As many of you know, last week was “Fix a Leek” week which was the primary focus of KB Tribes weekly Twitter chat (Group of Kitchen & Bath designers, builders, and manufacturers). During this chat on saving water, our friends @PfisterFaucets said “In the bath or anywhere – insulate your pipes. It saves.” Yep you might have guessed it; my reply to that was “I hate to say this – but no, not really…”
Needless to say this elicited some comments & questions;
- @PfisterFaucets “In our experience it depends on the circumstances and equipment, but could work”
- @TheDecorGirl “It depends on the situation – always do your research first…”
- @cabinetmakers “Let’s hear why Sean. #kbtribechat (insulate pipes or not?)”
As Twitter is not the best of mediums for in depth discussions, I simply punted & said to look for a blog article later. So keeping my word & to help clear up confusion one might run into while “researching” this…
 This article was originally written back in 2013 & while the information is still accurate, times have changed. For extensive remodeling & new construction projects you are required to follow the current codes which will necessitate one to insulate one’s water lines with some exceptions. The 2012 version is listed at the end of this article though you may be on a more current version. We recommend you check with your AHJ to see if your project is required to & what specifications they have adopted. |
Faster Hot Water Delivery?
One of the biggest reasons used to promote insulating your lines is so that your hot water heater doesn’t have to work as hard &/or the hot water will arrive at your tap faster. Well I hate to say this but someone needs to study up on hydrodynamics. In order for hot water to arrive at the tap it basically must push all the water already in the line out.
This principle is what allows for all the different types of fuel we need (cars, trucks & planes) to be delivered through a single pipeline instead of requiring multiple pipelines. For those with “instantaneous / on demand” hot water heaters, they will definitely know about this if they have ever had the dreaded cold water slug. If you really want water to arrive faster (without wasting it) you either need to shorten the run, or install a recirculating pump.
Raise Water Temperature?
“Insulating your hot water pipes reduces heat loss and can raise water temperature 2ºF–4ºF.” Really, just how exactly is a material made to help resist the flow of heat outward or inward magically going to heat the water aka raise its temperature? Yep it isn’t going to happen
 Yes I do know where some people get this idea, and that is because they have copper lines that seemingly run for miles in their super cold basements. As the water is rushing through the lines it is giving up a bit of its heat. In this case when you are dealing with major temperature extremes, it can mentally & maybe even materially pay off to insulate your pipes. A better option though is to fix the placement issues if at all possible. Of course if your pipes are located in a super cold basement, they should already be insulated as mentioned below… |
Reducing Heat Loss:
Ahhh finally we have hit one that has some merit. The simple fact is an uninsulated ¾ copper line loses anywhere from 22 to 34 BTU’s per linear foot an hour & that by properly insulating it you can drop that loss by a third or more. Shoot that sounds pretty good & by plugging some numbers into one of DOE’s programs (assuming 700 hours of hot water usage a year) I would see that I could save 16¢ a LF (a year) by installing it. If I was to top it off with the infrared picture below, I bet you I could probably sell you on it. There is just one small issue with this & that is frequency of use.
Commercial Water Heater with insulation around pipes – two hot spots are gaps
If you do insulate a hot water line in a house, then the heat of the water in that pipe will simply be retained longer. The catch is that time period is limited.
Just to use a simple example, let’s say that an uninsulated line reaches ambient (room) temperature in 10 – 15 minutes. Being nice, let’s say that the heat loss is reduced by half because you did an awesome job insulating it… Well what happens when you turn that faucet back on 30 minutes later? Oops it would be the same temperature as is I hadn’t insulated it. Now to take this one step further, what happens if you turn the same “insulated” faucet on 15 minutes after the last time? Well while the water will be warmer, you will still need to flush out the line for it to get up to that “hot” temperature you are looking for. So much for that “16¢ a LF” savings.
| If you really want to cut down on heat loss, consider lowering the temperature of the hot water heater. For example a ¾ copper line with 140° water continuously running through it will release 34 BTU’s per linear foot. That same water line with 120° water comes in at 22 BTU’s per linear foot. Of course, in most cases the water lines never reach the water temperature because we are only running them for a minute or so while we shave, or 5 – 10 minutes for a shower. |
Noisy Lines:
There is one other main selling point that some like to add to the “savings” & that is reducing the noise as they expand due to the heat gain. While it is true that pipes do expand as their temperature increases you have some other issues that you need to address & not try to muffle or hide if this is ongoing.
When to consider insulating:
- Continuous Use: In the case of the two water heaters shown above, that is for a commercial building where the water is constantly being circulated. In most homes not only would that be foolish but any perceived water or heating savings would be lost. With that if you have a line running directly to a hot water air handler, to a radiant floor run; it would definitely be worth it.
- To help prevent the water lines from freezing: In unconditioned areas make sure they are insulated, protected from drafts/ winds & if need be install heat tape.
- To help prevent condensation from forming on cold water lines: This is generally limited to very high humidity areas coupled with cold incoming well water.
- The first few feet: As you can see by looking at the safety valve heat does travel. While the savings might not be much, by insulating the first foot or two, one can help keep that heat from spreading out to the rest of your house
- Underground lines: I really shouldn’t even have to mention this but if you are building new or remodeling – if you have lines running under a slab they should be insulated & protected to help extend their life.
- You want to save every cent possible
 My friend David Butler of Optimal Building Systems in Arizona reminded me that the 2012 IECC (Section R403.4.2) calls out a number of situations where R-3 is required. So with that in mind, here is the applicable section;.
TABLE R403.4.2 MAXIMUM RUN LENGTH (feet)
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Thanks for going in depth on this issue Sean. As we discussed in #KBTribeChat, not all of these methods will work for everyone. Your insights will definitely help the community make more education decisions – hopefully in more than 140 characters!
My pleasure & thanks for kick starting the conversation and dropping a note.
I have a solar water heater on my rooftop. Its just Rainbird black pipe in concentric circles. Does a great job. Even on cloudy days I am getting 120 F up on the roof. Only problem is it loses a lot of heat before it gets to my pool which is 65 feet away and below. I use a thick garden hose for the hot water delivery line. I want to insulate it with Frost King 0.75-in x 6-ft Foam Plumbing Tubular Pipe Insulation, but it only delivers an R-value of 2.1. How can I get that wonderful hot water from my roof top to my pool without losing so much of the heat? I was told burying the hose in the ground was a big mistake as it will cool it off even more. Thanks in advance. Keith
Are you ready for this – yes, no & maybe. The ground is generally cooler than the air in many locals, but one also must factor in wind, etc… Personally I rather have mine buried for aesthetics & suffer that 1 degree (or so) of temperature loss.
With that – insulating it to help prevent heat loss. What you mentioned is better than nothing, but I would probably direct you to a plumbing supply house & see if you can get a pre-insulated pipe that they use for running hot water underground between buildings – as I recall it is about 4″ around (for 1″ pipe) & has an R Value of 7 to 10
I got to ask how are you getting the water to circulate – natural convection, a stand alone pump, or when your pump is running – if you are using your main pool pump, you might see about tying directly into it.
wrt reducing heat loss, how did you arrive at total heat loss in pipes in 15 minutes? Are there example values you’re working from? Also, is only doubling the heat loss interval enough for well insulated pipes? I think if insulating changed the calculus from “tap-temperature water at 30-60 minutes after last use to 80-90 degree water at 30-60 minutes” it might be worthwhile for many (if the water is at least somewhat warm it may be enough to jump in and start showering/washing hands, whereas if it’s 20 degrees colder most will simply wait until it warms up a bit more). So there is definitely utility to existing water in pipes being somewhat warmer longer (especially in cases that it takes > 1 minute for water to reach from heater to tap)
As I recall I used the simplified Q = UAΔT means for basing this off of. For more on heat loss calculations: https://thehtrc.com/2012/building-science-heat-transfer-mechanisms
There are numerous items that can effect heat loss, like wind / drafts, being close to a heated or cold area (for example my cold water starts at about 70 degrees in winter & then drops down to 50 due to how close to the furnace the lines are)
As for taking more than a minute – that is a lot of wasted water & I would urge you to look into an on-demand recirculating system like I listed above especially if you decide to switch over to a “WaterSense” / low flow faucet from a standard one- you wouldn’t necessarily be wasting more water but the lag time might be unacceptable (I think more than 15 seconds is in my book)
As an FYI / correction, while updating the piece to add in a bolder section on the newer codes, I noticed that it stated specifically I used a DOE calculator which I had linked to at the time. My mind instantly went click as I remembered this discussion. Unfortunately after an extensive search it seems to have been taken down & appears to no longer exist. The link was automatically removed as it became “broken”.
Hi Gang, I have plastic or pex (sp?) piping for my water lines from the manifold. What I noticed is that they bundled all the lines, hot and cold, together with zip ties and then ran through out the basement. Would it help to at least separate them and put some insulation between them to prevent the loss/gain between them?
How old is your place? It is probably pex, but if its gray & your house was built in the 80’s (as I recall) have a plumber check it
With that, yeah it drives me up a wall when they bundle them together. Separate is a good/best practice & insulating them will just help slow heat transfer / loss – i.e. keep cold water lines cooler, etc…
The house is 10 years old and the lines are opaque/clear-ish color. This is going to be one of my COVID-19 projects I believe. 🙂
Sounds like pex then & good luck – you won’t be able to anything when they duck inside the finished area but you should be able to handle the main runs exposed in the basement. Just be careful not to pull any connections loose & don’t forget to resecure them.
Thanks for going in depth on this issue Sean. As we discussed in #KBTribeChat, not all of these methods will work for everyone. Your insights will definitely help the community make more education decisions – hopefully in more than 140 characters!
My pleasure & thanks for kick starting the conversation and dropping a note.
You are assuming all hot water usage events are independent, which is not true in households that have many people. If events of hot water usage are close to each other, then keeping hot water in the pipes thanks to insulation means the next user will use less water and get faster hot water delivery. There is also a well known “warming up time” effect which is the hot water looses temperature as it goes through a cold pipe. If you insulate the pipes in a house that uses frequent hot water then you decrease this effect, saving hot water.
Thanks for dropping in but let me say that, no I didn’t assume – I mentioned the issue when they are & I did account for that effect under the first “tips.” Of course that effect is dependent on piping material, location, & length. Thanks again & have a great one