Minimum GPM into building


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Old 03-06-06, 06:47 AM
grizzley
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Minimum GPM into building

Just a random question from an uneducated person....

I was wondering of anyone might know if there is a minimum GPM that is required to enter a structure? I think that most water meters reduce the pressure to a max of 80 - 100 PSI or so, and since most residential (and some light commercial buildings) are on 6-8" mains, how does that effect the overall GPM that is delivered into that building? If nothing is required, is there a usually "minimum"? I know there are several factors: static pressure, pump station or gravity fed system, etc... but I don't need any exact numbers but just a rough guess.

Would it be safe to say that there is ALWAYS going to be AT LEAST 10 GPM coming from ANY water source? Or 5 GPM? Or 20 GPM?

If regulations mandate that shower heads can not flow more than 2.5GPM, I can only think that I can assume there is more than 2.5GPM inside any given line.... but how much more? 5 GPM? 10 GPM?
 
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Old 03-06-06, 07:37 AM
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Water meters do not reduce pressure.They reduce volume. Pipe codes are based on the volume you need to fill the requirements of the fixtures.
1/2" pipe = 4 GPM
3/4" 8
1' 13
1-1/4" 23
Hope this helps.
 
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Old 03-06-06, 07:51 AM
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A meter is not a pressure reducer. A given size meter will have a MAX gpm is can deliver before it starts to cause a pressure drop. The GPM for any structure is determined by the usage.....how many bathrooms, how many kitchens, etc. SO. there is no one right answer. The required GPM are deterimined by the architect, or the plumbing contractor. The meter size and main service line size can then be specified.
 
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Old 03-06-06, 08:45 AM
grizzley
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Thanks for the answers!

Based on the reply from majakdragon, can I assume that any given structure would have at least 4 GPM? I'd imagine that 1/2" pipe is the bare minimum...right?

If not, what is GENERALLY the bare minimum any plumber would install? 1/8" inch? (I dont know pipe sizes) But that seems small and insufficient for a building with (let's just say) 4 sinks, a dishwasher, and 2 bathrooms.

Of course, if this is true, and was tested, all other water outlets/faucets would need to be closed except for the one where the test GPM test was being preformed?
 
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Old 03-06-06, 09:28 AM
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If the building had permits, it probably has at least 1/2" pipe entering. Thats really small and would not support the appliances you mentioned. Ratings are not given for just one fixture. ALL fixtures are taken into consideration. When I worked for the water division in Ohio, the minimum size for a service to a building was 1". Then a 5/8" meter was installed. Most codes allow 2 sinks on a 1/2" line. Many contractors run a 3/4" line and tee off with 1/2" for each fixture.
 
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Old 03-06-06, 09:42 AM
grizzley
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Good information. Thanks a bunch!

So, to recap (for my info)

PER CODE YOU WOULD SEE:

1/2" for 2 sinks
1/2" flows 4 GPM

If both sinks are ON, your getting 2 GPM at each of those fixtures.
If only ONE sink is ON, your getting 4 GPM at that one fixture.

.... and if the contractor uses 3/4" (which is likely) you will see more than 4 GPM at the one fixture. Or will 1/2" ONLY flow 4 GPM MAX no matter what? Which would mean the sentance before this one is false... you will NOT see anything more than 4 at any given fixture with a 1/2" pipe running to it.
 
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Old 03-06-06, 09:51 AM
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Yep. 4 GPM through a 1/2" pipe is the Max. It may vary a small amount depending on the type of pipe. Some have thicker walls but that is pretty close. If you have a 3/4" header with 1/2" to fixtures, when more than one faucet is turned on, you are still feeding the 1/2" with an 8 GPM pipe so you should get full volume at both 1/2" lines.
 
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Old 03-06-06, 01:56 PM
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Cool

Originally Posted by grizzley
Just a random question from an uneducated person....

I was wondering of anyone might know if there is a minimum GPM that is required to enter a structure? I think that most water meters reduce the pressure to a max of 80 - 100 PSI or so, and since most residential (and some light commercial buildings) are on 6-8" mains, how does that effect the overall GPM that is delivered into that building? If nothing is required, is there a usually "minimum"? I know there are several factors: static pressure, pump station or gravity fed system, etc... but I don't need any exact numbers but just a rough guess.

Would it be safe to say that there is ALWAYS going to be AT LEAST 10 GPM coming from ANY water source? Or 5 GPM? Or 20 GPM?

If regulations mandate that shower heads can not flow more than 2.5GPM, I can only think that I can assume there is more than 2.5GPM inside any given line.... but how much more? 5 GPM? 10 GPM?
Minimum GPM that enters a structure should be 15 GPM's thats a small house or small retail/commerical building.

If the main has 80 - 100 psi you need a pressure reducing valve because; most plumbing codes require one on pressure over 80 psi, and yes you do have a drop in pressure through a water meter due to friction lose, any licensed plumber that knows how todo a water calculation work sheet knows that.

The only times you will see 6" or 8" mains in commerical buildings is for fire protection sprinkler systems, domstic water is connected to the building main prior to the fire protection sprinkler system. If you are refering to the mains in the street they are at least 6" for fire protection, todays fire hydrants are all 6".

If your shower head is flowing @ 2.5 gpm's and you have 3/4" M copper for a supply to your bathroom there is 10 gpm's in that line after your shower is on.
 
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Old 03-06-06, 02:39 PM
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Plumbill,
What code did you see that REQUIRED a pressure reducing valve? I have worked in 3 States and never seen that. From the complaints in these Forums, I guess lots of other people have not heard of it either. I got the flow info from Ohio State University website.
 
 

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