The Tank › Electric element types
- December 13, 2008 at 3:27 pm #10062spaceghost43201Participant
I will be buying a new water heater shortly and found a lot of good information on this site. One thing that i didn’t see was the importance of different types of heating elements in electric tanks. I’ve looked at tanks in stores and online that have different elements but still have the same specs (Watts, EF, GPH recovery). Many didn’t list the first hour recovery. Is there much of a difference?December 13, 2008 at 6:04 pm #10063energyexpertParticipant
A 4500 watt element will increase the temperature of 20 gallons of water by 90 F per hour. If you only had a lower element in a 50 gallon tank you would have about 40 gallons above the element. After an hour a 4500 watt element would change the temperature by about 45 F if there was no usage during the hour. My 105 gallon tank will require twice as long to completely recover as a 50 tank tank if they both have the same wattage. In buying a water heater you have to have enough storage to meet the use of maximum drawdown (ie do you take 2 showers back to back or 4 showers back to back?) and enough wattage to recover before the next major drawdown. Things like a gravity film drain heat exchanger can recover BTUs from waste water which means you might be able to reduce either the size of the WH and/or reduce the wattage. The reason I have a large tank is because I heat water off-peak at a reduced electric rate.
Multiply watts x 3.413 to get BTUs/hour. A BTU is the amount of heat required to change one pound of water one degree F. One gallon of water weighs about 8.33 lbs. 4500 watts = 15,360 BTUs/hr. 3500 watts = 11946 BTUs/hr.
A “long” 4500 watt element has a longer life than a shorter 4500 watt element. If you spread the same watts over a longer resistor then the linear heat generation rate is reduced (ie it runs cooler/foot).
DavidDecember 13, 2008 at 8:59 pm #10067spaceghost43201Participant
What about the difference in materials? How much better is a stainless over a copper? How many options are out there.December 14, 2008 at 4:13 pm #10070Larry WeingartenParticipant
Hello: You can choose from stainless, copper, tinned copper and a copper nickel mix. Your water has a lot to do with what’s needed. If plain copper elements last, there is no need to go with a more robust element. Asking local service plumbers what holds up might point you in a good direction. Or, simply watching how well the elements (particularly the lower one) in your new tank hold up, will give guidance.
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