# fans: to push or pull air?



## CoolAsAFan (Jun 3, 2009)

i always thought it was common knowledge that pulling air is more effecient than pushing air. I've read this statement in a few books on marijuana horticulture and on a few forums. ive been talking to the guys at Atmosphere in Canada, makers of the Vortex Series inline fans, because of another thread and we just kind of got to talking and he said...

"This is a mythe in fact the maximum static pressure rating is the same on inlet and outlet. So the ability to push is the same as the ability to pull. I know that a lot of my customers belive that inline blower are more efficient when they are pulling but again this is a mythe."

anyone care to ellaborate on this?


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## astrobud (Jul 20, 2009)

:bump:   anyone?


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## pcduck (Jul 20, 2009)

Oh I believe the static pressure rating is the same, I just do not like blowing air from a small cubic feet area to a large cubic feet area, then try to force it back into a small cubic feet area. I would rather pull air thru my reflector. This is just my $0.02 and I am losing that quickly:bolt::bong2:


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## jmansweed (Jul 20, 2009)

I've always found pulling is more efficient. If pulling does not seem to be doing the job, add a fan pushing from the other end. I actually just had a conversation with the can-fan guys at the " ask the pros " night at the Hydro store. They recommend pulling air adding that the outlet fan should be as close to the out-let as possible in a light cooling situation.  The pressure may be the same but the natural vacuum effect created by pulling through exhaust lines and hoods creates more effeciency. In pushing air, any leaks in the system will exhaust hot air into your room rather than suck some extra air out.


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## umbra (Jul 20, 2009)

I don't believe that the issue is static pressure. But rather when pushing air thru a reflector, it also carries the heat degenerated by the fan. When pulling thru reflector, heat of the fan is at the opposite end on the exhaust. IMO this is what is meant by efficiency. The ability to cool, not air flow. Big difference.


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## meds4me (Jul 20, 2009)

umbra said:
			
		

> I don't believe that the issue is static pressure. But rather when pushing air thru a reflector, it also carries the heat degenerated by the fan. When pulling thru reflector, heat of the fan is at the opposite end on the exhaust. IMO this is what is meant by efficiency. The ability to cool, not air flow. Big difference.


 


OKAY, first lets try to clarify a few things. 
1st:  pushing or pulling air you will have static pressure either way due to the resistance of the duct work. PERIOD . This applies to the water pressure in your house or how the heated air is ducted to each room. 
I tried to post this nice explaination but "server busy" and lost it all... 

2nd: pulling air thru the lite hood is another topic. but, "cooling the air" doesnt happen without mechanical cooling being applied. Exhausting air is just that the removal of heated air.also called venting... 

Just my .02 cents worth of 16 yrs of being a "tin bender" / HVAC tech.


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## crizzo357 (Jul 21, 2009)

I pull air though my hood, it was recommended by a bunch of folks here on MP. seems to work rather well for my application!

Criz


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## PencilHead (Jul 21, 2009)

We read and we read and no one ever stops to reason things out.

Put a medium to sharp ninety-degree bend in some flex duct and apply a vacuum to it, see what happens.

Here again, no air movement expert, just 40 years of building construction, and having to come back after "experts" and clean up their boo-boos so I could get paid at the end.


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## Shockeclipse (Jul 21, 2009)

I thought it was more to do with airflow.  I think someone on here at one point  said it like this:  picure you have a cube, with a small hole on each side.  Now if you blew air through one side, trying to make it out the other side you are going to have a lot of resistance from the air being forced into the walls before exiting.  Now if you sucked air through the hole its almost like the air is being "led" instead of "forced".  Think about a room filled with smoke... Putting a fan inside to blow the air out, and you'll have smoke bouncing around and little exiting.  Putting a fan in the doorwat sucking out the smoke and you would see the smoke all heading the same way.


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## meds4me (Jul 21, 2009)

Shockeclipse said:
			
		

> I thought it was more to do with airflow. I think someone on here at one point said it like this: picure you have a cube, with a small hole on each side. Now if you blew air through one side, trying to make it out the other side you are going to have a lot of resistance from the air being forced into the walls before exiting. Now if you sucked air through the hole its almost like the air is being "led" instead of "forced". Think about a room filled with smoke... Putting a fan inside to blow the air out, and you'll have smoke bouncing around and little exiting. Putting a fan in the doorwat sucking out the smoke and you would see the smoke all heading the same way.


 
correct, the "cube " being the resistance or "static pressure".


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## meds4me (Jul 21, 2009)

crizzo357 said:
			
		

> I pull air though my hood, it was recommended by a bunch of folks here on MP. seems to work rather well for my application!
> 
> Criz


 
Criz: correct application of moving heated air thru the hood reducing temps with in the room. Secondly, in doing so you are exchanging (hopefuly) the air with some new "fresh" air


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## PencilHead (Jul 21, 2009)

The analogies are all wrong here.  It has nurtz to do with cubes and walls--only friction, friction of the air.  I'm failing to see how guiding air through a contolled channel/airway is like blowing air into or out of a room.  I was once a fire department engineer and I can relate air movement and its resistance to hose friction, but not to cubes.  Don't see where container shape holding static pressure could possibly matter.  I mean physically. 

If I blow air into a controlled airway that is flexible, the pressure is going to expand that airway to its maximun dimension.  If I pull a vacuum on that same flexible airway, it most certainly will reduce the airway volumn.  Come on, people, this ain't rocket surgery.

I'm feeling simple today so forgive me my myopia.


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## meds4me (Jul 22, 2009)

PencilHead said:
			
		

> The analogies are all wrong here. It has nurtz to do with cubes and walls--only friction, friction of the air. I'm failing to see how guiding air through a contolled channel/airway is like blowing air into or out of a room. I was once a fire department engineer and I can relate air movement and its resistance to hose friction, but not to cubes. Don't see where container shape holding static pressure could possibly matter. I mean physically.
> 
> If I blow air into a controlled airway that is flexible, the pressure is going to expand that airway to its maximun dimension. If I pull a vacuum on that same flexible airway, it most certainly will reduce the airway volumn. Come on, people, this ain't rocket surgery.
> 
> I'm feeling simple today so forgive me my myopia.


 

Friction is static pressure ! It does make a diff what kind of ducting you use as round ducting is rated at one set of parameters and flex ducting ( the ribs on the inside) are another set. Federal set those standards not me...
Walls with-in your home operate on the same principle. Air in must equal air out. Thats why doors are under cut to allow the cooler air to be drawn back to the fan/ furnace. 

Same with the SEER rating thats all over the equipment today ( dryers to wash machines to you home a/c or heating unit !) SEER stands for Seasonal Energy Efffiventcy Rating. Again the feds set those standards for the ave consumer to be able to compare "LIKE" equipment on energy consumption and effeicenty of said equipment.... 
Do some research and you'll find these and many other "answers" are out there on the "net".
Even the "Vortec" manufacturer stated the same thing :static pressure exists on BOTH sides of the fan . Air being "drawn" out of the room and "pushed" out the ducting to outdoors. 

The anaolgies are the same for water pressure in your home......any movement of a "substance" is directly relatable to the "piping" of said material.


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