# Forum Home Renovation Plumbing  water running out qiuckly with electric heater??

## wozzzzza

in a house we just bought its got a 5 year old 250L rheem tank electric water heater in the laundry and the tennants reckon that after 2 people have had 10 minute showers its runs out of hot water and takes an hour or so to reheat.
is this normal?? ive never owned a electric hot water heater.

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## woodbe

Nope. Not normal. 
Assuming a 12L/minute shower head, and 50/50 hot/cold water mix, a 10 minute shower should use about 60L of hot water, so 120L or roughly half a tank for 2 showers. If the shower heads are high flow, say 20L/minute, then yes, you could use all the water in 2 showers! 
We have a 330L and four people, and have hardly ever run out. We have put 9L shower roses in though, and tried to imprint the kids with saving water. 
I'd check or just replace the shower heads with something more economical to see if it solves the problem. If so, also get the HWS onto offpeak, it must be costing a bomb if its on day tariff. 
woodbe.

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## murray44

It also depends what the temperature is to as well. 
If the temp is set too low, then you'll use mostly hot water in the shower, if the temp is set high then you'll use less hot with more cold mixed in and it will last longer. 
Obviously a higher temp costs more to keep it that way.

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## Smurf

Adjust the thermostat to 70 degrees if it's presently set lower and that should supply enough hot water. Depending on the model of heater, it may even be able to be set as high as 75. There will be a label on the heater (near the top on the side) that tells you the max temperature it should be run at - should say 70 or 75.  
I used to have the same unit, Rheem 250 litre electric, and it would run the shower for over 40 minutes with the thermostat in the heater set to 70. And since I'm in Tas, the incoming water during Winter is pretty cold. 
It is fairly common for thermostats to be set at 60 degrees - do the math and that's a much bigger difference in energy stored in the hot water than you might think, hence it runs out faster.

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## Bedford

Is this a twin element HWS, it may be only working on the top element? and no I am not a school teacher.

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## chrisp

The reheat time is fairly simple to calculate: 
If we assume that the water enters at 10 degrees and is reheated to 60 degrees, the temperature difference is 50 degrees. 
The energy required is:250 litres (actually kgs) x 50 degrees x 4200 (heat cap. of H2O) = 52.5 MJ.As a Watt (W) is a Joule per second (J/s), a kWh = 3.6MJ and the electric hot water system probably has a 4.8kW element.  The time to reheat from cold would be: 52.5MJ /(4.8 kW x 3.6MJ/kWh) = 3 hours

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## Wombat2

Open the safety valve and let more water into the unit ( that's the lever thing at the top of the tank) until it starts to flow out the overflow 
We have to do that every couple of months - it tops the tank up which drops as the water heats and expands and over flows.

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## wozzzzza

it definately hasn't got a water saving head on it, its an old water guzzler and temperature was down low the tennants said.  they said they turned it up to 70 so will see how it all goes.  dunno how they turned i tup as i wouldnt have a clue without pulling apart to see.

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## woodbe

> 52.5MJ /(4.8 kW x 3.6MJ/kWh) = 3 hours

  3 hours @ 4.8kw = 14.4kwh @0.20/kwh = $2.88 If you could get it on offpeak it should go under $1 a day. 
We have a more economical heater on offpeak, and our last quarter's hot water bill was $15.39 - 17.5c/day 
Worth doing something about! 
woodbe.

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## Wombat2

This is the type of valve I mean - lift up the lever until the water flows out the overflow - if it hasn't been done for a while it may take a couple of minutes  HOT WATER SYST TEMP/PRES TPR VALVE 1400 KPA HT-55 - eBay, Hot Water Heaters, Systems, Appliances, Home. (end time 22-Apr-10 16:54:54 AEST)

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## Bloss

> it definately hasn't got a water saving head on it, its an old water guzzler and temperature was down low the tennants said.  they said they turned it up to 70 so will see how it all goes.  dunno how they turned i tup as i wouldnt have a clue without pulling apart to see.

  Water saving head is user replaceable and cost under $30 - do it. Elements are often 3.6kW not 4.8kW - that will increase the re-heat time. 
IMO 10-min showers are just irresponsible in SA and anywhere with water constraints. 4 min max (tell them to get a timer! is more than enough with a little longer for a wash and condition of long hair a few times a week. 
High temp (>60) is certain and almost immediate scalding so better to use tempering valves and the other options first. And 70 costs more to get to than 60 of course. 
Then again the tenants are the ones that pay the bills - and should have the incentive to change their behaviour - you should just replace the shower head. 
BTW - Not wise IMO to ask the tenant to alter the temp on an electric HWS - although it is not all that difficult if you know what you are doing the removal of the metal access panel often means direct exposure to uninsulated 240v wires and fittings. If they turned the power off  OK, but if I were the landlord I wouldn't tell them to do that.  :Frown:

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## chrisp

> Elements are often 3.6kW not 4.8kW - that will increase the re-heat time.

  Psst, Bloss, don't tell anyone, but I checked that model on the web - they seem to have 4.8kW elements.  :Wink:

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## Smurf

> Psst, Bloss, don't tell anyone, but I checked that model on the web - they seem to have 4.8kW elements.

  You can fit any element to the Rheem water heaters. 
1.2kW - 1.8kW - 2.4kW - 3.6kW - 4.8kW - 6kW  
All those elements will fit the water heaters and are easily changeable. 
This does vary between states, but here in Tas a 250L unit comes standard with 3.6kW element. These are sometimes changed to 2.4 or 1.8kW where the wiring isn't adequate for 3.6kW however. Only last week I saw a new 160L heater with 1.8kW element fitted for this very reason - it's 1mm cable with an 8amp fuse that supplied a previous water heater in the same location. 
Also, there are regulations about element sizes imposed by some electricity authorities. In Tas it's a maximum of 16 Watts per litre in order to qualify for either off-peak or 24 hour heating tariffs in a domestic installation (32 W / litre for commercial installations). Anything larger than that and it must go on the (rather expensive) general supply tariff - I've never seen that done in a domesitc installation except for very small water heaters in flats (small units are now allowed an exemption from the 16 W / litre regulation by the way provided there's only one heater installed). 
Victoria with it's 6 hour off-peak tends to favour larger elements than the states with 8 hour off-peak. 
As for 60 degrees versus 70, again there's some local variation in what is considered "normal". In Tas, 70 has always been considered "normal" for domestic hot water although it's become somewhat more common to see 65. Very unusual to see one turned all the way down to 60. Lower temps seem to be more common in the other states however. 
Tank sizes also vary. In Vic it's common to have 315 or 400 litre on 6 hour off-peak. In Tas it's common to have 160 litre / 2.4kW on 24 hour heating rate and 250 litre / 3.6kW is considered a big water heater for domestic use. Never seen a house in Tas with 400 litre, and very very few with 315. In NSW the small 80 litre units seem to be somewhat common for domestic use. 
Twin element is another one with state based variations. In Vic you used to (still do?) get the off-peak rate (switched on 24/7 for the upper element only) for both elements as long as the tank meets the required minimum size. In Tas I've never seen a twin element tank installed for domestic use other than with solar - probably because you pay the high general power tariff for the upper element. 
As for the cost of 60 versus 70, it will make zero difference to the energy actually used in the shower per minute that it's running - you'll just mix more hot / less cold if you turn the thermostat down. Where the saving will be is in reduced heat losses from pipes every time you turn on the tap, and the tank itself 24/7.  
Topping up the tank as mentioned in another post - that's not required with the Rheem units but it can be necessary with the Saxon heat exchange units with an internal copper coil since those tanks are not pressurised and lose water to evaporation. 
Length of shower? Not an issue for me as there's more water than we could possibly use anyway but all the calculations I've ever seen for either household or commercial (hotels etc) hot water assume 10 minute showers. 
Tank size? The various manufacturers produce sizing charts but a look at an old electricity authority one shows that a 250 litre unit with 3.6kW element on continuous supply will be adequate for 6 people. On off-peak it would be adequate for 3 people (or 4 people on off-peak extended hours).

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## wonderplumb

Don't have ten minute showers!

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## Bloss

> Don't have ten minute showers!

   :What he said:  and that's what I said too . . .  :Biggrin:   :2thumbsup:

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