The 10 Best Psychrometers

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This wiki has been updated 20 times since it was first published in January of 2019. If you're an HVAC technician, dedicated gardener, or just someone who's extremely interested in relative humidity, you'll appreciate these psychrometers. They take a variety of atmospheric measurements via two built-in bulb thermometers, one wet and one dry, providing an accurate representation of what's happening in the air around you. Many of these options also calculate wind chill and more. When users buy our independently chosen editorial picks, we may earn commissions to help fund the Wiki.

1. Fieldpiece SDP2

2. Fluke 971

3. Extech RHT510

Editor's Notes

October 01, 2020:

During this round of updates, while the majority of our previous selections maintained their positions, we did decide on eliminating the PDI DP-110 due to availability issues, and also decided on removing the Mengshen M86 and General Tool EP8706, recognizing that our rankings already included superior offerings from these brands, with the Mengshen M350 and General Tools EP8710.

Our new selections this time around were the Fluke 971 — a solid device from one of the biggest names in metering, with memory to store up to 99 measurements; the Testo 605i — which features a flexible probe head, and can be hooked up to the company’s proprietary app with as many as five additional sensors, for complex diagnostic work; and the Fieldpiece JL3RH — which can also be connected with the company’s app, or alternatively paired with one of Fieldpiece’s wireless manifolds: the SM380V or SM480V.

A few things to think about for this category:

Display: Most of our offerings feature backlit LCDs that make it easy to observe your readings at the point of metering. The utility offered by these displays does vary considerably – the infinitesimal screen on the Fieldpiece PRH2, for example, argubally isn’t as convenient as the sizable display on the Extech RHT510 – but for the most part, they’ve got some sort of functional screen.

Two exceptions to this rule are the Fieldpiece JL3RH and Testo 605i. Neither of which have any sort of built-in screen, but both feature 350-foot Bluetooth ranges and the ability to connect multiple meters to the same smartphone app, which does make remote readings and complex diagnostics much more convenient, but it would still be nice to have some sort of display installed on these units. The Fieldpiece wireless manifolds that can be paired with the JL3RH are quite impressive pieces of machinery, presenting another means of observing readings for users who’d rather not be working with their phone in hand all day, but their prices dwarf that of the JL3RH itself, so it’s likely to be a toy that’s only considered by serious professionals and diehard gearheads.

Probes: Basic models in this category have their sensors housed in a single wand that protrudes from the unit, like an antenna. It’s a good design because, not only does it allow for ambient readings, but it also makes it simple to insert the probe into a small hole (that can easily be made with a drill bit, in a pinch) in a plenum, allowing for in-duct measurements.

Some selections – like the Testo 605i and Fieldpiece JL3RH – feature flexible probe wands, which makes it easier to maneuver them in tight spaces. The General Tools EP8710 is available, for a small additional fee, with an external, thermocouple probe that can make life a whole lot easier when you’re trying to work in cramped crawlspaces and cluttered utility rooms. And, the Fieldpiece SDP2 is the most advanced model we ranked, with two detachable leads that each feature wet- and dry-bulb sensors, making it a great choice for quick-and-easy superheat and supercooling calculations.

Transportation and Storage: Given that we’re wading through a category full of delicate instruments, I found that there was a disappointing lack of protective cases offered with most options, but some models do have some provisions that make them easier to store and carry.

By virtue of its small size and convenient clip, the Fieldpiece PRH2 isn’t much harder to transport than a fountain pen, and the UEi Test Instruments DTH35, Fieldpiece SDP2 and Testo 605i all have some provisions to allow for temporary magnetic mounting. The Extech RHT510 comes with a wrist strap and a bracket to mount it onto a separately purchased tripod, and while the soft carrying case for the Fluke 971 is sold separately, it does come with a convenient belt clip and holster.

One exception to the no-case rule is the Fieldpiece SDP2, which comes in a padded, blow-molded case.

February 04, 2019:

The Bacharach 0012-043 might seem a strange addition to this list, given its analog interface. It's not ideal for professional technicians, as doing all those calculations on the slide rule will slow you down, but schoolchildren and hobbyists who enjoy old-fashioned meteorology should appreciate it.

4. General Tools EP8710

5. Fieldpiece JL3RH

6. Mengshen M350

7. Testo 605i

8. UEi Test Instruments DTH35

9. Fieldpiece PRH2

10. Bacharach 0012-043

Will Rhoda
Last updated by Will Rhoda

After deciding that the pen was mightier than the pliers, Canadian electrical contractor William Rhoda abandoned his career and headed back to college, where he majored in marketing and advertising and won a scholarship along the way to earning a diploma in creative communications. His past career landed him a depth of knowledge in tools and hardware, while his current career schooled him in audio, video and camera equipment. During his leisure time, he’s learned lots about outdoor gear, and years of tiresome backyard maintenance have taught him all about pools and hot tubs. His recreational pursuits include rest, relaxation and revolutionary action, and his roommate’s a hairless cat.

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