Here is my take on bringing straight fresh cold air into your grow room and what you really need to know. first off as for screening / filters you can use furnace filter material but running fresh air in specially in cold climates is DEW POINT in your room cold air hitting warm air is like a perfect storm the hot mixes with cold creating air that holds lots of water molecules thus humidity, wet floors ,and walls sweating, this is not a good thing trust me MOLD is a 100 percent guarntee behind your panda film and then your into another whole world of hurt and possible health issues .
Fresh air is very important of course but how you get it ready to enter room
you need to make a hot box so really you need to make a box outside where fresh air will go into a thermostatically controlled heater to allow the cold air to heat up this way your dew point can stay low when both fresh air and room temps collide