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Hot Wire Anemometer

A hot-wire anemometer, or thermal anemometer, is a device used to measure fluid speed. The wire is generally made of either platinum or tungsten and is heated by running current through it. The change in current required to maintain a constant wire temperature is directly related to the wire heat loss to the fluid. Based on convective heat transfer, the heat loss can be used to calculate the fluid speed.

Hot wire anemometers are typically available as handheld devices that could be used in an audit or short-term test. They are sensitive enough for very low flow rates from vent or a bathroom fan. However, they are also fragile and will get dirty easily, so they should not be used when ducts are dirty. They will need to be calibrated often if dust is allowed to accumulate.

A handheld hot wire anemometer that is used to measure air flow speed.

A handheld hot wire anemometer used to measure air flow speed. 

Credit: Harke, Wikimedia Commons