... Do I need a fresh air intake from outside of the house? ...
If the air in the surroundings of the grow room is good, you shouldn't need to draw it directly form the outside. But if you are exhausting your tent into a small grow area and that forces the intake to pull in that exhausted air, then you should use an external intake. Managing heat can be tough if you are sucking in warm tent exhaust.
My 4" intake vent pulls air from the open part of our basement with the exhaust on the other side of the tent. Our basement door is opened at least 10 times per day continually exchanging the basement air with some new outside air. I will also keep a window slightly ajar to help bring clean air in.
I have had five successful harvests with that intake method.
But I still put a small piece of landscape cloth around the opening of my intake vent to try and prevent dust and shit from getting sucked in. I have found that landscape cloth works better as a filter than does a piece of screen.
