Replacing 120v water heater w/240v???

Hello all,
I have a cottage with a 120v (1500W 15 gallon) water heater. It's made by Simpsons-Sears so let's assume it's about 20 years old. It is located in the bathroom.
I'd like to relocate this heater to the attic and will follow the usual precautions (drain pain, drain tube to outside, etc.). While relocating the heater, I'm considering replacing it due to the age of the unit.
The only power this unit can have is 120v on a dedicated 15A breaker. This is a "circuit breaker" type fuse screwed into the original 60A panel in the cottage.
Can I use a 240V water heater and what will be the difference in recovery time? There is only one shower in the cottage (no tub, washing machine, dishwasher etc.) so there is very little hot water used. Max 2 showers/day plus whatever hot water is used in the sink.
I'd like to replace the 15gal unit with a 30gal 240V unit running at 120V. I understand that the unit will only heat up 1/4 as fast at 120V. So if the unit I'm looking at says "Recovery time to 90 degrees = 21 Gal/hr" does this mean my unit will recover at about 5 gal per hour or 6 hours to recover the entire tank? I can live with this considering we use 15 gals or less a day anyhow (based on the existing tank size).
Am I on the right path here thinking that 6 hours to recover the tank is about right, or will I be waiting longer for hot water? I may also consider turning the temperature up a bit on the tank (to minimize the hot/cold ratio of water produced) since there is a scald-proof fixture in the shower.
Thanks! Neal ( snipped-for-privacy@bhattmail.net)
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For 1500 W at 120V you'd need a 6000W 240V element (available but maybe special order) in the heater, 4500W is common and 5500W can be had, yielding 1125W and 1375W respectively, so you're 33% or 9 % slower to recover already. Now, you double the heater volume that becomes 66% or 18% slower recovery. I'd say you're in the ballpark w/ 6 hrs. Hotter setting and an antiscald (or at least a tempering valve) on the heater (even w/ the antiscald feature of the shower) will only get you a little, though it should stabilize the hot water temperature at the fixtures.
240V 20A to run a 3500W elemented 20 or 30 gal heater is not an option (even w/ a dedicated single duplex breaker/box and 12-2 vs 14-2 wire installed)? That would give plenty of hot water for the shower and reasonable recovery at reasonable current draw (14.5A at 240 V vs the present 12.5A at 120V). Failing that I'd get 120V 1500W element 20 or 30 (depending on availability) for the new heater and replace the 240V units so you had 20 or 30 gal and 1500W vs 15 gal and 1500W. Remember while a cold start is twice as long to ready, you can shower about twice as long before hot water's all gone too w/ a 30 gal
In any 120V case I'd remove the screw in breaker and use a conventional fuse.
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I changed a 240v circuit that a floor heater was on to 120v, and it probably puts out about a quarter the heat, as expected. I don't have a good feeling about doing it with a water heater though. Heat transfer is proportional to the difference in temperature. I think maybe the 120v heater simply won't get hot enough to heat your water properly. Unless someone knowledgable tells you it works, I wouldn't try it.
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Toller wrote:

I'd like to hear your explanation of why you think that's so Toller.
I say:
Each watt of electrical energy dissipated in the tank equals 3.4129 BTU/hour.
One BTU is the amount of heat required to raise one pound of water one degree Farenheit.
As long as there's equal amounts of electrical energy (Watts, which equals volts times amps.) being dissipated in the water, the rate of temperature increase will be the same. It matters not whether the voltage driving that dissipation is 120 or 240. (Or even 623.75 volts for that matter.)
Jeff
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It would be more accurate to say "each watt of electrical power..."
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

I dunno... I've always thought of it as being energy *before* it gets used and power (watts) after it is. <G>
Jeff
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Running a 240V water heater on 120V does work and produces reasonable temperatures, but the recovery time is just plain awful.
[My parents-in-law had one miswired that way. Probably for over 20 years. It worked, but took a whole day to recover from a couple of showers. How they survived with that, I'll never know.]
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Chris Lewis, Una confibula non set est
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Neal Bhatt wrote:

I had an old 60A service in my house when I bought it. Yours has 2 cartridge fuses for the mains, takes 4 or 6 plug fuses, and 2 cartridge fuses for the range, right? Do you have an elecric range? If not, can you put the water heater on the "RANGE" cartridge fuses? Also if you are running new wires, why are you limited to 15A? Those old fuse boxes take 30A fuses. Run #10 wire and use 30A fuses.
I don't know if you can run a 240V heater on 120V and have it work. But can you find a 120V heating element that will fit a new 30 gallon heater?
-Bob
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Why are you assumimg you can only have 120V? Are you sure you don't have both legs of a 240 system? Same number of wires (to the heater).
Tim S.
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Neal Bhatt wrote:

the small/low voltage H/W heater is located in the bath for a reason..... you gonna have a heat loss when you move it away from the bath...travel time.....
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Neal Bhatt wrote:

I suggest you call in a pro. There are other good options. I'll bet a pro will not stop with saying "The only power.." or "all you can do is..." They will tell you what the good options are, they know the tricks to making things work right.
You have gotten some good advice from others and maybe one will work for you, but if not let someone with the knowledge come out and see exactly what you have and make suggestions. Only by taking a look can someone really say.
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Joseph E. Meehan

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Right. Running a 240V heater on 120V is a pure hack. It'll _work_, but rarely to any great satisfaction. The OP should find out his full range of options first. Here, we'd have difficulty doing that because we can't "see" the full installation and what options the OP has. It may be a simple matter of re-arranging another fuse feed to get 240V.
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