Author Topic: 120V vs 240V why the difference?  (Read 49493 times)

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pepperhead1963

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120V vs 240V why the difference?
« on: May 16, 2006, 12:59:52 PM »
I live alone and take a 5 minute shower, cold water laundry and in winter dishes are washed in hot water from stove.  I want to downsize my water heater.  My electrician is trying to convince me to get a 240v, 3000 watt, 22 gallon water heater.  I want a 120V, 1500 watt, 10 gallon heater.


He says the 1500 watt will be 'harder' on the electric bill.


So if Volts X amps = Watts, who cares what the voltage is? as long as the result is the same, I pay for kwh, not amps...


I just need a bit of hot water and 1500 watts seems to fit the bill


I understand wiring size is bigger with 120v, but how is it harder on electricity.


Thanks

« Last Edit: May 16, 2006, 12:59:52 PM by (unknown) »

AbyssUnderground

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Re: 120V vs 240V why the difference?
« Reply #1 on: May 16, 2006, 07:48:15 AM »
Its probably harder on the electricity because it takes longer to warm it up, and over the time its warming up its losing some of the heat. Because of this its on slighly longer than a more powerful one to make up for the losses during the heating process. It wont be by much each time but it might become noticable over time.
« Last Edit: May 16, 2006, 07:48:15 AM by AbyssUnderground »

wdyasq

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Re: 120V vs 240V why the difference?
« Reply #2 on: May 16, 2006, 08:21:53 AM »
He is probably speaking how 220 takes half the energy on each "leg" of a single phase system.  I'm not sure how that will directly effect meter readings.


Of course, he could be ignorant or stupid.


Ron

« Last Edit: May 16, 2006, 08:21:53 AM by wdyasq »
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pepperhead1963

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Re: 120V vs 240V why the difference?
« Reply #3 on: May 16, 2006, 08:34:06 AM »
That is what baffles me, he is an electrician after all.


Watts is Watts

« Last Edit: May 16, 2006, 08:34:06 AM by pepperhead1963 »

Nando

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Re: 120V vs 240V why the difference?
« Reply #4 on: May 16, 2006, 09:27:37 AM »
let me explain some electricity facts.


The 1500 watter, 10 gallons will be "harder" on the electricity BILL because it will be running ON for longer time than the 240 volts unit, and the current will have higher power line drops.


The electrician is giving his response with the way that people use HOT water.


If you want to reduce the electricity usage, take one and INCREASE the thermal isolation to a maximum.


A friend of mine was complaining with the same reasonings and I , joking, told him that he should get a lot of insulation and fill the small closet where the electric water heater was placed to reduce the heat loss to a minimum.


about 4 or 6 months later he called me to thank me for the insulation idea, I do not remember the energy savings, he has one of those KW recorders and determined that the savings where there, then he changed the 240 volts connection to 120 volts power reducing his heating power further.


His tank is a 40 gallon and the equivalent insulation is about 18 inches, not counting the tank insulation.


I am wondering if my friend and pepperhead1963 are twins or what ?.


Nando

« Last Edit: May 16, 2006, 09:27:37 AM by Nando »

SmoggyTurnip

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Re: 120V vs 240V why the difference?
« Reply #5 on: May 16, 2006, 09:47:41 AM »
"So if Volts X amps = Watts, who cares what the voltage is? as long as the result is the same, I pay for kwh, not amps..."


I agree with you.  There will be no difference.



  1. 5 kilowatt = 5123  btu per hour.
  2. 0 kilowatt = 10246 btu per hour.


Electric heaters are close to 100% efficient.


It will take longer to heat the water but the

heat loss is proportional to the temperature

defference so you won't be lose alot of heat

when the water is heating up.


.

« Last Edit: May 16, 2006, 09:47:41 AM by SmoggyTurnip »

pepperhead1963

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Re: 120V vs 240V why the difference?
« Reply #6 on: May 16, 2006, 09:54:34 AM »
Nope, there is only one PepperHead ;)


Ok, so now I know what the probable reasoning is for my electricians statements.


What would you guys recommend (majority rules)



  1. A five minute shower every day (one person)
  2. Occasional dishes (three times a week)
  3. All cold water laundry


Thanks in advance to all..

« Last Edit: May 16, 2006, 09:54:34 AM by pepperhead1963 »

Titantornado

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Re: 120V vs 240V why the difference?
« Reply #7 on: May 16, 2006, 10:03:18 AM »
The heck with either tank style water heater.  Get an "on demand" instant water heater.  There's no sense in heating what you're not using.  Propane units are better (capable of heating water hotter/faster) than the electic ones, but cost more too.
« Last Edit: May 16, 2006, 10:03:18 AM by Titantornado »

pepperhead1963

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Re: 120V vs 240V why the difference?
« Reply #8 on: May 16, 2006, 10:12:22 AM »
Cost is a consideration, I priced them already, $2200 (cdn) and propane is insanely expensive up here (Prince Edward Island, Canada)
« Last Edit: May 16, 2006, 10:12:22 AM by pepperhead1963 »

jimjjnn

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Re: 120V vs 240V why the difference?
« Reply #9 on: May 16, 2006, 03:01:08 PM »
I believe that there are on demand electric water heaters too. I think they are more for kitchens( I may be wrong).

Try a Google for on demand water heaters. I had a nat gas unit in the house that I sold last year. We were able to take 2 showers at one time easily. Ours was the Takagi TK-1 water heater. My daughters have there own places now and want to install demand heaters, also. They have new water heaters now and hope they break down to have an excuse to replace them.
« Last Edit: May 16, 2006, 03:01:08 PM by jimjjnn »

kenputer

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Re: 120V vs 240V why the difference?
« Reply #10 on: May 16, 2006, 03:12:10 PM »
Pepperhead, look up Paloma demand water heaters,I think they have some good prices and sell out of Ont.

Ken
« Last Edit: May 16, 2006, 03:12:10 PM by kenputer »

richhagen

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Re: 120V vs 240V why the difference?
« Reply #11 on: May 16, 2006, 05:31:46 PM »
The main losses would be wiring losses, and thermal losses from the tank, assuming the piping to and from is the same.  For the wiring, properly sizing the wiring should minimize that loss in both cases.  Since the 10 gallon tank has a smaller surface area, if the insulation was of the same R value, then the 10 gallon tank would be way more efficient.  If you heat with wood, or even if not in the summer when it is hot, you could force the water to run through a dummy tank or other heat exchanger to take in some room heat before entering the electric hot water tank.  Solar hot water heating systems that preheat the water also seem to be very efficient, and economically worthwhile in most areas, although a bit more work to put in.  These are just my opinions.  Rich
« Last Edit: May 16, 2006, 05:31:46 PM by richhagen »
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RP

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Re: 120V vs 240V why the difference?
« Reply #12 on: May 16, 2006, 06:42:46 PM »
"Since the 10 gallon tank has a smaller surface area, if the insulation was of the same R value, then the 10 gallon tank would be way more efficient."


I think that's backwards.  The ratio of surface area to volume will be higher.  That's why elephants have such big ears to get rid of the heat they generate inside their (relatively) small surface areas and small animals eat so much to stay warm.


Another observation, skinny people seem to complain about being cold more often.  I can say that 'cause I used to be one.  ;-)

« Last Edit: May 16, 2006, 06:42:46 PM by RP »

terry5732

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Re: 120V vs 240V why the difference?
« Reply #13 on: May 16, 2006, 11:45:53 PM »
The electrician is trying to sell a service. Like the guy trying to sell you a Caddy stead of a Chev. They both get you where you're going. But he will extoll the virtues of why the Caddy is saving you money. There is prolly about three honest mechanics, two honest electricains and no honest plumbers in the US. I don't know about canuckland.

Skinny people got no insulation. I'm freezin.

Although 100% of your electricity is converted to heat, it comes from a producer that is only converting about 30% of their heat to  electricity, but you are paying for 100% of their heat. YOU are paying. You are paying for 330% of what you use. With propane you are only paying 100% of the 90% you get. I changed from electric to gas about two years ago. It would seem water was 75% of our electric bill. From $100/month to $25/month. Have yet to see an increase in gas consumption worth mentioning. If you have free electricty disregard this.
« Last Edit: May 16, 2006, 11:45:53 PM by terry5732 »

kenputer

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Re: 120V vs 240V why the difference?
« Reply #14 on: May 17, 2006, 05:36:16 AM »
What I have done on a few jobs is run 2 supply lines to the water heater,1 direct to the the supply and another is a longer run through the attic space for summer use this preheats the water suppling the heater,can also add small circulator throttled down to slowly send the water back around. Put an inline thermostat to shut the circulator down when tank reaches set temperture.Just put in some isolation valves and drains if you live in an area that has frezzing temps.
« Last Edit: May 17, 2006, 05:36:16 AM by kenputer »

jmk

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Re: 120V vs 240V why the difference?
« Reply #15 on: May 17, 2006, 05:53:48 AM »
 I would go with the one you want. That way it wont build stress every time you think about it. The other one will cause grey hair, and you will think about it  even more than you use it.
« Last Edit: May 17, 2006, 05:53:48 AM by jmk »

SmoggyTurnip

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Re: 120V vs 240V why the difference?
« Reply #16 on: May 17, 2006, 06:39:46 AM »
I have been thinking about this some more.


It seems to me that most of the wasted energy in a domestic

hot water heater comes from heating the water that you don't use.

If you have a 30 gallon tank and only use 10 gallons of water

a day you will need to heat 10 gallons of water from 50 degrees

to your set temp and maintain 20 gallons at the set temp for

24 hours. So all of the loss is maintaining 20 gallons at temperature.

This means to me that the smallest tank with the largest heater

would be the best option for energy conservation. I guess this

is what an on demand heater is.


.

« Last Edit: May 17, 2006, 06:39:46 AM by SmoggyTurnip »

pepperhead1963

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Re: 120V vs 240V why the difference?
« Reply #17 on: May 17, 2006, 06:52:44 AM »
Thanks to all who gave advice.


Now I have some decisions to make


Great board sysadmin

« Last Edit: May 17, 2006, 06:52:44 AM by pepperhead1963 »

jimjjnn

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Re: 120V vs 240V why the difference?
« Reply #18 on: May 17, 2006, 07:57:29 AM »
On demand water heater doesn't have any storage tank other than water in the copper coils of which there are many
« Last Edit: May 17, 2006, 07:57:29 AM by jimjjnn »

richhagen

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Re: 120V vs 240V why the difference?
« Reply #19 on: May 17, 2006, 07:58:45 AM »
If you were looking at the heat loss per unit of water, that would be correct, however the total heat loss is dependent upon the total surface area, so with more surface area to conduct, you have more losses.  Rich
« Last Edit: May 17, 2006, 07:58:45 AM by richhagen »
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Nando

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Re: 120V vs 240V why the difference?
« Reply #20 on: May 17, 2006, 02:17:50 PM »
Alternate solution is to have a timer to start/stop the heater when it is not needed.


the smaller tank will heat up faster since the volume is just 10 gallons.


Nando

« Last Edit: May 17, 2006, 02:17:50 PM by Nando »

BT Humble

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Re: 120V vs 240V why the difference?
« Reply #21 on: May 17, 2006, 07:21:05 PM »


I live alone and take a 5 minute shower, cold water laundry and in winter dishes are washed in hot water from stove.  I want to downsize my water heater.  My electrician is trying to convince me to get a 240v, 3000 watt, 22 gallon water heater.  I want a 120V, 1500 watt, 10 gallon heater.

He says the 1500 watt will be 'harder' on the electric bill.


If I were you, I'd wear gumboots, push a wheelbarrow and carry a shovel the next time I went to talk to that electrician.


BTH

« Last Edit: May 17, 2006, 07:21:05 PM by BT Humble »

Slingshot

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Re: 120V vs 240V why the difference?
« Reply #22 on: May 28, 2006, 09:19:04 PM »
Actually, everything else being equal, the water heater which heats more slowly will consume less energy.  The tradeoff is that you must wait longer for your water to heat.


This is because the input energy goes two places - (1) to heat the water, and (2) to replace losses (heat escapting outside the system).  


(1) Energy required to raise the water temperature is equal in both cases, ie rate of energy addition has no bearing on heat capacity of the water.  


(2) Energy lost through the tank walls is a function of water temp vs outside temp, integrated with respect to time.  Over time, the average temperature of the slow-heating tank is lower, therefore less losses to replace.  Consider an extreme case of a tank that could re=heat instantly - it sits 100% of the time full of the hottest water, and loses the most energy to the outside because of it's greatest temperature delta.


I agree with your assessment of wiring losses for the two voltages.  High-current applications such as this often result in energy wasted within the walls of the house.

« Last Edit: May 28, 2006, 09:19:04 PM by Slingshot »

jonas302

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Re: 120V vs 240V why the difference?
« Reply #23 on: December 09, 2006, 08:36:52 PM »
you have to remember most professionals are not educated or interested in alterative ideas on ly what keeps standard customers happy, the ones that don't look at the bill  on an intersesting note I also live alone and use the same amount of water the house has 2 80 gallon off peak electic water heaters and a 50 gal storage tank my water heating bill is 5.50 a month so a well insulated tank of any size shuld work well

Jonas
« Last Edit: December 09, 2006, 08:36:52 PM by jonas302 »

Dennisd

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Re: 120V vs 240V why the difference?
« Reply #24 on: December 09, 2006, 09:51:25 PM »
As an electrician, I can say that one difference is in the line losses from meter to house. 3 wire 120/240v systems will have the same amount of wire, the 120 v conducting on one hot and the neutral, 240 across both hots. for the same, amount of hot water heated, the losses will be double. however, with proper wire sizing, this should be so slight not to mater (code says line loss must be under 5%)

  A more common problem is that 120v heaters are usually built as small as possible, to fit under counters,and such, so usually lack enough insulation. As to on demand heaters, I currently have a Takagi JR gas demand heater, ($1200 plus install- Edmonton). this heats my home and hot water, no furnace. (I now have my solar pre-heater working) When I lived in Germany, all we had was electric on demand heaters, they work great with a low flow shower. For your requirements, a 220v under sink instant hot water "point of use" heater might make more sense (most people are so used to huge demands, that they don't even look at these, like someone with a big block V8 wondering why you want a extra small gas tank for your hybrid). Some more to think about

DennisD

« Last Edit: December 09, 2006, 09:51:25 PM by Dennisd »