Pipe insulation

I briefly touched on pipe insulation for our plumbing system in a previous post, but think it is worthwhile to go into a little bit more detail.

What pipes should be insulated?

It is a good idea to insulate the cold water lines. Yes, you heard right – the cold water lines. The rationale is a simple one.

You may have noticed that your toilet tank begins to sweat during a hot and humid summer day with the condensation dripping onto the bathroom floor. That same condensation can occur on the cold water lines buried in the walls where you can’t see the water or clean it up. If enough water and moisture accumulates, it can lead to mold growth and indoor air quality issue.

As mentioned in a previous post, all lines that carry domestic hot water should be insulated. This is to assure that we keep heat where it’s needed – in the hot water – and thus have it effectively delivered to the faucet.

Let me quote my friend and hot water guru Gary Klein:

“During the use phase, insulation on pipes surrounded by room-temperature air will, for a given flow rate, reduce the temperature drop over a given distance by roughly half.”

You may find some voices declaring hot water pipe insulation unnecessary. The argument is that no heat is lost, because it ends up in the conditioned space of the building and as such contributes to the space heating. That is true indeed – during the heating season. But do I really want to add that extra heat load to the conditioned space during the hot summer months? Maybe not.

The argument also ignores the issue of water conservation and quick delivery of hot water to the point of use.

How much insulation is needed?

I mentioned the recommendation by Gary Klein: A half inch pipe should be insulated with pipe insulation that has at least a half inch wall thickness, a three quarter inch pipe should be insulated with pipe insulation that has at least three quarter inch wall thickness, and so on.

Gary has a sound rationale for his recommendation. He aims for “equal heat loss per foot of pipe regardless of pipe diameter.” That said, he does not imply that his recommendation should not or cannot be exceeded.

I know that I have to achieve a minimum insulation value of R-3, if I am to meet the Chicago Green Homes requirements. I can achieve R-3 with closed cell pipe insulation that has a half inch wall thickness.

Increasing the pipe insulation wall thickness to three quarter inch bumps the R-value up to 5. The largest diameter on my domestic hot water lines is a three quarter inch. Using the three quarter inch R-5 insulation would put me squarely within Gary’s recommendation. Using the three quarter inch R-5 pipe insulation on the smaller diameter pipes would allow me to exceed Gary’s recommendation.


I dreaded the pipe insulation installation. It just seemed such a tedious task. All insulation has to be carefully and permanently glued at all seams and connections around the pipes. The plumbing is basically encased and sealed tight into the pipe insulation. Just imaging the measuring, puzzling, cutting, slitting and fitting involved.

But Cathy was right on it. She discovered that it is really easy to cut and slit the insulation with scissors. She has the skill, attention to detail and patience to fit the insulation around all pipes, bends, tees, valves, you name it… and she was moving along quickly.

There are special insulation fittings available for 90 degree elbows and tees. These make the job quite a bit easier, except we could not use the elbow pieces because of the long sweep fittings we used.

Here are some images of Cathy’s work on the basement plumbing system before we closed up the walls.

pipe-insulation-01 pipe-insulation-03

About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

3 thoughts on “Pipe insulation

  1. One other reason to insulate pipes–if they have to go through an uninsulated space, they can freeze in very cold weather. Maybe that doesn’t apply to good green construction, but I speak from painful personal experience.

  2. I agree, but it is worth while to notice that there are different kinds of uninsulated spaces. Installing plumbing (insulated or not) into an outside wall is a big no-no and usually prohibited by building code. Having plumbing run through an unconditioned crawlspace or attic would defiantly require good pipe insulation, although I would always prefer to have the plumbing run through conditioned spaces.

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