It's a little bit more complicated than it seems, but in general, you don't need in-fans, in fact, for most designs, in-fans will create more harm than good, there are two important components to perfect cooling, air volume and air velocity, injecting air at the fast speed into the farm would cause air turbulence. You should also know that the type of intake matters, louvers or not(air coming in through louvers has higher FPM), filtered or not, so it's a lot of things to consider to reach perfect cooling, the most important factor is your static pressure around the fans, the CFM labeled on all fans is usually reference against pressure of 0 PSI, the higher the PSI the less the CFM, enough high static pressure could make your fan spin without moving the slightest bit of air. I have probably not talked much about airflow for years, and whatever posts I wrote before were basically based on my own personal experience, they do the job, but probably far from perfect, I have learned too much over the years through educating myself more about HVAC, Airflow, Air pressure, and all related subjects, the size of the farms I set up (either for myself or for clients) has also changed, but I can give you one general rule that would be 90% perfect without going into many details. Do 0.1 square meter intake and 700 cubic m/hr per miner US folks do: 1 sq ft intake and  400 cfm per miner For 10 miners you would do 1 square meter (just a window in the wall sized 1m by 1m) and 7000  cubic m/hr exhaust fan US folks: for 10 miners you would do 10 square feet and 4000CFM Credit goes to Aviral of altairtech who gave me this simple rule which works perfectly.  
It's a little bit more complicated than it seems, but in general, you don't need in-fans, in fact, for most designs, in-fans will create more harm than good, there are two important components to perfect cooling, air volume and air velocity, injecting air at the fast speed into the farm would cause air turbulence. You should also know that the type of intake matters, louvers or not(air coming in through louvers has higher FPM), filtered or not, so it's a lot of things to consider to reach perfect cooling, the most important factor is your static pressure around the fans, the CFM labeled on all fans is usually reference against pressure of 0 PSI, the higher the PSI the less the CFM, enough high static pressure could make your fan spin without moving the slightest bit of air. I have probably not talked much about airflow for years, and whatever posts I wrote before were basically based on my own personal experience, they do the job, but probably far from perfect, I have learned too much over the years through educating myself more about HVAC, Airflow, Air pressure, and all related subjects, the size of the farms I set up (either for myself or for clients) has also changed, but I can give you one general rule that would be 90% perfect without going into many details. Do 0.1 square meter intake and 700 cubic m/hr per miner US folks do: 1 sq ft intake and  400 cfm per miner For 10 miners you would do 1 square meter (just a window in the wall sized 1m by 1m) and 7000  cubic m/hr exhaust fan US folks: for 10 miners you would do 10 square feet and 4000CFM Credit goes to Aviral of altairtech who gave me this simple rule which works perfectly.  

It's a little bit more complicated than it seems, but in general, you don't need in-fans, in fact, for most designs, in-fans will create more harm than good, there are two important components to perfect cooling, air volume and air velocity, injecting air at the fast speed into the farm would cause air turbulence. You should also know that the type of intake matters, louvers or not(air coming in through louvers has higher FPM), filtered or not, so it's a lot of things to consider to reach perfect cooling, the most important factor is your static pressure around the fans, the CFM labeled on all fans is usually reference against pressure of 0 PSI, the higher the PSI the less the CFM, enough high static pressure could make your fan spin without moving the slightest bit of air. I have probably not talked much about airflow for years, and whatever posts I wrote before were basically based on my own personal experience, they do the job, but probably far from perfect, I have learned too much over the years through educating myself more about HVAC, Airflow, Air pressure, and all related subjects, the size of the farms I set up (either for myself or for clients) has also changed, but I can give you one general rule that would be 90% perfect without going into many details. Do 0.1 square meter intake and 700 cubic m/hr per miner US folks do: 1 sq ft intake and  400 cfm per miner For 10 miners you would do 1 square meter (just a window in the wall sized 1m by 1m) and 7000  cubic m/hr exhaust fan US folks: for 10 miners you would do 10 square feet and 4000CFM Credit goes to Aviral of altairtech who gave me this simple rule which works perfectly.  

It's a little bit more complicated than it seems, but in general, you don't need in-fans, in fact, for most designs, in-fans will create more harm than good, there are two important components to perfect cooling, air volume and air velocity, injecting air at the fast speed into the farm would cause air turbulence. You should also know that the type of intake matters, louvers or not(air coming in through louvers has higher FPM), filtered or not, so it's a lot of things to consider to reach perfect cooling, the most important factor is your static pressure around the fans, the CFM labeled on all fans is usually reference against pressure of 0 PSI, the higher the PSI the less the CFM, enough high static pressure could make your fan spin without moving the slightest bit of air. I have probably not talked much about airflow for years, and whatever posts I wrote before were basically based on my own personal experience, they do the job, but probably far from perfect, I have learned too much over the years through educating myself more about HVAC, Airflow, Air pressure, and all related subjects, the size of the farms I set up (either for myself or for clients) has also changed, but I can give you one general rule that would be 90% perfect without going into many details. Do 0.1 square meter intake and 700 cubic m/hr per miner US folks do: 1 sq ft intake and  400 cfm per miner For 10 miners you would do 1 square meter (just a window in the wall sized 1m by 1m) and 7000  cubic m/hr exhaust fan US folks: for 10 miners you would do 10 square feet and 4000CFM Credit goes to Aviral of altairtech who gave me this simple rule which works perfectly.