A bit in trouble here choosing the lamp wattage and exhaust/fan and lamp choosing. So my space width:25", height:45", and depth:23". I will have two short strains, up to 60 or 70cm, or maybe even less, how strong hps lamp will be better, 250w or 400w,maybe 150w? Maybe later i will want to grow something more bigger, is it possible? Thanks a lot guys.
So you have about 4sq' of grow space IMO a 400w HPS is perfect for that much space. The volume of your room is about 16 cubic feet, as a rule of thumb I like to exchange my air in my room atleast every 2 minutes. a small 40 cfm bath fan would be plenty. Heat is gonna be your biggest issue I think. i would get a cool tube or a vented hood running with its own fan. make sure you exhaust the heat to the outside of the room otherwise you are just going to be pissing in the wind, constantly raising the ambient temp in the room. Also draw your fresh air from the outside, not from within the house.
so if i put fan 180 m³/h on exhaust with Activated carbon filter 100mm - 160m³/h at the top of my box, and non-return valve on down side of the box would it be ok? or do i still need the other fan? trying to make something without two fans (expenses). and there is one more problem, i can't draw fresh air from outside it's gona be from room. also it needs to be pretty silent.and how can i switch from CFM to m³/h which i see is measurment for fans.
m3/h is meters squared per hour I am assuming. A meter squared is approximately = 35 cu feet. So I would guess you would take your M3/h divide by 60 to get M3/minute and then multiply by 35 which should give you cu/per minute. If you are exhausting back into your room you are going to build up heat, no way around that. IMO you HAVE to draw fresh air from the outside at a minimum. Unless you are supplementing CO2 you will quickly see your levels drop to low in a closed loop system like you are describing. So 180m3 / 60 = 3m3 per minute x 35 = 105cfm fan, way more than enough for you 16 cu foot grow area.
From what I have read a 400w light is ideal for a 4x4 area. You can use what ever you want. Multiple CFL's might be a better bet for you too as they give off less heat from what I understand.
From what I have read 25w per sq foot is a minimum for healthy growth. so 16 sq' x 25 = 400w. I run 40w per sq foot personaly so that would be 600w for a space your size.
Do a google search for "watts per square foot cannabis" and you will get more info then you will ever need.
Actually I just did a little math and i am running closer to 50 watts per foot. IMO after seeing many really poor grow set ups and having more than a few rooms myself the single biggest mistake people make is having inadequate airflow/circulation. My grow room is 13x7x10 so around 910cu feet in volume. I use a 1200 cfm fan mounted on my roof then built a tunnel down through my crawl space to the ceiling of my room. I also have ample fresh air intakes. When my fan is running I struggle to open the door to my room because of the suction.
so i think if i can't take air from outside this 400w will get really hot and burn the plants? Temperature is about 20 degrees celsius now in room, but in winter it's gonna be a lot colder, because we have don't have a central heating, we use stove. I can't use CFL's because it's gonna be too cold in winter. Is really second fan which is taking air in really necessary since i draw the air in?
No the I was thinking of you had a vented hood or a cool tube you would have one fan dedicated to that and one fan dedicated to air circulation in the grow area. What you are doing with a vented hood or cool tube is essentialy creating two different environments with the grow area. It's not that you are going to "burn" the plants, its just that growth is seriously inhibited at temps above say 90 degrees (unless you supplement CO2 which allows you to run higher temps). I like to keep my plants at around 75 - 80. Drawing fresh air from the outside is not just about temp control, it also help control humidity and keeps co2 levels where they need to be. Would you want to be in a warm room with no circulation all day every day?
I knew this old hippy that had been growing weed long before I was born who told me something once that always stuck with me "If you can't sit in your room all day and be comfortable then your plants won't be able to either" So if your room is stuffy, musty, humid, too hot, too cold, whatever would make you uncomfortable, then your plants will be uncomfortable too. Cannabis likes the same things most people like... Temps in the mid 70's, humidity around 35 - 45%, lots of fresh air and sun.
ok, i think I can't afford to do all this stuff with cool tube and more ventilation, it will be to noisy, i need to hide it good. sure, i understand that part about sitting in a room without ventilation, fuhh, pretty sad. so i think i'am going to take 250w hps for first time try, am I getting something out of this?
You can grow a nice plant with a 250wmHPS, more is not always better. Do the best you can with what you got. I am not trying to tell anyone what to do. Just offering what I have learned over the years. I don't pretend to know it all. Do lots of research, get lots of advice then figure out what works for you. Good luck.