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Hotwire Anemometer And HVAC

For the most part,  you’d do well as a professional not to underestimate the power of a hotwire anemometer. When catering to your clientele’s HVAC needs, the testing instrument can complete your arsenal, helping you become more effective in the process - not to mention gain a reputation as a real pro. Armed to the teeth. As appearances can be deceiving, you might be tempted to think answering a client call without the gadget can be justifiable. You may never be more wrong. As diminutive as it is, there may not be a better tool in identifying air leakage than the thermal electronic gauge. 

In this sense, the merits of a hotwire anemometer cannot be ignored. While a powerful thermal camera can give you the big picture leading you to identify thermal hotspots, the air velocity tester can get you to locate the holes in your HVAC system as accurately as you need them to be. Down to the ground level. In a jiffy.  And with a little math. The best part is you need not lose a fortune when you’re on the prowl for a quality product offering. Read on. 

What Makes a Hotwire Anemometer Awesome

First up, know that an anemometer is more than just a glorified weather vane (otherwise known as a weathercock or wind vane).  To a farmer, a weather vane is an essential instrument as it points out the direction of the wind. But a weather vane is basically out of the radar of an HVAC pro - not unless he’s out on a boat fishing and wants to know where the wind is blowing. To better his chances.

Derived from the Greek word ‘animos’ meaning wind, anemometers give you more than just the wind direction; the measuring instrument shows you wind speed or velocity. Needless to say, this is essential in HVAC. Knowing how much pressure is in a residential duct system is key in troubleshooting its woes. For technicians worth their name in salt, it’s akin to finding the last piece of a huge jigsaw puzzle. And as it could help you plug HVAC holes in record time, it’s in no small way heavenly. 

Basically, these wind-velocity detectors cater to two environments:

  1. Contained flows


Airflow constrained inside a closed system. HVAC systems where air flows in a duct are specific examples of this. 

  1. Unconfined flows

When determining outdoor wind conditions, wind velocity is a piece of valuable information for an army of enthusiasts wanting the most out of it: weather forecasters, water sports enthusiasts, sailors, and avid hobbyists.

Don’t get the misconception though. There are hundreds of applications for an anemometer that is not HVAC related - from construction to harnessing wind power to weather forecasting. Over time, 3 kinds of anemometers have emerged, gaining traction depending on the particular job at hand. These are:

  • Cup anemometers   - also called Robinson anemometer is the oldest type of anemometer. Invented in 1845 by Dr. John Thomas Romney Robinson, cup anemometers are hard to miss. Those cups (hemispherical) mounted on a vertical shaft simply give the device away. One caveat though: As easy as it is to set up, cup versions are not as accurate as you want them to be when it comes to finding wind velocity. Nevertheless, this model fits the needs of weather forecasters and is often a constant in many weather stations across the country today. 


  • Vane anemometers - are also mechanical anemometers which use a windmill-like or propeller-like feature to measure wind velocity. Unlike the Robinson type, a vane anemometer has its axis parallel to the wind direction making it horizontal. To a certain extent, it’s much more accurate than a cup version as a vane anemometer combines a propeller and a tail. Like a darting arrow. When it comes to wind speed, this arrow-carrying anemometer is much more accurate to its much older predecessor. 

  • Thermal anemometers - are also dubbed as hotwire anemometers. Out of the many sensor types of anemometers, hotwire anemometers are most popular for HVAC air velocity monitoring. The rationale behind the device is simple; also, their internal dynamics give us a glimpse of why it fits best in monitoring and repairing HVAC systems.  Hotwire anemometer utilizes a sensor element that gets heated well beyond room temperature (i.e., ambient); as the rate by which airflow cools the sensor is directly proportional to air velocity, you can arrive at the desired number accurately. 

While extremely delicate, thermal anemometers outgun the other types of anemometer when it comes to speed of response. Meaning: it can give you the results in record time. Even better, the device performs best in turbulent flows - or flows wherein rapid changes in wind velocity is essential. This makes it a top candidate in keeping HVAC/IAQ (heating, ventilation, air conditioning/ indoor air quality) in tiptop shape. 

Plus, hotwire can accurately measure air flow even at very low velocities. It’s not unusual for the measuring device to read such velocities at under 2000 ft/minute, for instance. 

HVAC Dynamic Duo: Thermal Cameras and Thermal Anemometers

It may look obvious but the similarities between thermal anemometers and thermal cameras go beyond their names. Both devices complete a certified HVAC professional’s tools. Chances are, an aircon inspection may not reach its rightful conclusion if the repairman forgets any of these tools. 

To note, hotwire anemometers are anchored on the principles of Ohm’s law - specifically that which pertains to the cooling effects. As such, three basic types of thermal anemometers abound: 

  • Constant temperature anemometer (CTA)
  • Constant voltage anemometer (CVA)
  • Constant current anemometer (CCA)

Maintaining HVAC/IAQ isn’t exactly a breeze. Bioaerosols (e.g., dust mites) can easily thrive in these systems blocking HVAC ducts in the process. Spinning the whole house out of control. An air-flow meter, another name for anemometer, can prevent your equipment from unnecessary break downs.  

To this end, thermal imaging can play a huge part in keeping a house as livable as possible. For one, it can detect heat loss in a building via thermal bridging - sans the need for pricey and invasive testing. Moreover, it can help locate electrical and/or mechanical faults in a structure. By being able to uncover the source of the issue faster, a better solution is reached. Before everything blows upon the owner’s face.

By putting infrared technology to good use, a thermal camera can pick up thermal anomalies just like that, exposing problems in the process without having to resort to tedious routine inspections. Some of these most common issues include:

  • Water leaks/ moisture ingress (invasion)
  • Air leakage/ infiltration routes
  • Thermal bridging issues
  • Insulation damages (e.g., roofs, floors, walls)

Throughout all these, a thermal anemometer is instrumental in finding leakage areas in a building. You can do this by carrying out a thermal anemometer survey together with your standard Air Tightness Test. Also referred to as Air Pressure testing or Air Leakage testing, such a testing specifically aims to reveal how much air is lost through various leaks in the building fabric. 

By doing so, you will be able to identify areas of air leakage in the abode or building you’re working upon. More importantly, you will be able to quantify the exact leakage rate at that specific air leakage point. And when you put it all together, you will then have an inventory of these problematic leakage areas prioritizing them according to importance. 

How to Put an Anemometer to Use in Air Duct Traversing

C’mon now. Some perspective should help us. While it’s true a traverse can give a more accurate way of determining air flow, it has been shunned by many HVAC technicians due largely to its complicated nature. 

For starters, you would need more than one anemometer to record velocity readings of a particular duct at various points. Getting all that data, you should aim to arrive at the mass flow rate which is your mean velocity multiplied to the density and the duct’s cross-sectional area measurement. 

If you’re dealing with a cylindrical duct, using the log-linear method is most reliable as it factors friction along the pipe’s walls. Indeed, air duct traversing can be a lengthy process but it can give you the accurate information you need to serve your client best. 

For faster results, relying on state-of-the-art microprocessor-based anemometer is highly recommended.

Careful though, as diminutive and fragile are their wired components, hotwire anemometers are not as sturdy as you want them to be when doing a duct traversing. Dirt build-up could lead to your instrument’s breakage. A no-no in any HVAC technician’s handbook. If you’re looking at bigger projects, there are other bigger and sturdier anemometers available specifically designed for industrial applications. 

Take note. For a better reading of the velocity profile, employing a straight-duct section upstream (about 10 diameters long) from the anemometer station is wise. Deploy a conditioning nozzle to counter boundary layer effects. Then again, if a straight-pipe section is not possible, putting a honeycomb straightener into action in the sensor assembly should bid you well. 

Zeroing in on the Right Product

None of your skills will matter if you don’t have the right tool at hand. The same thing goes for anemometers. As you may be painfully aware by now, not all tools are created equal. The same goes for these velocity readers.

First stop, you should keep your needs in mind. This is pretty obvious. Unfortunately, many professionals forget this first rule. Especially so when roaming around or prowling the internet for better options.

Though hotwires are most usually called thermal anemometers, there are vane anemometers that carry the distinction. Vane can be more rugged since it does not rely on electronics to get the wind speed. But when it comes to accuracy in measuring turbulent wind environment, hotwire is tops. 

Today’s product offerings can give you better handles - a lot better than before. Not to mention more accurate than ever. Technology has made it all possible. Now, you get:

  • An easier-to-read screen for greater reading accuracy
  • A more rugged telescopic probe for faster tracking
  • A more intuitive control panel for quicker turnaround time

While all these are eye-popping to behold, the problem is you may break the bank when looking for good ones. That is where PerfectPrime’s WD9829 is up to the task. Getting to know the model better could give you much better chances of delivering quality service worth your ability’s time. A hotwire anemometer to expand your clientele in record time. 

Check out this review on our WD9829 anemeter

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