Positive Air Pressure Prevents Pests and the Need to Spray.

[Hash Zeppelin]

This thread is about preventing pests and powdery mildew in the grow room through positive air pressure, and air movement.

For years when I started growing I made the mistake in my grow rooms of having negative or neutral air pressure. I wasted so much time and money. This is very common practice in early grow room design. Unfortunately it has persisted.

The purpose of this was to contain odor. When I started indoor growing in 1999 grows were commonly busted and prison sentences were very harsh. For example my small grow in Texas back then could have gotten me 20 years in prison.

The unfortunate side effect of this design was that if your grow room was not perfectly sealed you would suck in microscopic things from outside. Including pest eggs and powdery mildew spores.

It wasn’t until about ten years ago that I had a friend teach me a few things about how labs were designed. The one that really changed everything though was the positive room pressurization. I have not had to spray a plant since I changed my rooms to positive air pressure. The best thing about this is that it is cheap and simple to do. It’s super effective.

Depending on the size and design of your grow the way you achieve positive pressure will vary. It could be as easy as just changing a few dials on your air systems. This thread though is going to focus on the solution for your average small home grower though that doesn’t have a 25k air system installed.

All you will need is two adjustable speed inline fans, two carbon filters, the proper sized ducting, and the reflective metal ducting tape.

The intake in-line fan and filter should be ideally installed to bring air in to the bottom of the room. This creates under canopy air movement. Which helps prevent moisture build up and wet spots. The fan speed should be set slightly higher than the exhaust fan.

The exhaust fan should be sucking air from the top. This creates airflow and effectively removes excess heat and water vapor. This fan will be set at a slightly lower speed than intake fan.

My AC infinity fans on my little two by two tent are set at 6 for the intake and 4 for the exhaust. I have both filter set up outside the tent. However if need be you can install one or both in the tent.

There are a few other things to do to help facilitate this process. You want to have good air movement in the room. I usually have a few oscillating fans in the room. You don’t want to blast your plants with wind, you just want to caress them. Imagine a gentle island breeze.

Also cleanliness is next to godliness. The cleaner you keep the grow room the better. Don’t wear clothes or shoes in the grow room that you wear outside. Don’t allow pets in to the grow room. Also wash your measuring equipment after each use.

These are my practices and I have not had to spray in a decade. This results in cleaner and higher quality weed. It makes a huge difference. It also saves money. Especially if you have a company. You don’t have to buy sprays and you don’t have to pay people to spray. Cuts down on cost and labor and raises the price of the finished products.

 

[growsjoe1]

@Hash Zeppelin, I've never run positive pressure before. I've always done it that way because of odor concerns and have never even considered it in my tent.

Everything you say makes a whole lot of sense. My concern Is the smell. Even though it's legal to grow where I live. I still don't want my neighbors to know.

I wonder how much odor escapes even with two carbon filter setups like yours.

 

[Hash Zeppelin]

@Hash Zeppelin, I've never run positive pressure before. I've always done it that way because of odor concerns and have never even considered it in my tent.

Everything you say makes a whole lot of sense. My concern Is the smell. Even though it's legal to grow where I live. I still don't want my neighbors to know.

I wonder how much odor escapes even with two carbon filter setups like yours.

None really, but I have 1 plant in a 2 x 2 tent.

I imagine if I had a 4x4 tent I’d have to double the size of my little carbon filters.

In reno I had a 3 car garage full of plants and it took 3 huge carbon filters to control smell, but even then I’d get whiff every once in a while.

I had a 5k square foot warehouse in Berkeley and that stunk a block away when we were harvesting. Lol

 

[Poptart Smoothie]

I did try out positive pressure in the past because I got powdery mildew at one point. Turns out, carbon filters are almost useless for spores, pollen etc. It's really only good for VOC's and large particles like dust. You want something like a MERV 13 filter or higher. The higher the rating, the more restrictive. Merv13 is a good middle ground because air can make multiple passes through the filter faster and cycle the room.

Positive pressure is used heavily in the custom pc world. All the air that gets pushed into the case from one point and gets filtered through a dust filter. Negative pressure means the air is being sucked out. Air and dust is pulled in from holes and cracks. For anyone wondering, you can still have exhaust fans, just set them lower than the intake.

I remember ACinfinity makes a filter box that takes standard 3M MERV filters. Other companies offer the same. It costs about 100$. Hooks in between your inline fan and carbon filter. Medical grade clean room type stuff. My solution was cheaper. I exhaust my air out the window. Bugs get sucked into the turbine fan and shot out, along with any spores etc.

 

[Hash Zeppelin]

I did try out positive pressure in the past because I got powdery mildew at one point. Turns out, carbon filters are almost useless for spores, pollen etc. It's really only good for VOC's and large particles like dust. You want something like a MERV 13 filter or higher. The higher the rating, the more restrictive. Merv13 is a good middle ground because air can make multiple passes through the filter faster and cycle the room.

Positive pressure is used heavily in the custom pc world. All the air that gets pushed into the case from one point and gets filtered through a dust filter. Negative pressure means the air is being sucked out. Air and dust is pulled in from holes and cracks. For anyone wondering, you can still have exhaust fans, just set them lower than the intake.

I remember ACinfinity makes a filter box that takes standard 3M MERV filters. Other companies offer the same. It costs about 100$. Hooks in between your inline fan and carbon filter. Medical grade clean room type stuff. My solution was cheaper. I exhaust my air out the window. Bugs get sucked into the turbine fan and shot out, along with any spores etc.

That’s really cool. I didn’t know those existed. Thank you for posting! I’m getting some of these!!! There are 3m filters so good that they get viruses and tiny cancerous chemicals out of the air. It’s good for your whole home health.

 

[Poptart Smoothie]

That’s really cool. I didn’t know those existed. Thank you for posting! I’m getting some of these!!! There are 3m filters so good that they get viruses and tiny cancerous chemicals out of the air. It’s good for your whole home health.

I almost purchased one myself. I only have a 3x3 but it offers health benefits too. It's kinda funny because it's cheaper than most air purifiers and it outperforms them. Crazy because it's a cannabis focused product. Usually it's overpriced.

 

[Creeperpark]

This thread is about preventing pests and powdery mildew in the grow room through positive air pressure, and air movement.

For years when I started growing I made the mistake in my grow rooms of having negative or neutral air pressure. I wasted so much time and money. This is very common practice in early grow room design. Unfortunately it has persisted.

The purpose of this was to contain odor. When I started indoor growing in 1999 grows were commonly busted and prison sentences were very harsh. For example my small grow in Texas back then could have gotten me 20 years in prison.

The unfortunate side effect of this design was that if your grow room was not perfectly sealed you would suck in microscopic things from outside. Including pest eggs and powdery mildew spores.

It wasn’t until about ten years ago that I had a friend teach me a few things about how labs were designed. The one that really changed everything though was the positive room pressurization. I have not had to spray a plant since I changed my rooms to positive air pressure. The best thing about this is that it is cheap and simple to do. It’s super effective.

Depending on the size and design of your grow the way you achieve positive pressure will vary. It could be as easy as just changing a few dials on your air systems. This thread though is going to focus on the solution for your average small home grower though that doesn’t have a 25k air system installed.

All you will need is two adjustable speed inline fans, two carbon filters, the proper sized ducting, and the reflective metal ducting tape.

The intake in-line fan and filter should be ideally installed to bring air in to the bottom of the room. This creates under canopy air movement. Which helps prevent moisture build up and wet spots. The fan speed should be set slightly higher than the exhaust fan.

The exhaust fan should be sucking air from the top. This creates airflow and effectively removes excess heat and water vapor. This fan will be set at a slightly lower speed than intake fan.

My AC infinity fans on my little two by two tent are set at 6 for the intake and 4 for the exhaust. I have both filter set up outside the tent. However if need be you can install one or both in the tent.

There are a few other things to do to help facilitate this process. You want to have good air movement in the room. I usually have a few oscillating fans in the room. You don’t want to blast your plants with wind, you just want to caress them. Imagine a gentle island breeze.

Also cleanliness is next to godliness. The cleaner you keep the grow room the better. Don’t wear clothes or shoes in the grow room that you wear outside. Don’t allow pets in to the grow room. Also wash your measuring equipment after each use.

These are my practices and I have not had to spray in a decade. This results in cleaner and higher quality weed. It makes a huge difference. It also saves money. Especially if you have a company. You don’t have to buy sprays and you don’t have to pay people to spray. Cuts down on cost and labor and raises the price of the finished products.

Very interesting friend, thanks for taking the time to explain your positive experiences with us.

 

[aqualungs]

None really, but I have 1 plant in a 2 x 2 tent.

I imagine if I had a 4x4 tent I’d have to double the size of my little carbon filters.

In reno I had a 3 car garage full of plants and it took 3 huge carbon filters to control smell, but even then I’d get whiff every once in a while.

I had a 5k square foot warehouse in Berkeley and that stunk a block away when we were harvesting. Lol

There is a point when the garden gets so big where you say, “carbon filter no bueno”, and you never buy another carbon filter again. If you smoke inside or around your property, your spot will smell like ganja from time to time anyways. Save your money if you are in a legal state/country.

As to this positive pressure, I have worked at a facility with positive pressure rooms and boy did they still have bugs. It may help but it won’t be your be all end all. A filter on the air inlet and exhaust will help catch those nasty buggars; in my later years I am becoming a big fan of sealed rooms. In a sealed room you are not exhausting terpene infused air anywhere but you may still want a carbon filter in the room depending on your situation.

Notice I am talking rooms so use what works best for your tent situation which may indeed be positive pressure.

 

[Nannymouse]

What i remember about positive pressure, is that they said it was needed (or really helpful) when using CO2. (It is CO2, right? Haven't had my first mug of coffee)

 

[gmanwho]

Positive pressure is common practice in Pharmaceutical industry or labs. Mushroom cultivation, Electronic industry "clean rooms". Laminar hoods.

As hash zep touched on, part of the idea is you have more control when u can filter the incoming air.

Hepa filter the air as it is forced into the room. This way you are not pulling in air from random spots witin the room/tent that aren't fully sealed.

This way, dust particles molds spores & pests are pushed thru those cracks or openings in a postive air pressure room. verse being sucked in through those openingings in a negative air pressure room.

When someone opens a door, the air is forced out, and not an inrush of unfiltered air.

Im willing to bet there maybe some truth that certain pests or molds etc may not do well with positive pressure conditions.

Also, an intake fan with a hepa filter and then using a passive air exhaust port maybe abit easier to control an less elec consumption. also less overhead cost with 1 less fan expense,

Now the trick is how to run positive room pressure with co2 and not exhaust all the co2 and increase unnecessary expenses. First thoughts would be a passive air damper exhaust, that opens slightly as the air pressure reaches a certain mbar.

Installing a spring loaded damper similar to ones used in clothes dryer vents to stop the outside air from coming in when the dryer is not on.

If the dryer damper is installed, there will be a restriction of air flow out of the room until the air pressure builds within the room/tent. Then once the air pressure overcomes the damper spring tension, it will then allow the air to exit. Combined with a fan speed adjuster, you could slow or increase the flow out finding a sweet spot of air flow.

Allowing you to find that variable sweet spot, when air is leaving, but not unnecessary amounts. Each room situation, or temps, that fan speed would vary

 

[Ca++]

There are ways to surround your tent with scrubbed air, while still keeping containment.

You need negative pressure for containment. If you use positive pressure you have displacement. Untreated air coming out the gaps.

Unfortunately most bugs will head to the light, even if it's up-wind.


I picked up an air purifier from eBay for about £20. It had a good sized panel, that £20 couldn't usually buy. Yet they sold the whole floor standing machine for that price. Such a machine could blow air across a tent, covering the usual air ingress points with clean air. It would be a half arsed attempt, but not a joke.
Ali sell a number of filter sets for dysons and such. Some are about 120mm, and can obviously bucket some air though, with a suitable fan.

 

[Hash Zeppelin]

What i remember about positive pressure, is that they said it was needed (or really helpful) when using CO2. (It is CO2, right? Haven't had my first mug of coffee)

I still kept a bunch of filters even in my big grows but not to control
Smell but to control dirt and dust. I agree that if rooms aren’t clean and air flow isn’t sufficient pressurization only helps so much. I super strict with grow cleanliness and I have some pretty major positive pressure though.

 

[Hash Zeppelin]

There are ways to surround your tent with scrubbed air, while still keeping containment.

You need negative pressure for containment. If you use positive pressure you have displacement. Untreated air coming out the gaps.

Unfortunately most bugs will head to the light, even if it's up-wind.


I picked up an air purifier from eBay for about £20. It had a good sized panel, that £20 couldn't usually buy. Yet they sold the whole floor standing machine for that price. Such a machine could blow air across a tent, covering the usual air ingress points with clean air. It would be a half arsed attempt, but not a joke.
Ali sell a number of filter sets for dysons and such. Some are about 120mm, and can obviously bucket some air though, with a suitable fan.

I don’t even worry about smell to be honest. I’m in a legal state though.

 

[Hash Zeppelin]

Positive pressure is common practice in Pharmaceutical industry or labs. Mushroom cultivation, Electronic industry "clean rooms". Laminar hoods.

As hash zep touched on, part of the idea is you have more control when u can filter the incoming air.

Hepa filter the air as it is forced into the room. This way you are not pulling in air from random spots witin the room/tent that aren't fully sealed.

This way, dust particles molds spores & pests are pushed thru those cracks or openings in a postive air pressure room. verse being sucked in through those openingings in a negative air pressure room.

When someone opens a door, the air is forced out, and not an inrush of unfiltered air.

Im willing to bet there maybe some truth that certain pests or molds etc may not do well with positive pressure conditions.

Also, an intake fan with a hepa filter and then using a passive air exhaust port maybe abit easier to control an less elec consumption. also less overhead cost with 1 less fan expense,

Now the trick is how to run positive room pressure with co2 and not exhaust all the co2 and increase unnecessary expenses. First thoughts would be a passive air damper exhaust, that opens slightly as the air pressure reaches a certain mbar.

Installing a spring loaded damper similar to ones used in clothes dryer vents to stop the outside air from coming when the dryer is not on, But install this damper backwards.

If the dryer damper is installed backwards, there will be a restriction of air flow out of the room until the air pressure builds within the room/tent. Then once the air pressure overcomes the damper spring tension, it will then allow the air to exit. Combined with a fan speed adjuster, you could slow or increase the flow out this reverse installed damper.

Allowing you to find that variable sweet spot, when air is leaving, but not unnecessary amounts. Each room situation, or temps, that fan speed would vary

I don’t run co2 but it’s heavier than o2. I image the light has would get pushed out first.

 

[Hash Zeppelin]

Ok so something important I forgot to add. Wash all your pots in soap and hot water before adding to your grow room. Even smart Pots. They’re all full of factory dust. This really goes with everything you put in the grow environment. I wipe down my tent with disinfectant wipes before I ever put a plant in it.

 

[JKD]

For small grows I don’t see why you couldn’t have positive pressure in the grow areas, and negative pressure in the room surrounding them.

 

[weedemart]

for small/medium rooms in a sealed environment enriched with co2, it seems to me much more efficient and much more affordable to simply install split air conditioning units and dehumidifiers to compensate for the thermal gain of the lights and cover the room during the summer .Then use the system in reverse cycle for the winter when the lights go out and the temperature drops. its much more easier to clean an ac unit than ventilation ducts.

for greenhouses on the other hand yes an hvac system is essential

 

[Ca++]

For small grows I don’t see why you couldn’t have positive pressure in the grow areas, and negative pressure in the room surrounding them.

That's an idea, if the room smelling is no issue.

We all have different kit at out fingertips, and different ideas about containment. I have both a 1.2 and a 1.4, so could play russian dolls. Growing in a 1.2 and using a 1.4 to put a 100mm (4") air gap around it.
Such an arrangement isn't limited to either approach. Though I do favour negative pressure in the 1.2 and the 1.4 over-filled with clean air from a cheap purifier.

The Tors & Olsson T32 is a remarkably cheap machine, to put positive pressure within the 1.4, even if the 1.2 has negative pressure. Though you would need balance that, depending on the weather

 

[weedemart]

That's an idea, if the room smelling is no issue.

We all have different kit at out fingertips, and different ideas about containment. I have both a 1.2 and a 1.4, so could play russian dolls. Growing in a 1.2 and using a 1.4 to put a 100mm (4") air gap around it.
Such an arrangement isn't limited to either approach. Though I do favour negative pressure in the 1.2 and the 1.4 over-filled with clean air from a cheap purifier.

The Tors & Olsson T32 is a remarkably cheap machine, to put positive pressure within the 1.4, even if the 1.2 has negative pressure. Though you would need balance that, depending on the weather

you can just circulate ambiant air into a filter for odors

 

[Ca++]

for small/medium rooms in a sealed environment enriched with co2, it seems to me much more efficient and much more affordable to simply install split air conditioning units and dehumidifiers to compensate for the thermal gain of the lights and cover the room during the summer .Then use the system in reverse cycle for the winter when the lights go out and the temperature drops.

for greenhouses on the other hand yes an hvac system is essential

Quite a few people run co2, and extract. It seems crazy, and the stuff of fancy timers. However, I fired up a tea light candle in a bedroom with a tent, that just blew into the bedroom. However, the door was wide open, and the window a few inches, while the bathroom fan pulled through. It was adequate air exchange for a square meter, and the candle had me around 1000ppm.

This has me thinking about the costs of gas, and keeping the extraction. Perhaps with gas interlock (so the gas stops, if the fan stops)