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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It's definitely 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.
PEX is a very good conductor. One of it's uses is for under floor heating systems, so if you are using it for delivering hot water the it's definitely worth insulating it. This is true of copper pipe as well.
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):
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.”
Note: This paper assumes the price of 3/4" insulation to be $3.30/ft. 1" insulation can be had for about $0.45/ft currently (Jan 2021), about 7x cheaper, thus reducing the payback period drastically.
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.”
There are two reasons to insulate hot 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.
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.
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.
Any insulation will prevent heat from transferring out of hot water pipes or into cold water pipes. There are several considerations:
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.
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.
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.
Yes it is good to insulate the lines, as mentioned before, if the Cold water runs in unconditioned space or your condition space is kept at a higher humidity level.
For Domestic Hot water many newer codes are requiring a Hot Water return (on demand) circulation along with 1/2" insulation on 1/2" piping. After 1/2" the benefits will depend on the particular setup and routing of the piping.
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):
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.
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.
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.