Insulating Your Hot Water Pipes can Save

Money and Protect the Environment

From the School of Hard Knocks.  Last updated Dec 17, 2007

     Better quality hot water:
        Less time to get hot water to the tap.
        The temperature at the tap is a little higher (maybe a degree or two)
        The water in the pipes doesn’t cool down as fast between uses.
     Saves money
     Good for the environment

This page first addresses the possibility of rerouting pipes, then covers the basics of selecting and installing pipe insulation. Additional pages provide calculations on how fast hot water cools down in pipes, hot water tank heat loss and other topics.

First, decide whether you should reroute any pipes

The plumbers who installed the hot water pipes in our house did not take the time to figure out the most efficient routing. The original routing from the hot water tank in the basement to the kitchen sink was 43 feet long, even though the hot water tank is relatively close to the sink!

We rerouted and ended up with a 27 foot length. At the same time, we downsized much of the pipe from 3/4 inch to 1/2 inch in diameter. Downsizing to 1/2 inch did not cause a pressure drop at the kitchen sink faucet, as that pipe only goes to the kitchen sink and dishwasher.

The combination of a shorter length of pipe and smaller diameter pipe meant that instead of taking three quarters of a gallon of hot water to reach the tap, now it takes only about three-tenths of a gallon. This may not sound like much of an improvement, but with thousands of uses over the course of a year it adds up. It isn’t worth shortening pipe by a couple of feet, but on some houses (like ours) the length can be reduced by much more than that.

Next, decide on the type of insulation

There are five basic types of insulation. The following discussion describes advantages and disadvantages of each. My guiding philosophy has been that as long as I’m investing the labor of installing pipe insulation I might as well spend a couple of extra dollars to get the best possible performance.

In the following discussion I use the term R-value. This is a measure of how well insulation keeps in heat. The higher the R-value, the better. Wall insulation in a typical American home is R-13. The insulation in the walls of our current hot water tank is R-16. In contrast, pipe insulation tends to have a much lower R-value--on the order of 2. I'll talk about how to do much better than R-2.

1) Spiral-wrap fiberglass insulation

Although this is the least expensive option, I would recommend against it because it has the lowest R-value (Frost King lists the R-value as 1.6 on the package) and requires the greatest labor to install.

2) Foam tubing with no sticky-strip

In most hardware stores you can buy foam tube pipe insulation for various sized water pipes. The foam tubes have a slit down the side so you can easily fit them over pipes. Once you install the insulation you may want to tape some or all of the seams, as they tend to pop open a little. Some pipe insulation has a sticky strip on the slit that allows you to easily seal it. I’ll discuss that as the third option.

Most foam pipe insulation sold at hardware stores has 3/8” thick walls, which yields an R-value of a little over 2. Frost King and Tundra also make a heavy-duty pipe insulation with 5/8” thick walls and an R-value around 4. This is well worth the extra cost.

Frost King brand insulation:
     Copper or
     CPVC pipe    Product       Wall           R-Value listed
     diameter        Number   Thickness     on package

          ½”               P10X          3/8”                2.2
          ½”               P10            5/8”                4.2

          ¾”               P11X          3/8”                2.1
          ¾”               P11            5/8”                3.8

I haven't been able to find the heavy duty Frost King insulation in stores, but have been able to order it on the Internet.

3) Self-sealing foam tubing

This foam tubing is fast to install because there is no need to tape it. Once you push the insulation onto the pipe you can peel off two plastic strips and the pipe insulation seals itself shut with a special glue. This is great for commercial installers where time is money.

I have seen two basic types of self-sealing insulation at hardware stores. One is a less expensive R-2 insulation intended for hot water pipes. The second is a more expensive R-3 insulation that is very flexible. This type is designed for use on the pipes associated with heat pumps and air conditioners, but there is no reason you couldn't use it on hot water pipes as well.

Although some people prefer the self-sealing type, I have avoided it for two reasons. First, I make a lot of mistakes and don't trust myself to do it right the first time. Second, I haven't been able to find a source of R-4 self-sealing insulation available to homeowners.

4) Fiberglass pipe covers

Unlike the spiral-wrap fiberglass insulation, these are hard tubular shells of fiberglass with a paper covering. They hinge open to go around the pipe. I have found these at Home Depot, made by Thermwell.

This type of insulation is intended more for high temperature pipes where the heat might damage foam-type insulation. Although it can be used for lower temperature pipes it is more expensive than the foam insulation and has an R-value of only 2. (The R-value is not marked on the store display, so I called Thermwell directly.) I have sometimes put these over foam pipe insulation as a way of boosting the R-value beyond what the foam alone offers.

5) Regular fiberglass attic insulation

The previous four options for pipe insulation have an R-value of at most 4.2. It is possible to jury-rig a high R-value pipe insulation out of regular attic insulation. This may be particularly useful on the vertical section of pipe coming out of the water heater, as this is where much of the heat loss occurs.

And the Winner is...

So what option(s) should you choose? I feel that the best option is a combination of R-4 foam insulation enhanced by attic insulation where appropriate (more on this later). Particularly if you are concerned about carbon emissions from burning fossil fuels, you should go for the highest possible R-value.

Installation:

To install the heavy-duty foam insulation you will need a measuring tape, a knife to cut the insulation, an appropriate cutting surface (I use plywood), and tape to seal the seams.

The right cutting tool makes this job go much easier, especially if you are insulating more than a few feet of pipe. I recommend against a utility knife--the blade is too short so it makes a sloppy cut and I feel that the lack of control makes it dangerous for this application. Try experimenting with kitchen knives on a wooden cutting surface. My favorite knife is a bread knife with small serations, shown below. This knife cuts cleanly with great control. It's perfect for cutting fiberglass insulation as well. (My wife made me buy a separate one for insulation work--it's a poor job that won't support buying at least one new tool.) I made a cardboard scabbard so the knife can't be dulled in my toolchest.

Where to start:

The vertical section of pipe from the water heater tank should receive the most insulation. This pipe tends to stay warm as hot water rises by natural convection up the pipe. Heavily insulating this pipe reduces standby heat loss 24 hours a day and keeps the water in this section of pipe hotter, which reduces the time needed to get hot water to the tap.
...to be continued…

Hot Water Usage Habits:

Just because you insulate your hot water pipes does not automatically mean you will save money on hot water costs. There is a strong tendency for people to subconsciously think "Gee, my hot water system is better insulated, so now I can use more!"

To really achieve savings it is important for those living in the house to examine their hot water usage habits, and to figure out ways to economize on their use of hot water. For example, when doing dishes at the sink, it is important to not leave the hot water running while placing a pot in the drain rack and reaching for another pot to wash. The hot water should be turned off as soon as you are done using it, and then turned back on when you need it again. Even 5 second periods of running the water when not needed will add up to a significant usage over time.

This site is still under construction…to be continued…

You can e-mail me at support(@ sign goes here)leaningpinesoftware.com.