Because if the controller doesnt see the fans the machine shuts down and will not hash. Honestly if you ut the PWM line and it is still not speeding up you most likely have a bad fan.

•Celeron G1840 Processor
•Asrock H81 Pro BTC motherboard
•4 x XFX Black RX 470 GPU
•Corsair Vengeance DDR3 8GB Memory
•Samsung 850 EVO 250GB SSD Hard disk
•EVGA 1000 GQ 80 Plus GOLD power supply

Power usage is of no concern to me as i have a source of free power, so what should i do, or maybe there is a better option??

where do you see this all?
is this all only in MSwindows?
I start in Linux with

Spring is coming soon and so will the hot weather.  I currently have 60+ Rigs in production.  If I stop now, my current infrastructure can handle the heat with a breeze.  However we do have plans on adding 10-20 more rigs.  So it's better to over Engineer to leave some cushions for worst case scenarios.  We all go into this phase.  When it's problematic, we say NO MORE RIGS!! That's enough!  When things are stable and we get bore, we say "Oh look at what's on sale, maybe a few more rigs won't hurt?".  Those last few GPU or rigs is usually the straw that breaks the Camel's back.  =)

My shed is very narrow.  If I put another rack to hold my Box fans, not only will that cover all the sexiness, but it will make it a nightmare to service my gears.  It would probably not be very safe working in that tight of a space.  The positive side to it being so narrow, is that I only have to push the heat a short distance to get it to the Exhaust side.  A lightbulb came into my head and say why not use some of those strong new 120MM Fans I just got?  However getting even 6 of quality Gooseneck holders is like over $100 easily which I can use for Fans instead.  

Luckily, I found this piece of metal that would do the job perfectly and only cost $1.29 at Lowes.  It have predrill holes and is very flexible so I can bend it at any angle I want.  IF I want wider flow, I just extend it more.  I can push it aside if I don't want it in my way.  2 of these at an angle especially Finksy version will sufficient for a 4 ft wide rack to keep the hot stale air from heating the gears above them.   I most likely won't be needing them but it's good to know, there's room for more efficiency and it could possibly help others.  You can power it simply with the spare Molex from your PSU for the side rigs.  All wood and Metal rack frames can be drilled to mount these.