Extech 445815 Hygro-Thermometer Humidity Alert with Dew Point - Digital Humidity Monitor with Programmable Alarms, Max/Min Memory, and Calibration for Home, Greenhouse, Lab, and Office

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.

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.

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.

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.

- Calibrated using Boveda - Well-built and BIG digital display...readings can be seen clearly from far away! - ACCURATE and FAST response time, almost INSTANT actually! - TEMPERATURE & RH% readings are very useful in any environment, but it does DEW Point readings as well...which is a BIG plus! - Probe can be detached to take readings behind walls if necessary, which is super convenient & handy - MIN & MAX can be reset, but can also be used to trigger a beeping ALARM which is more useful than it seems - This product only PROVES that EXTECH's already excellent reputation in this industry is WELL-DESERVED and 100% JUSTIFIED - Cheap analog meters do not guarantee fast, accurate & reliable readings...so stop wasting your time and invest in a good HIGH-QUALITY tool like THIS one and say bye bye to those analog meters for good!

Besitze seit Jahren ein Extech 445815, Nachdem ich in der Amazon-Suchmaschine nach Feuchtmessgeräten suchte, fand ich ein optisch ähnliches Gerät mit mobiler Sonde. Hiervon bestellte ich zwei Geräte und ward von der Genauigkeit schwer enttäuscht; wer das Lüften des Kellers und des Hauses ernst nimmt, kann mit TP-Differenzen von 3 Grad nicht zufrieden sein. Dann suchte ich gezielt nach dem Extech 445815, von welchem ich dann drei Geräte bestellte. Die drei Geräte haben eine gute vergleichende Genauigkeit und entsprechen auch dem langjährig benutzten Gerät. Ein Gerät musste in der Temperatur etwas nachjustiert werden - und dann stimmte auch dieses sehr gut. Und nun zu den Vorteilen dieses Gerätes: Das Gerät hat eine relativ sehr gute Grundgenauigkeit - die Grundmesswerte relative Feuchte und Temperatur lassen sich über zwei Potentiometer in Grenzen nachjustieren. Die externe Sonde sorgt für eine relativ schnelle Messwerterfassung (im Gegensatz zu Geräten mit integrierten Fühlern im Inneren des Gehäuses) - und dies ist sehr wichtig zur schnellen Entscheidung über das Lüften insb. des Kellers besonders in den Sommermonaten. Warum gleich mehrere Geräte - diese habe ich im Hause verteilt und eines dient der schnellen Feuchtigkeitserfassung der Außenluft (das Gerät sollte aber nicht dem Regen ausgesetzt sein - leidvolle Erfahrung vor einigen Jahren). Bei mir gibt es keinen muffelnden Keller - dazu muss aber auch die Einsicht der Frau beitragen, dass man bei schwülwarmen Wetter den Keller besser nicht wischt - ein oft mühsamer Überzeugungsprozess.

I bought this after much research and I'm sure I have made the right choice.I suffer badly with COPD and I need a more accurate reading of the air quality in my home so I can set my other equipment to fine tune the air for better breathing ....Firstly...It is very accurate and you also have the ability to calibrate it with the appropriate Kit but it is £30,but remember...DO NOT mess with these adjustment screws unless.A) you know what your doing and B) you own the calibration kit,,They are not there to tamper with otherwise and even when using the screws ,only very small adjustments have to be made each time allowing 30 mins between each adjustment if temp and Dew point is essential then look no further..It also comes with an 18" probe which sits on the side in it's own little holder...this is great for those hard to get to places that need to check if damp has set in. It's real easy to set up and it's quick to respond to the atmosphere around it which is handy as you don't always want to leave it hours on end for results...It's also very well made with a small kick stand at the rear to place on any flat surface..You also have the ability to set a high and low humidity (maybe more for those monitoring technical equipment) and also a reset button to see what changes have occured during the day. I will point out that it IS Green with a silver accent and not black as the main photo shows,but it looks quite smart none the less...£40 gets you a great accurate Temp gauge and Dew point monitor and it does a fantastic job.Highly recommended

Il prodotto mi è arrivato nei tempi previsti, amazon è impeccabile. Lo ho testato con termo igrometro professionale (250 € la sola sonda con compensazione barometrica) e ho visto che è arrivato tarato alla perfezione, non è stato necessario intervenire. Il funzionamento è molto semplice. Per questo prezzo è davvero un ottimo prodotto, potete settare allarme della U.R. al valore desiderato, unico allarme è sulla umidità ! Ottimo davvero. Utile per capire quando è ora di aprire le finestre.

A nice little until, the temperature seems to be quite accurate, not sure about the % of the relative humidity. The the dew point temperature is accurately calculated between the two figures. Maybe it's a bit over priced for what it is?