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Old 12-13-2015, 07:27 PM   #1
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being frugal with hot water — best ways to manage hot water cost

Has anyone here with more science or analytical skills than me done an analysis of breakeven points for managing hot water?
What I mean is, if you look at the energy cost to fully heat the 6-gal tank, vs the energy cost to keep it warm, when does it make sense to only turn it on an hour before demand, vs keeping it on?
The scenarios I would want to look at are either using the hot water once a day, or alternatively looking at using the hot water twice a day (once in AM, once in PM). For one or two showers, plus dishes.

In those scenarios, like the twice-a-day scenario, does it make as much sense to keep it warm than to let it go cold then reheat it? Or if not, where are those break points?
Does this all make sense?

In my new AS, I finally have the choice of electric or gas for hot water. I've used electric, and it doubles my monthly electric bill. I'm guessing propane would be cheaper at today's rates, though a little less convenient.

thanks!
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Old 12-13-2015, 08:22 PM   #2
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The scenarios I would want to look at are either using the hot water once a day, or alternatively looking at using the hot water twice a day (once in AM, once in PM). For one or two showers, plus dishes.
Or you could buy yourself a two-quart teakettle and heat water on your stove, barbecue grill, or campfire, mixing it with enough cold water to make the temperature bearable, and not use your water heater for dishes at all. Why heat six gallons if you're not going to use six gallons? If heating water is ever an issue for me, I can get by with much less than a gallon of heated water for bathing, since I don't have hair to wash and I'm fine with taking a sponge bath if necessary. I used the teakettle idea when my water heater thermostat went out, and made out just fine for the remainder of the trip.
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In those scenarios, like the twice-a-day scenario, does it make as much sense to keep it warm than to let it go cold then reheat it? Or if not, where are those break points?
Does this all make sense?
I suspect this is a non-issue for most RVers, let alone most Airstreamers.
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In my new AS, I finally have the choice of electric or gas for hot water. I've used electric, and it doubles my monthly electric bill. I'm guessing propane would be cheaper at today's rates, though a little less convenient.
Only an issue if you're hooked up to metered electric service. I've never stayed at a campground where I've had to pay extra for the electricity that I used, so the electricity costs are a non-issue for me. Probably a non-issue for campground owners as well, otherwise they WOULD meter every campsite and bill us separately for the electricity we use.

My choice of electric or propane for water heating water depends on two factors only— how many amps are my other electrical appliances using, and how much propane are my other propane appliances using? If I'm running the A/C, then I usually heat my water with propane to make sure my total 120vAC electrical usage stays under 30 amps if water heater and A/C happen to run at the same time. In colder weather when I'm running my furnace, I heat my water with electricity because that way I save my propane for the furnace.

Don't try to nickel-and-dime your water heating costs in your Airstream. It's not usually worth the hassles. Look at your Airstream as a whole, and manage your energy costs based on what's most efficient for the whole thing as a system.
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Old 12-13-2015, 08:40 PM   #3
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Being a tea drinking Brit it is essential to have an electric kettle! It does double as hot water for dishes too

I always crack up laughing when I start the genny to charge the batteries and the wife immediately puts the kettle on!!
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Old 12-13-2015, 09:40 PM   #4
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We have a tankless water heater. The tea kettle goes on the propane stove even if we are hooked up. We're not really truly Brits, but the kettle is the best way to make our cuppa multiple times a day!


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Old 12-13-2015, 10:07 PM   #5
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When camping I leave the hot water heater on full time. Tried turning it off at night only to forget to turn back on and wonder why the shower is so cold. I much prefer the convenience. Also leave the water heater in my home on 24/7. I think the Airstream furnace is the real propane culprit.
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Old 12-13-2015, 10:39 PM   #6
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This is a consideration when boondocking in more remote areas, when saving battery power, fresh water, and waste water tank space are important. It sounds like you might be staying long-term in a RV park, but maybe the following will still be helpful.

We found that the hot water heaters on the Bambinos are highly efficient and very well insulated. Without electrical hookups, we shut the water heater off at night, flipping it on first thing in the morning, then off again if we are going to be away for most of the day; or back at the site but just not needing hot water for much of anything. It goes on again about an hour or so prior to washing the dinner dishes; or earlier if we are showering in the pm. We don't have this down to a science, but turning the water heater on only prior to or during heavy uses works well for us.

The main thing with hot showers is to shower with something like a plastic tub or two on the ledge or floor that will capture a lot of the hot water, and bring a non-breakable mug. Get wet quickly, turn off the shower, and soap up. Use the water you've saved in the basin/s for a preliminary rinse using the cup. Then turn on the shower again briefly for a final rinse. This tub system enables giving your feet a good soaking. To conserve the gray water tank, we dispose of the captured water outside. (In the CG-provided utility sink or under a bush.)

You can go even more Spartan with a sponge bath.

Because we often camp with no electrical hookup, we heat up water in a stove-top tea kettle. (Yes, we're tea-drinkers, too.)

When desert boondocking where water is a big concern, we typically wipe down the dishes with one of those Lysol surface wipes for the pre-rinse cycle, then put a very little hot soapy water in a bowl or mug. The dishes get scrubbed with a European-style dish brush dunked into the soapy water. They get rinsed in a plastic tub of hot water, which again can be emptied outside to minimize filling the waste water tank.

Obviously in a RV park with full hook-ups, you wouldn't be concerned about disposal, but it many more remote places the sani-dump can be a long way away.
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Old 12-13-2015, 10:46 PM   #7
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Hi, we used to leave our water heater on 24 hours a day, but it sometimes kicks on at 2:00 AM, sounding like a blast furnace. Since our water heater in mounted right under my head, under my bed, It's best not to hear it come on. Also in some camp grounds, it's so quiet until someone's water heater kicks on. So We turn it off at night and back on in the morning. It's amazing how long the water stays hot. [our water heater in Propane only] Cost to run the water heater is not a concern.
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Old 12-13-2015, 10:55 PM   #8
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There is no practical way to answer the OP's questions. There are many many variables from the outside temp, the incoming water temp, the cost of electricity, the cost of propane, how much water you use, and other factors, that any answer, even a detailed engineering analysis, would be meaningless. Vary any factor mentioned, and the answer would be different.

I am an energy conserving nutcase, and a known cheap scape. Yet when I hook the Airstream up to my Tow vehicle and go any distance, the cost of getting there and back dwarfs the cost of the energy used to heat the hot water for the trip duration. I primarily boondock and leave my refrigerator on propane, and my water heater on propane as there is no power available. I don't turn the water heater off except when actually towing. In the summer, a 7 gal propane tank lasts me about 2 weeks, or slightly more that a dollar a day. It is not a killer cost all other things considered.
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Old 12-13-2015, 10:58 PM   #9
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Thanks all. Yes, I have used an electric kettle for dishes, face, and even hair in the past. And it also apparently works for tea. That was especially true when I had a wet bath that made showers more work, or like Protagonist, when my previous water heater circuit board needed replacing (also, joining a gym works for showers).
And I do like the convenience of always-on hot water.
But I do fulltime, I do pay for my electric, I do have 30 amps (so I like to avoid tripping the breaker), I am lazy, and I am also environmentally concerned, so I am still curious about a scientific answer to how heating up a cold tank compares to maintaining a hot tank.

A tankless unit sounds like a good long-term solution, but I just bought this thing as a new AS with warranty, so I don't want to tear into it just yet.

In water-starved socal, Len&Jeanne's ideas about capturing shower water sound worth trying. I could water the fruit trees outside my door... (organic soaps)

When I don't have guests, I will be switching to the "on only when needed" method and see how that changes my electric metering (though variable use of space heaters, heat pump, etc will pollute the results).

A side note: I believe, though I could be totally wrong, that parks would charge for electric if it wasn't so much work to read the meter at check-in and check-out, and do the math and paperwork for each short-term camper, and argue when they think you overcharged them. It's much easier to inflate the flat daily/weekly rate to cover average wasteful use.
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Old 12-13-2015, 11:07 PM   #10
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Ibdesign, generally we aren't heating up a cold hot water tank each day when camping, but a warm one. That doesn't take so long. If you've got a nice new 2015 unit, your hot water tank should be well insulated.
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Old 12-14-2015, 03:07 AM   #11
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Hi, we used to leave our water heater on 24 hours a day, but it sometimes kicks on at 2:00 AM, sounding like a blast furnace. Since our water heater in mounted right under my head, under my bed, It's best not to hear it come on. Also in some camp grounds, it's so quiet until someone's water heater kicks on. So We turn it off at night and back on in the morning. It's amazing how long the water stays hot. [our water heater in Propane only] Cost to run the water heater is not a concern.
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Ibdesign, generally we aren't heating up a cold hot water tank each day when camping, but a warm one. That doesn't take so long. If you've got a nice new 2015 unit, your hot water tank should be well insulated.
Ditto to this easy solution. If you turn the water heater off at 8 PM say, after doing the dishes, and back on at 8 AM, your neighbors will be happier, and there will be plenty of very warm water in the morning for doing some light dishes, washing your face, and so forth. Even a quick Navy shower if you are about to break camp and hit the road. No point in hauling a tank of hot water hundreds of miles IMO.

Our unit also uses both propane and electric to heat the water, and the recovery time is incredibly short if both heaters are on. I have not tried it, but I think you could run the water for a long time, and continuously still have warm water for dishes and a long shower (in summer anyway) -- treating the combined dual heating elements as one in-line on-demand heater . . .

Easy enough to experiment with anyway . . .
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Old 12-14-2015, 05:39 AM   #12
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Don't try to nickel-and-dime your water heating costs in your Airstream. It's not usually worth the hassles. Look at your Airstream as a whole, and manage your energy costs based on what's most efficient for the whole thing as a system.

Yes, tho I would go for the propane.

Unless showering inside, I generally turn the hot water heater on once a day, for 10-15 minutes, and it stays hot enough til the next day.

If boondocking, when also conserving use of dishwater, once in the evening, to wash up the days whatever...and me...is all that is needed. Don't have to have hot water every time you turn on the tap, IMO.

Too much figuring and analyzing, and gauges/monitors for this and that, detract from relaxation and enjoyment, in my opinion.


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Old 12-14-2015, 05:48 AM   #13
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Well said Maggie!

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Old 12-14-2015, 09:04 AM   #14
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When in areas with moderate-hard water, I've noticed that turning the water heater on and off after each use seems to generate more calcium deposits/crystals that get trapped in the faucet/showers fixtures. Maybe my imagination.... don't know for sure.
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Old 12-14-2015, 10:27 AM   #15
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Water conservation issues...sponge bath...shower pan (an idea I like personally)... I really hate to be indelicate, however, there are certain areas where my sponge wouldn't go. So, when primitive camping (we should be getting our airstream in 2016, FINALLY!!!) we sponge bathe and take along baby wipes for those areas where the sponge need not go.

We then get the added bonus of smelling like the fresh changed grandkids!!!!
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Old 12-14-2015, 12:49 PM   #16
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When in areas with moderate-hard water, I've noticed that turning the water heater on and off after each use seems to generate more calcium deposits/crystals that get trapped in the faucet/showers fixtures. Maybe my imagination.... don't know for sure.
Could be!

The constant heating eventually bakes the calcium carbonate knocked out of the water by heating, into a solid coating that will break up but it will likely be larger flakes that stay put in the tank. Starting and Stopping the heater still makes scale but it may be smaller flakes because the heating cooling cycle dislodges the scale on the wall of the tank as metal expands and contracts. Smaller particles are carried away to the taps.

I'm not sure about savings on only heating when you need it. I do that, and logically the heat lost from a continuously hot tank has to be made up if you try to keep the tank hot all the time, so you use gas just to keep it hot. But it still uses a lot of gas to get the water back to temperature and the determining cost savings factor will be whether more heat is lost "up the chimney" when the heater is working so hard to catch up. I suspect the most efficient approach is to heat when you need it.
I usually only heat the water to the temp I need it for dishes or shaving then shut it off, unless I'm planning to shower.
I also do not like the noise of the heater when I'm sleeping so it is off all night
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Old 12-14-2015, 12:54 PM   #17
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All of these issues are just part of the reason we went with a tankless water heater. The primary reason was wife enjoys her hot hotel showers on the road, and we rarely boondock long enough for water or propane conservation to be an issue. Besides, not having 42 pounds of water that far forward of the axles helps with weight distribution.


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Old 12-16-2015, 03:09 AM   #18
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I would leave it on all the time so hot water will be there when you need it. On my 10 gal suburban water heater I've found that the pilot light will keep the tank warm and have used just the pilot position for long periods of time in the summer, not even needing the main burner. However the last several years I've used just the electric option adding extra insulation all around the water heater including filling the burner compartment with insulation. This seems to be the most energy efficient approach. I was careful that rain can't get the insulation wet. Leland
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Old 12-16-2015, 05:32 AM   #19
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I asked this same question last year

I wondered that because water took a long time to cool off that it might make sense to turn the water heater off.

I suspected that the water heater would use more propane heating a tank full of cold water than it would use to keep hot water hot

But the bottom line was, the cost to leave it on was not a big deal. Someone did the math and thought that leaving the heater on would only cost about 25 to 50 cents a day. ( actual cost may vary )

Most people didn't care about the money, and opt for convenience

I don't imagine a trailer of your age has a heater with a pilot light.
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Old 12-16-2015, 05:09 PM   #20
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That was a question on a Thermodynamics Final exam in my engineering class. It's always better to turn it off. The rate of heat loss is reduced as the water slowly cools. Even with electric heating (basically 100% energy conversion) it's more efficient to heat the cool water than keep it hot.

Nobody would question heating water on the stovetop 2x per day is cheaper than leaving the kettle running all day.

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