AC? EC? Understanding Duct Fans
By Hydro Harvest
- 27 February 2025
You’re looking for a duct fan. You see two listings. Same manufacturer, same look, same diameter, same capacity. One is 33-50% cheaper than the other. Why?
Take a closer look and, likely as not, you’ll see a couple of letters on that cheaper listing in the shape of ‘AC’. The pricier option? ‘EC’. Understanding the difference between these is important if you want to make an informed choice about the fan you buy – which, let’s face it, is the heart of your ventilation system and therefore a very big deal in terms of your growing environment.
The Technology
AC (Alternating Current) Fans – take the electrical current from your mains and ‘resist’ it to meet your desired fan speed. Say you want to run your fan at 70%. An AC unit will effectively resist 30% of the current to hit that mark.
EC (Electronically Commutated) Fans – use a Printed Circuit Board PCB inside the unit to draw only the amount of power required to run the fan at your desired speed. If you want to run an EC fan at 70% it’ll draw 70% power from the mains.
The Outlay
Because AC fans rely on more traditional, basic engineering they are naturally less expensive to buy. Obviously, this makes them appealing to those just getting involved in growing and those keen to keep their outlay on kit to a minimum.
As the digital technology behind EC fans is newer such unit’s command higher prices. However, as you’ll probably suspect already, the way they run can bring serious savings in terms of operating costs.
Operating Costs
As AC fans draw 100% power regardless of the required speed they are, by definition, somewhat inefficient. As EC fans offer digital modulation, they will definitely save you money when in use.
For some, the combination of newer tech and lower running costs will be decisive. A few hundred pounds more on an EC fan might seem a no-brainer. There are, however, good reasons for the continued popularity of AC units.
Save Today?
Let’s be real. Outlay is a huge factor in a growers decision-making process. That makes AC fans from reputable manufacturers a very attractive proposition. Add to that, they’re every bit as capable as EC fans in terms of shifting air and are based on rock-solid mechanical technology.
Whilst EC fans will recoup the difference in cost in the long term that saving is also a little less cut-and-dried than it might at first appear. For those who don’t grow indoors on a regular basis the economic benefits of EC are much less immediate. Same goes for those who aren’t all that concerned about power consumption.
Before you ditch the EC fan in your cart there are, however, a few more things you should know.
What Price Precision?
Because of their simpler technology AC fans can usually only run at five speeds. True, you can get around this by adding a Step Controller. But the cost of these controllers negates the initial savings on your AC unit.
EC fans offer you 1% speed increments. That is a big deal for several reasons. Firstly, precision control means you can tailor your growing environment to your plant’s exact needs. Potentially that can result in better growth, improved health, and heavier yields. 
The Cost Of Compensation
Another issue with AC fans inherent lack of precision is the power required to compensate climatically. As your AC fan under- or over-shoots optimum speed you’ll be forced to use other appliances to cool or warm your environment to the desired level.
Sure, you’ll need to have these other appliances as part of your setup anyway. But when combined with the precision of an EC fan you only must run such appliances as required – saving you yet more money.
Keeping appliance use down also has the benefit of keeping noise to a minimum. On a fan-specific note, the noise created by an AC or EC unit can also be important consideration when choosing between the two.
A Sound Decision
Resistance is a noisy business. An AC fan resisting 100% power to meet a given speed creates a buzzing and humming sound that few indoor growers will welcome. Again, you can get around this with a Step Controller. Again, the cost of that controller wipes out the savings you make by buying an AC fan.
Contrast that to an EC fan where the PCB ensures quiet operation and you’ve another compelling reason to fork out a bit more in the beginning.
It is worth remembering though that there are growers out there who will not be concerned by higher levels of noise. For them AC units are perfectly sufficient.
In Conclusion
It is important to emphasise that for all the modern convenience of EC fans there is still a place for their AC counterparts. If you’re looking for a tough, reliable, high-performance fan that perhaps you don’t use year-round and if noise or power consumption are not big concern for you then AC fans still represent an excellent option.
If you want those same levels of performance combined with quiet, economical operation and yield-enhancing, pinpoint-accurate control over your environment then EC units are well and truly worth the extra outlay.