium Chloride solution. The older non-certified Extech 445815 unit was 6% off (lower) – I already knew that but the test confirmed it. I attempted to adjust the unit in accordance with the Extech instructions, but the unit would NOT adjust; again, I already knew that as well. Finally, the new Extech 445815 units were 8-9% off (higher). I attempted to adjust the unit in accordance with the Extech instructions, but the unit would NOT adjust. I conducted three sets of tests in total. #2) For the first set of tests, I used a standard Sodium Chloride solution, which is used for a higher humidity fixed point at a 75% relative humidity threshold. For the second and third set of tests, I used both a standard Sodium Chloride solution test (75% RH) as well as a standard Magnesium Chloride solution test, which is used for a lower humidity fixed point at a 33% relative humidity threshold. All the tests were conducted by inserting the unit probes into separate short glass bottles, i.e., the Sodium Chloride and Magnesium Chloride solutions were tested in their own distinct bottles. For each test, the bottle was capped off with an airtight seal and placed along with the unit in an airtight Ziploc bag. The tests were carried out for both 12 and 24-hour periods. For each test (on the non-NIST-certified units) the calibration pots failed to adjust, and each of the units remained between 6% and 9% off from an accurate RH reading. I tested a total of 5 Extech 445815-model units. #3) There are many humidity fix points that can be tested using a variety of saturated salt solutions (over 20 in all). The two most common are the Sodium Chloride solution (75% RH) and the Magnesium Chloride solution (33% RH). Both Sodium Chloride and Magnesium Chloride are readily available and inexpensive. For only a few dollars (literally) anyone can make their own solutions. If you can manage to mix salt and water, then you're more than capable of creating these solutions. The standard reference for hygrometer calibration is an article published in 1977 by Lewis Greenspan, titled "Humidity Fixed Points of Binary Saturated Aqueous Solutions." -- referenced below. Here's the kicker. Extech claims that you must use their proprietary test kit to accurately calibrate the 445815 model. The Chinese manufacturers who produce Extech's RH300-CAL test kit NOT ONLY use the same information and test solutions from Greenspan's 1977 article but they have copied and pasted directly from Table 2 on page 92 in the article itself. You can see this for yourselves. The fonts and formatting on the kit labels for the calibration jars are exactly the same as found in the article. They couldn't even bother to print out the labels in a modern font! Lewis Greenspan (1977) "Humidity Fixed Points of Binary Saturated Aqueous Solutions." Journal of Research of the National Bureau of Standards - A. Physics and Chemistry, Vol. 81A, No.1 (January - February): 89-96.

Using this currently to keeps numbers for our bearded dragon eggs. Its a nice unit and works as designed. The only thing I really don't like about it is the fact that it's focused more on humidity then tempature. So I guess if your looking for something more in the humidity department, this is the unit for you.

My Extech 445815 hygrometer is not accurate. I ran this meter through the standard salt humidity test before I used it. I tested it along with a few other hygrometers that I had on hand. The salt test creates a stable known humidity in a sealed container. An accurate hygrometer should read 75%RH. My Extech 445815 only reached 68%. I was surprised by this, so I repeated the test trying to find errors in my test methodology. Each time, the 445815 read 68%. So, my unit reads 7% low. The low reading should not be a problem because the 445815 has a multi-turn pot that allows the user to trim the RH adjustment. The 445815 even includes clear instructions on how to do this, but the procedure proved impossible. The trim pot was already adjusted to its upper limit. Turning the trim pot further, did not affect the relative humidity reading. As another reviewer wrote, there is a soft click sound when the RH trim pot reaches its upper limit. The trim pot did work in the other direction (I could decrease the RH value) but that was not helpful. Having said all of this, I do like products from Extech. I have an amazing Extech multimeter on the bench next to me right now. Other than this hygrometer, Extech instruments have always proven themselves to be high quality and a good value. Other reviewers report good results with this meter. I must have received a dud. You should test your meter before use.

I've had this for only a few days now. I opened it shortly after it was received and placed it alongside an analog humidor hygrometer and a Netatmo networked indoor base ststion. Within a very short time the Extech was reporting the same humidity as the Netatmo. The analog humidor meter was reporting about 2% less humidity. The temperature on all 3 devices was within 0.4 degrees. Easy to read large display on this device. I like the detachable sensor on this Extech model. I bought this to use in my RV. I can place the sensor inside various compartments and other spaces and position the display where I can read and monitor it. Monitoring humidity within an RV is essential for comfort, health, and proper maintenance of an RV. This portable device will allow me to monitor the environment inside the RV, the compartment space underneath, or outside. It calculates and displays the dew point too, which is necessary to know if you want to avoid condensation on your windows and such, especially in the evening as it cools outside. I consider this an essential piece of gear for my RV and would not leave home without it. This one stays in the RV.

Have had my Extech 445815 for 15 years. Temperature was accurate. RH was OK and sensitive. This winter my Extech RH readings were way off, so I decided to calibrate RH. As an engineer, I am familiar with using saturated salt solutions to calibrate instruments. Unfortunately, as others have discovered and commented on, and despite Extech's claims to the contrary, the RH adjustment did nothing. My own pure sodium chloride saturated salt test gave a meter reading of 59% RH at 70 degrees F - way off. I turned the humidity adjustment screw. No change in RH reading. The screw just turned and clicked every so often. No difference which way turned. Extech sells a very expensive humidity calibration kit, but if you cannot actually adjust the calibration then that kit is not worth the price. It will only tell you if your meter is close or completely off. Despite Extech's claims otherwise, you can do your own testing easily and cheaply as there are well researched and standardized test values available for using different saturated salts with RH values at various ambient temperatures. My conclusions: I enjoyed having this meter for many years. Loved having Dew Point as that is much more valuable than RH. Was looking forward to more years with a calibration. However, RH calibration screw just turns and does nothing. I will not buy an Extech replacement. I don't know, but perhaps their NIST certified models have RH calibration potentiometers that work. Extech's written product statement about ability to adjust the 445815 RH calibration is clearly wrong. Three stars as I did get years of use, but expensive for just a temperature-relative humidity meter.