Vacuum hoses come in many different sizes, and they often play a part in many people’s purchasing decisions when shopping for a new wet/dry or shop vacuum.
Smaller diameter vacuum hoses are often more maneuverable and flexible, not to mention lighter, and for certain applications there are performance benefits.
Advertisement
Larger diameter hoses can pick up bigger debris, and with less likelihood of clogging.
The other day, I talked about some issues I had with my Shop Vac, when using it to pick up water. Afterwards, I thought about some future testing I want to do, to see how its performance compares with other vacuum types.
With shop vacuum sizes, 2-1/2″ is a good size for general cleanup tasks. Sometimes a vacuum will come with a smaller hose, other times an intermediate size.
My Festool dust extractor has a 27mm hose, which works great with many handheld power tools, such as sanders. Smaller shop vacuums come with 1-1/4″ hoses.
What’s the difference between a 1-1/4″ hose, and a 2-1/2″ hose? The diameter is doubled, and so the cross sectional area is quadrupled. (Remember, the area of a circle is pi*r^2.)
I recently tried to split the vacuum connection of my dust extractor, so that it could connect to a portable table saw’s lower and guard ports. Most of the dust was collected through the 2-1/2″ port via my 50mm hose, and the 27mm connection was able to clear the blade guard port, albeit with much-weakened suction. Why? Because I was now asking the vacuum to work with 4.43X the hose cross section, combined, with the 27mm connection only receiving 22.6% of the full suction power.
Imagine you buy a small shop vacuum, and it comes with a smaller hose. What happens if you buy a 2-1/2″ hose to use with it? With the same suction power applied to 4x the hose size (remember, 2x diameter, 4x cross sectional area), the airflow velocity will decrease.
Some shop vacuums and dust extractors come with intermediate-sized hoses, for maneuverability and attachment benefits, without compromising too much.
With my dust extractor, I have found that a 27mm hose works great with sanders and my plunge-cutting circular saw. I bought a cleaning set, and it came with a 36mm hose, which works better with routers. Sometimes I will use it with the circular saw, and supposedly performance is supposed to be a little better. And then I have a 50mm hose that works even better for cleanup tasks. The 50mm also connects to the 2-1/2″ port on certain tools, such as portable table saws.
When using my 27mm hose with sanders, I often have to dial down the suction, or else there is too much suction power, and the sanding pad can “stick” to the work.
In my post the other day, some readers hypothesized that my use of a wet-rated filter had hampered the vacuum’s performance. While still possible, I think that the 2-1/2″ hose and large nozzles simply couldn’t produce enough velocity to perform as fast and effectively as I had anticipated. Switching to a Fein, with its 1-1/16″ (27mm) and smaller nozzle, resulted in higher airflow velocity.
I probably would have seen better performance from the Shop Vac if I had swapped things over, but the Shop Vac had other downsides that would have led me to reach for the Fein anyway, such as the lack of a good top handle.
I have taken hose sizing for granted. I figured it would help to create a visualization, since working out differences on paper (yay, math!) might not always be clear.
With my router table, I’ve been wanting to add a below-table box, to help better contain the dust. Most product manufacturers recommend their under-table dust accessories be used with a 4″ hose, but they don’t explain why.
Surely I can just branch off my dust extractor, right? Or even use a second one?
A 4″ hose is recommended so that it moves enough air to cool down the router motor, at least that’s the consensus on woodworking forums. If there’s not enough airflow, there’s no escape for built-up heat, and the router motor could be damaged.
Why not use a second shop vacuum or dust extractor with a step-up adapter? A 4″ hose is 60% wider, with 2.56X the cross sectional area. Remember, most larger shop vacuums and dust extractors are designed to work with 2-1/2″ hose diameters – at the most. There’s a good chance that there just wouldn’t be enough airflow.
Selecting the right vacuum hose for the job is tough.
A smaller diameter hose, such as 1-1/4″ or 27mm, will often work better with smaller handheld power tools, such as sanders, jig saws, and even circular saws (at least those with dust ports).
A medium diameter hose, such as 1-1/2″, 1-7/8″, or 36mm, is a good middle-ground for cleanup tasks, and tools produce lots of chips and dust that can clog smaller hoses, such as routers.
A larger diameter hose, such as 2-1/2″ or 50mm, are great for general cleanup tasks, and for connecting to tools with similarly sized dust ports. You don’t want to use a step-down adapter, if you could help it.
Use a small hose on leaves, and you’ll spend a lot of time sweeping over an area, and then cleaning out the clogs. Use a large hose on fine dust or water, and you might lose enough airflow velocity to hamper performance.
Update and More Hose Sizes
Someone asked about how 27mm, 36mm, and 50mm hose sizes compare.
What I’ve found, by measuring all the hoses immediately accessible to me, is that metric hose sizes are measured in terms of their inner diameter, while inch-sized hoses are measured in terms of their outer diameter and accessory connection size.
For instance, I measured a Shop Vac 2-1/2″ vacuum hose, and a Festool 50mm vacuum hose, and they both measured ~2.4″.
Wall thicknesses can vary, and as such, the diagram was always meant to be a rough visualization.
But, it seems fair to compare metric hoses against each other.
Kman says
Another dimension to consider is hose length. As a painting contractor we have a 20′ 1 1/4″ hose. We can put our vac in one spot and sand patches in a whole room. Actually we use a porter cable drywall sander in most cases but corners and small areas we use a hose and sanding pad. It is also convenient for cleaning the floors after we are done painting. The long hose is really nice for these types of uses but I would imagine it affects suction. I don’t think it would be great for wet pickup.
Merlyn says
Actually, not suction but airflow
HTG says
If I remember my fluid mechanics correctly, flow rate is proportional to r^4, so the effect is bigger still. Also, and probably as a consequence, large diameter houses tend to be more appropriate for high-volume low-pressure applications. It is hard to set up a pressure gradient when the resistance to flow is so low. In other words, this is 4” dust extractor territory, ideal for a planer etc. The 27 mm festal hose shifts a much lower volume of air, but at higher pressure. This sort of design works really well for hand held power tools. If you step down the a 4 inch dust extractor and connect it to a power tool, you get a very low flow rate, because the pressure gradient is too low. The most important lesson, though, is never to step down the diameter of the hose unless you really have to do, because the flow rate plummets. Use the biggest size you are practically can. I hope that’s helpful.
Wilbur says
I’ve got 2 identical 6.5 HP Home Depot shop vacs, bought together when they were on sale, both with 2.5″ hoses; one is stationary and gets hooked to tools used on the bench with the appropriate adapter and short smaller hose, the other available to roll around the shop. I’ve occasionally thought about making both stationary and building an 8-10 gallon centrifugal dust filter that both can connect to and using a 25-30 ft 2.5″ hose connected to the filter for pickup instead of having one vac available for “rolling around.”
farid says
Back in the day, I worked as safety consultant for a few years and I evaluated and designed industrial ventilation. I used to have table of recommended air velocity required to capture dust/debris/fumes. The higher the cutting speed , the higher the capture velocity required. Paint booths and test lab hoods required a minim velocity of > 100fpm or so, but grinders and cut off wheels required extremely high velocities reaching in thousands. I’ll see if I can locate the table and post some numbers when I get a chance.
The size of the main duct was determined after calculating all the required flow rates from all the branches, taking into consideration the minimum settling velocity ( total flow Q /pipe cross section area = velocity) . Obviously, heavier particles like metal grinding require higher velocity than Styrofoam dust. The goal is to maintain the velocity all the way to the vacuum. Therefore, the main duct starts out at minimum size at the far end and gradually becomes larger as you get closer to the collection device and more branches are added along the way.
In a number of plants I visited, the ventilation was often designed by either maintenance or HVAC contractors who had no experience with industrial ventilation. . The typical design used a a largest diameter trunk pipe they had (often 20″ 24″ dia or more) and dropped 3 or 4″ flex to each machine along the line. While this design works for HVAC, it is exactly the opposite design requirement for extraction. In HVAC you want equal air distribution for all vents, so the main duct or plenum is designed as as large as possible to equalize pressure (assuming reasonably close pressure losses in the branches).
The typical result was the main duct became a debris storage tank. Once the air reached the main duct, the velocity would drop so low that everything would settle, leading to clogs. Workers would eventually stop using the system or remove shrouds form machines, leading to higher exposure levels. Sometimes fires would start inside the ducts. There has been an instant or two of collapsed overhead ducts due to the the weight. It was interesting to drill a hole in some of the ducts and using a bore-scope see what was stored inside!
Anyway, if you want to capture debris from further away (i.e can’t get nozzle close enough to work) or being thrown at higher velocity, reduce the pipe or nozzle size to a smaller size. If dust and debris tend to sit in your pipe and not make it to your vacuum, it is also a sign the velocity is too low and the pipe is too big.
Most wet/dry shop vacs cannot handle more than one device effectively at once and most don’t have enough flow rate to generate high enough velocity to do a good job of capturing dust from a grinder or saw. Even for small dust collection systems, it is best to install vent gates at each branch so as to maximize suction at the working device.
Finally, and probably most know this, don’t collect ferrous grinding and aluminum girding particles in the same system!
Have a happy DIY weekend.
Stuart says
Great insights and advice, thank you!
Ryan says
Interesting, why no ferrous and aluminum particles together?
Farid says
aluminum powder + iron powder + spark = thermite fire
fred says
As I recall – the iron has to be in the form of an oxide to get the reaction going – but rusty iron (ferric oxide) filings should do the trick. Aluminum atoms really want to replace the iron in the oxide – liberation lots of heat in the process. Once the activation energy for the reaction is supplied – the powdered aluminum melts quickly – and the reaction usually proceeds rapidly in the pool of molten aluminum. You can’t put a thermite fire out in the usual way either since the ferric oxide is supplying the oxygen.
Farid says
Thanks, Fred. You are correct about the oxide state and thanks for the chemistry explanation. I was in a hurry and just did a quick reply.
Depending on the type of iron being ground, some of it can have rust already on it, and small filings can easily rust.
We don’t do that much on our grinder (actually 12″ disk sander with replaceable sanding disks and a deburring flap wheel in reply to your comment below) , so the dust collection system does not get emptied that often giving the fillings a chance to rust.
We’ve never had an issue since I started working here, but my understating there was a small incident long time ago, when production volume was much higher.
I use a steel brush to clean my files if I have to work on aluminum. A loaded grinding g wheel is another issue that we don’t have to deal with at work, since we don’t normally grind aluminum (except if someone is prototyping something).
Using Lye has it’s own dangers too, doesn’t it.
Farid says
Thanks, Fred. You are correct about the oxide state and thanks for the chemistry explanation. I was in a hurry and just did a quick reply.
Depending on the type of iron being ground, some of it can have rust already on it, and small filings can easily rust.
We don’t do that much on our grinder (actually 12″ disk sander with replaceable sanding disks and a deburring flap wheel in reply to your comment below) , so the dust collection system does not get emptied that often giving the fillings a chance to rust.
We’ve never had an issue since I started working here, but my understating there was a small incident long time ago, when production volume was much higher.
I use a steel brush to clean my files if I have to work on aluminum. A loaded grinding g wheel is another issue that we don’t have to deal with at work, since we don’t normally grind aluminum (except if someone is prototyping something).
Using Lye has it’s own dangers too, doesn’t it. I hope there was some automation or PPE involved at that scale.
bj says
Farid,
I guess I don’t fall into the “most know this,” category so I had to google. Here’s an interesting read:
https://www.osha.gov/laws-regs/standardinterpretations/2009-10-08
Thanks for sharing. Most of the terms you presented were flying over my head, but that last tidbit you shared was insightful from a waste collection management standpoint.
farid says
Excellent find Bj. We have a sign on our grinder used for iron “No Aluminum Grinding”. Good advice to follow.
Static electricity is another big one when using plastic piping, but that is discussion for another time.
fred says
@farid
Aluminum grinding on a grinding wheel would probably be self-limiting. The metal melts into the surface of the grinding wheel – clogging it up in short order.
Even filing aluminum is better done with special or coarse tooth files – let you clog the file up. Back in the WWII aircraft manufacturing plants – I’m told that they use hot lye (sodium hydroxide) in pots to dip the clogged files in to clean them up.
Framer joe says
Other factors can change performance..ex. using a ” dut deputy” dust separator on the Festool vacs CT…makes a huge difference in performance and dust collection
bj says
This is an interesting read as dust collection is new to me (I’m just a weekend DIYer). I have been using a Craftsman shop vac to connect to my Makita track and miter saw, but the hose is thick and stiff. I never really thought about hose diameter other than bigger is better, but I was totally off base.
BTW, finding an adapter to mate the larger hose to the Makita dust collection port was no easy task (I had to rig an adapter). I kind of wish sizing was standardized for dust collection but what do I know…
Chris says
linked in a separate article — these tapered hoses are another consideration (and require additional DIY for compatibility).
https://car-wash.kleen-ritecorp.com/search?w=tapered%20hose
Russell Carolla says
my hoses are 2″ ID, 2.25″ OD
EngineerJohn says
Are hose sizes based on ID or OD?
Stuart says
Good question.
Honestly, I’m not sure. It tends to be based on the connection standard these days. Two different 2.5″ hoses won’t necessarily have the same geometries, aside from a usually-standard port interface.
Kenni says
I wonder if the problem I ran into was that I used a large 2.5″ hose almost the entire (8′) length to a portable 7″ angle grinder, then reduced size (via an adaptor) to the 1″ or 1.25″ port on the grinder’s shroud port?
Would it have worked better to use the small size hose for the entire 8′?
I was grinding a concrete surface, so the dust is fine.