Need info on ventilating grow room in 50 degree poll barn

Hello I have studied a lot of things on the Internet and only become more confused my room is a 5 by 5 by 7 I have 3 1/2 inches of insulation on all sides ceiling and floor I have a 6 inch exhaust fan and a 12 by 12 passive air inlet like I said I have a 50 degree barn this is built in how do I keep the humidity and heat right in the room bringing in fresh air how often do you bring in fresh air have used this for a number of years now and I get good results flavor taste and potency of buds but the size of the buds are not big enough like cheech and Chong I need bigger buds any help from anybody that actually does this would really appreciated sorry for the long post but I'm an old guy that don't type well so I'm trying this voice typing I believe it has better spelling than I do again any help would really be appreciated

50 degree Fahrenheit?

You might be bettercwith a sealed room.

But here's a calculation that might be useful

CFM = 3.16 X Watts / DT(f) dt is allowable temp rise .


So say desired temp is 75f minus 50f equals a DT of 25 degrees f.

We will say 1000w hps lighting

CFM = 3.16 X 1000/25

So 3.16 X 40 = 126.4

So you want 126.4cfm fan to be running at 75f while lights are on.

But this doesn't take into account impedance from filter or duct so add 30% ish.

Gives you a cfm of 165.

However this is when your lights are on.
You'd need heat when lights are off.

coreywebster said:

50 degree Fahrenheit?

You might be bettercwith a sealed room.

But here's a calculation that might be useful

CFM = 3.16 X Watts / DT(f) dt is allowable temp rise .


So say desired temp is 75f minus 50f equals a DT of 25 degrees f.

We will say 1000w hps lighting

CFM = 3.16 X 1000/25

So 3.16 X 40 = 126.4

So you want 126.4cfm fan to be running at 75f while lights are on.

But this doesn't take into account impedance from filter or duct so add 30% ish.

Gives you a cfm of 165.

However this is when your lights are on.
You'd need heat when lights are off.

Click to expand...

In my opinion thats good as a baseline, not every fan produces same pressure with same cfm so some can lose as much as 50% some only 30%. Plus LED's convert more watt to light in contrast to hps if i understand it correctly. There is lot of good explanation on another forum in thread "ventilation 101" with some HVAC geek stuff.

Thank you very much for all your help I really appreciate it I working out the math It looks good now can you can you recommend a good heater are oil heaters the best or ceramic thanks again. On another note when you say I might be better off with a sealed room does that mean running CO2 thanks again

EPC111 said:

Thank you very much for all your help I really appreciate it I working out the math It looks good now can you can you recommend a good heater are oil heaters the best or ceramic thanks again. On another note when you say I might be better off with a sealed room does that mean running CO2 thanks again

Click to expand...

As far as heaters go, I think what’s best depends on the person. I use a small $50 ceramic I bought off Amazon with a thermometer set at the temp I want and forget it. Uses quite a bit of energy compared to my fans/lights and that’s the trade off. I think oil heaters are cheaper in the long run.

EPC111 said:

Thank you very much for all your help I really appreciate it I working out the math It looks good now can you can you recommend a good heater are oil heaters the best or ceramic thanks again. On another note when you say I might be better off with a sealed room does that mean running CO2 thanks again

Click to expand...

CO2 might be a limiting factor in a 5x5 room full of plants and a very cold air intake. The cold air that you intake might not bring in enough fresh air and CO2 before reaching your desired set temperature. I think that's why coreywebster mentioned a sealed room. You could seal your room to keep out the cold and introduce CO2 with a tank and controller. Another option (if you have the space) is to build another room around your 5x5 so that you have a lung room to act as a buffer between your 5x5 and the cold air in your barn. You could then control the environment in your lung room so that you intake fresh CO2 and air into your 5x5 room that isn't so cold.

Radiant oil heater is what you'll need. If you can afford it though, I would put in an electric radiant floor instead. They make small thin panels that are made to go right under tiled bathroom floors. Can scale up to whatever size you need.. Tile over it too, so it holds onto the heat better. It's the best you can get, without a heater rolling around in the way all the time, and is pretty affordable.

I would run it sealed with c02, especially in the winter, unless you can afford a heat recovery ventilator, that will capture back 90 percent of the heat that you would otherwise be exhausting into the atmosphere. Its the only feasible way I can see to ventilate a cold outdoor room like that, without wasting tons of energy.

1000W HPS...
8 inch Intake Fan + AC Infinity Carbon Filter + 8 inch Output Fan

That 1000W will heat up real quick...
The 8 inch fans should take you thru the summer...
Plus Your Odor free,,, in tight areas

Just My 2 cent

S1 Maker said:

1000W HPS...
8 inch Intake Fan + AC Infinity Carbon Filter + 8 inch Output Fan

That 1000W will heat up real quick...
The 8 inch fans should take you thru the summer...
Plus Your Odor free,,, in tight areas

Just My 2 cent

Click to expand...

No intake fan needed. If you pump air in with the same size fan as the exhaust fan that has a carbon filter on it you will be blasting stinky air out every little gap in the room so the carbon filter will miss a lot of it. For the carbon filter to do it's job you need a bit of negative air pressure in the room so any air leaks are fresh air getting into the room thru those gaps and there will be gaps unless you hermatically seal the room. Passive air intake is fine as long as the intake hole(s) add up to about twice the area of the exhaust.

I thought 800 cfms in with 800 cfms out would balance the room...
maybe im wrong...
I do know that 1000W is going to GLOW hot
good for winter...bad for summer