Keg Line Length Balancing – The Science of Draft Beer

by Brad Smith on July 14, 2011 · 50 comments

This week we take a look at the science behind designing a good draft beer system for your kegged homebrew. Everyone loves draft beer, and I consider my keg system to be one of the best purchases I’ve made in my brewing career. Kegging makes everything easier, and if you want to start kegging, please read my earlier article on how to keg. This week we’re going to look at the more advanced topic of balancing your keg lines.

In my previous article we covered how the temperature of the beer and carbonation level desired in volumes of CO2 drives the overall carbonation pressure – a number you can also calculate easily using BeerSmith. You will need to know your keg pressure as a starting point for designing your overall system. However this is not the complete story – as the lines of your keg play a very important role. In general the longer your keg lines are, the lower the serving pressure at the tap. If the tap pressure is too high or too low, the overall system is said to be out of balance and your beer will either foam or be flat.

Line Resistance is Not Futile

So how does one design a draft beer system to maintain proper balance at the tap? The pressure drop depends on resistance in the beer line. Beer lines have two types of resistance – one due to elevation change (i.e. the keg being higher or lower than the tap), and a second due to the beer lines themselves which generate friction as the beer flows through the lines.

Lets look at resistance first to keep things simple. Here are some sample resistance ratings for various popular beer lines:

  • 3/16″ ID vinyl tubing = 3 psi/ft
  • 1/4″ ID vinyl tubing = 0.85 psi/ft
  • 3/16″ ID Polyethylene tubing = 2.2 psi/ft
  • 1/4″ ID Polyethylene tubing = 0.5 psi/ft
  • 3/8″ OD Stainless tubing = 0.2 psi/ft
  • 5/16″ OD Stainless tubing = 0.5 psi/ft
  • 1/4″ OD Stainless tubing = 2 psi/ft

Generally plastic tube of smaller than 3/16″ ID is not recommended – it provides too much resistance for practical use!

So now that we have the resistance factors how to we go about designing a keg system that is in balance? For the purpose of our example lets assume that you have pressurized your kegging system at a nominal 12 psi, which at a 40F refrigerator temperature represents a mid range carbonation level of about 2.5 volumes of CO2 – typical for an average American or European beer.

At the tap end of our balanced keg system we want a slight positive pressure to push the beer out, but not enough to foam. Generally this would be between less than 1 psi. So let’s target a tap end pressure of 1 psi. The math from here is pretty easy to calculate the balanced line length (L):

  • L = (keg_pressure – 1 psi) / Resistance

So starting with our example of 12 psi keg pressure, and some typical 3/16″ vinyl keg tubing (which loses 3 lb/ft) we get L= (12-1)/3 which is 3.66 feet. So a 12 psi kegging system would provide 1 psi of pressure at the tap with 3.66 feet of tubing.

Note that some authors leave out the 1 psi tap pressure (i.e. use zero tap pressure) and simplify the equation to L= (keg_pressure/Resistance) which makes the math even easier (the simplified equation would give you 4 feet of tubing vs 3.66 ft). The truth is that you can target anywhere between zero and 1 psi at the tap and still be in balance – the difference is relatively small, though a slight positive keg pressure will give you a better flow rate.

The four foot example with 3/16″ ID vinyl is great if we only have a few feet to go (i.e. in a fridge) but what if one needs to go further? A simple switch to 1/4″ ID vinyl tubing will get us there – looking at the same 12 psi keg system we get: L = (12-1)/0.85 = 12.9 feet. So with the larger tubing we can deliver our beer to just under 13 feet. For other applications we can consider polyethylene or stainless. However if going a long distance one needs to also consider refrigeration – as you don’t want a large volume of warm beer in the lines.

Beer Line Length and Elevation

Changes in elevation also come into play if you design a more complex serving system. The rule of thumb is that your beer loses 0.5 psi/foot of elevation gain. So if your tap is 1 foot higher than the keg it loses 0.5 psi, and conversely if it is lower than the keg it will gain 0.5 psi per foot of elevation.

So if we roll this into our equation, we get the following for a given height (Height – in feet) of the tap above the keg itself:

  • L = (keg_pressure – 1 – (Height/2)) / Resistance

So lets go back to our original example of a 12 psi keg pressure, 3/16″ ID vinyl tubing and this time put the tap 2 feet above the keg itself. We get L=(12-1-(2/2))/3 which is 10/3 or a line length of 3.33 feet.

Another example with longer lines: 12 psi keg pressure, 1/4″ ID vinyl and a tap four feet above the keg gives: L=(12-1-(4/2)/0.85 which is 9/0.85 or 10.6 feet of line length.

Thanks!

Using the above equations, it is pretty easy to calculate the ideal line lengths for a given keg system operating at pressure. Hopefully this will help you properly balance your own keg system for home use. I intend to roll the line length calculator into a future update for BeerSmith. I hope you enjoyed this short article on balancing your kegging system. Thank you for joining me on the BeerSmith blog – and please subscribe to my newsletter or give my home brewing software a spin for some great ways to improve your homebrewing.

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{ 32 comments… read them below or add one }

Jack July 14, 2011 at 1:27 pm

Great article, Brad. I just wanted to point out a couple small errors or typos:

– “Generally plastic tube of greater than 3/16″ ID is not recommended – it provides too much resistance for practical use!” I think you mean less than 3/16″. Resistance per foot increases as diameter decreases.

– “A simple switch to 1/4″ ID vinyl tubing will get us there – looking at the same 12 psi keg system we get: L = (12-1)/0.85 = 12.9 feet. So with the smaller tubing we can deliver our beer to just under 13 feet.” I think you mean “with the larger tubing.” 1/4″ tubing is larger than 3/16″ tubing.

Eric Faden July 14, 2011 at 1:55 pm

Hey,

Nice article, but what about 1/8″ line. I actually use it in my kegerator for soda. I am currently running my soda (and seltzer) at 30PSI @ 40F with a 4′ 1/8″ Vinyl Line. It yields a very nice pour and doesn’t leave a pile of line in my fridge.

-Eric

Brad Smith July 14, 2011 at 2:36 pm

Thanks Jack,
My brain must have been stuck in reverse when I wrote this – corrections made!

Brad

signal7 July 15, 2011 at 12:23 pm

I don’t know where everyone is getting these numbers. I’ve had a kegging system for 10 years and the math doesn’t match my experience at all.

I’m using 3/16″ tubing and 12psi on the keg. Now, if what I read above is to be believed, if the line is more than 5 feet long, I shouldn’t be able to get beer out the other end. In fact going by math alone, it should suck air backwards up the line since my serving line is just over 12feet long. :-)

In reality, I get a full pint in about 9 seconds with minimal foaming. Shorter line lengths do not work – I will get nothing but foam. I can’t say what the difference is, but I’ve been reading this advice for years and it just doesn’t match my system at all. I’ve even used different kinds of plastic serving line and it didn’t make much of a difference.

ymmv.

Jim July 15, 2011 at 6:35 pm

Thanks for the figures… I think I may need to make some changes, but it may lead to solving some long standing issues…

dave August 4, 2011 at 11:58 am

Great article Brad, just couple of comments

I’ve seen alot of variation in serving pressure from 0 to 5 psi (BYO) with words about preference etc. I think 1 psi sounds right and is typical homebrew as we don’t care about speed and have beer that can foam abit more than commercial beers

What about the pressure drop in the stainless tube in the corny keg, this is about 2 ft long and 1/4inch (3/16?) or so, i assume that would aslo add a few psi drop (for corny keg users).

One final note, BYO mentioned a .5 psi drop for a picnic (cobra) style tap.

Michael Laugesen September 12, 2011 at 1:16 pm

How does this translate to the metric system just in case you don’t have an excact way of measuring feet? :-)

L = (keg_pressure – 1 – (Height/2)) / Resistance
would be roughly the same as
Length in m = (Keg pressure in bar – 0.069 bar – (Height in m*1 bar/m))/resistance in bar/m
(Sounds about right?)

What do you do if you need a longer line, and can’t afford stainless steel piping, 12 feet doesn’t sound like a lot. Say you have a beer cellar with your refrigerator system and a pub in the attic, you kick up the keg pressure I suppose?

Brad Smith September 15, 2011 at 9:30 am

Hi,
I have not done the math in metric, but it should be simply a matter of applying the right unit conversions first. You could use the unit converters in BeerSmith to do it.

For very long lines you need to go to larger diameter tubing, which will have less line resistance. This is better than increasing keg pressure which would lead to improper carbonation for the beer, and subsequently poor carbonation at the tap. A secondary consideration with really long lines is the fact that you need to keep them clean and cool – as they could contain a significant volume of beer.

Brad

Mike June 6, 2012 at 1:41 pm

Signal7,

Remember that we are talking about resistance… a resistance force can never be more than the force it is acting against.

The bottom line: the longer the tube gets… the slower the beer flows until eventually it stops.
mike

Justin August 9, 2012 at 7:31 pm

According to the math I can’t get where I need to. I know I need larger tubing to get the balance, but I am having trouble finding figures for resistance in larger than 1/4″ polyethylene tubing. Where can I find this information?

Brad Smith August 11, 2012 at 1:19 pm

I don’t have a good number having never done larger than that – you might want to try a beverage supplier who might be able to help.

Jason Kaan September 6, 2012 at 5:47 am

Hi, I’m just wondering, will The system work without having the system ‘balanced’, with the line I’ve got and height etc it’d have to be about 20 feet long. Is there a way to work out the pressure I should pour at untill I can buy smaller line?
also should I be turning the pressure back up (or down) to carbonating pressure once I have finished a drinking session?
Cheers

Brad Smith September 6, 2012 at 4:18 pm

Try running the calculations with a different size line – you should be able to find one that works for your scenario.

Mike Soltys September 19, 2012 at 12:59 am

Hey, great article! If you REALLY want to get into the science behind draft beer, the formulas are a lot more complicated! It has to do with conservation of energy (Bernoulli’s Equaiton) and frictional losses (Darcie-Weisbach). It even changes with the SG of the beer! I’ve done a little writeup ( http://www.mikesoltys.com/2012/09/17/determining-proper-hose-length-for-your-kegerator/ ), and made an excel sheet in google docs ( https://docs.google.com/spreadsheet/ccc?key=0ApGb-vIKLq7FdGtzN3BrY2xZSldORzQ2bHVVX0hzaEE ) if you’re interested in checking it out. Realistically, this is just a more nerdy approach: the results are about the same.

Locan December 18, 2012 at 9:11 am

Hello,
We are the beer keg factory, we can supply Europe keg, DIN keg and US 1/2 beer barrel and 1/6 beer barrel,ect.
more information pls do not hesitate to contact me ,thanks

looking forward to cooperate in the near future!

BR
Locan
website:www.beerkegbeerbarrel.com

Chris Mackrell May 3, 2013 at 3:53 pm

Do taps with flow control achieve exactly the same result as a longer pipe? I’m about to buy a direct to cornie tap, with flow control, and fear I’ll just pour foam.

Brad Smith May 4, 2013 at 3:03 pm

If you have flow control you can adjust the flow rate to match your desired carbonation level. Balancing the lines is still important, but you can probably set them a bit on the higher pressure side since you can adjust the valve on the tap to suit your preferences.

Erik July 1, 2013 at 6:31 pm

Brad,

Great article. I’m surprised that I haven’t seen any Jockey Boxers chime in yet. I’m currently using, and will be for a fall party, a jockey-box with my home-brewed Cony kegs. Lets tackle my main issue currently. I am using a 150′ coiled SS line to cool the beer as its served. Should I really be using 70 psi to serve my beer correctly?

Second is, I am adding another coil to the box but its shorter? Is this not gonna work at all?

Thanks for sharing all of your wisdom.

Erik

brian September 16, 2013 at 9:18 pm

I am finding conflicting information on what the correct resistance for 3/8″ od ss beer line is, and 3/8″ I’d vinyl line is. I have done a lot of research online and have came up with numbers from .09psi/ft to .2psi/ft for the SS and .1 to .3psi/ft for vinyl.

These little differences turn into monumental differences when multiplying them by 100ft of tubing.

Karl December 3, 2013 at 4:02 pm

How does this translate for Nitro systems? Euro taps with restrictor plates have a higher pour resistance, but I don’t know what that resistance is. Is there some way to measure the pour resistance of a restrictor plate tap?

Bt January 14, 2014 at 12:55 am

I built a bar in my basement and want to have my home brews on tap. My chest freezer kegerator will be in the unfinished area of my basement, about 50 feet from the beer tower on top the bar. Here’s what I have done. I ran 3″ PVC for the freezer to the beer tower area and looped back around to the freezer. The 3 1/2 ID beer lines run through one side of the PVC to the beer tower. My plan is to install a blower fan on the other side of the PVC loop and have it blow into the freezer. The idea is that the fan will cause cold freezer air to be sucked in trough the side of the PVC loop where the beer lines are ran and keep the cool. I also insulated the heck out of all the PVC. Is my idea sound? Do you guys think it will work or can you offer better suggestions

Landis January 25, 2014 at 12:30 pm

@Bt I haven’t actually had to make a run like that, but you might want to look into something akin to the multi-tap bundled and insulated glycol cooled lines that they use for commercial installations. You’ll get better cooling from conduction via the integrated glycol circulation tubes compared to convection with an air cooling system. There’s an example of the bundles I’m referring to in Accuflex’s catalog here: http://www.accuflex.com/images/Acrobat/UltraCat.pdf

Ed January 29, 2014 at 5:38 pm

I have 5 feet of air line and 5 feet of 5/16″ beer line and get a lot of foam. I’ve been reading I need to make one of the lines longer but which one do I change out?

Ed January 30, 2014 at 8:07 am

I tried posting yesterday but it didn’t take.

I have a refrigerator keg conversion kit with Lagunitas IPA inside. I am have 2 5 foot lines, 5/16″ for both the air and the beer.

My beer comes out foamy. Some of the reading I have done says to lengthen one of the lines. Which line do I lengthen based on the formulas in this forum?

Ben March 7, 2014 at 12:56 am

I am trying to pump kegged coffee up to a tower faucet in my coffee shop from the first floor. Will nitrogen be sufficient when running pipes up one floor(8ft floor to ceiling), and horizontal to the tower faucet, about 25ft in total?

Steve April 28, 2014 at 9:18 pm

Gotta admit – I’ve tried to run the numbers and they don’t match my experience at all and I can’t figure out why. I’ve got a kegerator with 5′ gas and beverage lines (pretty sure 3/16″, definitely poly). So, roughly 30″ corny height, then 5′ tubing (though there is slack, so the rise above the keg is only about 12″). I typically force carbonate with about 12 psi for a week, but once that is done, I serve with only 2-4 psi and get a nice head. What am I missing?

Hunter July 3, 2014 at 8:47 am

This advice worked for me! Refurbished an older upright fridge kegerator…with my beer at 12 psi, 38-40F temp and lines that accompanied it (right at 3 ft, 3/16″ ID vinyl) I poured about half a pint of foam. I have about 6″ of vertical distance from keg top to tap inlets. So, I took the 3/8″ ID vinyl line from a picnic tap, measured it and cut at 4 feet…installed…and perfecto! Nice pour, a pint in about 10 seconds with a perfectly creamy 1/4″ head. Thanks for the advice!

Hunter July 3, 2014 at 8:48 am

Correction…3/16″ ID picnic line – sorry about sloppy fingers.

Booy Watt | Home Brew Supplies Gold Coast August 18, 2014 at 2:59 am

Served by your own tap is one the pleasure of draft beer. Volumes which is measured for the total amount of Carbon dioxide dissolved in the beer. It should be kept at standard temperature and pressure (STP – (32 F)).

Robert Morgan November 6, 2014 at 5:49 pm

Hey, this is a great article – but i’m confused with the equation once you add in height.

Your first equation – you say that your line should be 3.66 feet.
But then your second equation – when the tower is actually up 2 feet, your line only has to be 3.33 feet.

That sounds counter-intuitive to me, as you said for each foot in additional height you lose .5 PSI.

Should the equation be : L = (keg_pressure – 1 PLUS (Height/2)) / Resistance ???
If so, that would give us L = (12-1+(2/2) / 3 = 4 feet.

That makes more sense to me that you’d need a longer run if your tap is above your keg.

jehan kothari November 20, 2014 at 6:20 am

Hi…in the above calculation you have considered 1 psi at tap…So is it so because here you assumed the keg to be at greater height than tap?

jehan kothari November 20, 2014 at 6:23 am

Hi.. In the above calculation you considered 1 psi at tap. Is it so because keg is assumed at greater height than tap?

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