How many gallons of water in a 10 foot length of 1/2" copper.. is my math correct?

Lithnights · Mar 3, 2006

I am trying to figure out how many gallons reside in a 10 foot piece of 1/2" copper pipe.

I have researched and learned that the inside diameter of 1/2" pipe is actually .545 inches.
Thus the radius is .2725 inches
Thus the Area = Pie x r squared... thus 3.14 x .2725 inches x .2725inches = .23 square inches
Thus the Volume = Area x length... thus .23 square inches x 120 inches = 28 cubic inches in 10 foot length

1 cubic foot of water = 7.48 gallons
1 cubic foot = 12x12x12 = 1728 cubic inches

28/1728 = .0162 .0162x7.48 = .12 gallons

So does it sound right that in a 10 foot length of Â½â€ copper, that only .12 (about 1/10) gallons is sitting in there? I checked the math but it still seems a bit low. If so, can you see where my math is incorrect?

Thanks,

Mike Swearingen · Mar 3, 2006

And that depends on if the 1/2" copper pipe is Type M, L or K.
(I aint even touching the math.) LOL
Mike

Sponsor · 2022-01-29T12:20:58-0800

Finnegan · Mar 3, 2006

I have no idea on the math, but that sounds about right. If you are motivated to test your math, you can always cap a 10' length of pipe, fill it up and dump it into a measuring cup.

hj · Mar 3, 2006

capacity

It is actually about an 1/8th of a gallon, or a pint, so that seems about correct.

Lithnights · Mar 4, 2006

I am assuming L.. K is a tiny bit difference in inside Diameter from what I've read.

I figured nobody would touch the math, I'm surprised I spent the time but I'm a numbers guy so it wasn't too too bad. But it appears that the result seems about right.

And .12 gallons is actually about 1/8 (.125) gallons, which is what HJ stated. So it appears right.

With that said..

Let's assume our kitchen sink faucet is 40 feet (of 1/2" copper pipe) from our hot water heater.
Also assume that all the hot water in the hot water line has cooled down to room temperature (hasn't been used all day).
Are we saying that when we turn on the hot water, we are flushing out 1/2 gallon (.125 x 4) of cooled water to get to the hot water?

Thanks all!

Breplum · Mar 4, 2006

Water and Energy Waste

The consequesces of waiting for hot water to arrive has been estimated by Gary Klein with the California Energy Commission, in calculations that he presents at training seminars. Assuming 20 million existing homes, the total combined costs for water, waste water treatment and energy is $200 million in California, $2 Billion per year nationally.

It only amounts to about $130 per household annually with gas WH, ($268 with electric WH), but multiplies into a serious waste of resources.

We promote hot water recirculation on every job and even discount the costs as a way to sweeten the appeal.

From standard pipe tables 1/2" Copper type M Pipe:
.0132 gal/ft. or 76 ft./gal.

hj · Mar 4, 2006

water

lithnights said:
I am assuming L.. K is a tiny bit difference in inside Diameter from what I've read.

I figured nobody would touch the math, I'm surprised I spent the time but I'm a numbers guy so it wasn't too too bad. But it appears that the result seems about right.

And .12 gallons is actually about 1/8 (.125) gallons, which is what HJ stated. So it appears right.

With that said..

Let's assume our kitchen sink faucet is 40 feet (of 1/2" copper pipe) from our hot water heater.
Also assume that all the hot water in the hot water line has cooled down to room temperature (hasn't been used all day).
Are we saying that when we turn on the hot water, we are flushing out 1/2 gallon (.125 x 4) of cooled water to get to the hot water?

You used the figure for "L" copper. Since the differences in diameter affect the outer circumference, the reduction for "K", or the increase for "M", can be significant. Actually more than that, since the pipe itself will be cool so the water also has to heat the pipe, and the air around it, as it passes through it. If this is a slab house and the pipe is buried underground, then you also have to heat the earth that is in proximity to the pipe.

KorasDad · Mar 4, 2006

It's actually 0.102 gallons. The formula goes something like this... Paste this into your excel sheet and put the pipe diameter in the A4 cell and length in feet in the B4 cell... This calculation assumes nominal internal diameter is used.
=((3.1416*((0.5*A4)^2))*(12*B4))/(1728/7.482366)

Regards, KorasDad

Lithnights · Mar 6, 2006

KorasDad said:
It's actually 0.102 gallons. The formula goes something like this... Paste this into your excel sheet and put the pipe diameter in the A4 cell and length in feet in the B4 cell... This calculation assumes nominal internal diameter is used.
=((3.1416*((0.5*A4)^2))*(12*B4))/(1728/7.482366)

Regards, KorasDad

Looks good, that's basically what I have set up in Excel except I used the actual internal diameter where you used the nominal diamater. I plug in .545 (actual diameter) into your formula and I get my .12. Beautiful.

Thanks,

Lithnights · Mar 6, 2006

hj said:
lithnights said:

I am assuming L.. K is a tiny bit difference in inside Diameter from what I've read.

I figured nobody would touch the math, I'm surprised I spent the time but I'm a numbers guy so it wasn't too too bad. But it appears that the result seems about right.

And .12 gallons is actually about 1/8 (.125) gallons, which is what HJ stated. So it appears right.

With that said..

Let's assume our kitchen sink faucet is 40 feet (of 1/2" copper pipe) from our hot water heater.
Also assume that all the hot water in the hot water line has cooled down to room temperature (hasn't been used all day).
Are we saying that when we turn on the hot water, we are flushing out 1/2 gallon (.125 x 4) of cooled water to get to the hot water?

You used the figure for "L" copper. Since the differences in diameter affect the outer circumference, the reduction for "K", or the increase for "M", can be significant. Actually more than that, since the pipe itself will be cool so the water also has to heat the pipe, and the air around it, as it passes through it. If this is a slab house and the pipe is buried underground, then you also have to heat the earth that is in proximity to the pipe.

Click to expand...

How would one know if their pipe is L, K, or M? It is running through my basement (I can see it all) in my 40 year old house... is that likely one kind over another? Or does it state on the pipe somewhere what it is...? just curious..

Cass · Mar 6, 2006

I'm curious. Why do you need to know the info. requested about how much water is in the pipe?

hj · Mar 6, 2006

grade

"M" will have a continuous red line on the side of it, "L" will be blue, and "K", which is unlikely, will be green. The lines are fairly durable so your tubing may still have the marking.

Lithnights · Mar 6, 2006

Cass said:
I'm curious. Why do you need to know the info. requested about how much water is in the pipe?

Trying to figure out how much water I am wasting by heating up water, having it sit there all day and cool down, then running the hot water waiting for hot water to get to the faucet again later that day. My newly constructed master bath takes way too long to get hot water so I am analyzing the option of installing a recirculation system.... that analyzing includes figuring how much water I am wasting waiting for hot water to get there...

Lithnights · Mar 6, 2006

hj said:
"M" will have a continuous red line on the side of it, "L" will be blue, and "K", which is unlikely, will be green. The lines are fairly durable so your tubing may still have the marking.

Thanks I will take a look.

Cass · Mar 6, 2006

If your basement is not finished and you can change over to plastic that will save you more energy as you won't have copper to be drawing away the heat and the hot water will get to the fixture faster, less waisted water due to this. Heat loss due to cool down in the line when you stop using hot water will be the same reguardless of the kind of pipe.

Bob NH · Mar 7, 2006

Save money

"Trying to figure out how much water I am wasting by heating up water, having it sit there all day and cool down, then running the hot water waiting for hot water to get to the faucet again later that day. My newly constructed master bath takes way too long to get hot water so I am analyzing the option of installing a recirculation system.... that analyzing includes figuring how much water I am wasting waiting for hot water to get there..."

There is a way to solve the problem, but it is not sufficiently complicated to make a lot of money for the business. Since you seem to be mathematically inclined, here it is to prove it for yourself.

First, realize that a recirculating system is simply a way of making up the heat that is lost. In fact, it makes more heat available to be lost because it keeps the pipe hotter and usually adds another pipe which will be at least warm.

Now compare that with a small 2.5 gallon point of use heater, such as the Ariston GL2.5 installed in the hot water line at your master bathroom. They operate on a 115 Volt 15 Amp circuit and cost about $140 on the internet.

When you turn on the hot water, you have instant hot water while that 0.5 gallon of water in your pipe gets from your big heater to the point of use heater. Nothing lost down the drain waiting for it to get hot. The temperature will drop a little, but not so much that it is not usable and your shower control valve will control temperatre. After 0.5 gallon of use, your big hot water heater is feeding the POU heater and your bath/shower.

Now this is not nearly as expensive or impressive as a complicated instant heater, or even a recirculating system, so if you are out to impress people this is not the solution. But it works and is an easy do-it-yourself job if you are so inclined. Also, it really saves energy (=money) over a recirculating system which is actually heating up your house and increasing the load on the air conditioning.

It will also cost a lot less than repiping with plastic pipe, which is itself an issue and which will slightly reduce but not eliminate the problem and which is not as effective a bit of that black foam insulation that you can buy at HD.

So do your analysis and pick your poison.

Master Plumber Mark · Mar 8, 2006

pick your poison

That's a good way to put it... pick your poison

Because you are only going to save a few pennies per month
either way you do this ,

Yes maybe I am wrong and if you
do the math, divide by the hypotunuse of the type of
copper...by the length of the run, the angle of the dangle divided by
the heat of the water ... ect

you might save a dozen QUARTERS a month...

Why not just insulate the pipe run and forget about it...

If you really want to save money--energy you are really
looking down the wrong path to do it ..

Their is only soooo much you are gonna squeeze out of this
turnip before it is simply not cost effective.

To really save money-energy INSULATE the ceiling of your home extra deep
put extra insulation in the walls.....THAT is the best place to save the big money.

Don't worry so much about that .12 gallon of heated water...

The real heat loss is in the water heater itself, why not insulate it with a blanket?? It is supposed to save about %25 per year doing this...

as BOB NH said, pick your poison

Lithnights · Mar 8, 2006

Bob NH said:
"Trying to figure out how much water I am wasting by heating up water, having it sit there all day and cool down, then running the hot water waiting for hot water to get to the faucet again later that day. My newly constructed master bath takes way too long to get hot water so I am analyzing the option of installing a recirculation system.... that analyzing includes figuring how much water I am wasting waiting for hot water to get there..."

There is a way to solve the problem, but it is not sufficiently complicated to make a lot of money for the business. Since you seem to be mathematically inclined, here it is to prove it for yourself.

First, realize that a recirculating system is simply a way of making up the heat that is lost. In fact, it makes more heat available to be lost because it keeps the pipe hotter and usually adds another pipe which will be at least warm.

Now compare that with a small 2.5 gallon point of use heater, such as the Ariston GL2.5 installed in the hot water line at your master bathroom. They operate on a 115 Volt 15 Amp circuit and cost about $140 on the internet.

When you turn on the hot water, you have instant hot water while that 0.5 gallon of water in your pipe gets from your big heater to the point of use heater. Nothing lost down the drain waiting for it to get hot. The temperature will drop a little, but not so much that it is not usable and your shower control valve will control temperatre. After 0.5 gallon of use, your big hot water heater is feeding the POU heater and your bath/shower.

Now this is not nearly as expensive or impressive as a complicated instant heater, or even a recirculating system, so if you are out to impress people this is not the solution. But it works and is an easy do-it-yourself job if you are so inclined. Also, it really saves energy (=money) over a recirculating system which is actually heating up your house and increasing the load on the air conditioning.

It will also cost a lot less than repiping with plastic pipe, which is itself an issue and which will slightly reduce but not eliminate the problem and which is not as effective a bit of that black foam insulation that you can buy at HD.

So do your analysis and pick your poison.

A point of use heater sounds intriguing. I will do some research on this. And the only person I'm trying to impress here is my wife.

Also, I have every foot insulated with the black foam insulation already. Just trying to be even more efficient if possible.

Thanks,

Master Plumber Mark · Mar 9, 2006

You will never will impress your wife....

That is your first mistake ----

Trying to impress your wife......

She already KNOWS you are nuts.....

That is like Barney Feif trying to impress Andy Griffith on Mayberry....

Just keep trying to impress her and

You are going to do the exact opposite

Good luck with that poin tof use idea...

Lithnights · Mar 15, 2006

For my actual master bath, I'm really looking at a total run of about 50ft of 3/4 copper so the sitting water is almost 1.5 gallons every time we want hot water. I guess I thought that was a lot but perhaps not worth my worry.

Water waste aside, I would like to get almost instant hot water so perhaps the point of use heater is a possibility in that respect.

Also, I have already insulated every foot of copper I could with black foam insulation AND I have recently put on an insulation blanket on the heater AND last fall I completely covered my existing R19 attic insulation with R25 on top.

I think I have OCD with efficiency. Make me stop...

Thanks for all the feedback.

How many gallons of water in a 10 foot length of 1/2" copper.. is my math correct?

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