Need help with ventilation for new flower room

[peacegrower]

Hi guys! First of all I hope all of you have plenty of smoke to last you through this fucked up time! So heres my problem, i'm building a new flowering room and I can't decide on what ventilation set up i should have regarding enough air flow, negative pressure etc.
The room will be 3.5 x 2.2 x 3 m high so 23.1m3. There will be 4 lights set up each with a grow area 1.1m2 and a walkway down the middle. the red line represents the window which will be used for the intake and outtake vents.
I want to achieve full air replacement every 90 seconds at the very least. So would I be better with 1 large(10 inch) out take fan and filter which would hang over the walkway or 2 smaller (6 inch) fans each with it own filter each hanging above 2 grow areas. and with the inlet system would just fan pumping fresh air low down in the corner be enough so get fresh air to every part of the room (I will have at lest 4 oscillating fans to help with movement obviously) or 2 inlet vents pumping air in different areas.

I was thinking something like this: 2 6inch out take fans each hanging above 2 grow areas which will give me 1100m2h after the loss from the carbon filters. then 1 8inch intake fan which will then divide into 2 6inch ducting pipe which will run along the lower back edges of the grow areas (1 duct running across the backs of 2 grow areas and the other running across the other 2 grow areas) with vents along them to let the fresh air be pumped in across a larger area. Then finally a 6 or 8 inch passive intake vent to help with too much negative pressure. But I'm reluctant to pull the trigger on this plan because I cant help thinking using a large out take fan could be better but i cant find any reliable info on them. I am also considering the MDF box fans. Noise is a factor as well if having many small fans is a lot louder than 1 large one

I am looking for advise from growers who have grown with this sort of size room before or bigger and had experience with large extraction fans like mdf box fans and also any advise on negative pressure because only recently found out that too much negative pressure is a thing and it's quite common.

Let me know if I have missed any important info. TIA

 

[TorturedSoul]

If you don't find anything that appeals at an "indoor gardening store," there's always a Dayton blower like they use on forced-air furnaces, lol. Those things are virtually indestructible - and they pretty much have to be... It's not unusual for someone to get a furnace that includes one, not pay any attention to the "Clean and add a few drops of oil annually" notice - and then complain 50 years later when the thing starts to make a little noise . They're not the cheapest things in the world, new - when I typed "dayton furnace blower" into a web-search box just now, the first thing that came up for sale was one priced at $251.99US. However, I've seen "fancy grow room" extraction fans advertised in that general price range. And, personally, I'd feel more comfortable running an old used Dayton that came out of a broken furnace from the late 1960s than I will when I take the brand new el cheapo semi-generic fan out of its box and set it up for my next grow.

And a Dayton "squirrel cage" (centrifugal fan) will be better at moving air against an obstruction (carbon filter) than an axial fan, which can end up flowing a fraction of its rated airflow if it has to deal with pressure. Which is a good thing, because a lot of the people who never perform maintenance on their furnace blower also go way too long between filter changes - yet they manage to stay warm in Winter and cool in Summer.

You seem to want a lot of airflow, and mentioned 1100m³/hour. The specifications for that Dayton show a rating of 1,009 ft.³/minute. (and while running at only 1,070 RPM instead of 2,000+ like a lot of those "extraction fans" do). Give me a moment to convert that... <scratches head, takes off one shoe, licks pencil end and mutters something about "naught naught, carry the naught.. goes into... UNCLE JED, HELP!!!">

That quiet, bulletproof, lasts for decades of use, (relatively) low-speed Dayton blower is rated to flow approximately 1,714.3019 cubic meters per hour. So you might be able to go with a lower-capacity one that would, presumably be cheaper.

 

[Listersmeghead]

Hi guys! First of all I hope all of you have plenty of smoke to last you through this fucked up time! So heres my problem, i'm building a new flowering room and I can't decide on what ventilation set up i should have regarding enough air flow, negative pressure etc.
The room will be 3.5 x 2.2 x 3 m high so 23.1m3. There will be 4 lights set up each with a grow area 1.1m2 and a walkway down the middle. the red line represents the window which will be used for the intake and outtake vents.
I want to achieve full air replacement every 90 seconds at the very least. So would I be better with 1 large(10 inch) out take fan and filter which would hang over the walkway or 2 smaller (6 inch) fans each with it own filter each hanging above 2 grow areas. and with the inlet system would just fan pumping fresh air low down in the corner be enough so get fresh air to every part of the room (I will have at lest 4 oscillating fans to help with movement obviously) or 2 inlet vents pumping air in different areas.

I was thinking something like this: 2 6inch out take fans each hanging above 2 grow areas which will give me 1100m2h after the loss from the carbon filters. then 1 8inch intake fan which will then divide into 2 6inch ducting pipe which will run along the lower back edges of the grow areas (1 duct running across the backs of 2 grow areas and the other running across the other 2 grow areas) with vents along them to let the fresh air be pumped in across a larger area. Then finally a 6 or 8 inch passive intake vent to help with too much negative pressure. But I'm reluctant to pull the trigger on this plan because I cant help thinking using a large out take fan could be better but i cant find any reliable info on them. I am also considering the MDF box fans. Noise is a factor as well if having many small fans is a lot louder than 1 large one

I am looking for advise from growers who have grown with this sort of size room before or bigger and had experience with large extraction fans like mdf box fans and also any advise on negative pressure because only recently found out that too much negative pressure is a thing and it's quite common.

Let me know if I have missed any important info. TIA

If noise is a big factor, then running 2 big fans dialled down makes for a quiet system.noise is essential for me.
I use a gekko fan, a mdf box fan rated at 1500m3, I have a temp fan controller that has 5 gears,usually the fan cycles between gear 1 (300m3) and gear 2 (600m3) to control temps. This makes it almost silent, I often have to put my hand on the fan box to make sure it's running.
Combined with insulated ducting it's great for noise and efficiency.

 

[peacegrower]

If you don't find anything that appeals at an "indoor gardening store," there's always a Dayton blower like they use on forced-air furnaces, lol. Those things are virtually indestructible - and they pretty much have to be... It's not unusual for someone to get a furnace that includes one, not pay any attention to the "Clean and add a few drops of oil annually" notice - and then complain 50 years later when the thing starts to make a little noise . They're not the cheapest things in the world, new - when I typed "dayton furnace blower" into a web-search box just now, the first thing that came up for sale was one priced at $251.99US. However, I've seen "fancy grow room" extraction fans advertised in that general price range. And, personally, I'd feel more comfortable running an old used Dayton that came out of a broken furnace from the late 1960s than I will when I take the brand new el cheapo semi-generic fan out of its box and set it up for my next grow.

And a Dayton "squirrel cage" (centrifugal fan) will be better at moving air against an obstruction (carbon filter) than an axial fan, which can end up flowing a fraction of its rated airflow if it has to deal with pressure. Which is a good thing, because a lot of the people who never perform maintenance on their furnace blower also go way too long between filter changes - yet they manage to stay warm in Winter and cool in Summer.

You seem to want a lot of airflow, and mentioned 1100m³/hour. The specifications for that Dayton show a rating of 1,009 ft.³/minute. (and while running at only 1,070 RPM instead of 2,000+ like a lot of those "extraction fans" do). Give me a moment to convert that... <scratches head, takes off one shoe, licks pencil end and mutters something about "naught naught, carry the naught.. goes into... UNCLE JED, HELP!!!">

That quiet, bulletproof, lasts for decades of use, (relatively) low-speed Dayton blower is rated to flow approximately 1,714.3019 cubic meters per hour. So you might be able to go with a lower-capacity one that would, presumably be cheaper.

hey torured soul, thanks for the reply, and for taking the time to convert the measurements. we dont get squirrel cage fans here but they're basically the same mdf acoustic box fans (which i can get here) and between you and the info from Listersmeghead, I'm pretty sold on them. Thanks again. PG

 

[peacegrower]

If noise is a big factor, then running 2 big fans dialled down makes for a quiet system.noise is essential for me.
I use a gekko fan, a mdf box fan rated at 1500m3, I have a temp fan controller that has 5 gears,usually the fan cycles between gear 1 (300m3) and gear 2 (600m3) to control temps. This makes it almost silent, I often have to put my hand on the fan box to make sure it's running.
Combined with insulated ducting it's great for noise and efficiency.

hey Listersmeghead, Thanks for the reply, Sound is important but shit gets hot here in the summer so I really like the sound of running it at half power normally and having the option to increase when i need to. I did keep looking at the gekko box fans but i but didnt want to shell out that sort of money and be left disappointed. But what you saying really makes sense and now im thinking to a 12'' one as outtake and a 10'' one for intake and then i can adjust them accordingly to get the right negative pressure and with such a large diameter ducting the airflow wont be so 'forced' out and again make less noise. Well i'd better get saving my pennies, I want this room to be as good as I can get it without having to swap new equipment because its not up to scratch. Thanks again you've really helped to me make a final decision. I'll make sure i post some photos when its done and let you know how it goes! PG.

 

[TorturedSoul]

we dont get squirrel cage fans here but they're basically the same mdf acoustic box fans (which i can get here)

I did keep looking at the gekko box fans

Both of the ones you mentioned are examples of centrifugal (aka "squirrel cage") fans.

 

[Bob Loblaw]

Squirrel cage fans can be had at the local pluming & heating place for dirt cheap (used). Paid $30 for mine, it came with a 1/4hp 2 speed motor that looked to be brand new. For reference a 4" inline will run about $190 here, a 1/4hp motor about $150.

Availability will differ dependent on location. Our readers span the globe.

 

[Listersmeghead]

hey Listersmeghead, Thanks for the reply, Sound is important but shit gets hot here in the summer so I really like the sound of running it at half power normally and having the option to increase when i need to. I did keep looking at the gekko box fans but i but didnt want to shell out that sort of money and be left disappointed. But what you saying really makes sense and now im thinking to a 12'' one as outtake and a 10'' one for intake and then i can adjust them accordingly to get the right negative pressure and with such a large diameter ducting the airflow wont be so 'forced' out and again make less noise. Well i'd better get saving my pennies, I want this room to be as good as I can get it without having to swap new equipment because its not up to scratch. Thanks again you've really helped to me make a final decision. I'll make sure i post some photos when its done and let you know how it goes! PG.

No worries peacegrower, glad it helped.
As both TS and Bob mention the gekko is a squirrel cage fan. Also you can purchase one from heating firms here in the UK, so you could build your own version of a gekko for a fraction of price,it's only a fan in a wooden box with sound insulation foam and a electricity cable point (p.c).
Only issue with the box fans is, they're heavy mofo,work perfectly but heavy.
If you're looking at spending the money, have a look at the ISO-MAX range of fans, similar performance to box fans but 1/2 the weight. They look like a jet engine, a metalic tube.
Keep us posted.