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Author:
ddbbp (KS)
How is water heater "stacking" controlled or stopped?
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Author:
bernabeu (SC)
not actually stopped
however, that is the reason for a top as well as a bottom element
for practical purposes it becomes a non-issue
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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638
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Author:
ddbbp (KS)
should have mentioned, gas.
Edited 2 times.
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Author:
bernabeu (SC)
There is a water heater condition called stacking.
Stacking is caused with repeated short draws of hot water.
Each time hot water is drawn out of faucet, cold water immediately enters bottom of water heater tank through the dip tube.
Dip tube is a plastic pipe connected to cold water inlet. Cold water enters at bottom of tank.
So cold water enters bottom of tank near gas water heater thermostat, or near lower thermostat on electric heater
How stacking occurs:
Let's say water heater if fully heated and burner or elements are turned off.
A short draw of hot water causes cold water to enter tank.
Another short draw. And then another short draw, each draw happens near same time as other draws.
Water at top of tank is plenty hot, but bursts of cold water cause thermostat to turn on burner or element.
Water heater heats more hot water, and more hot water rises to top of tank.
Top of tank was hot before, but with added heating, the water becomes hotter than usual.
Water at top of tank becomes overheated each time stacking occurs.
This can cause TP valve to release water, and cause ECO energy cut-off to trip on upper thermostat of electric water heater.
Stacking may not be the cause of your water heater problem.
However, remember if single-handled faucet is opened straight upward, then that will draw both hot and cold water out of water lines.
As soon as hot water runs out of faucet, cold water enters tank. This is ingredient for stacking, and is energy-wasteful.
Crossover can cause stacking.
Only when single-handled faucet is lifted with handle fully to the right, does faucet draw only cold water.
But some single-handled faucets have 'crossover' between hot and cold sides because of defect faucet cartridge.
When crossover is present, hot water draws each time any faucet in house is turned on.
To test for crossover: Turn OFF water to heater. Cold water pressure is still ON. Next, turn on hot side of all faucets in house and wait 10 minutes and check for water flows. There should be no water flowing. If water flows, then that means one or more faucets has crossove problem. To test which faucet, turn off all faucets except hot side on one faucet. Put ear against each single-handled faucet in house and listen for flowing water. Also check mixing valve on water heater if one is installed. Defective check-valve can also cause crossover.
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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638
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Author:
ddbbp (KS)
great info!
So how do I lessen the effect? Will simply lowering the thermostat help?
Short draws of hot water sounds like normal everyday use to me.
Edited 1 times.
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Author:
bernabeu (SC)
SHORT draws of hot water are NOT normal everyday use.
Hot water to wash one's hands is NOT a short draw.
ACCIDENTAL short draws as when a single handle faucet is used without actual hot water reaching the faucet is one cause.
REREAD the possible solutions.
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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638
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Author:
ddbbp (KS)
I don't have any single handle mixing faucets in the house and no mixing valve.
Edited 1 times.
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Author:
george 7941 (Canada)
I see stacking occurring in my gas water heater at home, repeated short draws causes the water to be extra hot. However, I am not sure I fully understand how stacking occurs in a gas water heater. Is it the case that after the hot exhaust gas has heated the cold water at the bottom of the tank, this somewhat cooler, but still hot, exhaust gas travels up the baffle (turbulator) and further heats up the already hot water at the top of the tank?
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Author:
asktom (MT)
What are symptoms of your problem? It could be a broken dip tube rather than stacking if you run out of hot water quickly.
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Author:
bernabeu (SC)
ddbbp (IN),
you could try lowering the stat to 120 degrees
you could add an (or service existing) expansion tank to prevent TPRV from 'pissing' due to overheat
you could contact the heater's customer service department
(imo: a broken dip tube would NOT lead to stacking, merely a 'shortness' of HW)
Best of Luck
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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638
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Author:
JLNY (NY)
Do you have a humidifier on your furnace that draws water from the hot side? If the solenoid valve is bad on the humidifier, that may also cause stacking to occur.
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Author:
george 7941 (Canada)
Here is what I do not understand about stacking.
Each time the heater heats up cold water at the bottom, say to 140F and it migrates to the top of the water heater, the water at the top is at 140F. Repeated short draws of water will generate more 140F water. Whether you have 10 gallons of 140F water at the top of the heater or 20 gallons, it is still 140F at the top. How does the water at the top get heated to 160F?
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Author:
packy (MA)
with a gas heater, the t-stat is near the bottom. that is where the 140 is determined. by the time the water at the bottom is 140 the watewr at the top is somewhat hotter.
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Author:
george 7941 (Canada)
Ok, but that still does not explain why short draws heat the water up to a higher temperature. I see more quantity of hot water but not higher temperature,
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Author:
bernabeu (SC)
no 'draw'
the water on top is 140
the water on bottom is 135
short draw(s)
heater 'fires' due to cold entering at bottom (dip tube) and near bottom stat
ALL water is heated due to venturi/turbo tube heating
stat on BOTTOM satisfied quickly to 140
previously 140 water 'stacked' on top has received heat input - ? now 150 ?
repeat until TPRV 'pops'
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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638
Edited 1 times.
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Author:
george 7941 (Canada)
Thanks, bernabeu.
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