House of Hacks

Monday, November 16, 2015

How to quiet a shop vac - efficiency measurements


How well did Harley meet his goals by setting up the shop vac to be a centralized system? In this episode, the changes are quantified with measurements for noise, vacuum and air flow.

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For a written transcript, go to How to quiet a shop vac - efficiency measurements

Music and sound effects under Creative Commons License By Attribution 3.0 or 4.0.
Intro/Exit: "Hot Swing" by Kevin MacLeod at
Light switch effect:


Today at the House of Hacks we compare some efficiency parameters of the shop vac's original configuration and its new one.


In this earlier episode, I presented some problems I had using my shop vac, some goals I wanted to meet by reconfiguring how I use it and how I actually made some of the changes. In this episode I want to show some of the before and after measurements to see what actually changed.

To recap, my goals were to 1) have minimal daily setup; 2) be convenient to use; 3) be much quieter; 4) and all this at minimal cost. I attempted to do this by converting it to a DIY central vac system.

Today I am going to show how well I accomplished my goals. I’ll show what it takes to use the new configuration, a couple specifications between the old and new systems: the loudness, the vacuum pressure and the air flow.

Overall I’m really pleased with the ease of operation. I typically just leave everything plugged in, setup and ready to go. All I need to do is grab the hose and press the power button. Of course if I’m working on a piece of equipment, I have to do some setup, but that is pretty minimal. I just move the hose to the closest outlet and connect to the equipment.

One of the goals was noise reduction. I used a freely available decibel app on my tablet to measure the noise levels. Admittedly this is an uncalibrated device and won't give exact results, but it does give a good idea as to relative differences.

In the shop, the vacuum runs around 85 db.

And when it's outside the box on the other side of the wall, it runs about 70 db.

When it's inside the box I made for it, it drops down to about 62-63 db.

Overall a reduction of over 20 db. Quite a bit. For comparison purposes, that's like going from being next to a food blender to being in an office.

A side effect of adding the plumbing is reduced efficiency of the vacuum pressure and air flow. Devices are available to measure these parameters accurately, but they're not cheap and I was more interested in relative loss, so I hacked together a couple instruments.

First vacuum. This is a simple DIY vacuum gauge that I made out of a simple loop of vinyl tubing, some water and a ruler. I explained how I made it in this other video over here. One end is open to the atmosphere and the other is connected to our vacuum. The difference in water levels tells us how much vacuum is being generated.

As you can see, we’re getting about 38, 39 inches of water here. And I'll consider this 100% of baseline for what the vacuum is capable generating, for comparison in future measurements.

Connected to the first port it reads 31.5 inches.

Connected to the second port it reads 32 inches.

Connected to the third port it reads 31 inches.

So, the ports have a reading of about 31.5 inches of water on average or a loss of about 20%.

To measure air flow, I picked up an inexpensive anemometer off Amazon.

Connected directly to the shop vac, this reads as an overload. The vacuum is advertised as 150 mph, but I suspect, based on the noise of the anemometer, that it’s not really that fast. For the purposes of this test I’ll estimate this to be about 110 miles per hour (MPH). Like before, this will be the 100% baseline for the other measurements.

Connected to the first port it reads 89 mph.

Connected to the second port it reads 88.5 mph.

Connected to the third port it reads 86 mph.

So, on average, the ports read 87.8 mph or a loss of about 20%.

While there's a loss of 20% in both vacuum and air flow, in practical application, I don't really notice any difference. It still picks up about what I need it to in about the same way.

In summary, I'm really pleased with the new setup. It's much easier to work with so I'm more diligent at keeping things cleaner.

In conclusion, I’d love to hear in the comments below what you think about vacuums versus dust collectors as a means of keeping the shop clean.

If this is your first time here at House of Hacks: Welcome, glad you’re here. We’d love to have you subscribe. Through these videos I hope to inspire, educate and inform makers in their creative endeavors. Usually this involves various physical media like wood, metal, electronics, photographs and other similar materials. Thanks for letting me encourage your creativity. So subscribe and I’ll see you again in the next video.

Now, go make something. It doesn’t have to be perfect, just have fun!