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Old 04-02-2009, 09:32 PM   #1 (permalink)
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Hot water!

I've been having a thought on hot water. It would seem to me, that a tanked heater is inherently inefficient. My father has tried to explain to me that the incoming cold water is heated by the hot water already in the tank, which while being true, wouldn't it still require the same energy to maintain the temperature of the tank while cold water is rushing in, as it would be to heat the water on demand in a tankless unit? And then you have to maintain the temperature of the tank during periods of non-use...

I'm using tankless to describe a non-centralized strategy, with individual heaters at the points of demand, say one per bathroom, one for the laundry room, etc.

I figure that the tankless units would at least as much, and possibly just slightly more power than the central unit when supplying hot water, but would offer large savings during periods of non-use, which by my estimates is roughly ~23 hours daily.

Anyone happen to have such a setup and would be willing to tell how it works out?

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Old 04-03-2009, 01:34 AM   #2 (permalink)
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this is part of why you should have a timer on your water heater, you have 50 gallons of hot water, my water bill showed that my house of 3 uses 53 gallons of water total per day, half of that or more is the toilet, being that it is a 30 year old 5 gallon per flush jobber, so my hot water heater heats up the 50 gallons and keeps it hot for a good chunk of the day, then it turns off at night,, late night shower? it's still hot 5 hours after it's turned off, hot enough for a nice shower, as soon as I get more timer trippers in the mail it will be off most of the day too, only turning on long enough to heat up then turning off again right before peek demand.
would you make a cup of tea then fill the pot back up with cold water and put it back on the stove? of course not! so why do that with your hot water heater, use what is hot and let it sit with cold water when you are done.
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Old 04-03-2009, 02:50 AM   #3 (permalink)
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Tankless water heaters do exist and they are more efficient because they don't leave 50 gallons sitting losing heat.


Tankless Water Heater Buying Guide
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Old 04-03-2009, 03:56 AM   #4 (permalink)
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Newer hot water tanks have digital thermometers so that the water has a specified temperature at a specified time of day. The rest of the time it's cooler. There's usually lots of insulation, so it doesn't lose that much heat overnight, or between morning and evening. Also, if it's electric, you might be able to take advantage of cheaper electricity at night, warming water when it's cheaper and then "coasting" through the rest of the day. Also, tanks can take advange of other sources of hot water, like solar or heat pump, they can also be used to dump extra power from wind turbines when it's windy. If you're planning on not being home for longer periods, then you just turn it off.
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Old 04-03-2009, 01:06 PM   #5 (permalink)
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Quote:
Originally Posted by The Atomic Ass View Post
My father has tried to explain to me that the incoming cold water is heated by the hot water already in the tank, which while being true, wouldn't it still require the same energy...
"Honor thy father..." if you like, but don't depend on him as a source of technical advice :-)

Your analysis is correct, but I thnk a better & cheaper solution than using on-demand heaters everywhere would be to get a solar hot water system to maintain the temperature in your storage tank.
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Old 04-03-2009, 10:11 PM   #6 (permalink)
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Originally Posted by winkosmosis View Post
Tankless water heaters do exist and they are more efficient because they don't leave 50 gallons sitting losing heat.


Tankless Water Heater Buying Guide
I am aware of them, actually. They're going into my RV design.
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Old 04-03-2009, 10:14 PM   #7 (permalink)
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Quote:
Originally Posted by Piwoslaw View Post
Newer hot water tanks have digital thermometers so that the water has a specified temperature at a specified time of day. The rest of the time it's cooler. There's usually lots of insulation, so it doesn't lose that much heat overnight, or between morning and evening. Also, if it's electric, you might be able to take advantage of cheaper electricity at night, warming water when it's cheaper and then "coasting" through the rest of the day. Also, tanks can take advange of other sources of hot water, like solar or heat pump, they can also be used to dump extra power from wind turbines when it's windy. If you're planning on not being home for longer periods, then you just turn it off.
It's an older heater without an automatic thermostat, so that's a no-go.

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"Honor thy father..." if you like, but don't depend on him as a source of technical advice :-)

Your analysis is correct, but I thnk a better & cheaper solution than using on-demand heaters everywhere would be to get a solar hot water system to maintain the temperature in your storage tank.
I'm thinking theoretically, and yes, in the case of a house a solar heating system would be better, but it would also require lots of installation. Add to that he's too poor for either solution.

I just like arguing with the old goat.
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Old 04-04-2009, 12:24 AM   #8 (permalink)
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Tankless heaters would also require a lot of installation work. There'd be one at every hot water faucet. You'd have to plumb them in, of course, and run power to them. The circuits would have to be able to carry the needed power, so you might even have to go to 220 volt.
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Old 04-04-2009, 02:07 AM   #9 (permalink)
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Originally Posted by The Atomic Ass View Post
It's an older heater without an automatic thermostat, so that's a no-go.
Retrofit it. Temperature sensor in the tank, timer on the power cord.
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Old 04-04-2009, 10:52 AM   #10 (permalink)
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Quote:
Originally Posted by Piwoslaw View Post
Retrofit it. Temperature sensor in the tank, timer on the power cord.
That may be the way we're going to go.

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