A duct fan is an essential part of an extraction system. Until recently the only type of duct fan available on the hobby growers scene were AC (Alternating Current) types. Recently though, a different type of fan has come onto the market called EC (Electronically Commutated). AC and EC refers to the type of motor that drives the fan.
Mains electricity is AC. AC fans run on an alternating current whereas EC fans run on a combination of AC and DC (direct current) which is made from mains electricity by a power supply.
Because the two different types of motor run on different types of power, you can’t use an AC fan speed controller with an EC fan. Or vice versa.
AC fans are cheaper than EC fans. EC motors are newer technology than AC motors and the price will come down as time goes by and they gain popularity.
EC fans are more efficient and use less power to run than AC fans for a given amount of air flow. While AC fans are between 60-75% efficient, EC fans are 80-90% efficient. So while EC fans are more expensive to buy they will save you money on your electricity bills for years to come. They can end up actually costing less than AC fans when the price of the electricity is taken into account.
If an AC fan is used with a cheap fan speed controller it can produce a noisy rumble due to the way that it adjusts the power. It is possible to get around this with a stepped hybrid controller but these are very expensive. Also, you are stuck with only a few fan speeds to choose from. EC fans do not produce a rumble when they are turned down and they have no step so they can be turned up from minimum to maximum and every position in-between. EC fan speed controllers are more efficient than AC fan speed controllers which further reduces the running costs.
EC motors are smaller for a given power rating than AC motors. This means the fan unit enclosures that they go into can be made smaller. Space savings in a grow space can be very useful leaving more room for the grow light and other equipment.