Why do electric fans lose their effectiveness?
October 9, 2013 7:15 PM   Subscribe

Something I've noticed with the two electric floor fans I've had in the past few years is that, over the course of many months, the air flow becomes dramatically weaker. Why is this, and can it be remedied?

I first noticed it with a cheapo box fan -- at first it was great, but by the following summer, I could barely feel a breeze coming out of it, even though the blades seemed to be spinning as fast as ever.

Thinking maybe something was happening to the blades over time, I bought one of those expensive big all-metal fans. Which was initially awesome -- it turned my house into a wind tunnel -- but over the course of a year or so, I noticed the airflow decreasing with that one as well. This one is about three years old now, and even on high, it creates maybe a soft breeze. Yet, again, the blades seem to be moving normally on all speeds.

What is happening here? I've tried taking the grill off and cleaning out all the dust, but it doesn't help. Mystified!
posted by Mo' Money Moe Bandy to Home & Garden (11 answers total) 3 users marked this as a favorite
Best answer: The spinny bits inside get all gunked up too, with dust and whatnot, and even though it looks like it is turning as fast as it used to, it is not. It can help to squirt some WD-40 inside, although this is only a temporary fix and can eventually (IME) make it worse.

"spinny bits" sorry about this highly technical terminology
posted by elizardbits at 7:23 PM on October 9, 2013 [4 favorites]

Best answer: A lot of fans have plastic internal gearing. It might be worthwhile to open one of the older ones you've already ditched and look inside. If it's full of dust, it might be fixable, but if the gears are just stripped, you might want to look at other fans. I have a Vornado that is years old and will still blow every paper off of every surface in the room if you turn it on high while facing the wrong way.
posted by feloniousmonk at 7:27 PM on October 9, 2013

I kept several older box fans going for years, the newer ones are JUNK. Lost all my old ones in a fire. Box fans don't have gears, BTW....
posted by raildr at 7:37 PM on October 9, 2013

The blades need to wiped clean periodically. Dirt and grease will lower their efficiency.
posted by Raybun at 8:21 PM on October 9, 2013

Response by poster: All righty, it looks like I've got a weekend project. I will open 'er up and see what's what. Thanks!!
posted by Mo' Money Moe Bandy at 8:47 PM on October 9, 2013

Please let know what you find.
posted by alms at 8:57 PM on October 9, 2013 [1 favorite]

Ditto on WD-40 being only a temporary fix. With time, WD-40 turns sticky.
posted by Bruce H. at 9:11 PM on October 9, 2013

Best answer: A light machine oil and not WD40 would be a better fix. Bearing grease is sticky, but it hands around. WD-40 contains a lot of volatiles and does not.
posted by Kid Charlemagne at 10:16 PM on October 9, 2013 [1 favorite]

Best answer: FYI, the motors that drive most of these fans are synchronous to the power line frequency. What that means is that the RPM remains extremely constant and if it drops below the design frequency of the motor, more current is added (by the design of the motor) and it speeds up. I find in highly improbable that you are seeing a reduction in RPM from the motor, and if one presumes your perceptions (as opposed to actual measurements) are correct, the only thing that would result in lower air flow is gunk on the blades, which is quite possible. If not gunk, then surface alterations of some sort. Air transports gunk, and it collects. I would not bother with lube for the motor, much. (You did say box fan, but reciprocating fans use the same motor type and gearing to feed off enough energy to move them. Lube moving parts on the reciprocator portion. The motors are usually factory lubed at the bearings and don't need it.) Get the dust out of the inside of the motor, though. Compressed air and a shop vac should be enough.

I prefer actual measurements, but am a geek and have an anemometer for air flow measurement. I don't use it often, but just did. Handy little thing. It has a windmill blade in it that spins at a frequency proportional to the air flow speed, and a little sensor to sense the RPM, which is converted to a unit you select and displayed on a little LCD. It's only about 1" or so in diameter, which makes in sensitive to local flow variations, but I found in pretty consistent measuring some air flows into/out of a small ventilation system. I think mine was $100 or so, but they are pretty cheap.

If you want to actually and finely adjust the speed of the fan, you need a power line frequency converter. It's called a variable frequency drive (VFD). There is a single phase version made (most are three phase) that is good for centrifugal loads (as opposed to high torque applications.) $200 or so. Overkill compared to a new fan, but hey, ...geek! Sometimes you need precision.
posted by FauxScot at 12:15 AM on October 10, 2013 [5 favorites]

Best answer: There's basically one place you need to oil, where the shaft intersects with the motor. This video shows how. It also shows you a type of lube you can probably get at your hardware store, as he says. It's a high-endurance lubricant especially suited for motors and other rotating machine parts. For your average household fan, a good cleaning once or twice a season and a lubrication at the beginning of the season are likely all you need (dirty environments, go more frequent). Not only does this improve airflow but it will help your fan last many years. Without lubricant, the shaft will contact the motor, both will deteriorate, the shaft may become wobbly (further impacting performance), and ultimately the motor will have to work so hard it burns out (with a small risk of fire in the fan itself or possibly inside your wall wiring, depending on $FACTORS).

I see so many crappy box fans discarded on the street, at the dump, etc. and they probably just needed a spot of oil (perhaps well before being trashed, of course).

I have a Vornado that is years old

Yes, the Vornado fan is still well-made and will last many, many years. I have a plastic one that's pushing twenty, and before that we had a metal mid-century Vornado hassock fan that I only stopped using because it didn't have enough protection for my cat.
posted by dhartung at 4:45 AM on October 10, 2013 [1 favorite]

My fan started working a lot better when I washed the cage and blades.
posted by windykites at 1:33 PM on October 10, 2013 [1 favorite]

« Older Anyone else for the Victoria Cross?   |   Get Me Over the Hump Newer »
This thread is closed to new comments.