Efficiency of water heater changeout


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Old 11-29-18, 08:51 AM
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Efficiency of water heater changeout

A family member lives alone in a house with an 80 gallon water heater. He seldom has company and due to travel demands only is at the home on an alternating schedule of 3 nights a week one week and 4 nights/week the following week. So he has relatively small shower use, basin use, and perhaps 2 loads of dishes per week. Clothes washing is primarily with cold water.

Can anyone generalize with any knowledge whether adding a 30 gallon water heater into the plumbing system and valving off the existing tank would make economic sense? We can do the work ourselves. Electric rates are about .15/kwh.
 
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Old 11-29-18, 07:13 PM
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Sure..... a 30 gallon or even 40 gallon tank would make more sense. Less standby loss. You could even install a seven day timer on it so that it heated the water when needed. Probably allow 4-6 hours before needing hot water to heat it. The exact recovery time will be listed in the heater specs.
 
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Old 11-30-18, 09:54 AM
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Thanks, Pete: I am assuming it costs the same to heat a certain volume of water in a 40 gallon tank as it does a 80 gallon tank. If that is correct I would think the savings between the two tanks would be solely from the reduced heat loss. He would need to save enough KWH to overcome the appx cost of $450 to buy the tank and associated valves, etc. So at .15/kwh, he would need to save 3000kwh. Assuming the two tanks have the same insulation, can you estimate how many years that KWH savings would take.

Thanks for your help.
 
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Old 11-30-18, 11:29 AM
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I wouldn't bother with the cost of changing out the water heater. All I would do if I were that person is turn the breaker off when I was leaving for more than just one night. Heating 50 gallons probably wouldn't take more than an hour once I returned.
 
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Old 11-30-18, 04:12 PM
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Might be a good application to have a timer that would allow the heater to operate only a short period of time each day. Maybe experiment with a one hour burn every 24 hours and then bump up the operating time if needed. At 4500 watts, that would cost .675 cents per day or $246/year which is about half the cost shown on the yellow sticker on the heater.
 
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Old 12-01-18, 08:03 AM
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If the heater requires a one hour burn every 24 hours then if you left it powered of for two days it would require about a 2 hour burn to get back up to temperature then. (By the time you got to the fourth consecutive day, the heat loss per additional day will be noticesably less since the difference between the water temperature and room temperature will be smaller.)

Put an insulated blanket around the outside of the existing heater rather than buy another, smaller, heater. Also insulate both the hot and cold pipes on top for several feet and insulate the pipe coming down from the relief valve.

Incidentally the standby heat loss depends on the surface area of the tank as opposed to the volume of water inside.

For an all electric water heater, if it had sat on an insulating pad (rigid enough or framed to not get squashed and letting the heater tilt) the standby loss would have been reduced further.
 

Last edited by AllanJ; 12-01-18 at 08:24 AM.
 

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