Stupid pipe insulation questions

[AllstonParkingRefugee]

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

[Eigenvector]

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.

[Eric9822]

Pipe sizes are nominal, not absolute. As far as everything else, what Eigenvictor says. Have Fun.

[Edwin Pawlowski]

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.

[Bob M.]

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.

[Ralph Mowery]

Here is a chart for pipe sizes.

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.

[** Frank **]

I measured the circumferences with a piece of string

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.

[Sacramento Dave]

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.

[AllstonParkingRefugee]

But

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

[BobK207]

Sacramento Dave" wrote:

1/2" copper 5/8" OD , 3/4" 7/8" OD ( outside diameter)

But

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

[mm]

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.

>

[BobK207]

MM-

Insulation on hot water pipes is only useful for........

1. reducing temperature drop as the water is delivered

1. 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