Airflow meter covers three instruments that measure the same thing in different places. A hood captures everything leaving a grille, a hot wire probe reads velocity inside a duct, and a vane reads open air at a face. This hub sorts nine current listings by what each manufacturer publishes, and explains why a CFM figure depends on a duct dimension you have to supply.
Balance the Duct
Prove the Flow
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Instruments were sorted by the sensing method each manufacturer listing describes, the velocity range and accuracy published, whether volume flow is calculated and how, and how the reading reaches you. We did not run laboratory tests and publish no measurements of our own. Where a listing gives no figure the entry reads Not stated.
A capture hood that measures the whole grille rather than a point in front of it.
A pocket hot wire probe that calculates volume flow once you enter the duct size.
A vane anemometer with app connection and five selectable speed units.
No pick matches that combination yet. Try a wider budget or a different measurement.
| Product | Type | What the listing states it measures | Stated range or accuracy | How you read it | |
|---|---|---|---|---|---|
| Testo 420 flow hood | Capture hood | Air velocity, volume flow, temperature, relative humidity | Under 6.4 lbs stated | Handheld hood with tiltable display | View |
| testo 405i smart probe | Hot wire anemometer | Air velocity, temperature, in-duct airflow and volume flow | Not stated | Bluetooth to a phone app | View |
| Elitech ANE-200W | Hot wire HVAC anemometer | Wind velocity, air flow in CMM and CFM, temperature | Not stated | Handheld with Bluetooth | View |
| BTMETER hot wire anemometer | Hot wire anemometer | Air velocity in m/s, km/h, ft/min, knots and mph | 0.2 to 67 mph, plus or minus 5 percent | Handheld display | View |
| Primyteion PM8915 | Hot wire with telescopic probe | Wind speed, wind temperature, CFM and CMM | 0 to 67 mph, plus or minus 3 percent plus 0.2 | Handheld, telescopic probe | View |
| VVV-Group AM-286 | Hot wire HVAC anemometer | Duct and vent air velocity, CFM and CMM air volume | Not stated | Handheld display | View |
| BTMETER BT-100APP | Vane anemometer | Wind speed, temperature, wind chill and battery level | Five speed units stated | Handheld with Bluetooth app | View |
| BTMETER BT-100WM | Vane anemometer and barometer | Wind speed, wind chill, humidity, dew point, barometric pressure | Not stated | Handheld display | View |
| POROMETISTO AEM01S | Vane anemometer with alarm | Air velocity and air flow | Three colour alarm, eight vane blades stated | Handheld, green backlight | View |
Every figure here is taken from the manufacturer listing for that product at the time of research. Where a listing publishes no value the cell reads Not stated rather than an estimate. Nothing on this page is a measurement of ours.
Four questions settle the purchase:
A hood measures a whole grille, a hot wire works inside a duct at low velocity, a vane suits open air and fast uniform flow. The wrong sensor in the wrong place is the usual source of a bad number.
Every handheld measures velocity. A CFM or CMM figure is calculated from a duct area you type in, so the flow number is only as good as your measurement of the duct.
The BTMETER hot wire states a lower limit of 0.2 mph and the Primyteion states from zero with plus or minus 3 percent plus 0.2. Low velocity performance is what separates a duct instrument from a weather gadget.
The testo 405i, the Elitech ANE-200W and the BTMETER BT-100APP all state a wireless link. That frees a hand at the top of a ladder and keeps the readings after you come down.
Two of the product records supplied with this topic point at the same Testo 420 flow hood under different listings. Showing it twice would have used a row without adding a product, so the table carries it once and uses the remaining rows for instruments that differ.
A vane counts the rotation of a small propeller, so it needs enough velocity to overcome friction and enough space to sit in the flow. A hot wire measures how quickly moving air cools a heated element, which works at much lower speeds and fits through a small test hole. Vanes suit grille faces and open air; hot wires suit ducts.
By multiplying the measured velocity by a cross-sectional area that you enter. That is exactly what the testo 405i listing describes when it says volume flow is calculated when duct dimensions are supplied. The consequence is that an accurate velocity reading and a badly measured duct give a confidently wrong flow figure.
Because velocity varies across a duct. Flow is fastest near the centre and slows at the walls, and bends, dampers and fittings distort the profile for some distance downstream. Duct traverse methods exist precisely for this: several readings in a defined grid, averaged, taken well away from any fitting.
If you are balancing a system and signing off a flow rate per outlet, a hood is the instrument the procedure expects. If you are checking that something moves air, tracing a fault or comparing before and after, a probe is faster and far cheaper. Many technicians carry a probe daily and hire a hood for commissioning.
Measuring flow at a ceiling diffuser with a handheld probe is an exercise in estimation. The air leaves a grille as several jets at different angles and speeds, and the reading you get depends on exactly where the probe was held, so two technicians measuring the same outlet can disagree by a wide margin. A capture hood removes the argument by putting a fabric shroud over the whole outlet and measuring everything that comes through it.
That is why balancing work is specified around hoods. This listing states air velocity, volume flow, temperature and relative humidity measurement, and it makes a point of stating a weight under 6.4 lbs with a tiltable display, which matters more than it sounds: a hood is held overhead, and the difference between a light one and a heavy one is the difference between a full day of readings and a sore afternoon.
The listing does not publish the flow range, an accuracy figure, the hood sizes supplied or the back pressure compensation method. Back pressure is the real technical question with any hood, because putting a shroud over a diffuser changes the system slightly and a good instrument corrects for it. Confirm the range against the outlets you actually work on, because a hood that bottoms out on a small extract point is no more useful than a probe.
Inside a duct, a vane is the wrong sensor. A rotating vane needs a reasonable velocity to overcome its own friction and it has to be large enough to average the flow, so at low duct velocities it under-reads or fails to turn at all. A hot wire sensor measures how fast moving air cools a heated element, which works down to very low speeds and fits through a test hole.
This listing states precise measurement of air velocity, temperature and in-duct airflow, with volume flow calculated when duct dimensions are supplied. That last part is the honest description of how every handheld produces a CFM number: the instrument measures velocity and multiplies by the cross-sectional area you tell it about. Enter the wrong duct size and the meter will confidently report the wrong flow.
The listing does not publish a velocity range, an accuracy figure, a probe length or a battery life. The probe length in particular decides which ducts you can reach into, and the absence of a stated accuracy makes this an instrument for comparative balancing rather than for a certificate. Working through a phone app is also a genuine trade: it frees a hand and logs readings, and it stops working when the phone battery does.
A vane anemometer is the right instrument for open air and for the face of a grille, where the flow is reasonably fast and reasonably uniform. It is also the easier instrument to trust, because you can see the vane turning and judge immediately whether the reading makes sense, which is not true of a hot wire element you cannot see.
This listing states wind speed, temperature, wind chill and battery level on a single LCD, with five selectable speed units covering metres per second, kilometres per hour and others, plus a wireless Bluetooth connection. For checking that a fan is moving air, that an extract is pulling, that a window vent is open or that a rooftop plant item is running, that is a complete answer at a low price.
The listing does not publish a velocity range, an accuracy figure, a vane diameter or an air volume calculation. The missing volume function is the important one: without entering a duct area this reports velocity only, so it will not produce the CFM figure that a commissioning sheet asks for. It is also the wrong sensor for low duct velocities, where the vane simply will not turn reliably.
Short answer: the Testo 420 flow hood is the instrument for balancing work because it captures a whole outlet instead of sampling one point in front of it; the testo 405i is the pocket hot wire probe for in-duct velocity, calculating volume flow once you enter the duct size; and the BTMETER BT-100APP is the value vane anemometer for open air and grille faces.
The nine listings above use three different sensing methods and they are not interchangeable. A capture hood puts a fabric shroud over an entire diffuser or extract and measures everything passing through it, which is what commissioning and balancing procedures are written around. A hot wire probe measures how fast moving air cools a heated element, works at very low velocities and fits through a small drilled test hole, which makes it the in-duct instrument. A vane anemometer counts a spinning propeller, needs a reasonable velocity to turn and reads open air or a grille face well. Using a vane inside a duct, or a probe in front of a diffuser, is the most common reason two people get different numbers from the same system. Vane vs hot wire anemometers covers the choice in detail.
Every handheld instrument in this group measures a speed. None of them measures volume directly. A CFM or CMM figure appears only because the instrument multiplies the velocity it measured by a cross-sectional area that the user typed in, which the testo 405i listing states plainly when it says volume flow can be calculated when duct dimensions are entered. Elitech, Primyteion and VVV-Group all advertise CFM and CMM on the same basis. The practical consequence is that a tape measure is part of the instrument. A five percent error in a duct dimension produces roughly a ten percent error in the flow figure for a rectangular duct, which will swamp any accuracy advantage between one meter and another.
Two listings publish a velocity specification and both are worth reading closely. The BTMETER hot wire states 0.2 to 67 mph with accuracy of plus or minus 5 percent. The Primyteion PM8915 states 0 to 67 mph with accuracy of plus or minus 3 percent plus 0.2, and specifically claims the ability to measure extremely low airflow velocities. That trailing constant matters more than the percentage at the low end: at a genuinely slow velocity, a fixed offset dominates the error. Residential extract grilles, natural ventilation openings and filter face velocities all sit at the slow end, which is where a vane anemometer becomes unreliable and a good hot wire earns the difference in price.
Air leaves a ceiling diffuser as several angled jets with quite different speeds, and there is no single point in front of it that represents the average. Holding a probe there gives a number that depends on your hand position, which is why balancing specifications call for a hood. The Testo 420 listing states air velocity, volume flow, temperature and relative humidity, and states a weight under 6.4 lbs with a tiltable display. Weight is a real specification for a hood because it is held above head height repeatedly through a day. The listing does not state a flow range, an accuracy figure or which hood sizes are supplied, so confirm all three against the outlets you work on before committing.
Several of these instruments report temperature, humidity, dew point or barometric pressure alongside velocity, and the BTMETER BT-100WM listing states all of them. That is not padding. Air density changes with temperature, pressure and to a lesser extent humidity, and volume flow at one density is not the same mass of air as the same volume at another, which is why altitude and hot supply air both shift the calculation. For everyday balancing the effect is small. For a rooftop plant in summer, a high altitude site or a heated supply duct, recording the conditions alongside the flow is the difference between a defensible figure and a rough one.
Listings were compared on the sensing method described, stated velocity ranges and accuracy, whether volume flow is calculated and from what, probe form factor, units offered and connectivity. Owner feedback was reviewed for recurring reports of unstable readings at low velocity and probes that fail early. We did not run laboratory tests, we publish no measurements of our own, and no figure appears on this page unless the manufacturer published it. Amazon data supplies images, availability and links only.