When do I need a filter

How many lights have you got? Why so many lights in the room and how can you afford electricity cost I only have 2 lights and pay £50 a week with fans and controller and heater I think you could use half them lights units and still get same results and you will need a big filter to get rid of the smell once they start flowering at least 8inch or bigger bit you could fit double plants in the area you got happy growing

Depends on ..... 1. The strain your growing. I have a Zkittlez that STINKS like mad and she started to reek 2 weeks before going into flower, while my caramelo smells very faintly like a dry piece of lavender only if you brush her a bit. So thats one point...lets say you have a stinky strain...well then go to point two. 2. How much plant material you have VS room size. A few smaller plants in a big room Vs a room FULL of plants-the amount of odour particles in the room matters when your talking how long it takes for them to get out. 3. 4 inch fans/4 inch filters are a joke and a waste of money. 6 inches at the least ok. Get the biggest you can afford and fit. That way if you add lights and plants later on the filter will still cope..Go big if you can. 4. In general in a stealth grow where you dont want ANYONE knowing at all about the crop, start to run the fan when you can stand outside the closed room with a closed door and still smell it.- Us growers have shit sense of smell so if we can smell it outside the grow room with the door shut, a non grower thats knows the smell will smell it outside the house if they are on the property.

I would say around week 3 flower . That's when plants starts to get smelly , not that bad but it's noticeable . As for filter size , see what your fan is rated for and buy one with 200-300 CFM(cubic feet per minute) more then the fan is rated and you'll be fine

Untill you can’t stand the smell or your neighbors or local cops notice