How to combat cold grow box temps with exhaust letting in freezing outside air

[Morriston55]

Hey guys, Im about to start my first grow, have done ALOT of reading the past weeks before making my decisions but have one seemingly fatal flaw in my design I cant figure out what to do with.

I live in Canada, so 30% of the year the outside temperatures will be below 30*F (freezing), my grow box will be fairly small only 2 plants, Im thinking 3X3X4' high, lighting will be 240w from T5 flourescents. Im also lucky enough to own the house so the box will be going in the heated loft, but my concern is the exhaust vent. Since I will have it venting outside, what is stopping all the freezing cold air from coming into the sealed box and drastically dropping the temps inside the box? Is there a way to combat this like a valve or louver system possibly?

Curious any ways people have found out or tested. I havent boughten an exhaust fan or a fan to gently blow on the plants yet, I was thinking 2 intake vents taking air from the warm house (no fan though) but am unsure if or how much the exhaust vent will lower the box temps, as the flourescents certainly wont be heating the box much.

During spring/summer fall I should be fine with outside temps, but those 3-4 months of winter here can be brutal! And a space heater inside the box throws the energy costs through the roof and the biggest risk of a fire

Appreciate any help

 

[evergreengardener]

just hook up a fan to exhaust the air and the air pressure should keep your cold air out u need a exhaust fan anyway so problem solved

 

[Morriston55]

But the exhaust fan wouldnt run constantly, the 2 indoor setups Ive been around only run the fan 20miin/hour to exchange the air, but theey only grow during spring and fall so they dont need to combat hot summer temps or freezing winters

 

[evergreengardener]

my exhaust fan runs 24/7 and you can get ones that are only pulling like 80w so they arent expensive to run that way

 

[Morriston55]

Im assuming yours runs 24/7 because you are using HID lighting though right? Which would mean your exhausting constantly because your bulb/bulbs are making to much heat. Not the case with my flourescents, the box temps without a vent stayed right at 80* completely sealed up with all my lights on my 18hours in the test box I built for the garage, but Ive convinced the wife to let me grow inside, just upstairs in a locked cabinet.

 

[thewanderingjack]

Well, mostly, if you are running the exhaust all the time (at low speeds) your have warm air blowing out, which keeps most of the cold from coming in.

If the vent is not constantly going then the cold will creep in around it and create a cold spot around that area. In that case there's a lot you can do:

Use this kind of vent on the outside: https://deckerville.doitbest.com/product_images/dryer-vent-draft-blocker/265179/54bd4b5469702d57b6f1751e/zoom.jpg?c=1464868955 so that flap opens out (when the fan is blowing) and shuts when it is not. You can also use two with a flap like that, so that when they're closed they create an air space between outside and your grow... that will slow the cold down even more. Make sure to insulate well around the edges of the cutouts for that vent.

You can also create more space between the grow and outside opening using a vent hose. I still recommend the flap of course, but this way a) the cold air has longer to travel to your box b) it warms up a bit as it travels.

You could also add a filter to the vent (outside or in... it's a requirement where I live... and necessary for stealth ops)... this will restrict air flow when you're exhausting, but even more so any air creeping in.

 

[evergreengardener]

i do run hid but even without a fan my temps never reach over 90f i keep my fan on because i dont want any stale air to settle in my area also helps to combat smell when i run 24/7 as i grow some very stanky stuff i agree with the post on top of this one get one of those vents

 

[MichiganMedGrower]

Hey guys, Im about to start my first grow, have done ALOT of reading the past weeks before making my decisions but have one seemingly fatal flaw in my design I cant figure out what to do with.

I live in Canada, so 30% of the year the outside temperatures will be below 30*F (freezing), my grow box will be fairly small only 2 plants, Im thinking 3X3X4' high, lighting will be 240w from T5 flourescents. Im also lucky enough to own the house so the box will be going in the heated loft, but my concern is the exhaust vent. Since I will have it venting outside, what is stopping all the freezing cold air from coming into the sealed box and drastically dropping the temps inside the box? Is there a way to combat this like a valve or louver system possibly?

Curious any ways people have found out or tested. I havent boughten an exhaust fan or a fan to gently blow on the plants yet, I was thinking 2 intake vents taking air from the warm house (no fan though) but am unsure if or how much the exhaust vent will lower the box temps, as the flourescents certainly wont be heating the box much.

During spring/summer fall I should be fine with outside temps, but those 3-4 months of winter here can be brutal! And a space heater inside the box throws the energy costs through the roof and the biggest risk of a fire

Appreciate any help

You will need an exhaust fan (and probably carbon filter) to passively bring the intake air in for good fresh air turnover. You must replenish the air at least as you stated but you will solve all the other problems and help keep mold and pests away with the constant exhaust.

It doesn't necessarily have to blast out of there. You. An slow down with a fan speed controller.

It will also help maintain a steadier temp and humidity level.

Stability in the right environment is as important as light and temp.

 

[Morriston55]

Thank you very much for the suggestions, I suppose the fan running constantly, on a low speed will be my best option, and I will just have to monitor temps once winter hits and see where it puts me, still a good ways a way, just want to be prepared and have it setup the first time to avoid modifying the box. A carbon filter will be looked into aswell

 

[SPLFreak808]

Put an active intake that runs 24/7. You will loose negative pressure with the light and exhaust shuts off but will constantly have airflow from the exhaust. When the light turns on the exhaust turns on again bringing negitive pressure back. Filter or flap would work too as stated.

 

[Morriston55]

A passive intake that runs 24/7? I dont quite understand. I thought passive meant it was simply a hole/vent

Thats another thing, if its simply a hole/vent to intake the air, wouldnt the potent smell still come from that hole? Not really a way to hide that

 

[evergreengardener]

It's all about negative pressure you can have passive intakes many as you want if your exhaust is pulling enough air. the passive intakes won't let out smell as there's always air being pulled thru them never air going out of them so no smell. That's a quick description there's lots of good threads in the grow room design section on setting up exhaust and negative pressure

 

[SPLFreak808]

A passive intake that runs 24/7? I dont quite understand. I thought passive meant it was simply a hole/vent

Thats another thing, if its simply a hole/vent to intake the air, wouldnt the potent smell still come from that hole? Not really a way to hide that

No. Active, meaning a fan driving intake air. If the box is constantly under positive pressure, your exhaust has no choice but to exhaust air doesn't matter if its on or off.

If you have leaks then positive pressure is no good for smell and you cant do it that way unless everything is air tight with a filter, if this is so then look at another option.

 

[evergreengardener]

No. Active, meaning a fan driving intake air. If the box is constantly under positive pressure, your exhaust has no choice but to exhaust air doesn't matter if its on or off.

If you have leaks then positive pressure is no good for smell though, which i assume you dont have any leaks since smell is an issue.

Why though if he doesn't need a a fan to intake air why run 2 fans when all you would need would be an exhaust 24/7 doing the exact same thing (keeping air flowing through his exhaust so cold doesn't creep in) but more efficiently ?

Edit: not a pissy reply more a serious ?

 

[Morriston55]

I think SPLfreak is pointing out that if I put a fan on the intake instead of the exhaust, that the pressure created from this fan running 24/7 will negate even needing an exhaust fan since the air will have to escape. Assuming the box is perfectly air tight (which it certainly will be)

Id love to read any data if I am correct in understanding you, if a certain size fan would be needed for that etc. Id like to keep the electricity bill low so being effecient and not going to overkill is definetely what I am after, but if the wife is getting blasted with the sticky smell evertime she walks in the house I will be forced back outdoors!

 

[MichiganMedGrower]

Thank you very much for the suggestions, I suppose the fan running constantly, on a low speed will be my best option, and I will just have to monitor temps once winter hits and see where it puts me, still a good ways a way, just want to be prepared and have it setup the first time to avoid modifying the box. A carbon filter will be looked into aswell

The fan speed controller becomes like a "volume knob

 

[evergreengardener]

I understand but you would still want to run a carbon scrubber right? So therefore you need and exhaust anyway

 

[SPLFreak808]

Why though if he doesn't need a a fan to intake air why run 2 fans when all you would need would be an exhaust 24/7 doing the exact same thing (keeping air flowing through his exhaust so cold doesn't creep in) but more efficiently ?

Edit: not a pissy reply more a serious ?

Because the exhaust doesnt run 24/7 allowing you to use a lower powered fan when its too cold outside.
If he wants to run the exhaust 24/7, he can as long as the intake temp doesnt get too low during lights out but if it does, he needs to slow it down or shut it off and prevent air from coming back through the exhaust. The other suggestions sound worthy too (filter to prevent backwards draw) or ( flap to prevent backwarda draw). Whatever suits his area better for him

Im talking about using a two fan setup on two different timers so you can have the exhaust shut-off during the colder parts of the day while the active intake just pushes through enough to keep the exhaust from drawing in cool outside air, the house is always warmer then outside and It's just one out of multiple ways to do it.

 

[MichiganMedGrower]

I think SPLfreak is pointing out that if I put a fan on the intake instead of the exhaust, that the pressure created from this fan running 24/7 will negate even needing an exhaust fan since the air will have to escape. Assuming the box is perfectly air tight (which it certainly will be)

Id love to read any data if I am correct in understanding you, if a certain size fan would be needed for that etc. Id like to keep the electricity bill low so being effecient and not going to overkill is definetely what I am after, but if the wife is getting blasted with the sticky smell evertime she walks in the house I will be forced back outdoors!

No you need negative pressure in the box. I suggest you read about growroom ventilation.

Look at how others are venting tents and small boxed. Some use pc fans and diy carbon filters.

But you will absolutely need an exhaust fan. A fan pushing in will force the smell and humid stale air through every crack and fill the room it is in.

You have some work to do. You can and should avoid as many problems from the start.

 

[evergreengardener]

Because the exhaust doesnt run 24/7 allowing you to use a lower powered fan when its too cold outside.
If he wants to run the exhaust 24/7, he can as long as the intake temp doesnt get too low during lights out but if it does, he needs to slow it down or shut it off and prevent air from coming back through the exhaust. The other suggestions sound worthy too (filter to prevent backwards draw) or ( flap to prevent backwarda draw). Whatever suits his area bettwr for him

OK OK I see what your saying. My exhaust runs 24/7 so that my carbon scrubber runs 24/7