# Slowing Down a Vent Fan



## closet.cult (Jul 24, 2007)

I hate to revisit this topic but...

A user started a thread recently and I've searched but can't find it.

So, I have a vent that is at least double CFM overkill for my space. It's a bathroom vent, 50CFM, standard 110V power supply. Can I slow it down someway? 

Anyone know any options?


----------



## Destrukto (Jul 24, 2007)

Well, what type of fan do you have? Aside from it being a bathroom vent fan... 2 wire, 3 wire, 4 wire?


----------



## Destrukto (Jul 24, 2007)

I'll make this as plain and simple as I can, the easiest way to determine a way of slowing down your fan is for one, to find out if its a 2 wire, 3 wire or 4 wire, most bathroom vent fans are 2 wire which mean it's ON and OFF only, the only real way to conquer that would be to connect something known as a "rehastat" onto the circuit, also known as a Light Dimmer.. You could basically completely control the speed of the fan, although you would never be able to speed it up past the 50 CFM, however you could control it completely from full speed > off mode..

I hope this helps..


----------



## babygro (Jul 24, 2007)

closet.cult said:


> Can I slow it down someway?
> 
> Anyone know any options?


Fan speed controller. Don't use a dimmer switch itll mke it buzz.


----------



## videoman40 (Jul 24, 2007)

Dude, how is a 50cfm fan too much, theres no way its enough.
In my humble opinion.
Peace



closet.cult said:


> I hate to revisit this topic but...
> 
> A user started a thread recently and I've searched but can't find it.
> 
> ...


----------



## Destrukto (Jul 24, 2007)

Dimmer switches won't make it buzz at all.. don't buy cheap dimmer switches and they work fine, fan controllers commonly only work with 3 and 4 wire fans but ok, not to mention fan controllers are a lot more pricey


----------



## babygro (Jul 24, 2007)

Destrukto said:


> Dimmer switches won't make it buzz at all.. don't buy cheap dimmer switches and they work fine, fan controllers commonly only work with 3 and 4 wire fans but ok, not to mention fan controllers are a lot more pricey


Really? Have a read, courtesy of Overgrow - 

A little bit of info on what can control shaded pole and other general types of AC motors:

Potentiometer NO
Dimmer NO
Rheostat NO
Solid-State Speed/Power Controler YES
Variable Hertz/Frequency Drive YES

Potentiometers, Dimmers and Rheostats can not be used to control the speed of an AC motor. They all use forms of voltage resistance.
From first hand experience I know that even low draw Hz drives can cost well over $100 (I have seen them as high as $500 at a 1 Hp rating). Hz drives are a waste unless you need to precisely control the speed/pulse of something beyond/below the input frequency (or a capacitor run/start motor). The next best thing is a solid-state adjustment device.


$10-$15 Solid-State Controler (I.e. fan controller)
$1.50 #16 (or bigger) extension type cord, with ground (2 feet)
¢80 3/8 cable connectors (x2)[/b]
$5 1 male & 1 female standard rubber 3-prong electrical plug
$3 Deep set 2x3 electrical box

All of this can be bought at an home improvement store for around the same price (such as Home Depot or Lowes).

Note: you need to have some basic wiring skills to do this.

The first thing you need to do is confirm your not buying a Rheostat or Dimmer. Look at the price and what\'s printed on it (fan controls are more expensive). You need to make sure it says it can control attic and/or whole house fans. I chose the 100% controllable one, they also make them with a Low/Med/High setting. The next part isnt much harder, basically all you do is strip your cable & wires and put on your plugs. In this case I already (knowingly) left some on the M/F ends from a previous project. Strip your cable and wires at the other end, then using the supplied wire nuts connect all commons (white wire) together. Connect one hot (black wire) to ether hot lead (black wire coming out of device). Now for the ground/s (green wire) use an extra wire nut. Or you can strip about 2 off all of them and twist them together nice and tight (if you don\'t have a wire nut). Next push the fan controller into the box, before doing so tuck the cluster of grounds under the other wires. There should also be 2 supplied machine screws that you will use to attach the mounting plate to the box.

Thats all there is too it, it can be used just like a regular fan (only now you can adjust the CFMsspeed).

Notes: Dont load it to max capacity. In this case using the 5 amp model dont use it to control a fan/motor the uses more than 4 - 4.5 amps. These CAN NOT control capacitor start or run motors (you would need a Hz drive for that.). When used, the motor will get warm/warm-hot as if it where running regularly, this is normal. Another thing I would do is let the motor run for at least 3 hours (check on it from time to time) on the lowest setting just to make sure it wont over heat.


----------



## Destrukto (Jul 24, 2007)

Babygro, You really don't want me to have to prove you wrong but I will anywho I assume..

Bathroom fans run off of 2 wires, which means it can be turned OFF and ON ok? now, Fan controllers run off of 3 wire circuits, with a bathroom fan it has 2 wires and there is this little thing that fan controllers require which is called a tachometric wire (3 wire fan) Bathroom fans are not designed to be used for speed variation which is why the only way to do it is with a Rheostat or a Light dimmer, If it were a 3 wire fan that post would be valid.. However it's not and your point is null and void.

Maybe next time you should pay attention to the actual type of fan he's talking about...

Back to your point on the other post about "people posting stuff that is not helpful at all"


----------



## babygro (Jul 24, 2007)

Destrukto said:


> Bathroom fans run off of 2 wires, which means it can be turned OFF and ON ok? now, Fan controllers run off of 3 wire circuits, with a bathroom fan it has 2 wires and there is this little thing that fan controllers require which is called a tachometric wire (3 wire fan) Bathroom fans are not designed to be used for speed variation which is why the only way to do it is with a Rheostat or a Light dimmer, If it were a 3 wire fan that post would be valid.. However it's not and your point is null and void.
> 
> Maybe next time you should pay attention to the actual type of fan he's talking about...
> 
> Back to your point on the other post about "people posting stuff that is not helpful at all"


Strange how I've got my two wire Systemair RVK100 175m3/hour duct fan running on two wires connected up to a solid state fan speed controller then isn't it? And that fan IS designed to be used with a fan speed controller.

So, it looks to all intents and purposes that you're talking a bunch of bullshit!

And dimmer switches WILL cause the motor to buzz and whine at low speeds, regardless of which type you use.

So it looks like both I and the chap from Overgow both disagree with you, sorry.


----------



## Destrukto (Jul 24, 2007)

I never said that a solid state fan speed controller wouldn't work, that's basically a PWM and it's not necessarily good on the motor because of how it works to run that, Now on the other hand, funny because I've seen many situations dimmers and rheostats have been used and they don't cause clicking and or whining, I like how you throw in little story details every other post, it's quite fascinating that real life experiences < what someone reads on a forum, btw I would really like to see your fan setup and the speed controller 

Not to mention that's an Inline fan which is basically designed COMPLETELY different than a household bathroom vent fan..


----------



## babygro (Jul 24, 2007)

Destrukto said:


> I never said that a solid state fan speed controller wouldn't work, that's basically a PWM and it's not necessarily good on the motor because of how it works to run that,


No but you said a two wire fan couldn't be controlled by a fan speed controller! Which is obviously complete bull.



Destrukto said:


> Now on the other hand, funny because I've seen many situations dimmers and rheostats have been used and they don't cause clicking and or whining, I like how you throw in little story details every other post, it's quite fascinating that real life experiences < what someone reads on a forum, btw I would really like to see your fan setup and the speed controller


And I've heard plenty of horror stories of people using dimmer switches to control their fans and getting more noise and whine from the motor when the fan is used at low speeds than the actual noise of the fan itself, which is why I never recommend anyone use them.

You're welcome to see my fan setup, but I can't take pics of it at the moment as it's lights off, but you can similar products here -

GroWell > Fan Speed Controllers
GroWell > Systemair Lti RVK Extractor Fans



Destrukto said:


> Not to mention that's an Inline fan which is basically designed COMPLETELY different than a household bathroom vent fan..


Which is completely irrelevant to what we're discussing - which is the attenuation of a hp inductive motor. Inline duct fans only differ from axial fans in the fan blade construction and the extraction power and back pressure they create, they're both still run from hp motors.


----------



## Purple_Ganja (Jul 24, 2007)

I'm just dropping in on this thread to make sure some smart ass doesn't say "oh hey yeah use a light dimmer to control your fan speed" because I see people saying that crap ALL - THE - TIME. I don't know why though, its just more bad advice to recirculate.

Anyone that's done proper research on how to setup a proper grow room knows this does NOT work. I forget why, but I know I don't need to know why, I know it doesn't work and that's enough knowledge for me. If you want more details you'll have to find them. I think I even saw something about this in the Grow Faq here on rollitup, check it out. -peace, PG (always lookin' out for my fellow stoners)


----------



## Destrukto (Jul 24, 2007)

Purple_Ganja, Light Dimmers will work....

babygro.. I would like to apologize and say that the way I explained myself in understanding to what you just explained was wrong... What I meant to really make clear is the fact that what your using, a solid state speed controller is in efficient in power because all it does is lower the voltage of the fan and as it lowers the voltage it has to do something with that excess power in which it is absorbed into a heatsync causing it to be inefficient, so your paying for the exact same power but instead your taking the power out of the fan and it's being wasted inside the switch instead.. That is basically a form of a rheostat as well, although rheostats can be more power efficient, although the amount of power wasted isn't much of a big deal, but still theres more efficient ways of going about it and I'm not saying a light dimmer is that alternative but it is a cheap one, cheaper than buying what your using..

The whole reason I was posting my original post was giving him a cheap alternative to setting a fan up and by personal experience I have never had clicking or whining problems of the motor.. I'm not going to sit here and argue.. I realize what I said was wrong due to my misunderstanding..

I will be more than happy to post pictures of my grow room once I am done remodeling it, and that will pretty much re-assure you that I am not "smart ass" or whatever you want to call it, I have done my research and I would have to say my room is probably one of the more advanced that I've seen..

Yes, I am going to come here for help and if you don't wanna help me thats your prerogative but there is still many things I do not know and would like to find out, hence why I signed up here


----------



## FilthyFletch (Jul 24, 2007)

A dimmer switch can be used.Im actually in the trades and we install them all the time on these low cfm bathroom fans both knob and slider switches work fine.Not sure what buzz your refering too but as stated a good quality switch will work just fine.Just did one last week in a new bathrrom and it works fine and will pass electrical inspection without issue


----------



## FilthyFletch (Jul 24, 2007)

I forgot...Im with video 50 cfm is almost nothing so unless your in a shoe box it should be barely enough for anything


----------



## Destrukto (Jul 24, 2007)

I have a couple 1000 CFM fans that I use with a rheostat and it works flawlessly for me.. shrug


----------



## Purple_Ganja (Jul 24, 2007)

I stand some-what corrected, but if anyone's gonna suggest using a dimmer switch, you need to specify what kind. Yeah, you CAN use a dimmer, but not a damn light dimmer dude. If you use an incandescent light dimmer to control your fan speed, you might as well have copper wiring running through your house and I feel sorry for you if you turn out to be one of the poor individuals that "thinks" it works because... temporarily you WILL achieve the desired effect... until your house burns down and your grow is discovered and you've lost your home as well as I don't know how many years of your life... whatever you spend in jail after the firemen discover WHY your house caught fire. But check this out.

After seeing people argue with me about this, I realize what a common misconception it is to see a "dimmer" switch and think they're all the same, not so. What you need, friend, is a fan speed controller. I've already found something I think might solve your problem after doing a little more research on the subject for you.

Creative Homeowner - Dream ~ Design ~ Create.

*wipes forehead* WHEW!!! Yeah thanks yall, thanks for putting me through ALL that extra work to explain this better lol.

I recommend a 150 cfm fan. Hope this clears everything up.


----------



## beenthere donethat (Jul 24, 2007)

Yo da man Purp G.

Folks in the US...here's a cheap alternative..about the same $$ as buying the WRONG dimmer....this is at Harbor Frieght....

Harbor Freight Tools - Quality Tools at the Lowest Prices

good luck

bt dt


----------



## Purple_Ganja (Jul 24, 2007)

think maybe that extra effort was worth maybe a tad extra rep? lol I love it.


----------



## closet.cult (Jul 24, 2007)

Thanks and props to all who answered my question.

At first I was excited...I have a light dimmer at home! But, alas, I am not fond of fires.

So, I'll will have to invest in a fan speed controller. $9.99! I'll have to tap into my car change for that one. oh...



FilthyFletch said:


> I forgot...Im with video 50 cfm is almost nothing so unless your in a shoe box it should be barely enough for anything


I am growing in apprx. 6 cubic feet. (see my grow journal if you don't believe me) 50 CFM = 8 air changes a minute. Bigger then a shoebox, but the fan is still a little overkill, wouldn't you say?

Plus, I'm venting my home's A/C into my attic at that speed. It would be a waste.


----------



## FilthyFletch (Jul 24, 2007)

wow that is small.could use a timer and set it for 15 minutes every hour


----------



## closet.cult (Jul 24, 2007)

actually, i intend for a timer to shut it off for a short spell thrice a day just to keep it safe from overheating.

but this grow space is in my garage and the temps in south U.S. hit triple digits in summer.


----------



## Purple_Ganja (Jul 24, 2007)

what about just adding a small window A/C unit to the grow area to keep it cool? I guess maybe there wouldn't be room for that huh. Yeah now that I look back at the dimensions of your grow room, it is a bit small, I agree that a 50 CFM fan would work just fine. I'm gone, TTYL


----------



## FilthyFletch (Jul 24, 2007)

I feel ya I just had to buy a portable ac unit and Im in the north.Could run and ac line from your attic ducts to the garage cieling


----------



## beenthere donethat (Jul 24, 2007)

Here's something else...it isn't "cheap"...but I swear it's worth EVERY cent
and would work incredibly well in anything from a cab to a full-sized room.

Quantem Moisture Proof Wall Mount Variable Speed Controller - QC Supply

top dial is the rheastat. The dial is in % of full speed. The fan runs at this user-set speed until...

the set/chosen TEMP limit on the second dial is exceeded then the fan runs FULL speed until the room cools down past the set temp. At that point the fan again runs at the rheastat setting/ratio/%of full speed until the room again heats up above the set point.

Great for auto adjustment of lights on/full speed..lights off/partial speed. You can look all over and there isn't a big $$$ controller out there that has this feature on it. they all just turn the fan (outlet) on or off....

There's also a digital model.

fwiw. I hope the link helps someone else out there. This has been a great thing for my room.


----------



## closet.cult (Jul 24, 2007)

FilthyFletch said:


> Could run and ac line from your attic ducts to the garage cieling


that's exactly what i've done. but i have to use a vent to pull it thru the room and out over my lamp to air cool it.

but it's recommended to have 5 air changes a minute. that's equal to a 30 CFM fan. i could use this fan at about half speed.


----------



## chabnock (Jul 24, 2007)

Hmmm.. Years back I had to take a year course in electronics and Home wiring. In one of these course, they taught us how to cut down the electical use in a house. One of the ways was to install dimmer switches on the fans. These dimmer switches do work. BUT!!!! You can not slow down the fan passed 60-70% or you will end up getting a Buzzing noise. If you have a 50CFM fan,, which that is very small to start with, and this 50 CFM fan is to much, and 65% of the 50 CFM is still to much volume. Then I would suggest going and buying a smaller fan. Either that or just place a restrictor over the inlet or outlet of the fan.

You need to move 30 CFM? that is just over 3'X3'X3'. And that suggestion is a MIN, not an EXACT number. More is good,, less is not. Use the 50 CFM full blast.


----------



## frog3850 (Jul 29, 2007)

I agree with what chabnock says can't have to much the more circulation you have the more co2 gets to the plants. helps keep down on the mold and some pests too Let RIP it wont hurt your plants


----------



## WutangFinancial (Jul 30, 2007)

If you have a set speed you would like to run the fan at, you can always just place a simple resistor in there for like 2 dollars.

On the fan look for a voltage and amperage value. 

Using this, calculate the resistance of the fan by R=V/I.
So if you had a 12V fan running at 0.2A, you would do 12/0.2, giving you your resistance value.

Then, say you want to run the fan at 1/2 speed, you would want a new voltage drop on the fan of 6V.

So now you must find out your new current. This would be:
6V=(Calculated Resistance)*(New Amperage)

Now, you know you want a voltage drop of 6 on the resistor(Half speed), so now you can calculate your resistor value.
6V=(New Amperage)*(Resistance Value Needed)

Then just put that bad girl in series with your fan and you have a 1/2 speed fan.


----------



## closet.cult (Jul 30, 2007)

cool.i always wondered how to use resistors but had never research it. i'll check it out. thank you.


----------

