Some musings about copper pipe

[chuckthin]

I replumbed the entire house when I remodeled 12 years ago. Used type M copper pipe throughout.
Some simple arithmetic shows that to get hot water to the kitchen sink - or to a 1/2 bath at that end of the house we are heating 10 lbs of copper pipe each time we wash our hands or rinse a cup.
I am thinking about replacing the copper hot water pipe with Pex. The heat loss would be much less so less energy used, we would get hot water sooner and we'd use less water.
The water lines are exposed and run across the joists in the cool basement so it would be an easy job to run the pex in the same pipe hangers that the copper is in.
I have the skills and the pex tools so it would be afternoon's work and maybe $60 in parts.
I'm thinking it's worth doing but what says the brain trust here?

OK so I ran 1qt. cold water which is 1/2 pex and it took 13.21 sec.
I then ran hot water and it took 13.49 sec. and it was hot in 6 sec.
My 3/8 run is 9 ft from heater.
Used same faucet and it has 1/8 in hole at exit.

 

[BarnyardEngineering]

Mostly faster hot water.
But faster hot water would also give an energy savings and use less water.
I'm not disagreeing with anyone here.
But here is my thinking:
Yes, I will insulate the pipe after I install the pex.
Should have done that long ago.
First, the basement is pretty cool - about 60 degrees in winter. Yes, the insulation will keep the pipe warmer longer.
But after the water in the kitchen has been unused for several hours, insulated or not the pipe will inevitably cool down to 60 degrees.
Second, I was able to compute the total weight of the copper pipe I'm warming - it's about 10 lbs. I did not find specs on the weight of pex.
However, go to Home Depot and grab a 10' stick of copper pipe in one hand and a stick of pex in the other.
I'm guessing the pex weighs 1/4 to 1/3 of what the copper weighs. So I would be warming 66-75% less weight in pipe which might? speed up getting hot water where I want it - might? use a wee bit less energy and - might? use a little less water.
Is it worth doing?
I don't know.
But I'm willing to spend a few $ to experiment even if it is wasted.
I've wasted more $ on dumber things before.
Just look at the old tractors and junk I have.

The pipe doesn't have to be "hot water" temperature before hot water will come out of the faucet, though. This whole notion of "warming up" the pipe doesn't really happen in any considerable way unless you run the hot water for a long time, but usually not until AFTER you're done using the water. "Warming up" the pipe has negligible effect on how quickly the hot water reaches the faucet.

Try it yourself. Have someone upstairs on the kitchen sink turn on the hot water and shout the moment they feel hot water. Then you touch the pipe downstairs. It will be barely warm, nowhere near hot.

You're chasing the wrong thing here. Changing to pex won't appreciably shorten the amount of time it takes for the hot water to reach the sink, when both pipes are the same diameter.

 

[Janicholson]

The pipe doesn't have to be "hot water" temperature before hot water will come out of the faucet, though. This whole notion of "warming up" the pipe doesn't really happen in any considerable way unless you run the hot water for a long time, but usually not until AFTER you're done using the water. "Warming up" the pipe has negligible effect on how quickly the hot water reaches the faucet.

Try it yourself. Have someone upstairs on the kitchen sink turn on the hot water and shout the moment they feel hot water. Then you touch the pipe downstairs. It will be barely warm, nowhere near hot.

You're chasing the wrong thing here. Changing to pex won't appreciably shorten the amount of time it takes for the hot water to reach the sink, when both pipes are the same diameter.

I disagree. The heat transfer of copper is a reflection of its atomic structure and conductivity. Copper has very great conductivity compared to PVC. It takes much less heat to change copper than it does PVC. Heat a copper pipe to 200 degrees on one end, and compare that to a PVC pipe of similar mass heated the same. You would drop the copper way before the PVS if held on the opposite end from the heat. Not only does it transfer heat, it takes little heat to rais its temperature. (specific heat) compared to PVC.

copper is 413 watts/meter one of the highest conductivity , PVC is .19 watts/meter Jim

 

[DoubleO7]

I expect improper joints.

Erosion of the copper and/or joints is dependent on the water ph, city water chemicals, etc.

 

[Frank(Mi.)]

I still say the recirculating pump with a timer is the best way to get what you are after...

 

[NoDakInMN]

Frankly, the energy savings are so miniscule that it isn't worth doing anything. The amount of heat to raise 10# of copper from 70 degrees to 120 degrees is 45 BTU. 10# of 1/2" M copper equals about 50' and that would hold .6 gallons of water. It takes 30 BTU to raise that much water the same amount of temperature. Assuming it is an electric water heater, 75 BTU takes .0219 KW.

So you would have run the water until it is warm at least 45 times to use 1 KW of electricity. But it would probably take more than that because the water and copper probably would not completely cool down between uses and you most likely have the water heater set cooler than 120 degrees. And since the cost of a KW varies, but usually runs around 10 cents per KW, you would be going through a lot of time and expense to save around 60 cents a month.

 

[BarnyardEngineering]

I disagree. The heat transfer of copper is a reflection of its atomic structure and conductivity. Copper has very great conductivity compared to PVC. It takes much less heat to change copper than it does PVC. Heat a copper pipe to 200 degrees on one end, and compare that to a PVC pipe of similar mass heated the same. You would drop the copper way before the PVS if held on the opposite end from the heat. Not only does it transfer heat, it takes little heat to rais its temperature. (specific heat) compared to PVC.

copper is 413 watts/meter one of the highest conductivity , PVC is .19 watts/meter Jim

None of that matters in this case because it all ignores the time factor, and time is what we're concerned with here.

Copper is more conductive, but, it won't pull enough heat out of the water to make an APPRCIABLE difference in how long it takes the hot water to reach the kitchen sink. You will not notice the fraction of a second difference.

 

[NoDakInMN]

None of that matters in this case because it all ignores the time factor, and time is what we're concerned with here.

Copper is more conductive, but, it won't pull enough heat out of the water to make an APPRCIABLE difference in how long it takes the hot water to reach the kitchen sink. You will not notice the fraction of a second difference.

While you are correct, but time isn't the real factor, energy savings is. And the simple truth is, that for all the nitpicking, and don't get me wrong, as an intellectual exercise, nitpicking can be fun, there simply isn't a payback in energy savings that make the effort anything more than a fool's errand. We are talking about tiny fractions of a kilowatt. The rule of thumb for energy savings is that it should pay itself off in 3 years. So unless he can do for less than $20, including giving credit for his time, it is just not worth it.

 

[Janicholson]

While you are correct, but time isn't the real factor, energy savings is. And the simple truth is, that for all the nitpicking, and don't get me wrong, as an intellectual exercise, nitpicking can be fun, there simply isn't a payback in energy savings that make the effort anything more than a fool's errand. We are talking about tiny fractions of a kilowatt. The rule of thumb for energy savings is that it should pay itself off in 3 years. So unless he can do for less than $20, including giving credit for his time, it is just not worth it.

The only thing I think worth considering is to install a circulation pump and return line to the input pipe of the water heater. Included would be a timed run cycle and push button at the sink for the user to push. This would make the heated water flow faster than through the (likely) restricted faucet, and save the water from being wasted. Wasted water can be a major issue, I have lived in AZ and Montana where water was carried to homes every week in 500 gallon or larger tanks for consumption. Often being the only water, or only potable water. Jim

 

[BarnyardEngineering]

While you are correct, but time isn't the real factor, energy savings is. And the simple truth is, that for all the nitpicking, and don't get me wrong, as an intellectual exercise, nitpicking can be fun, there simply isn't a payback in energy savings that make the effort anything more than a fool's errand. We are talking about tiny fractions of a kilowatt. The rule of thumb for energy savings is that it should pay itself off in 3 years. So unless he can do for less than $20, including giving credit for his time, it is just not worth it.

Selling the copper pipe he removes as scrap may well pay for the pex and fittings to replace it.

 

[Mark-Mi]

With just two of you living in the house, the best energy savings for you would be to install a on demand water heater.
And yes I know that's not what he asked about.

 

[Ultradog MN]

I have been up north cleaning up a piece of property I'm selling. Two old semi trailers had to go and a bunch of other junk laying around that the buyers want gone before the closing.
So this hot water project has been put on hold. I will get back to it and will do that test I talked about in an earlier post.
Might be a while but I will reread this thread and make an update with my findings when I get back to it.
Thanks to all.

 

[LTCMIKESR]

OMG! Wow, so much knowledge. In high school, belonged to local Ham Radio club. Guys dad’s generation but lots of them were professional engineers. They were on my personal teenage idol list! Didn’t get thru engineering but went to USU (Uncle Sam’s University-Army) Those fellows got me hooked on technical knowledge + EDUCATION!

 

[JMOR]

My personal experience with pex & mice

 

[olddavid]

I had ordered the PEX and fittings to redo the feed line under my mobile home when I stumbled on a thread about how mice like PEX. Fortunately, I was able to cancel the order. Not a good plan for exposed plumbing like that.

 

[Ultradog MN]

I have been up north cleaning up a piece of property I'm selling. Two old semi trailers had to go and a bunch of other junk laying around that the buyers want gone before the closing.
So this hot water project has been put on hold. I will get back to it and will do that test I talked about in an earlier post.
Might be a while but I will reread this thread and make an update with my findings when I get back to it.
Thanks to all.

I'm about to start on this waterline stuff again.
I posted about a shower curtain rod a few days ago and today I can show a hole I made in the floor. All three are related to finishing this bathroom and a bathroom needs water for it to work properly.
Am ambivalent about replacing 40' of copper hot water line - that's only 14 years old and works fine - for the sake of a hunch or theory. Then again, faster hot water to what will be 3 sinks on that end of the house?
Hmmm...
The new stuff will go in in pex of course. Not one mouse since I came here.
The squirrels did eat the acetylene hose on my torch in the garage tho. Twice!

 

[showcrop]

My personal experience with pex & mice
View attachment 67461View attachment 67461

Was there any reason for the mice to eat it? As in where the PEX passed through a wall that the mice wanted to get through?

 

[olddavid]

Was there any reason for the mice to eat it? As in where the PEX passed through a wall that the mice wanted to get through?

That's a good thought as I had mice gnaw on a Romex wire eventually opening the neutral and I think it was to enlarge a hole that the wire fed through. Having said that, mice just like to gnaw on stuff and some things suit their tastes better than others.

 

[Gary Mitchell]

Why would anybody care? Because this is a community, and we all help each other. One asks for help in an area out of his/her area of expertise, and those with more experience will give him/her helpful information. THAT is why I or anybody else CARES!!!!

The man asked a legitimate question. Why are you jumping his azz? gm

 

[SARG]

Another advantage of being at the end of the rainbow .......... You no longer "spend dollars to save dimes" ........... because when you realize you're in your last decade you know you'll never break even.