240V Water Heater Fed 120v

[infinity]

My mind was working opposite of the math.

I was thinking since the voltage was half the amperage would double like in a motor application.

Why is it different? I have to say, calculations are my weakness. I completely had this wrong in my mind.

JAP>

This is a resistive load (mentioned in post #11) where the current and voltage are directly proportional, one goes up the other goes up. One goes down the other goes down. You're thinking of an inductive load like a motor where the current and voltage are inversely proportional, one goes up the other goes down and vice versa.

 

[jap]

Thanks for all the feed back.

I'm starting to feel guilty about changing it to 240v.

It just didn't seem right to have a tank of that size on 120v.

Jap>

 

[Hv&Lv]

Didn’t know who to reply to but wanted to kick in..
The resistive loads being Directly proportional is how we work our CVR. (Conservation voltage regulation)
we lower our system voltages during peak times in summer and winter.
Winter, we save a TON of money on our demand...
summer, not so much. Realistically, about all we’re catching is water heaters in summer.

 

[Eddie702]

on 120 volts the heater will draw 9.4 amps so that's why the cord didn't burn. Instead of 4500 watts the heater would put out only 1,128 watts 1/4 capacity as texie pointed out

 

[jap]

With the lower wattage output of a 4500w element being ran at 120 volts (which is actually now 1125 watts)

Would there be a higher temperature setting on the Water Heater that the lower wattage element (being run on 120v) simply couldn't get to?


JAP>

 

[ActionDave]

Sure. It's all about how much heat loss there is in the system. No different than putting heater in a room with all the windows open or closed.

 

[jap]

So it would be safe to say although you can run a large water heater on 120v for roughly the same cost as running it 240v, it's really not practical to do so.

To me it just results in long recovery time of hot water and energizing elements for much longer than they need to be..

JAP>

 

[Barbqranch]

So it would be safe to say although you can run a large water heater on 120v for roughly the same cost as running it 240v, it's really not practical to do so.

To me it just results in long recovery time of hot water and energizing elements for much longer than they need to be..

JAP>

It is practical if your needs for hot water are spaced such that the tank will supply what you need and have time to recover. If you have a backup generator (more common now in California w/ the POCOs shutting down when fire danger is high) it could allow a smaller generator or not the cost of setting up load shedding.

 

[kwired]

So it would be safe to say although you can run a large water heater on 120v for roughly the same cost as running it 240v, it's really not practical to do so.

To me it just results in long recovery time of hot water and energizing elements for much longer than they need to be..

JAP>

Takes same watt-hours to heat same amount of water same number of degrees. Operating cost isn't going to change much at all. Problem is going to be recovery time will be longer or if water demand is high enough it may never completely recover.

 

[jap]

Takes same watt-hours to heat same amount of water same number of degrees. Operating cost isn't going to change much at all. Problem is going to be recovery time will be longer or if water demand is high enough it may never completely recover.

I was thinking that since the wattage output of the lower voltage is nearly 1/4th of what it could be, it would actually take more time to get the water to the same temp than if it was fired at 240v with the full 4500w output.

That along with the question of the lower wattage element actually being capable of getting the temp of the water to the higher temp settings of the thermostat at all.

JAP>

 

[drcampbell]

Takes same watt-hours to heat same amount of water same number of degrees. Operating cost isn't going to change much ...

The operating cost might go down if everybody's forced to take really quick showers, or double up.

 

[broadgage]

It is fairly common to connect a 240 volt water heater to a 120 volt circuit, during power outages. This allows a much smaller and cheaper generator to be used. If hot water demand is limited than it will still reach the same temperature. If the hot water demand exceeds the now very slow recovery rate, then the water will still be somewhat warmed.
Just 1Kw will heat a lot of hot water in a well insulated tank. 1Kw for 4.5 hours will have a similar heating effect to 4.5Kw for 1 hour.

Drifting a little O/T, here in the UK my water heater is only 1Kw and works just fine. It is normally energised via a time switch for 7 hours every night in order to use an off peak tariff. It came with the house, and probably dates back to when the premises had a restricted service of only 20 amps.
UK water heaters are commonly 3Kw, about 12 amps at 240 volts. Higher and lower wattages are available but 3Kw is more or less standard unless there is a special reason to select something else. The smallest readily available element is 750 watts, and the largest is 7Kw to fit a standard domestic hot water tank.

I recently installed a 3 phase 21KW water heater for showers at a sports ground, that is an uncommon type though. Natural gas is preferred for large scale water heating.

 

[drcampbell]

... here in the UK my water heater is only 1Kw and works just fine. ...

How big is the storage tank? How many people use it?

 

[StarCat]

The other thing that can be done is you can set up a PRE HEAT tank wired for 115V ahead of your main unit when you have very cold incoming water. These units can be wried in more than one way, and also the setpoint does not need to be as high for this duty.

 

[PaulMmn]

The operating cost might go down if everybody's forced to take really quick showers, or double up.

Running out of hot water tends to shrink shower times dramatically!!

 

[jap]

Just 1Kw will heat a lot of hot water in a well insulated tank. 1Kw for 4.5 hours will have a similar heating effect to 4.5Kw for 1 hour.

That's both good information, and, good to know.

Thanks,

JAP>

 

[broadgage]

How big is the storage tank? How many people use it?

The storage tank is about 100 litres. Only used by myself at present but proved ample when my late mother was here as well. Only used for dishwashing, and handwashing. I seldom use the bath, preferring to take a shower. I have an electric shower with a loading of about 9Kw.
These electric showers are very popular in the UK, less so in other countries.

 

[kwired]

The storage tank is about 100 litres. Only used by myself at present but proved ample when my late mother was here as well. Only used for dishwashing, and handwashing. I seldom use the bath, preferring to take a shower. I have an electric shower with a loading of about 9Kw.
These electric showers are very popular in the UK, less so in other countries.

Baths and showers are where the most demand for hot water is in a typical dwelling and you have that covered already (at least the shower), though 100 litres (about 26 gallons) is probably enough for at least one average bath, may not have enough recovery time if someone wants to have a second bath in a short time, but then maybe you go back to what it was like years ago and share the water from previous users.

 

[broadgage]

When my late mother was here, the 1KW water heater was ample for a bath, and barely sufficient for two baths. Perhaps the storage volume is a bit more than 100 litres, no capacity is marked on it, my estimate was 100 litres.
Electricity was first supplied to the premises in about 1955 and was originally a 20 amp service at 240 volts. Primarily for lighting and the odd appliance such as a clothes iron, a vacuum cleaner, and perhaps a 1Kw electric kettle, possibly a basic washing machine.
Water heating back in the day was probably primarily from a solid fuel cooker with a back boiler. The electric water heater was probably only used in the Summer when the fire was not lit.

The present day service is 60 amps, single phase, 240 volts. Ample for my simple needs, but 100 amps would be preferable for a family.

 

[LarryFine]

Running out of hot water tends to shrink shower times dramatically!!

That's not the only thing cold water shrinks. :happysad: