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Fan/blower selection: What type would be best for pulling air through a dryer vent

Jeff7

Jeff7

Lifer
I'm planning to build an exhaust system to vent varnish vapors out a vindow.

I recall seeing somewhere that "muffin fans," of the style used in computers are not ideal for this application. I would need to pull air through up to 16 feet of dryer hose.

Two fan types I have already:
- 4 11/16" AC square muffin fan, NMB brand. 4715FS-12T-B40. 100 CFM.
- Comair Rotron, similar to this style. It's powerful, but I have no idea how to mount it to something, as it lacks mounting holes.
- A centrifugal blower from a wood pellet furnace. However, it vibrated when running at high speed (which is why it was removed), and I don't know how to go about slowing it down. It is also AC powered.


What fan type would be ideal for this application?

 
How many CFM do you require? A dryer vent hose is only four inches. You really want 8 or 10" min for this. Although the risk is not high, per OSHA requirements anything electrical in a paint booth must be explosion proof. 😉

A plenum just above the work area with a pair of 10x10" square vents on the suction side of a 1/3hp "squirrel cage" blower - the type used in the common house furnace - will draw plenty of air. The discharge can be adapted to 10" flex line and vented out of the work area. Wire it well and use a solid state relay so absolutely no sparks are created in normal operation and you should be good. Mount the power switch outside of the work area or if you must have it inside the work area use a proper (Killark) enclosure.
 
A furnace blower should do the trick, if you can slow it down even better, as it's overkill, but very quiet compared to a washroom fan blower or a hot water heater blower.

The "in line" one posted looks like a good one though and dryer hose will probably fit nicely on there with ring clamps (they probably have a more official name).
 
Originally posted by: Greenman
This is what you want.

http://www.smarthome.com/3016/...-Duct-Fan-DB204/p.aspx
Click to expand...
Well that looks just dandy. 🙂

But what about that whole explosion thing? I'm going to be varnishing wooden bowls up to 6" diameter. Will there be enough fumes coming off that to be a danger?

This is the varnish.



Originally posted by: Rubycon
...
A plenum just above the work area with a pair of 10x10" square vents on the suction side of a 1/3hp "squirrel cage" blower - the type used in the common house furnace - will draw plenty of air. The discharge can be adapted to 10" flex line and vented out of the work area. Wire it well and use a solid state relay so absolutely no sparks are created in normal operation and you should be good. Mount the power switch outside of the work area or if you must have it inside the work area use a proper (Killark) enclosure.
Click to expand...
I can't really build anything above the work area. For one, it's an apartment. The second issue is that this is sort of a finished attic - the ceiling might reach 7 feet high, though it's probably less than that.


Redsquirrel - noise isn't much of an issue, as it's a room filled with power tools. 🙂


 
Originally posted by: Jeff7
Originally posted by: Greenman
This is what you want.

http://www.smarthome.com/3016/...-Duct-Fan-DB204/p.aspx
Click to expand...
Well that looks just dandy. 🙂

But what about that whole explosion thing? I'm going to be varnishing wooden bowls up to 6" diameter. Will there be enough fumes coming off that to be a danger?

This is the varnish.


Redsquirrel - noise isn't much of an issue, as it's a room filled with power tools. 🙂
Click to expand...

haha true. If that's the case a hot water heater fan may do the trick. The type of pipe it is usually made for is similar size as dryer spiral tubing.
 
Elicent is a respected brand when it comes to blowers. They build high quality units without inflated CFM ratings and have a reputation for being quiet.

How big a room is it? Is there a specification for how many times per hour you need the air to circulate?
 
Originally posted by: DayLaPaul
Elicent is a respected brand when it comes to blowers. They build high quality units without inflated CFM ratings and have a reputation for being quiet.

How big a room is it? Is there a specification for how many times per hour you need the air to circulate?
Click to expand...
This would certainly qualify as "light duty."
The room is about 10' x 13'.
It might run for......oh, I don't know, 4 hours at a time, maybe a day or two a week.

Something like Greenman posted seems ideal, and it's about in my price range.




 
I would not underestimate the dangers of flammable fumes and fan motors. Depending on the amount of product being used, it could very well be a concern.
 
What about just using the exhaust fan unducted to create negative pressure in the room? The fumes would have a chance to diffuse throughout the room first.

And I've already got lots of other electric motors in the room.

 

Duct booster fan are perfectly fine with vapor, however you must calculate the return air opening (or open a window) to supply the CFM of the fan to allows for efficency.

<--- Plumbing/Gas/HVAC
 
Originally posted by: NoShangriLa

Duct booster fan are perfectly fine with vapor, however you must calculate the return air opening (or open a window) to supply the CFM of the fan to allows for efficency.

<--- Plumbing/Gas/HVAC
Click to expand...
This apartment leaks air like a screen door, and window options are rather limited. There are just two windows on the second floor, and they're both in the room to be vented.

 
Originally posted by: Rubycon
How many CFM do you require? A dryer vent hose is only four inches. You really want 8 or 10" min for this. Although the risk is not high, per OSHA requirements anything electrical in a paint booth must be explosion proof. 😉

A plenum just above the work area with a pair of 10x10" square vents on the suction side of a 1/3hp "squirrel cage" blower - the type used in the common house furnace - will draw plenty of air. The discharge can be adapted to 10" flex line and vented out of the work area. Wire it well and use a solid state relay so absolutely no sparks are created in normal operation and you should be good. Mount the power switch outside of the work area or if you must have it inside the work area use a proper (Killark) enclosure.
Click to expand...
4" is perfectly fine for exhaust, because the only draw back is the friction ratio calculation go up, noiser, and not at many CFM as larger duct work, rule of thumb is 5' lost for every 90 degree elbow, and so on.

If you like I can calculate the duct size vs. noise & CFM for area, however it is not that critical because it is not for industrial usage, therefore the vapor built up to ignition/toxic level is minimal to nil.

CFM required for vapor calculation

 
Originally posted by: NoShangriLa

4" is perfectly fine for exhaust, because the only draw back is the friction ratio calculation go up, noiser, and not at many CFM as larger duct work, rule of thumb is 5' lost for every 90 degree elbow, and so on.

I you like I can calculate the duct size vs. noise & CFM for area if you like, however it is not that critical because it is not for industrial usage, therefore the vapor built up to ignitio/toxic level is miniml to nil.
Click to expand...

Please check on the actual specifics. I've never seen a paint booth with low flow. Most have enough air movement that you can feel it! A four inch pipe cannot move a fraction of the air without squealing and needing a much stronger fan than a long run register booster. Then again with an informal "home/hobby" installation on a constrained budget they do what everyone else does: open a window and prop up a box fan! :laugh:
 
Originally posted by: Rubycon
Please check on the actual specifics. I've never seen a paint booth with low flow. Most have enough air movement that you can feel it! A four inch pipe cannot move a fraction of the air without squealing and needing a much stronger fan than a long run register booster. Then again with an informal "home/hobby" installation on a constrained budget they do what everyone else does: open a window and prop up a box fan! :laugh:
Click to expand...
I'd have to wedge a block of wood in the window for that...and buy a smaller fan. The window in the room are old. Wooden frames, rope with a counterweight in the wall, and single pane. And yes, there's a rather constrained budget here. 🙂

I don't need "professional" looking or anything like that. I simply need a way to get the vapors out of the room without the solution being overly obtrusive or cumbersome. I prefer the idea of sucking the fumes out through the dryer vent because I am already going to have a modular ducting system installed on the underside of my workbenches. This system will have a "switch" at one point so I can switch the ducting's outlet between the exhaust fan (whatever it may be) and the vacuum, for sucking away wood shavings and dust.

So I'd do my lathe work and sanding with the vacuum hooked up, then switch the ducting over to the exhaust fan outlet and do the varnishing.



 
Problem is in order to get the vapors out (do the smells bother you?) of the room you have to create a negative pressure. Not gonna happen with a mere 120CFM fan. Keep in mind that's a free air rating and as long as your run is not too long and relatively straight will stay close to that. But you rally want 1000+ CFM if you want full capture and discharge of fumes.

It's a funny fetish but I like the smell of most fumes from shellac and thinners. :Q
 
Originally posted by: Rubycon
Originally posted by: NoShangriLa

4" is perfectly fine for exhaust, because the only draw back is the friction ratio calculation go up, noiser, and not at many CFM as larger duct work, rule of thumb is 5' lost for every 90 degree elbow, and so on.

I you like I can calculate the duct size vs. noise & CFM for area if you like, however it is not that critical because it is not for industrial usage, therefore the vapor built up to ignitio/toxic level is miniml to nil.
Click to expand...

Please check on the actual specifics. I've never seen a paint booth with low flow. Most have enough air movement that you can feel it! A four inch pipe cannot move a fraction of the air without squealing and needing a much stronger fan than a long run register booster. Then again with an informal "home/hobby" installation on a constrained budget they do what everyone else does: open a window and prop up a box fan! :laugh:
Click to expand...
It could be that he is building a spray booth, and if that is the case he shoul look into purchase one with build in fan/ducting becasue it is aprove and likely cheaper or as much as a home made at much less work.

However, my feeling is that he is building a low/slow vapour DIY exhaust therefore I suggestedd that 4" is fine, 16' of light gauge 6-12" ducting and elbows isn't going to break the bank because he should be able to get it for less than $50 however he have to built a transition plenum (which I could bulit in less than 15 minutes with a pair of snips, measuring tape, and straigh edge).
 
Originally posted by: NoShangriLa
built a transition plenum (which I could bulit in less than 15 minutes with a pair of snips, measuring tape, and straigh edge).
Click to expand...

Aren't you forgetting the jersey lock machine, slips and drives part? 😉

I still say that fan is not going to do squat to pull air to make a real difference in an open area.
 
Originally posted by: Rubycon
Originally posted by: NoShangriLa
built a transition plenum (which I could bulit in less than 15 minutes with a pair of snips, measuring tape, and straigh edge).
Click to expand...

Aren't you forgetting the jersey lock machine, slips and drives part? 😉

I still say that fan is not going to do squat to pull air to make a real difference in an open area.
Click to expand...
Obviously he gonna look at several thousand CFM if he go through the trouble to size the big duct and cut the wall, and set up everything eles, the cost and work isn't worth it as said above. Therefore I suggested a pre built package.

PS. I understand the complication of venitlation...worked on a system that had 240,000 CFM, and the main trunk is 30'x20' (you can drive a couple of semi trucks side by side and still have room)

 
Originally posted by: Rubycon
Problem is in order to get the vapors out (do the smells bother you?) of the room you have to create a negative pressure. Not gonna happen with a mere 120CFM fan. Keep in mind that's a free air rating and as long as your run is not too long and relatively straight will stay close to that. But you rally want 1000+ CFM if you want full capture and discharge of fumes.

It's a funny fetish but I like the smell of most fumes from shellac and thinners. :Q
Click to expand...
Yeah, but it kind of gets old after the first few hours....and days.


 
Originally posted by: Jeff7
I'm planning to build an exhaust system to vent varnish vapors out a vindow.

I recall seeing somewhere that "muffin fans," of the style used in computers are not ideal for this application. I would need to pull air through up to 16 feet of dryer hose.

Two fan types I have already:
- 4 11/16" AC square muffin fan. I don't know its airflow, but it definitely moves a lot of air.
- Comair Rotron, similar to this style. It's powerful, but I have no idea how to mount it to something, as it lacks mounting holes.
- A centrifugal blower from a wood pellet furnace. However, it vibrated when running at high speed (which is why it was removed), and I don't know how to go about slowing it down. It is also AC powered.


What fan type would be ideal for this application?
Click to expand...

I tried using the comair rotron idea a year or so ago to vent solder fumes. It was only powerful enough to pull from 2-3inches from the end of the hose. I used the shiny collapsible dryer vent "hose"

If I were to bother again, I would use a squirrel cage blower, similar to what you would find on the exhaust blower of a high efficiency gas furnace or hot water heater
 
Originally posted by: RU482
I tried using the comair rotron idea a year or so ago to vent solder fumes. It was only powerful enough to pull from 2-3inches from the end of the hose. I used the shiny collapsible dryer vent "hose"

If I were to bother again, I would use a squirrel cage blower, similar to what you would find on the exhaust blower of a high efficiency gas furnace or hot water heater
Click to expand...
Well I've never seen a water heater blower (the one back home was electric, and I never saw a blower on it), but I do that the one blower from a wood pellet furnace.

PU-4C442 Convection Blower


It's too bad I can't just rig up the vacuum to switch its output from the dust bag straight to outside. 😛

 
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