Hot Water Pipe Insulation Findings

Not sure if this really fits here but I found it interesting and I don’t know anyone in the offline world that would care so…
Our house has a crawlspace (sealed, passively conditioned) that’s the typical 2ft high to the bottom of the joists type setup. Our water heater is something like 40ft away from the master bathroom so we had to run the shower water a long time before it’d get hot. There is one main 3/4 line that runs the length and branches off as needed.
A few months ago I installed a Rheem 6gallon POU inline right before the master bathroom branch. World of difference.
When installing the POU I got a Zen15 just in case I wanted to shut it off, not really thinking about monitoring the energy.
A couple of weeks ago I started monitoring it and noticed that it kicked on for 3 minutes every 114 minutes (1 hour 54 minutes) on average. Very little deviation. This was just idle periods since naturally being used would throw off the intervals.
I went down there to feel it and the case was room temp but as expected the release valve and the input/output pipes were hot.
Yesterday afternoon I installed foam pipe insulation on these along with the rest of the hot water pipes.
I did this at 2pm.
I wasn’t sure it would make any difference and while not earth shattering, it actually did.

It’s not a huge sample set and not really easy to see in the graph but with the same minor deviation, the average is now 150minutes. Same 3 minute duration.

So, will it ever be noticeable from a cost standpoint, surely not but going from 114min to 155min is something. :laughing:

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It’s a win IMO. The thermal loss through pipes is not insignificant. When you installed the POU, do you remember if dialectic union on the hot water side had a check valve?

Thanks RJ.
That’s a good question. I used the Shark bite flexible braided whip with ball valve for easy future replacement and that mfg said a dialectic union wasn’t needed so honestly never thought more about it. Is it not common for water heaters to have check valves built in? I can call Rheem on Tuesday to see if tech support knows.

My large electric water heater is a Rheem also with the smart capabilities. It doesn’t report energy usage but the integration does show on/off in regards to heating. Just looked at it on my phone so haven’t done the math but it has several hours between short ‘on’ periods when idle.
I realize the larger tank will take longer to drop temp than the 6 gal but still wonder if I can significantly improve the standby loss off the pou.

The check valve are normally incorporated into the dialectic unions (if so equipped) on new water heater (they normally come with the unit). They are NOT part of the unit itself. At least not on the unit I’ve serviced.

Good to know! Sounds like it may be a worthwhile addition I’ll look into. Went down there again this afternoon and I really can’t see (well, feel) that adding insulation around the unit itself it will do anything. I’ve got some leftover r19 pieces though and since it’s easy enough to quantify changes with HA, may poke some around it anyways and monitor.

Realized I also had some leftover r15 roxul and enjoy working with it much more than batts. Plus it would do better at being cut to fit for this test.

Before I go all out and build a frame to insulate the 5 exposed sides, going to see if just adding some to the top makes any difference in the interval.


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Ok well…
Haven’t given it long enough without anyone taking showers to get numbers but went down there this morning with the temp gun.
Checked the face of the unit and then lifted up the roxul and scanned there.
64 face and 101 top.
Now this is where the release valve and ports are so a lot of that is going to be from those.
One nice thing about a perpetual diy remodel is that there is always scrap around so made a box and insulated the sides and bottom. Will give it a couple days to monitor idle energy usage and check temps under the side insulation to see if it makes a difference.

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great thread btw. :slight_smile:

Is that sucker 120v!? i can se why you would want to save as much power as you can. Can it be wired for 240v? that would be a huge savings

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Thanks! I am finding this really enjoyable. :slight_smile:
Been doing energy efficient improvements to this house since we moved in and had an audit done but they’ve all been ‘feel’ type results with too many variables to really quantify a difference. This is the first thing I’ve been able to fairly accurately control everything but my changes and see the energy usage in such a informative hands-off way. The crawlspace maintains pretty constant temp and it’s not hard to find periods of time when no one is using the master bath hot water.

Good question. This one is 120v and while the element might be able to be changed out for 240v my crawlspace subpanel is 120v only (long story on how that came to be). Plus, unless I am missing something the energy cost would actually be the same and the only impact would be how fast it recovers. Normally with heating water the faster recovery would be very important but since I plumbed this inline, it’s rare that this has to heat up the full 6 gallon of water at ground temp.
The only “cold” water this should be heating is that which has cooled down in the pipes between the 50gal heater and this. Once that passes through, the input water to this POU with be hot…unless the 50gal is ran to cold.

Still premature on reporting anything but since I am making a reply anyways…
The first (and only) interval since I added the roxul box was from 3:15pm to 7:06pm.

3 hours 51 minutes OR 231 minutes

Definitely need more samples and I finished the box at 4pm so not an accurate test but if doing this actually takes the standby behavior from the original 114min to 231min, I’ll be blown away.

Tangent: This reminds me of a commercial from years ago in an office setting where a worker runs up with a coin (nickel?) and excitedly tells his boss that he just saved them a nickel on shipping. A fellow coworker scoffs but then the boss does the math in his head (outrageous number of shipments daily so the nickel adds up quickly) and starts skipping around with the first guy.

I like to think this is similar but sadly the only real correlation here is the nickel. It’s just that mine is saving ONE nickel per day :rofl:

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Why would it provide any savings? While amperage will be lower because of the higher voltage, the overall wattage will be the same. The utility power meter is measuring energy used on both split phases so whether it is all on one or half and half on both, does it matter? Just trying to learn something new :slight_smile:

@kramttocs Interesting thread! I recently replaced my traditional 40/50 gallon gas water heater with a tank less water heater. While I now enjoy endless hot water without any delay compared to the tank water heater I had before (which started leaking at around its 7th year of life!), I still have your same issue of having to wait and waste lots of water for it to reach my master bathroom (I think it is last in line). I had not considered your solution as an option so I am quite interested in vetting it compared to what I was planning. The thankless water heater has a circulation pump that can be activated remotely so if I add another pex pipe (easy as I have direct access via the attic) I could circulate the water in the pipes speeding up the availability of hot water to the master bathroom… Or I could use a device like the one you installed. At first thought, I think it is simpler to do the recirculation as I would not have to bring 120/240 to that attic space (quite a long run too) and I would not need a “sink” underneath it to prevent water damage from leaks (I think it is a requirement as I have never seen a water heater without one).

BTW, have you reviewed the paperwork for the unit you installed to ensure that blocking off all ventilation from it is not going to cause a malfunction of worse…? You will generally find notes stating what the clearance around it has to be.

Hi @aruffell ,
Ugh 7 years and was already leaking. That’s frustrating. I really like the idea of the tankless and have looked into them multiple times. For our house, getting the additional circuits to the needed location would be very intrusive so I always rule it out. Now I am excited about the heat pump options for when our 50gal needs replaced.

At least for our use case, this 6gal one has made a huge difference in wasting water and annoyance. I would do it again in a heartbeat. It really checked all the boxes and has performed wonderfully.

I could see in your case since you don’t have electrical there that it wouldn’t be quite as easy. While I understand the purpose of the circulation pump I’ve never looked into the numbers as far as energy cost to run it vs water saved. Would you have a way to add the POU inside the bathroom itself under a sink? Would likely require some plumbing changes though to get the hot water from the sink to the shower…

Excellent question on the clearance. I never found a thing in the specs/manual for this one regarding clearance. Guessing since it’s electric and designed to be used in small, under sink spaces that they’ve made it with no requirement. Of course that still isn’t the same as putting it in an insulated box :slight_smile: At the temps we are working with, I don’t envision any problems but it is a possibility. While I made the box long enough on the sides and bottom to easily take some face insulation, I don’t plan on doing so just out of caution to avoid fully enclosing it.

Well it would be more efficient and maybe save a few cents a month I would think if it was 240v. Either way a great thread

Will set a reminder to check the energy in a couple weeks and report back with a better sample size but to wrap it up until then:

9:31pm to 4:00am
6 hours and 29 minutes = 389 minutes
Ran for the same <3 min


Morning showers messed up the next standby time of 4am to 7am

7:03am to 1:01pm
5 hours and 58 minutes = 358 minutes
Ran for the same <3 min

Not too shabby of an improvement from the 114 :slight_smile:

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