Serious backdraft problem

[Richard Pryor]

I recently built a pole barn (36x48). I have a medical marijuana grow in part of the barn (30x36) and I live in the remaining area (18x36).

Here is the layout.



The whole building was insulated with spray foam. A wood stove was installed in the living room and up until this morning everything was fine. I think I experienced backdraft a few times but nothing serious. This morning it’s different. It's like a hurricane coming down and I think I know the cause. I need a fix.

The problem I suspect is the following: last night I turned on the inline fans inside one of the grow rooms to combat the heat caused by the lights. I have an 8” inline fan bringing air in from the outside and a 10” fan removing air from the room.



When the fans are on I can feel the air from underneath the door in the grow room being sucked in to the grow room. As soon as I turned them off this stopped, and the backdraft also stopped. I tried putting a towel under the door with the fans turned on but backdraft was still there.



I need these fans otherwise I can’t grow medicine for my daughter. She has serious epilepsy attacks and this is the only thing helping. We’ve tried all sorts of things and moved to Oregon for this reason.

I guess worst-case scenario I don’t use the wood stove. The house has spray foam and keeps it pretty warm. But due to the severe backdraft this morning, the house was freezing (it was 15 F outside).

Thanks for your time gentlemen.

Very respectfully,

Richard

 

[Richard Pryor]

The wood stove is a Regency F1100

 

[BrotherBart]

Yep. Even a kitchen exhaust fan can cause backdraft. Mine caused the CO detectors to go off one time with a low burn.

 

[Richard Pryor]

Is there a fix for this? It's freezing cold right now because the outside cold air is coming inside through the wood stove at a rapid pace!

 

[Jan Pijpelink]

Not related to the original question, but how close is that stove to the (dry)wall?

 

[Richard Pryor]

About a foot.

 

[velvetfoot]

an 8” inline fan bringing air in from the outside and a 10” fan removing air from the room.

Airflow not balanced-why not fans the same size? You could cut a hole in the grow room wall and put a damper in it so that it would open when there was a vacuum in the room. Why the 2 fans anyway; wouldn't an exhaust fan and louvers for the intake work? Maybe an agricultural reason? Can't leds be used for less current draw?

 

[bholler]

switch it and have the 10" pushing in and the 8" pulling out. That should give you a little positive pressure. Or just try using the intake fan and notthe exhaust see if that gives you enough air movement to take care of the ventilation needs

 

[Richard Pryor]

Airflow not balanced-why not fans the same size? You could cut a hole in the grow room wall and put a damper in it so that it would open when there was a vacuum in the room. Why the 2 fans anyway; wouldn't an exhaust fan and louvers for the intake work? Maybe an agricultural reason? Can't leds be used for less current draw?

This is my first time doing this. I spoke with a local grower and he recommended those size fans and was specific in saying the fan removing air should be bigger.

I'm not sure I follow about the damper. The reason for the fans is because these plants need total darkness for 12 hours per day for them to flower. If they get just a little light during their sleep time they turn hemaphrodite and pollinate themselves and the flowers end up with millions of seeds and the labs that make the oil don't take flowers with seeds because they can't make oil that way.

 

[jatoxico]

Possibly better balance of intake and exhaust air would help. Seems you are exhausting far more air than you're taking in and creating severe negative pressure.

Sounds like the potential for some real issues. If the exhaust fan pulls air from the stove while it idle it could cause the nuisance smell of creosote etc. Of course if the stove is running you have the possibility of introducing exhaust gases into the house.

A key damper would help when idle but if you need to exhaust that amount of air I'm not sure how any heating appliance would work in the house. They all need to exhaust and cannot operate in high negative pressure.

If the central heat is for some reason not subjected to the negative pressure you'll still be exhausting heated air. Can you send the warm air from the grow room to the living space and do you have CO detectors?

 

[Richard Pryor]

Possibly better balance of intake and exhaust air would help. Seems you are exhausting far more air than you're taking in and creating severe negative pressure.

Sounds like the potential for some real issues. If the exhaust fan pulls air from the stove while it idle it could cause the nuisance smell of creosote etc. Of course if the stove is running you have the possibility of introducing exhaust gases into the house.

A key damper would help when idle but if you need to exhaust that amount of air I'm not sure how any heating appliance would work in the house. They all need to exhaust and cannot operate in high negative pressure.

If the central heat is for some reason not subjected to the negative pressure you'll still be exhausting heated air. Can you send the warm air from the grow room to the living space and do you have CO detectors?

I will try switching the fans.

Yes I have a CO detector.

I can't exhaust the warm air from the grow room to the house because of the smell of the plants. Even though it's legal in Oregon I would get fired.

 

[jatoxico]

I can't exhaust the warm air from the grow room to the house because of the smell of the plants.

Figured that was the case but worth asking. Definitely need better balance of incoming and outgoing air. If possible maybe install switches to allow variable speed control of the fans so you could dial it in day to day..

 

[Richard Pryor]

I just turned on the intake fan and turned off the exhaust and problem is solved immediately. I actually have the opposite of a backdraft right now.

 

[Ashful]

Solution 1: Install Outside Air Kit (OAK). Then interior space pressure / vacuum has no effect on stove operation.

Solution 2: Balance your supply and exhaust fans, whether by variable speed or re-sizing.

The OAK is the preferred solution.

 

[velvetfoot]

I can't exhaust the warm air from the grow room to the house because of the smell of the plants. Even though it's legal in Oregon I would get fired.

If you switch the fans, the grow room will have positive pressure. The air will want to go somewhere. What makes you think it won't go into your living area? It'll want to go out that chimney instead of coming down the chimney.

Couldn't you put in a damper, like for a range hood or something, in reverse, and then build a light baffle around it, paint it flat black inside? Stuff like that.

 

[Richard Pryor]

If you switch the fans, the grow room will have positive pressure. The air will want to go somewhere. What makes you think it won't go into your living area? It'll want to go out that chimney instead of coming down the chimney.

Couldn't you put in a damper, like for a range hood or something, in reverse, and then build a light baffle around it, paint it flat black inside? Stuff like that.

Yes, I just noticed the air is coming out of the chimney more than before and I'm guessing that's not a good thing either?

Put a damper where?

I also noticed that with just the intake fan on, the exhaust fan's blade (turned off) is moving and exhausting some air to the outside.

 

[velvetfoot]

Solution 1: Install Outside Air Kit (OAK). Then interior space pressure / vacuum has no effect on stove operation.

Solution 2: Balance your supply and exhaust fans, whether by variable speed or re-sizing.

The OAK is the preferred solution.

That's an idea. Are these OAK's airtight? Don't those things have safety damper in case the outside intake gets blocked?

 

[velvetfoot]

Put a damper where?

In the grow room wall. Build a light baffle box around it, like a light muffler so it still breathes.
Maybe there's a botanical reason you want negative pressure in the grow room. I've got no idea.

 

[Richard Pryor]

I have no idea either but i'll ask.

Would the exhaust fan turned off act as a damper? It is currently turned off but for some reason the blades are moving and pulling some air out.

The opposite was true. With just the exhaust fan turned on, the intake fan would bring some air inside the room.

 

[velvetfoot]

If the fans were both the same size, the flow would be balanced.
Now, I said, 'put in a damper' to assist the flow to be balanced , but to be truthful, I wouldn't know what size to make up the difference between the 8 and 10 inch fan flow.

The moral is: the air's gotta go somewhere.

 

[MtnBURN]

There's no botanical reason. It (negative pressure) is usually created so the grow room smell can be filtered and heat can be controlled.

you may need speed controllers on the fans to fine tune them so you get a balance in the house. I also wonder with the intake/exhaust so close in proximity if you are somewhat just "looping" the airflow. Every grow space/house it is located in is different. I've seen a small range hood turned on and chaos ensue...so it can be a fine line.

I hope you figure it out soon. Either way....my hat is off to you and I salute in your general direction for putting it all out there and for advocating/doing all you can for your child.

 

[Richard Pryor]

you may need speed controllers on the fans to fine tune them so you get a balance in the house. I also wonder with the intake/exhaust so close in proximity if you are somewhat just "looping" the airflow. Every grow space/house it is located in is different. I've seen a small range hood turned on and chaos ensue...so it can be a fine line.

Yes, they are not in their final position. I will use some ducting so that the intake blows more towards the middle of the room. Good observation.

I hope you figure it out soon. Either way....my hat is off to you and I salute in your general direction for putting it all out there and for advocating/doing all you can for your child.

Thank you, sir. It hasn't been easy. Left it all behind because the risk of me being in jail made no sense. She's doing great. Medicine here is really clean and cheap. And it's a beautiful state.

 

[MtnBURN]

I was actually looking at how close the source/outflow ducting was on the wall. Either way...the more separation, the better you will circulate the air, IMO. since it is yer first rod-a-o.... would be amiss if i didn't ask if you've sat in the room for 10 minutes..in the dark? I see a possible light intrusion through those fans/ducting. It's something I've seen overlooked before and the results are..well...you know 'cus you described it all above.

Tip: If you spiral the ducting it often nixxes the intrusion. Those straight tubes worry me though... just sayin'...

Colorado here. Same, wide open kinda thing...both in the views... and in the laws. It's good to be free!

best of luck

 

[Richard Pryor]

I was actually looking at how close the source/outflow ducting was on the wall. Either way...the more separation, the better you will circulate the air, IMO.

Ah, I see. And you're probably right.

since it is yer first rod-a-o.... would be amiss if i didn't ask if you've sat in the room for 10 minutes..in the dark? I see a possible light intrusion through those fans/ducting.

Yes, there is some light intrusion. I haven't finished setting up the room yet. Just installed the fans yesterday and came here to ask about the backdraft. I will put panda plastic and cover those holes. Light intrusion pretty bad at the moment.

Tip: If you spiral the ducting it often nixxes the intrusion. Those straight tubes worry me though... just sayin'...

Indeed! Never thought I'd be getting this type of advice here lol.

Colorado here. Same, wide open kinda thing...both in the views... and in the laws. It's good to be free!

best of luck

Colorado is beautiful. We considered it as well. Thanks!!

 

[electrathon]

Quickly read through most all of this. First you need an outside air source directly connected to the stove, very badly. If you install is correct you will have very little inside the house air moving through the stove no matter what house pressure does. You should have this anyways.

Second, with this amount of airflow creating a negative pressure in the grow area you need that area totally sealed from your living space. This needs to be done properly no matter if you use the stove or not.