GPM Capacity of 2" Shower Drain

Users who are viewing this thread

GAtkins

New Member
Messages
2
Reaction score
0
Points
0
Greetings gang and thanks in advance for any help:

we are remodelling our shower and are looking to put in multiple shower heads and some body sprays.

our current drain is 2".

My question is what is the maximum GPM flow that this drain will handle? Also, is there somewhere on line where I can look at the calculations, etc?

Thanks again for any help.
 

Thatguy

Homeowner
Messages
1,454
Reaction score
3
Points
0
Location
MD
Greetings gang and thanks in advance for any help:

we are remodelling our shower and are looking to put in multiple shower heads and some body sprays.

our current drain is 2".

My question is what is the maximum GPM flow that this drain will handle? Also, is there somewhere on line where I can look at the calculations, etc?

Thanks again for any help.
http://www.engineeringtoolbox.com/pressure-loss-plastic-pipes-d_404.html

http://www.engineeringtoolbox.com/darcy-weisbach-equation-d_646.html

You need to know pipe length and height above the opening into the next larger pipe, pipe materials, # of elbows, etc.
 
Last edited:

Jadnashua

Retired Defense Industry Engineer xxx
Messages
32,770
Reaction score
1,190
Points
113
Location
New England
Assuming you don't have anything greater than say 1" pipes supplying water, it should not be a problem. Now, if it is a really large area of shower, you may want a second drain to limit how far the water has to go to get to the drain.
 

TedL

New Member
Messages
602
Reaction score
0
Points
0
Location
NY Capital District
I'm not sure that the links above are an answer, as they deal with pressurized flow, and you're asking about gravity flow.

I think you can get a workable answer, though not exactly to the question you asked, by looking at your code to see how many fixture units it assigns to the shower heads and how many it allows for the drain pipe size. You're going to have to work within that code if you plan to pass inspection.

Here's the IPC as an example, not intending to say it controls for you.

http://publicecodes.citation.com/st/index.htm
 

GAtkins

New Member
Messages
2
Reaction score
0
Points
0
Thanks for the help so far, but I remain confused.

Arkansas has adopted the codes in the link. Our house was built circa 2003.

our master bath shower has a 2 inch drain, 1 shower, 1 toliet, 2 sinks, 1 bath tub separate from the shower.

the remainder of our house has 2 additional toliets, 3 additional bath sinks, 1 kitchen sink, and 1 washer.

If I total this up correct with what I have, it comes to 22 units. The rating for a two inch drain if I am reading the table correctly calls for a maximum unit value of 21 for a 2 inch drain with only one quarter inch of slope per foot.

for a slope of one half inch per foot, it apparently allows up to 26 units.

I want to add to my existing master show 1 additional shower head (total of 2), and 4 body sprays. The gpm rating of the two shower heads will be 2.5 gpm each for a total of 5 and for each of the body sprays 1.75 gpm for a total of 7 for the sprays and a grand total of 12 gpm for the entire shower.

When I consulted my plumber this afternoon he said that the maximum GPM for a 2" drain is 12gpm, so according to him this will work.

I would like to get some independent confirmation of this.

Will the above work with a 2" drain?

Thanks again in advance for any help/replies.

I don't want to remodel the entire shower and then not have it drain.

Glenn
 

Thatguy

Homeowner
Messages
1,454
Reaction score
3
Points
0
Location
MD
The rating for a two inch drain if I am reading the table correctly calls for a maximum unit value of 21 for a 2 inch drain with only one quarter inch of slope per foot.
That's what I get from my 2000 IRC, assuming no water closets: 21.
 

Jadnashua

Retired Defense Industry Engineer xxx
Messages
32,770
Reaction score
1,190
Points
113
Location
New England
I think you're missing something...your toilet drain is at least a 3" pipe, and the whole house may go into a 4" pipe. The outlet of the house drain system is at least 3".
 

JohnfrWhipple

BATHROOM DESIGN & BUILD
Messages
3,225
Reaction score
102
Points
48
Location
North Vancouver, BC
Flow Rates of a 2" Shower Drain

I found this old post and thought I could add in my own two bits.

I have done a load of private testing on the subject of flow testing and have found many of these 2" drains can handle easily between 8-16 GPM (Gallons Per Minute). In my tests most drains see no build up of water (above grate) at 8-10 GPM or less. When the flow rates creep up higher so does the water level above the grate.

At 18 GPM I have measure 3/8" of water above the drains grate.

We have also noticed that flow rates drop when the drop to the P-Trp is not vertical. We also noticed that the higher the drop the better the flow rate. We have also noticed that any mis installed fitting can greatly lower the flow rates.

Hope this helps.

Greetings gang and thanks in advance for any help:

we are remodelling our shower and are looking to put in multiple shower heads and some body sprays.

our current drain is 2".

My question is what is the maximum GPM flow that this drain will handle? Also, is there somewhere on line where I can look at the calculations, etc?

Thanks again for any help.
 

Derek Sutherland

New Member
Messages
18
Reaction score
0
Points
1
Location
Illinois
I know this post is old but here is my input. I to0 was concerned about the GPM for a 2 inch drain. I am in the middle of remodeling my master shower. I have seven fixtures - all of which can be turned on at the same time due to separate volume controls. I just performed a flood test on my pan liner. I had 14 gallons of water sitting in there for 12 hours. None of the water leaked. When I went to drain it I timed it with a stop watch. At around 30 seconds into the drain enough volume had drained out where the water is now collecting below the surface of my drain. By about 40 seconds all the water was completely drained. Therefore, I can conclude that I will have no problems whatsoever with running multiple fixtures with my 2 inch drain. This test showed I have at minimum 20 GPM and probably much more. Hope this helps.
 

James-engineer

New Member
Messages
1
Reaction score
0
Points
1
Location
North Carolina
http://www.engineeringtoolbox.com/pressure-loss-plastic-pipes-d_404.html

http://www.engineeringtoolbox.com/darcy-weisbach-equation-d_646.html

You need to know pipe length and height above the opening into the next larger pipe, pipe materials, # of elbows, etc.
I know this post is old but here is my input. I to0 was concerned about the GPM for a 2 inch drain. I am in the middle of remodeling my master shower. I have seven fixtures - all of which can be turned on at the same time due to separate volume controls. I just performed a flood test on my pan liner. I had 14 gallons of water sitting in there for 12 hours. None of the water leaked. When I went to drain it I timed it with a stop watch. At around 30 seconds into the drain enough volume had drained out where the water is now collecting below the surface of my drain. By about 40 seconds all the water was completely drained. Therefore, I can conclude that I will have no problems whatsoever with running multiple fixtures with my 2 inch drain. This test showed I have at minimum 20 GPM and probably much more. Hope this helps.
For a shower drain the driving force is the height of the drain above the p trap weir. The greater the distance above the p trap, the higher the possible drain flow rate for a given drain size and downstream configuration (lengths, number of bends etc). Hope this helps.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks