Blow air in or out? shop ventilation - Chevelle Tech
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post #1 of 32 (permalink) Old Jul 17th, 19, 6:18 AM Thread Starter
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Blow air in or out? shop ventilation

I want to work on ventilating our shop in this heat. Probably will be 90-100 degrees the next few days with hair wrecking humidity. Our shop is about 4000 sq ft. 14' ceiling. right now the guys just kind of drag around drum fans to where they are working. We have 2 huge garage doors on one side, then really nothing but a man door on the other end, sort of in a hallway and an exhaust fan in that same corner by the man door.
I think the first thing i need to so is jimmy the flaps on the exhaust fan open, which will at least let more air in or out. they normally only open when the exhaust fan runs. The exhaust fan makes a ton of noise when it runs, so we dont really like to put up with it running for too long. I was thinking about putting a drum fan up next to the exhaust fan to bring air in.

Is it best to focus on pushing air out of the shop, or bring new air in? I think one of the big issues is with the garage doors on one end, and a much smaller opening on the other end, we are just kind of swirling the air around in the shop. I tried once to put a fan by the man door blowing air into the shop, but that fan got scooped up to put in someones work area.

Should i put fans up high to try to get the hot air close to the ceiling out of the shop? We have 2 solar powered vent fans that were "supposed" to take care of that, but i knew from the get go those two little fans werent going to do much.

Anybody have one of those "big a** fans"? Our waste oil heater guy was pushing one on me last year. kind of expensive. And we had ceiling fans before, and pretty much knocked them all down with forklifts, dumptrucks, backhoes, etc.
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post #2 of 32 (permalink) Old Jul 17th, 19, 7:00 AM
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Re: Blow air in or out? shop ventilation

Depending on how often the man door gets used I think i would put as big a fan as possible in that door sucking air out of the shop. That way you will get some cross flow.

That being said you should seriously consider planning for putting in AC. I cannot imagine not having it and most of the better auto repair shops I deal with have installed it too. It will be a big initial hit but the boost in productivity will pay for it pretty fast. My shop is 1800 sq ft and it adds about $150 a month to the electric bill during the summer. If you work 20 days a month that is only $7.50 a day. It was 95 here yesterday and is supposed to be even hotter today but it will be right around 75 in the shop
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post #3 of 32 (permalink) Old Jul 17th, 19, 8:22 AM
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Re: Blow air in or out? shop ventilation

Unless you have the shop so airtight there are no ways for air to infiltrate then exhaust air out. Replacement air will come in through all the different nooks and crannies. And the higher you install them the better. Gets the hottest air out first. my $.02. They make 'barn fans' that go in the wall and have louvres on them that blow open when the fan starts. Might be a quick fix or at least help.
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post #4 of 32 (permalink) Old Jul 17th, 19, 8:52 AM Thread Starter
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Re: Blow air in or out? shop ventilation

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Originally Posted by BillK View Post
Depending on how often the man door gets used I think i would put as big a fan as possible in that door sucking air out of the shop. That way you will get some cross flow.

That being said you should seriously consider planning for putting in AC. I cannot imagine not having it and most of the better auto repair shops I deal with have installed it too. It will be a big initial hit but the boost in productivity will pay for it pretty fast. My shop is 1800 sq ft and it adds about $150 a month to the electric bill during the summer. If you work 20 days a month that is only $7.50 a day. It was 95 here yesterday and is supposed to be even hotter today but it will be right around 75 in the shop
The way things come in and out of here during the day, basically we wouldnt be able to shut the doors more than a few minutes at a time. it would kind of be fruitless.
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post #5 of 32 (permalink) Old Jul 17th, 19, 9:11 AM
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Re: Blow air in or out? shop ventilation

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Originally Posted by 70montee View Post
The way things come in and out of here during the day, basically we wouldnt be able to shut the doors more than a few minutes at a time. it would kind of be fruitless.

Funny because I just had this discussion with one of my repair shop customers. I had them check something on my Tahoe before I went on a trip a few weeks ago and I was commenting on how nice it was in his shop. He said he thought the same thing when he first decided to do the AC but said that they quickly learned a routine to keep the door openings at a minimum. He is a very busy shop so he also has cars coming in and out all day.
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post #6 of 32 (permalink) Old Jul 17th, 19, 11:04 AM
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Re: Blow air in or out? shop ventilation

My shop is a concrete tilt up with a well insulated flat wood roof. Ceiling is about 18í. I have two whirley fans on the roof that draw hot air out by convection.
I find that if I keep all the doors shut itís liveable inside @ about 80 degrees for about three days of over 100 outside temp. After that, the concrete has just absorbed to much heat.
At our home we keep it closed up all day too and we donít have AC. Once the temp drops in the evening, I use a whole house fan and one open window at the opposite end of the house to suck all the hot air out and cool air in. Our whole house fan is huge.

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post #7 of 32 (permalink) Old Jul 17th, 19, 11:36 AM
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Re: Blow air in or out? shop ventilation

Either way will bring dirt and bugs in but I say blow air in and here's how I see it, although maybe a little exaggerated but you get the idea.

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post #8 of 32 (permalink) Old Jul 17th, 19, 12:07 PM
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Re: Blow air in or out? shop ventilation

Dean, your first diagram is a classic illustration of a poorly designed system. I saw this all the time on indoor generator set installations.
By locating the air intake and discharge so close to one another, the air flow is ďshort circuitedĒ.
With air intake and discharge located properly on opposite sides of the room, preferably air-in down low and air-out up high, drawing air out is far better than blowing air in.

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post #9 of 32 (permalink) Old Jul 17th, 19, 2:58 PM
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Re: Blow air in or out? shop ventilation

Yeah, using an exhaust fan can work fairly well for cooling IF everything is closed up tight except where you want the outside air to come in at near you.

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post #10 of 32 (permalink) Old Jul 17th, 19, 3:26 PM
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Re: Blow air in or out? shop ventilation

If you pull it out, you're going to get unfiltered air coming in, as well as possibly sucking in water around your door and window openings during a rain.

If you push it in, you have the option too filter it if you'd like, and it will push the water away from the leak points.

*I'm a door & window guy, not an HVAC guy*
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post #11 of 32 (permalink) Old Jul 17th, 19, 3:36 PM
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Re: Blow air in or out? shop ventilation

Also pulling air out can cause exhaust flue pipes on furnaces, water heaters and such to reverse, pulling fumes in.

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post #12 of 32 (permalink) Old Jul 17th, 19, 4:27 PM
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Re: Blow air in or out? shop ventilation

blow the heat out the top suck it in on the shady side of the building, or leave a ceiling vent open and blow it in at floor level. Either way, make actual inlet locations that you can add filters to if you want.
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post #13 of 32 (permalink) Old Jul 17th, 19, 4:39 PM
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Re: Blow air in or out? shop ventilation

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Originally Posted by Pioneer4x4 View Post
blow the heat out the top suck it in on the shady side of the building, or leave a ceiling vent open and blow it in at floor level. Either way, make actual inlet locations that you can add filters to if you want.
To control where the air is entering in a big shop would be impossible to do though.

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post #14 of 32 (permalink) Old Jul 17th, 19, 7:23 PM
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Re: Blow air in or out? shop ventilation

As Dean says, need to be carefull with fuel appliances for sure. Best is a balanced system, not too negative pressure or a positive pressure. if you exhaust 500 cfm then you should bring in 500 cfm. Just a water heater running probably not an issue. But if you are mainly concerned about removing heat then remove it! and let the outdoor (supposedly cooler) air find its own way in to replace it. As far as filters go if your doors are open as much as you say it wont matter if you blow or suck as far as dust goes anyways.

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post #15 of 32 (permalink) Old Jul 17th, 19, 10:59 PM
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Re: Blow air in or out? shop ventilation

I worked for many years in unairconditioned shops in Maryland, suck it up and get to work!!

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