Negative air in house

[BlueSkye]

So I've been slowly setting up a small closet grow space and something just dawned on me. First of all my grow area is rather small, about 65 cubic feet. I have a vortex 4" 172 cfm fan that will be throttled down to around 50%. I planned to us a passive intake from an adjacent room and vent my exhaust out through a roof vent. My house is around 1500 square feet.

Am I creating a problem with negative pressure in my house? Or is the vented exhaust so small that there shouldn't be a real problem. I guess I could just vent the exhaust to another room but I would like to avoid that if possible. Thanks for the input

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[Wallykazam]

I would say try some smoke around your closet if its getting sucked in then you have negative air pressure

 

[BlueSkye]

There definitely will be negative pressure in the closet. What iam worried about is since I'm venting all this air outside and not bringing in more air to replace it, there will be negative pressure in my house. Will this have some sort of negative effect to the house somehow......

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[Thunderbrain]

Your house has plenty of leaks, unless you paid to have it hermetically sealed.

This is a non-issue.

(Or does your exhaust fan have a "hurricane" setting? If it does, don't use it at that setting.)

 

[Wallykazam]

About all i could see happening is you will have better air movement in your house

 

[BlueSkye]

Your house has plenty of leaks, unless you paid to have it hermetically sealed.

This is a non-issue.

(Or does your exhaust fan have a "hurricane" setting? If it does, don't use it at that setting.)

The fan is only a 4 inch 172cfm and I plan to dial it down to 50% or so. So it will be the equivalent to a bathroom fan I imagine. The only thing that worries me is my house is pretty sealed to start with and I don't want to draw CO in from the furnace or hot water heater. I'm probably over thinning this. Thanks for the reply guys.

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[Oldbear]

Do you have a passive air intake by the furnace? Often its a 4 inch pipe installed near the furnace down near floor level.

The fan doesn't have a lot of power. If there is no easy airflow path, it will struggle to get close to rated airflow. Some sort of outside air intake will help a lot. It just needs to be close to the tent/closet

 

[Wallykazam]

Im not growing atm but i run a 6 inch hurricane can fan in a 2*3*5 tent and my house has much better airflow when it is in use lol....its overkill i know but you wont ever smell anything inside my house lol...and its just a passive intake

 

[Dave Groomer]

I run a 500cfm fan. I haven't run out of o2 yet.

 

[BlueSkye]

I run a 500cfm fan. I haven't run out of o2 yet.

So you vent to outside the house and don't use any kind of intake for fresh air in your house and have no issues.

I realize air will find its way in somehow, I just wanted to make sure I wasn't setting up a problem for later.

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[BlueSkye]

Do you have a passive air intake by the furnace? Often its a 4 inch pipe installed near the furnace down near floor level.

The fan doesn't have a lot of power. If there is no easy airflow path, it will struggle to get close to rated airflow. Some sort of outside air intake will help a lot. It just needs to be close to the tent/closet

Not sure if the furnace has a passive intake. It's in the attic and believe its a sealed system. Not sure on that. I guess I can just crack a window and be done with this thought. Or just vent out to another room in the house. I'm using LEDs so heat isn't to much of an issue.

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[Dave Groomer]

In all seriousness. If you think about the math, you will realize you won't have an issue. If you house is 1500 sqft and you have 8' ceilings, you have 12,000 cf. If you were running your fan on full you would only be moving 172cf / minute of your 12,000. A drop in the bucket.

 

[BlueSkye]

In all seriousness. If you think about the math, you will realize you won't have an issue. If you house is 1500 sqft and you have 8' ceilings, you have 12,000 cf. If you were running your fan on full you would only be moving 172cf / minute of your 12,000. A drop in the bucket.

Your probably right and like always I'm over thinking shit. But with the math and the fan running half speed I will have completely vented my entire house in 140 minutes. Thanks for the info guys!

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[Oldbear]

Its a legit issue and a good question. A typical house here (near Ottawa Canada) built in last 10 years or so, will have 1 to 2 air changes per hour just sitting there with no fans running. Thats because of chimney effect and wind pressure and temperature differences between in and out.

If there is no easy make up air, the fan wont exhaust anywhere close to its rated capacity. You need the exhaust fan for smell, humidity control as well as heat control.

 

[AKgramma]

Yes, Friend. You are overthinking.

A small fan is essential to move air across the plants. I have a small double window fan blowing out all year and no fancy ducting. It's all passive. If the grow room gets too hot, I leave the door open a crack so there is more airflow going into the room and out the window fan. Have had no issues for 2 years growing indoors in Alaska.