However, if you resign from the electrical circuit and instead have a fan spinning freely as the air moves through it, you just made yourself a wind speed measuring device. And the best part is that you don't even need the answer to the question, "what does CFM mean". Simply put an outdoor fan wherever you wish to control the wind speed and look at it. The faster it spins, the faster the wind is, and the higher the CFM is at that moment.

Want a fan that ties in with the rest of your smart tech? Look for a WiFi- and voice control-enabled model that can be operated remotely or from another room in the house. Our tester found app control particularly helpful – no more struggling to get the remote to connect if you're not sitting right next to the fan. Air purification You might be thinking that fans always work on air. And that's reasonable since most of the examples we've talked about (ceiling fans, bathroom fans, USB/battery powered fans) work like that. But actually, water-fans are a thing. Think about the propellers on a boat. They are indeed indistinguishable from regular air fans. The reality is that they work on the same principles as everyday fans, namely the Bernoulli equation. What makes them different is the use of the third of Newton's law to move a boat instead of moving the air/water around them. A very creative way to use a fan. We measure each fan’s noise levels to find the quietest models for dozing off to, as well as its energy efficiency to find out how affordable it is to run, and its oscillation range to see how well the fan distributes air around a room. Many fans offer different breeze styles, allowing you to adjust the feel of the air. For example, the SmartAir Cool+ Purify Bladeless Tower Fan has four different modes on top of its air settings, including a day mode and a night mode. The latter is a key one to look out for as it sets the fan to operate at a quieter volume, and sometimes dims the display, limiting any disruption to your sleep. OscillationThe more settings, the greater control you’ll have over the fan’s air flow. Look for a minimum of three – any more and our tester found the differences between them negligible. Modes

These costs will obviously add up if you run your fan for hours on end. But if you’re after one for occasional use, none of the models on our list should add much to your energy bill. We also have bathroom fans which could fall into the ventilation category since bathroom fans are barely ever meant to be seen. The best known are outdoor and standing fans like the ones you would pull out on a hot summer day in the hope of a refreshing breeze. They strike a balance between mass flow rate (don't fret, we will explain later what it is) and noise. They are also available in a wide variety of designs, sizes, and prices. Here we can include computer fans easily, both the fans used to cool it and the USB or battery-powered fans that cool you. Even the least energy-efficient – the Princess Smart Air Cooler – wasn't much more expensive, averaging about 2p an hour. Use the advanced mode to calculate the power output using the voltage, current, and efficiency of the fan.Keep this in mind if you’re after a fan you can easily move around the house. If it’s going to stay in one place, a heavier one should be fine, but opt for a lightweight model if you’ll be carrying it between rooms every day. Smart capabilities Now that we have talked about the types of fans and their places, it's time to talk about the things that make one fan different from another.

Lastly, a panel of testers sit in a room kept at 30 degrees with each fan for half an hour and assess how comfortable it makes them (yes, really). Every model is then scored according to its performance, ease of use, design and product information. The term "mass flow rate" refers to the amount of material that passes through the fan per unit time. The mass flow rate mathematical definition is: dm/dt which is the derivative of the mass with respect to time. The unit of measurement for the flow rate is CFM which stands for Cubic Feet per Minute. It might sound a bit strange since cubic feet as a unit of volume and not mass or weight. However, if we use the density of whatever substance is going through the fan, we can easily convert volume to mass.This 30" (75 cm) Fully ERP compliant Portable Drum Fan from Prem-I-Air is ideal for large venue cooling and drying and the large easy-grip handles and wheels make it easy to maneuver. The low and high settings mean that a controlled flow of air can be maintained. For full peace of mind, the unit has an automatic overheat cut-out function Not all fans do this, but some, including every Dyson and the SmartAir, also help to clean the air they're distributing. Some have filters that trap pollutants, while the Dimplex Ion Fresh Cooling Tower Fan freshens air around it by emitting neutralising ions. Do fans use a lot of electricity? Note that fans don’t generate cool air (apart from this Princess model, which houses a water tank), so limit their usage to when you’re in the room and can feel the benefits. To get the most comfort from your fan, these GHI-approved tips will help boost its ability to circulate cooler air. How we test fans Firstly, we consider its power, looking at the strength of each setting and the difference between them. To do this, we use an anemometer to understand how much air it blows, measured in feet per minute. The greater the range of speeds and the wider the difference between them, the more you can adjust the fan to suit you. Regarding what types of fans we expect to find in each place, we should start with the obvious: most fans exist in hot places and closed spaces. For ventilation purposes, fans tend to be ugly and big but powerful and optimized for performance rather than silence. Because they are generally hidden they barely ever serve any aesthetic purpose. On the other hand, ceiling fans tend to be quiet since, apart from the obvious function of moving air, they should not disturb people having conversations under them. Finally, they should, at the very least, not detract from the appearance of the room they are located in.