Outdoor Hot Water Line, Heat Loss Question

[JoelM]

I live in California (local temp ranges 40s in winter, to 80s in summer). I want to run a hot water line to an outdoor fixture, which will require about a 20ft outdoor run.

There is no concern of freezing, nor waiting a little for the hot water, but I do care about energy efficiency. I wonder if the exposure of the 20ft hot water line to the elements 24/7 has big effect on the water heater (gas, 40 gal)?
My armchair understanding is that the upstream hot water in the pipe would keep mixing with the lukewarm/coldish water in the outdoor run, prompting the water heater to turn on more frequently. But maybe this overestimates the effect of a mere 20ft outdoor run in temperate climate on a 40 gal water heater?

Lastly, I thought maybe I should add a shutoff valve right before the water line crosses the building envelope to the outdoors. My thinking is that this shutoff valve in the off position would prevent such mixing of water, and basically prevent this outdoor hot water line from adding any burden to my water heater. What do you think??


PS, freezing isn't an issue (bc my temperate climate), and I know on-demand units could be an alternative, but I'm still leaning towards the 20ft outdoor run.
I appreciate these forums -- I've always found answers to my plumbing quandaries through reading.

 

[LLigetfa]

My armchair understanding is that the upstream hot water in the pipe would keep mixing with the lukewarm/coldish water in the outdoor run, prompting the water heater to turn on more frequently.

Modern water heaters have heat traps so I doubt there would be any convection flow. Convection is unlikely to happen unless it is a vertical run going straight up from the top of the water heater.

 

[Sponsor]

 

[Jadnashua]

Hot water is lighter, so the cold in the outside run would be heavier, so unlikely to try to flow up, unless the WH is say in the basement, and is feeding that line above it. A heat trap should eliminate it, and I'd plan to insulate the pipe really well.

 

[JoelM]

Interesting, didn't know about the heat trap and upwards mixing physics, thank you both for the info!
So does that mean the shutoff valve as I imagined it is unnecessary? For energy efficiency reasons I mean

 

[Jeff H Young]

I expect no detectable energy loss

 

[Jadnashua]

I don't know what the requirements may be for depth of water lines where you live. IOW, you probably don't have to worry about a frost line in that part of California, but to help protect the line from what may happen on the surface, there still may be some minimum depth required. Being in contact with the earth, without insulation, the water will get to the soil temperature after sitting, and keep in mind, insulation only slows the heat transfer, so the longer it sits there, it will eventually get to the soil temp. If the soil gets wet (you might wish in CA!), that will transfer heat faster away from the pipe.

Make sure to call DigSafe before you dig the trench! It's free.

 

[JoelM]

Thanks for all the responses yall. I think I'll go ahead with the outdoor line, without the shutoff valve, and I'll keep it above ground, run alongside of the house, and not worry too much about the low level of heat loss!

Cheers!