"sweaty" cold water supply pipe

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The humid weather is resulting in "sweaty" cold water pipes in our basement.
I have read the suggestion to insulate the pipes just like with hot water pipes. However, I am concerned that while this may reduce the sweating, there still will be some condensation, but now the condensation will be trapped against the pipe.
Should I be worrying about this? If so, what should I do to minimize the potential for mildew and mold in this trapped moisture?
Second, I find that the condensation only occurs on the first few feet of pipe in from the grounde. Is it possible that conduction causes the water in the first few feet of pipe to stay cold all the time leading to heavy condensation while beyond that the water for the most part has warmed up (except when the water is actively running) so that there is much less active condensation?
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Pawlowski is, again, correct. The water on the pipe surface comes from the air. Thus, a well sealed insulation jacket will not allow moisture to fomr on the pipe. TB
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And it may increase the water heating bill.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Not in any measurable way. I assume you are meaning the heat the cold water picks up in the line while waiting for some draw. It is minimum. Even a few degrees rise in a pipe run of 40 ft doesn't add up to a sneeze.
Harry K
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I disagree.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Care to expound on why? The amount of water contained in a 3/4" pipe say 20 ft long is not very much. About 5 cu in/ft (after heavy rounding off) unless my long ago math is out of whack. Water in the cold intake pipe also doesn't usually sit there long enough to pick up much ambient heat.
Harry K
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I get 0.19 lb/ft, so 20' would hold 3.8 pounds.

That depends on how fast the heat flows... 20' of 3/4" pipe has about 4 ft^2 of surface. With still air and no condensation, it might have a thermal conductance G = 1.5x4 = 6 Btu/h-F, so the time constant RC = C/G = 1 hour, ie a 3.8 lb slug of water would warm from 50 to about 57 F (1/e th of the way to 70) in 1 hour in a 70 F room.
Recall Charlie Wing's TV show in which he built a tempering tank in a basement, a 20' length of 6" PVC pipe tucked up under the rafters? Well pressure tanks can warm water too.
And condensation might raise G to 1000, so flowing water can warm to the dew point in real time as it moves along the pipe. As I recall, the OP described "a few feet" of condensation near the pipe entrance. I don't recall that the entire pipe had condensation when water was flowing. If not, the pipe warmed flowing cold water to the dew point.
With no cold water pipe insulation, we have 4 potential savings in water heating: the small warm slug of still water before flow begins, the large flowing gain to the dew point, the small flowing gain from the dew point to room air, and the effect of having warmer cold water at a sink or a shower, which can allow using less hot water in a mix to achieve a certain temperature. The latter may come from a lot more cold water pipe in the house, unrelated to the pipe that goes into the water heater. Harvard physicist William Shurcliff has written about these savings.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Good discussion of the -theorectical- savings. Just how much savings dollar wise do you think it comes down to in practical life? You won't see it on your power bill. Most of your warming is coming from having water stand still in the pipe for long periods. That doesn't happen in an active house. The tempering tank could have some small advantage. I wonder about the well tank (basically same as tempering tank). Think I will test my incoming water temp as opposed to the tank out temp after sitting all night.
Harry K
Harry K
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The biggest might be from condensation on active pipes. If we spend (say) 50K Btu/day warming 1000 pounds of 60 F well water to 110 in a water heater, and insulating the cold water pipes lowers the 60 to 50, we have to spend 1000(110-50) = 60K Btu/day, ie 20% more, eg 10K/3412 = 2.93 kWh/day or 1070 kWh/year, eg $107 at 10 cents/kWh.

I disagree.
Nick
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Nick, according to my calculations, there 5.3 cubic inches of water in a foot of pipe, that is equal to .0229 gallons. At 8.33 pounds per gallon, that is .191 pounds of water per foot of pipe. Assume 10 feet of 3/4" pipe that sweats that is 1.91 pounds of water. To warm that from 40 degrees incoming temperature to 70 degrees, at 1 BTU times 30 degrees times 1.91 pounds = 57.3 BTUs. At 8 cents per therm (100,000 BTUs) the cost savings gained by leaving the insulation off is.0045 cents every time you have to warm the water in the pipe. If the people in the house use the water 40 times each day, the total savings per day is .183 cents per day. Times 30 days per month is 5.49 cents (per month). Nick, that is not enough to worry about. Even if you allow for inefficiencies, it is still less than 10 cents per month. Nick, that is not worth the time I just spent on it. Or do I need to write that into a BASIC program to get the point across to you?
Stretch
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Stretch wrote:

Thanks. My last physics was in HS 50 years ago. I was beginning to think I'd have to do some real research to make the point. I was running off of common sense and practical application. There are a lot of things out there that look good in theory but don't work out in practical application. Of course Nick can argue that any savings is worth it but to me dripping pipes trumps that one.
Harry K
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Common sense and practical application don't seem to apply with Nick. His math may be correct, but his assumptions often go awry. He has some interesting points, but if he had customers that had to live with his assumptions, he would soon go broke.
Stretch
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We all seem to agree on that.

And that...

Yes...
You can buy oil for 8 cents a gallon? :-)

I make this 0.115 cents at $2/gallon.

And 4.6 cents/day.

And $1.37/month.

You might check your math for glaring errors and read more carefully. I said this savings is small compared to warming an active pipe with condensation, which might save 20% on a water heating bill.
And you might modify your arrogant attitude and be more polite. Apologizing is optional.
Nick
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Nick, You assumed oil heating the water, I assumed gas. Although my gas rates may be off a bit, he did not say what he is heating the water with. Also the calculations assume the water is completely warmed to room temperature each time, which is not likely. There are a lot of suppositions involved here, most of them are overblown. The daily savings are likely exagerated to the extreme. Also, pipe insulation slows down the rate of heat transfer and increases the area of surface area exposed to ambient conditions. It does not stop heat transfer. As well, as the temperature in the pipe approaches room temperature of the basement, heat transfer slows down, so it will take too long for all this heat transfer to tane place. Certainly each complete temperature change is not likely to take place in in 36 minutes. So an apology is not likely. Still not enough cost to worry about.
Stretch
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Stretch wrote:

Even using Nicks figures there is a glaring assumption that way inflates the figures. Although you did point it out, I will do so again. Water in the intake pipe is -not- going to warm up to ambient in less than several hours. In my house with just the two of us, water in that pipe will only remain there until the pump kicks in again. Given normal useage that will occur at least once per hour, oftener when watering. In a house on city supply, there will be an exchange of water in that pipe any time a faucet is opened or toilet flushed, etc. That will occur several times/hour for zero savings.
I am on oil for heat, electric for water heating.
Harry K
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There was no such assumption.
The important savings happens when flowing water is completely warmed to the dew point by condensation in real time.
Nick
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A factor of 10, but that was the UNportant savings...

No. Please reread them more carefully.
Nick
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Nick, If gas is that expensive in your area, maybe you should move here! :-)
Stretch
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A factor of 10, but that was the UNportant savings...

No. Please reread them more carefully.
Nick
OK Nick, you got me on this one! I WAS off by a factor of 10 on my gas costs. Please pass the salt with the crow!
CHEW, CHEW, CHEW, CHEW, ..... Boy, this stuff is tough!
Stretch
CHEW, CHEW, CHEW, CHEW....................
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:-)
Now you might ask yourself what's really going on here:

I think the OP is saying the incoming water is warming up to the dew point of the basement air. If condensation never occurs beyond the first few feet of pipe, even when water is flowing, the pipe is warming flowing water in real time, which is a much more important saving than the warming of small amounts of water between uses.
Nick
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