hi guys

https://www.amazon.it/dp/B07V9VC67T/ref=cm_sw_r_wa_apa_i_hgfUEbQJ0ST1Y

here's a comment i wrote a few days ago about choosing the right fan.. In your case the most limiting factor will be the length of the fan and filter, unless you mount them outside, as with 40cm the space is really short.. i have two 40x40 grow boxes, but i have 3D-printed my own filters for them and use 14cm PC-fans to save space.. anyways here's my earlier comment about selecting fan-size: Usually the best way to calculate what size extraction fan you need is to calculate the volume of the air inside the tent (length x width, x height) and then factor in how often per minute this air should be renewed.. i would say at least once to twice a minute.. then add about 25% loss due to the the carbon filter, and if growing with hot lamps, like a 1000w HID, then another 10%.. you mentioned LED, so this will not really be necessary. Ducting can be added as well (about 10% per 3 meter). This will give you the minimum requirement for how strong the fan should be. This is for people in the US that use CFM (cubic feet per minute) for fan-measurements. If you're in a country that sells fans based on cubic meters per hour, then it requires a bit more math, but all in all the calculation is similar. To make things simple for m3/h here's a calculator where you can put in your measurements: https://thehydroponicsstore.com/extraction-calculator This will tell you the minimum capacity of the extraction fan, and recommendation for intake fan. Just be sure that your intake fan doesn't push too much air, so it won't be stronger than the extraction fan, else the extracted air won't go through the filter, but it's being pushed out at other spots of the tent. Be careful when getting a too strong fan, as the air will need some time to go through the carbon-filter, else (if this happens too quickly) the filter won't be able to filter out the smells sufficiently.. getting a bigger fan is no problem, but then ensure that it's dimmed down properly!

i think you might have posted the wrong amazon link..