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Is it worth the time and expense to put the foam pipe wrap on pex hot water pipes? I've seen mixed statements.

What is your thought? But more importantly, can you back it up?

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15 Answers 15

up vote 7 down vote accepted

It's probably worth it if you are running new pipes or the existing pipes are easily accessible, but if you have to lift boards etc. to gain access probably not.

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For a water usage POV, if you kitchen, and bathrooms are at all connected. you will find that when you sporadically use any faucet, you can still make use of the warm/hot water in the pipes (with insulation), my bathroom requires me to run the water for about 30s before it gets warm, then if i try again in about 5 mins, i need to run it for 30s again. -- waste of water and electricity. – Hightower Jan 9 '15 at 7:41
PEX is used for radiant floor heating and for radiant heating to de-ice driveways. Which means it is a very good thermal conductor. So there is definitely a benefit to insulating it, because it has no significant insulating properties of its own. – Craig Jan 16 '15 at 4:15

There are two reasons to insulate hot pex pipes:

  1. Keep them hot in cold temperatures
  2. Keep them from heating up cold pex pipes

When we ran our pex, we were very careful to keep the hot and cold pipes from touching, so #2 wasn't an issue. In my climate, I was more concerned with keeping the cold pipes from freezing and insulated them, particularly where they were near the exterior of the house or where they crossed near a cold air intake/vent.

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Maguire, Fang, and Krarti have developed a simulation model to estimate the energy losses for prototypical domestic hot-water distribution systems. As an example application of their model, they assessed the impact of insulating pipes in unconditioned space (Figure 12):

Figure 12

When they combined this with estimates for the cost of insulating the pipes, they found that “In the most cost effective case of adding ½ in. (12.7 mm) insulation to the distribution system of a high use home in Atlanta, the simple payback is estimated to be 26 years. Adding insulation to just the section of piping in unconditioned space appeared much more cost effective, with simple paybacks less than 10 years possible for homes in colder climates.”

These results were all with copper pipes. Another report quantifies the heat loss from copper pipes and PAX pipes (a 3-layer composite of high density cross-linked polyethylene (PEX), aluminum, and another layer of PEX) but not for straight PEX. They note, however, that “½ inch thick foam pipe insulation performs almost as well as ¾ inch thick foam pipe insulation.”

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Yes, I'd insulate: not least because the water in the pipe will stay warmer longer. Although PEX is a better insulator than copper, having hotter water come through the pipe faster is a good thing.

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The PO did it in my house, but we have a well. He insulated the cold-water pex wherever he could, probably because it sits in a pressure tank and he was hoping it would stay cold.

When you touch the cold and hot copper, you can feel cold and hot which means the heat transfer for copper tubing is efficient. (should insulate)

Grab your pex and see what you can feel.

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The hot water pipe is quite warm. If the water runs for a bit the piping heats up to the temperature of the water though. – dilbert789 Jul 26 '10 at 12:41
Adding insulation then would definitely help. I am not sure how long it would take you to recoup your investment. I would only think about it if you are running the pex through a cold area, and you live in a colder climate. – Matt Dowell Jul 26 '10 at 20:29
Actually - the opposite. If you can feel hot or cold through the pipe then it is an efficient /conductor/ of heat, not an insulator at all: it's conducting heat to your fingers! – Jeremy McGee Jul 30 '10 at 19:09
If you're in a humid climate, it's good to insulate the cold pipes to prevent condensation, which will eventually start dripping onto whatever is below the pipes. – gregmac Jul 31 '10 at 6:30
Jeremy: That's actually what I wrote. The heat transfer is efficient, not the insulation. – Matt Dowell Oct 12 '11 at 19:31

It depends where the pipes are, if within a well insulated house, the return in efficiencies will not be that great. But if it is in an area where extereme cold could come (under the eaves, or in the loft) normal loft insulation will not be enough. So if you can get (like this year in Europe) a long term cold spell of -10°c to -20°c - pipe covering insulation (the grey foam type) is well worth it with regards to stopping freezing.

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Any insulation will prevent heat from transferring out of hot water pipes or into cold water pipes. There are several considerations:

  1. Cost of insulation
  2. Cost of labor to install insulation
  3. Heat conductivity of tubing (copper transfers heat more than PEX tubing)
  4. Amount of water that must be run through the piping to get hot or cold water at the faucet

    a. Cost of unused heated water that goes down the drain (both water charges and heating charges) b. Cost of sewer charges for that water

You may want to consider a circuit setter (like Circuit Solver) with a hot water return line so that hot water circulates (does not run to drain). The result will be that hot water is more quickly available. However, the circulation speeds up heat transfer out of the pipe, so insulating is still desirable.

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Any insulation will reduce heat from transferring out of hot water pipes or into cold water pipes. The question is how much reduction and its value. – Philip Ngai Mar 1 '13 at 19:30

I really doubt it is worth it and I have never seen it done.

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Do the PEX feel warm to the touch? If so, you're losing heat, and thus would benefit from insulation.

The cost of pipe insulation is negligible, and it lasts for decades, so the cost/value is skewed in favor of insulating.

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Probably not worth it.

Considering how much the insulation costs (not to mention install costs though this is diy so that should be $0) I think it would take a long time to make up for the cost of water that goes down the drain to get to the hotter water from the tank and well as the cost to heat that extra water to a temperature that the insulated pipe water would have been.

I would need (or technically, that guy from XKCD would need):

  1. water costs in your area
  2. Length and diameter of the pex from the tank to an average faucet
  3. average temperatures inside and outside your house and
  4. the percentage of the pex that is inside your house
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I have insulated my PEX tubing and found that it does make a difference. My master bedroom is over my garage (unconditioned space) and the tubing runs through knee walls (unconditioned space). This is the only room we heat with oil. The rest of the house we heat with wood pellets. But ever since I insulated the tubing the boiler does not run as much. So yes, I would insulate.

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this is very unclear. is your pex carrying water for drinking and washing or water for heating? it makes a difference. – Philip Ngai Mar 1 '13 at 19:31

The cost benefit is very difficult to accurately calculate. The convience of having a hot water pipe charged with hot water while several people are in the house, washing hands, washing dishes, taking showers, combined with having hotter water to work with, is the biggest reason to insulate hot water pipes. I used 4 inch diameter fiberglass around my 3/4 inch copper main line. That gives me 1.5 inches of thermal conduction resistance. The water stays warm in the winter for about an hour. It stays hot for fifteen minutes. Without the insulation the water cooled in five minutes.

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Here is an unusual use for the insulation. At a commercial building they had chunks of insulation all over the PEX, hot and cold. They had the PEX secured all over, though they had the insulation between the places it was secured. They said the reason was to prevent the PEX from vibrating the studs they were attached to.

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It just makes sense to spend a few dollars to ensure your hot and cold water PEX pipes are well insulated for energy consumption if no other reason, but with the winters we have been experiencing here in the northeast during the last few years, it pays to do what you can so the pipes don't freeze. I used the fiberglass tubing on the hot water lines and the foam tubing on the cold on the advice of a plumber.

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Check out the link to Nomaco Insluation: http://www.nomacoinsulation.com/pdf/polyolefin%20faq/TA65%200512.pdf

Basically, the r-value of PEX insulation does not meet energy code requirements for piping insulation.

Also, according to ASHRAE Research (2015 HVAC Applications, page 50.4): "Table 1 also shows that all of the plastic pipes tested to date exhibit moderately to significantly higher heat loss rates than comparably sized copper pipes when tested uninsulated in air. However, when insulated, they exhibit moderately to significantly lower heat loss rates than comparably sized copper pipes with the same insulation."

So, I think you would be silly not to insulate PEX piping.

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