Stupid pipe insulation questions

So I'd like to install some pipe insulation on my heating and domestic hot water pipes to save energy, and I have some really dumb questions.
First, how big is a 3/4" pipe? I assumed the heating hot water pipe leaving the boiler was 3/4" and the return was 1/2", but then I tried measuring them. I measured the circumferences with a piece of string and then divided them by pi, and came up with about .9" and .6" respectively. Is the exterior diameter of 3/4" pipe actually some other size, like how a treated 2x4 piece of wood is actually smaller than 2" by 4"? What diameters are common in the U.S.? The insulation for 3/4" pipes seems to have an interior opening of about 1" -- is there extra room for irregularities?
I heard from a plumber that black foam pipe insulation is useless and doesn't even have an R value, and that I should get the paper-wrapped fiberglass insulation instead. Is this true?
What precautions do I need to take when dealing with fiberglass? Are rubber gloves enough? What's the best way to cut it?
Thanks, Apr
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I can't speak about the value of foam rubber pipe insulation, but as to the outer diameter of pipe, it really depends on the pipe type. Galvanized pipe has thick walls and copper pipe has thin walls. But I think galvanized 3/4" pipe is about an inch in diameter. 1/2" is about 5/8" or 3/4" in diameter. Doesn't really matter that much except for when drilling holes. Even 3/4" PEX tubing is about an 1" in diameter.
As to working with fiberglass, wear a mask, eye protection, and leather or rubber gloves and long sleeves. That stuff is terrible to work with and if you don't wear a mask you'll be hacking it up for hours.
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On Jul 6, 8:09 pm, snipped-for-privacy@hotmail.com wrote:

Pipe sizes are nominal, not absolute. As far as everything else, what Eigenvictor says. Have Fun.
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Before you do, think about the situation. Where do the pipes run? Are they in a place that you do not want to heat? If so, insulation may help. Are the pipes in the basement where you want at least a little bit of heat? Then leave the insulation off.
In most basement piping setups, heat that is "lost" from the pipes goes into the rest of the house that you are going to heat anyway, so there is no loss, no energy savings to be had. If they are in a crawl space that you don't want to heat, there will be savings.
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What do you think you'll save? The pipes coming out of the boiler - if they're not insulated, what's the difference? The heat they radiate is keeping some part of the house warm. Waste of time & effort here.
Now, the hot water heater, I can see a need there. But I wouldn't bother with insulating the pipes, I'd build a heat trap. They're far more effective. I don't care for the screw-in heat traps you can buy at the local plumbing shop, I think they'll fail after a few years so I built one out of copper pipe. It is nothing more than a loop. Simple physics says this will work always and with no moving parts, it won't break, rattle or do anything other than work properly. I only made one, for the hot side. But if you're after saving the extra 1% of heat, put one on the cold side as well. It wasn't real easy to do on mine and not really necessary anyhow.
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Here is a chart for pipe sizes.
http://techcalcs.com/technical/pipetable.php
Yes, it is like the 2x4 s except instead of smaller, they are bigger. The actual size also depends on the thickness of the pipe usually referred to as schedule or SCH in the chart. That is usually a number and sch 40 is probably what you have in the house . It could be 80 as that is the two most common.
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I measured the circumferences with a piece of string

(Amazon.com product link shortened)83814248&sr=1-61
Its better to use one of this to measure inside and outside diameters.
I have an ok one in the shop and a cheap one from the dollar store in the glove compartment of my truck.
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1/2" copper 5/8" OD , 3/4" 7/8" OD ( outside diameter) Then you have to decide how thick of insulation you want I would suggest 1". I would wear some light cloves, dust mask, long sleeves. The insulation is cut with a knife ( butcher knife) They make a special tape for the insulation joints the have plastic 90tys that you stuff with insulation. It's really pretty simple to do, you might have to notch around pipe hangers, joist. http://www.owenscorning.com/comminsul/products.asp?product '3
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But http://techcalcs.com/technical/pipetable.php says that 1/2" pipe has an outer diameter of 0.840", and 3/4" pipe is 1.050". Who is right? And which size pipes are the ones I have which measure .6" and .9"?
-Apr
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On Jul 7, 11:46 am, snipped-for-privacy@hotmail.com wrote:

1/2" copper 5/8" OD , 3/4" 7/8" OD ( outside diameter)
But http://techcalcs.com/technical/pipetable.phpsays that 1/2" pipe has an outer diameter of 0.840", and 3/4" pipe is 1.050".
Who is right?
Apr-
Short answer........ both are correct
Dave's answer is for copper "tube" which is what I think you have
steel, brass, stainless, PVC "pipe" has the dimensions given in

Here's my best answer based on the info........you do not have "pipe" you have copper "tube" 1/2 (5/8 od) & 3/4 (7/8 od)
also short answer on the foam...
its fine & foam (5/8" wall thickness) will give you about R4 which is plenty unless you're running a constant loop through unheated space or air conditoned space
I tried to post this last night but it wouldn't go.
it's LONG but correct & thorough
When you describe "pipe" or in your case "tube" ,,,,,,,,,, you have to give the material it is made from as well
When I first saw your the results of you od measurement / calc..... I thought "man those numbers are really off!"
but taking another look they might be ok
galv steel pipe nominal 3/4" 1.049" od nominal 1/2" .840"od
what I think you've got is copper tube
copper tube nominal 3/4" ,875" od nominal 1/2" ,625" od
these numbers correlate well with your string measurements
check out the info in the McMaster catalog www.mcmaster.com
when you dig all the way down to the single item level....they'll give you a tech drawing with real dimension on it.
domestic water plumbing done in copper is done with copper tubing.....it is incorrect & confusing to call it "pipe"
Now as for insulation,,,,,,since the od's for 3/4" pipe & 3/4" tube are fairly close the foam stuff is made to fit both. I'm not sure if the insulation for 1/2" is different for tube or pipe.
Whether it's worth the effort & cost is matter of the particular situation.
for example if the hot water runs through a basement & you have to heat the basement, then the heat "lost" to the basement is not really lost....it's heating the basement
BUT if the water is run through an unheated crawlspace OR through an air conditioned basement then the heat is actually lost or is fighting the A/C.
Also if you've got long runs to bathrooms or kitchen having the hot water cool off on it's way can be annoying
As to the comment of the plumber that black foam is useless, I would say wrap your hand around an uninsulated running hot water pipe & compare that to a running insulated hot water pipe. I'll take the foam insulation over bare copper.
His comment that the foam doesn't have an R value is nonsense...... 5/8" foam is about R4
coffee in a copper mug will cool off a lot faster than a copper mug with a 5/8" foam sleeve
again whether or not its worth the effort depends on the situation
cheers Bob
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On Fri, 06 Jul 2007 20:09:44 -0700, snipped-for-privacy@hotmail.com wrote:

Do you live alone. I insulated in my basement my hot water for sinks, showers, and the bathtub, but it's cold anyhow by the time I need hot water again.
I don't know how many people it would take before this wasn't true.

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MM-
Insulation on hot water pipes is only useful for........
1. reducing temperature drop as the water is delivered
2. reducing ongoing heat loss in a "instant" hot water loop.
Pipe insulation will keep standing water in the pipes hot between uses only if you're taking about consecutive showers ie hot water demand every 5 to 10 minutes.
cheers Bob Bob
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