# Combining two fans for more power.

1. Sep 23, 2008

### cajun79

I have 2 computer fans which are used to exhaust heat.

They are both 120mm x 38mm and run at 70cfm.

If I was to put them both together to create 1 fan would this create a fan running at 140cfm, or maybe not work very well at all and maybe cancel each other out?

2. Sep 23, 2008

### stewartcs

What do you mean by put them both together (i.e. in series or parallel)?

CS

3. Sep 23, 2008

### FredGarvin

Assuming that the inlet to the case can handle that increased flow, you would need the fans in parallel to increase the flow rate. Putting them in series should increase the head rise but fans are funny in that they would probably perform poorly in series like that.

4. Sep 23, 2008

### cajun79

Hmmmmm.

Maybe I need to explain more! The fans are not actually for my PC at all.

Im actually using them in a small project for exhausting heat from a box cant really go into anymore detail.

What I really need is a more powerful fan altogether like 120 cfm but seeing this is a physics forum I was just wondering how two fans running the same way exhausing heat would perform.

For instance if one fan was connected to the end of some ducting it would be pulling at a rate of 50 cfm, if I then pushed the fan say 3-4 inches into the ducting for arguments sake and connected the second fan also rated at 50cfm.

Would the exhaust now be running at double power (100cfm) or would this not work properly?

5. Sep 23, 2008

### stewartcs

No, since they are in series, they would still be 50cfm. However, the pressure would be the sum of the two.

CS

6. Sep 23, 2008

### rcgldr

You would get an increase in flow, but not much. The issue is that the pitch of the blades are designed to operate in their own induced wash, and not the induced wash from another fan. Why not buy a 120mm fan with a higher flow rating?

A review of fans:

A range of fans up to 220CFM:

http://www.sidewindercomputers.com/delhigper.html

If 100+CFM s enough, look at the FM12X fans on this page:

http://www.silverstonetek.com/products/fan.php?area=usa

Last edited: Sep 23, 2008
7. Sep 24, 2008

### LURCH

However, if you put the two fans in two seperate holes in the box, then you would get something very near 100cfm (through the box). As Fred said; that's assuming the intake of fresh air into the box is large enough to allow the increase in volume of flow.