Will This Improve My Water Pressure?

Before I start cutting up pipes, would this idea improve my water pressure noticably?

I have an older home with low water pressure in the second-floor shower on either hot or cold. Sink in same bath also has less flow than the downstairs fixtures. Flow is about 1.5 Gpm at either shower or sink.

The cold water supply and hot water tank are located in the basement. There are 1/2" copper pipes which run from the basement to the second floor bath. The toilet is fed by a smaller 3rd copper pipe (only 3/8") also run from the basement.

Somewhere under the upstairs bathroom floor, the hot and cold 1/2" pipes reduces to 3/8", as that is the size of the pipe I see connecting to the shower faucet when I peer behind the plumber's access panel. I suspect there is a "T" to 3/8" pipe for feeding both the shower and sink. The downstairs fixtures (kitchen and bath) are fed with 1/2" pipe and their flow is better as might be expected.

I don't want to rip up the bathroom floor (dining room celing) to replace the 3/8" pipe so here is my idea. I have 3/4" copper coming into the basement (city service) but it has been "T" 'ed almost immediately into two 1/2" pipe outputs. One side is capped off; the other side (1/2" copper) goes across the basement to the water heater. Here there is another "T" with 1/2" outputs. One feeds the inlet of the water heater, the other the home's cold supply.

Would there be any benefit to running a second 1/2" copper pipe from the capped off output (at the 3/4" pipe) and tying this directly into the inlet side of the hot water heater? So essentially the hot and cold supplies (still 1/2") are fed from separate sides of the "T" on the 3/4" pipe. Or do the laws of plumbing say I wouldn't notice any difference (?). Maybe the clothes washer (running both hot and cold) would fill faster. Maybe the 3/8" pipe in the upstairs bath is an overriding factor, and would diminish any benefit?

Finally, extending the 3/4 copper to the water heater would probably work also, but I think it may be easier for me (with little experience) to add a second 1/2" pipe in parallel rather than cut out the existing 1/2" pipe and try to snake around a larger pipe and be without water during that process.

Any help or suggestions greatly appreciated!

fwif, i just finished repiping my whole house. first time i ever did any sort of plumbing with copper, 1/2" and 3/4". turned out great, as inspected by a buddy of mine who works as a pipefitter. not much difference, i think, between 1/2 and 3/4. but get mapp gas, not propane. and practice a little. plenty of demo videos and advice here and elsewhere online.

Fluid dynamics laws state that velocity increases while flow decreases through a restriction, but pressure will stay the same. We learned this as kids when we put our thumb over the water hose to squirt our siblings. 1/2" typically runs to the shutoff valves under the sink, then 3/8" flexible lines connect to the faucet. I don't think showers get reduced below 1/2". Somehow you have flow restriction.

Condensed Explanation of Plumbing Issue

Thanks to those that replied. Here is a condensed version of my plumbing question. Any additional insights welcome.

Which of the following scenarios would provide better water flow at a shower which is fed with two 3/8" copper pipes? The faucet itself is 1/2" but it was attached via reducers to 3/8" pipe. It's an old house.

Scenario A
----------
The street-sourced 3/4 copper cold-water pipe is split into two 1/2" pipes. One of these is connected to the inlet of the hot water heater, the other feeds the household cold water circuit.

Scenario B
----------
The street-sourced 3/4 copper cold-water pipe is reduced to 1/2" pipe. This 1/2" pipe is split into two 1/2" pipes, and these two pipes connected as described in Senario A.

Currently my house is configured as Scenario B. Scenario A seems it would provide better flow - would plumbers agree? HOWEVER, due to the flow limitations of 3/8 pipe, would it be a meaningful increase at the shower? Am I correct in thinking that improved flow, if any, would only be noticed when both HOT and COLD are open at the shower (which is normally the case).

scenarios

I am having a hard time believing that ANY reasonable warm body, would run a 3/8" line ANYWHERE except from the wall to the faucet, even if you are referencing i.d. rather than o.d. Dynamic and static pressure are two different things. Dynamic pressure is a function of both volume and pressure which are affected by pipe size. Up to a certain point the larger the pipe the greater the volume and also the dynamic pressure AT THE faucet.

quinocampa said:

Fluid dynamics laws state that velocity increases while flow decreases through a restriction, but pressure will stay the same. We learned this as kids when we put our thumb over the water hose to squirt our siblings. 1/2" typically runs to the shutoff valves under the sink, then 3/8" flexible lines connect to the faucet. I don't think showers get reduced below 1/2". Somehow you have flow restriction.

Click to expand...

I disagree. As velocity increases, there will be a pressure drop (bernoulli principle). In this case you will encounter a loss of pressure due to friction etc

Huge difference in volume between 1/2" and 3/4" copper tube. You need 3/4" to your 2nd to last fixture, minimum.

Pipe Sizes

All the pipe sizes mentioned in my posts refer to what I believe is I.D. The pipes were measured using a set of standard open-end wrenches. It took a 5/8" wrench to fit around what I'm calling a 1/2" pipe, and a 1/2" wrench to fit around what I'm calling the 3/8" pipe which leads to the shower faucet.

I'm sill seeking an answer as to which scenario (A or B) would provide better flow, or if it wouldn't make a difference. Changing a pipe in the basement is something I could do very inexpensively, if it would help improve flow to the shower.

hj said:

I am having a hard time believing that ANY reasonable warm body, would run a 3/8" line ANYWHERE except from the wall to the faucet...

Click to expand...

Here's my theory. The previous homeowner had 6 children under one roof and I suspect he had a very miserly attitude toward his hot water bill. So it's possible a request was made to the plumber to intentionally restrict flow to the shower when the bathroom was undergoing renovation. This was years ago, possibly before water-saving showerheads were widely available.

The other theory is the plumber was a short on scruples but long on left over pipe, and figured no one would be none the wiser.

The effect will depend on the lengths of all the pipes involved. In general, your scenario A is preferable, although as you pointed out, the primary benefit would be when both hot and cold are flowing.

It is very difficult to predict how much of an improvement you will see, but increasing the pipe diameters in the basement is certainly a step in the right direction. You really should have 3/4" pipe running for both hot and cold lines in the basement. Replacing as much as possible will certainly help.

A short length of 3/8" pipe under the floor in the bathroom should not make it impossible to get a decent shower, if the rest of the piping is sized properly.

Thanks

jastori, thank-you for taking the time to analyze my particular plumbing situation and the two connection scenarios presented. I don't have much plumbing experience to draw upon so your well-reasoned response is much appreciated.

I had convinced myself that since the cross-sectional area of two 3/8" pipes is larger than a single 1/2" pipe, the water flow thru the 3/8" pipes is being limited by the 1/2" pipe in the basement that sources both hot and cold water. At least it seems that way intuitively. As you mention other factors such as length of pipe, and probably the rise of the pipe to the upstairs bath, come into play.

Ideally, I suppose a 3/4" pipe should go into the water heater, and exit the water heater. That would be a lot of re-work as everything at the water heater is 1/2" pipe now, as is 99% of the house. Plenty of water at all fixtures except the shower is a little weak. So if I enlarge the section of 1/2" pipe in the basement that sources both hot and cold water I'm thinking that the 3/8" pipes under the bathroom floor will then operate at maximum capacity.

Just wanted to get a second opinion before I begin cutting. Thank-you!