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Old 07-18-2009, 03:56 AM   #1 (permalink)
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Water heating using ONLY the pilot light

I know it sounds crazy, but this guy claimed to have been doing it for at least 4 years. This got me thinking...

Basically, he took a propane hot water heater, set it on "Pilot Light Only" mode, and made the opening for the flue smaller. He chose not even to vent it, which at first sounded sketchy. Now I'm inclined to agree - after all, you don't need a vent for the (multiple) pilot lights in your stove. I still recommend a Carbon Monoxide detector, just to be safe.

Well, I tried it, and I can say that this has worked for me for almost a year. I (unlike the 'inventor') can mix cold water in my shower, so I just heat it as hot as I can get it. A comfy shower is about a 50/50 mix.

A couple things I love about this setup:
  • Natural gas is already one of the most efficient/inexpensive ways to heat water.
  • Since there's no thermostat control, I can take long, guilt-free showers, knowing that it won't be working any harder!
  • I don't have to compromise between turning up my water temperature VS running the heater in the dishwasher. The water is already hot enough for dishes.
  • Ditto with the washing machine.
  • My *normal* domestic hot water energy use is most people's *energy saving vacation mode*. That's just a great feeling.
  • With a 50 gallon tank I get 2-3 regular, non-conserving showers per day... on the energy that's wasted in most people's tanks.
  • If I *do* ever run out of hot water, no-one suffers but me. No dead dinos are going to come bail me out (and contribute to global warming) to satisfy my impatience. How's that for personal responsibility?

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Old 07-18-2009, 10:45 AM   #2 (permalink)
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Not a bad idea. All it needs is some planning on when you're using hot water.
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Old 07-18-2009, 11:46 PM   #3 (permalink)
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Pretty much. Really, I was probably being overly conservative with how much water it actually provides. Once I tried to run out the hot water as an experiment, and after running the tub for 15 minutes the water coming out was still shower warm. The water ends up being far hotter than I would ever set it with the thermostat.

The only planning I've ever done is to try and run the dishwasher right after I get out of the shower.
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Old 07-19-2009, 12:12 AM   #4 (permalink)
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Um... this is a great idea... and I'm not sure how it compares, but my dad takes a shower at the same time every day... and he uses a timer to make sure that there is enough hot water to take his shower each day.

When he gets home from work up to 14 hours later, the water is usually still warm enough to wash your hands, etc.

Electric - 30 Gal. Bought last year.

If I were using a gas water heater, I'd consider trying this out. If he decides to go back to gas (he's been talking about it) I'll have him try it. He doesn't like the idea of a pilot light, though, which is the only reason he's not gone back to gas.
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Old 07-19-2009, 01:20 AM   #5 (permalink)
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For an electric water heater that is 240v, what about rewire it for 120v so it's only 1/4 the power? While it will not make for a direct energy savings, it will reduce thermal cycling (and thus prolong the life of the heater) and peak load on the grid. (In some cases, reducing the peak load can save money. If you also have A/C, install a relay to turn off the water heater whenever the A/C is running.)
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Old 07-19-2009, 04:08 AM   #6 (permalink)
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Any idea how much gas it does use to do this?
My parents have a gas water heater with the electronic ignition so the gas water heater is on a timer, it only comes on twice a day for around an hour each time, 5-6am and 3-4pm so that it turns off before much of the hot water is going to be used, kind of like heating up a tea ketel on the stove, you heat it up then use it, after you make your cup of tea you might fill it up but you don't turn the stove burner back on, so why turn your water heater back on after taking a shower, turn it on right before you take the shower, or wash the dishes.
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Old 07-19-2009, 02:56 PM   #7 (permalink)
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Quote:
Originally Posted by Christ View Post
Um... this is a great idea... and I'm not sure how it compares, but my dad takes a shower at the same time every day... and he uses a timer to make sure that there is enough hot water to take his shower each day.
Yep, the methods are pretty comparable. Electrics lose most heat through the tank, whereas natural gas loses it through the flue.

Of course, you should be aware that the carbon emissions of 3 units of natural gas energy is equal to around 1 unit of electric energy. The power plant isn't 100% efficient, nor are the transmission lines.

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Any idea how much gas it does use to do this?
Since water heater companies aren't required to disclose how much the pilot light consumes, it's hard to say. I've seen estimates from 50-1000 Btu/hr. Since my stove also runs on natural gas (and the oven has a pilot light) it's hard to determine the water heater usage alone. Subjectively, it looks a little larger than my oven pilot light, which I'm guessing is on the low end. Ballpark figure, maybe 350 Btu/hr?

Including everything, most water heaters are around 60% efficient. A *lot* of that wasted heat goes out the flue. Even with the burner off, the pipe was warm to the touch. Now the temperature rise is only barely perceptible.

I've insulated the pipes (hot and cold) to cut down on the cycling and losses. I went a little overboard, installing foam pipe sleeves (conductive loss) and then wrapped them with reflective mylar strips (radiative loss), securing it all with cable ties.

Since the water cools down a little after use, the average temperature of the water is lower which reduces standby losses. Taking these three improvements into account, I would say the efficiency has gone to between 80 and 90 percent.
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Old 07-19-2009, 03:45 PM   #8 (permalink)
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Propane figures are comparable to Natty, right?
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Old 07-19-2009, 07:56 PM   #9 (permalink)
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Your hot water demands must be very low! My family could never do that!

A modern high efficiency gas water heater, one that is condensing, brings the temperature of the exhuast gases below 100 C. Like most thermodynamic cycles, even a flame is more efficient at higher temperatures. These units have no pilot light, as they feature electronic ignition. When they're off, no natural gas is being consumed.

You can also put a insulating jacket on it.

There are get a reverse flow heat exhanger that goes in the drain pipe to warm the water going into the tank. This can save a lot of hot water from going down the drain.
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Old 07-19-2009, 10:29 PM   #10 (permalink)
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Quote:
Originally Posted by stevey_frac View Post
Your hot water demands must be very low! My family could never do that!
I use .5 GPM aerators on the bathroom sink, 1.5 on the kitchen, and 1.5 in the shower. I never wash hands with warm water (the water in the pipe is room temperature, and it's the scrubbin' that gets you clean!) The dishwasher gets run maybe 4x/week, and we get in about 1.5 showers/day with no problems (mine is absurdly low water ). Even if I take a 15 minute shower after someone else, I don't have to adjust the temperature at the end.

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Originally Posted by stevey_frac View Post
A modern high efficiency gas water heater, one that is condensing, brings the temperature of the exhuast gases below 100 C. Like most thermodynamic cycles, even a flame is more efficient at higher temperatures. These units have no pilot light, as they feature electronic ignition. When they're off, no natural gas is being consumed.
Cool. I had never heard of this kind of water heater. Here's the EnergyStar page on them.

Do you have a reference for what you said about flames being a thermodynamic cycle? I don't see how that could be, since there's no work being done.

Quote:
Originally Posted by stevey_frac View Post
You can also put a insulating jacket on it.
I've thought about it, but I worry about the over-temperature valve going off!

Quote:
Originally Posted by stevey_frac View Post
There are get a reverse flow heat exhanger that goes in the drain pipe to warm the water going into the tank. This can save a lot of hot water from going down the drain.
Those are so cool. If I had my druthers I would install one in a heartbeat.


That sounds like a great integrated system for hot water, stevey_frac. You might be interested in this low-cost, low-energy shower instructable.

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