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# CFM OUTPUT IN SERIES FANS

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## CFM OUTPUT IN SERIES FANS

(OP)
thread403-131064: Fans in Series

Does the 5000 CFM rating for each fan add up (5000 + 5000 = 10000 CFM),does it stay the same (5000 CFM) or does it become a value somewhere in between (i.e. 7500 CFM)

Thank You in advance

### RE: CFM OUTPUT IN SERIES FANS

Both fans theoretically will operate at the same CFM. So if you have correctly determined/calculated the pressure of your system, and the sum of the pressure from your two fans equals that (at the 5,000 CFM you want), then they will both operate at the 5,000 CFM you want.

It can be more complicated than that if you are looking at part load (if your system has that) or if you are selecting two fans at 5,000 CFM but at different pressures. This link may be helpful

https://www.achrnews.com/articles/106299-multiple-...

### RE: CFM OUTPUT IN SERIES FANS

Google "fans in series":

### RE: CFM OUTPUT IN SERIES FANS

Fan applies the same laws as pump to a certain extent. In Series you will get the same flow, however total pressure will increase.

### RE: CFM OUTPUT IN SERIES FANS

Bear claw - No one knows as you haven't given any real technical detail.

All you can say as others above have done is that the mass flow through both fans will be the same assuming there is no leakage inbetween.

It is highly unlikely that the flow will be 10,000 cfm as then both fans would be operating at 200% of their nominal flow. It all depends on the shape of your fan curve for flow vs pressure and what is downstream of the second fan. If you read your referenced post properly you'll see what I mean.

It would help if you could explain what your issue is and what you are trying to do with two fans in series. It's usually much better to have a single fan sized correctly for the required pressure and flow for your particular system.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: CFM OUTPUT IN SERIES FANS

BearClaw, fans in series generally means higher pressure and no more flow. Fans in parallel means higher flow and not much more pressure. Reality, based on fan curves, means a mix of both. Fan and pump laws are only approximations..

### RE: CFM OUTPUT IN SERIES FANS

Total flow is not the sum but the same. It is the total pressure of the fans that is additive. You have to calculate the total pressure through the system at different CFMs then compare with the fan system cure to come up with the situation meeting the above requirement. You can refine your next trial CFM by interpolation.

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