Water Heater Temp

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Mikeyboy

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I have a 50 gal electric water heater and my temp on my water heater is set to 130 deg and it seems that there is enough hot water for no more than 3 showers. Once the 4th person takes a shower, you have no hot water left. Should I increase the temp or it wont matter?
 

Jadnashua

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If you have a teenager, you might run out after one shower!

A new showerhead can't legally be sold that uses more than 2.5gpm. So, how long are those three showers and how old is the showerhead? You might want to run it into a bucket while timing it to see what you have. You can't get 50-gallons of 130-degree water out of the tank, as the incoming cold dilutes it. Figure anything over 70% a bonus.

Yes, you can effectively make the tank look bigger if you raise the temp, but for safety reasons, you should also install a tempering valve to limit the output. They're required where I live. Basically, it's an adjustable valve that mixes some cold with the hot let and 'tempers' it so it isn't quite as hot...it's like mixing the cold at the shower, but done at the outlet of the tank to help prevent excessively hot water from harming someone.

honeywell_tempering_2.jpg
 
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Mikeyboy

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Both bathrooms have new showerheads that my wife bought at Bed Bath and Beyond within the past year.

What's the logic in making the tank look bigger if you raise the temp?

Is setting it to 140 degrees OK?
 

SewerRatz

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I have a 50 gal electric water heater and my temp on my water heater is set to 130 deg and it seems that there is enough hot water for no more than 3 showers. Once the 4th person takes a shower, you have no hot water left. Should I increase the temp or it wont matter?

Turning up the temp of a water heater, you run the risk of scalding. Gamma and the water heater manufactures recommend you do not have the temp any higher than 120 degrees. A low flow shower head can help a lot and shorter showers is a huge help too.
 

Redwood

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What's the logic in making the tank look bigger if you raise the temp?

Is setting it to 140 degrees OK?

It's all about BTU's The higher the temp of the water stored in the tank the more heat you have stored.

You then will mix more cold and less hot so you will in effect be "Making the water heater look bigger."

The problem is that this hot water presents a very real danger of scalding someone. Especially young and elderly people! 3rd degree scald injuries occur in about 1 second at 160°F, 5 seconds at 140°F, 9 minutes at 120°F, 6.7 hours at 110°F. Scald Information click here

The water must be tempered to a safe temperature as it leaves the water heater when elevated temperatures are used. One of the valves pictured below would be required. Watts 70A & L70A Tempering Valve click here

70A-F.jpg
 
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Jimbo

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There is the 70% principal in action here. A water heater will deliver 70% of its gallon capacity, at "shower" temperature, that is within about 20º f set point. SO, you 50 gallon tank will give you 35 gallons. ~2 gallons per minute, 10 minute shower....20 gallons. You are lucky to get 3 showers, and you can just forget 4!

There are remedies, and they have been described in the posts above mine.
 

Scuba_Dave

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My 50g electric indicates that it can provide 58 gallons of hot water in the 1st hour. At 20g a shower then the 3rd shower would start to go cold. I think this also depends upon how hot you like the shower
 

SewerRatz

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My 50g electric indicates that it can provide 58 gallons of hot water in the 1st hour. At 20g a shower then the 3rd shower would start to go cold. I think this also depends upon how hot you like the shower

Well in todays code for residential the showers are supposed to have a temperature stop built in and set to no higher than 115 degrees, and for public showers they should be set to 110 degrees. So I bet they are using the 110 degree mix to say you would get that much out of it.
 

Jadnashua

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The point is, if at the tank, the water was say 160-degrees, then you mixed it with enough cold to get 120-degrees out, on that hot water supply line, for every 1-gallon of hot, you might get 1.25-gallons (or more depending on how cold the cold is and the dilution factor) at 120-degrees. You aren't emptying the WH as fast because you are mixing in more cold to the now very hot water. So, effectively, the tank 'looks' bigger. To be safe, you must temper it at the tank, rather than doing it at the shower, since if someone accidentally used all hot, they could get injured quite quickly. The higher the differential between the tank and the room, the faster it will leak heat (i.e., cool off), so your efficency will decrease some, but maybe not as much as adding a second tank which would have much more surface area to dissipate heat. Since you'd be working the tank harder, it may not last as long.
 

GabeS

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Is installing a mixing valve a widely accepted practice? Is it up to code? Are there any precautions that need to be taken?

I'm assuming the knob on the valve controls the amount of cold water entering the mixture. Is that correct?
 

SewerRatz

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Is installing a mixing valve a widely accepted practice? Is it up to code? Are there any precautions that need to be taken?

I'm assuming the knob on the valve controls the amount of cold water entering the mixture. Is that correct?

Here is the Illinois code say so on using mixing valves if the temp is set higher than 120 at the heater.

A) A thermostatic mixing valve, conforming to ASSE 1017-1999, shall be installed on the hot water line to the plumbing fixtures. (The mixing valve shall be set to prevent temperatures exceeding 120°F from reaching the plumbing fixtures.)

B) A single check valve shall be installed in the cold water line supplying the water heater. (This will prevent hot water backing up from the heating unit to the plumbing fixtures.)

C) A properly sized and approved expansion tank shall be located on the outlet side of the check valve in the water heater's cold water supply with no shut-off valve between the heater and expansion tank.

 

Jadnashua

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As I said before, my city REQUIRES a tempering valve to be installed on any new (as of 4-5 years ago) WH replacment or original installation. So, yes, they are fairly common. It's another thing to fail, but they are pretty reliable.
 

GabeS

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OK. Understood. What I don't understand is when is a expansion tank required to be installed for a water heater?

I guess in Illinois that was one scenario, where mixing valve is installed with temps above 120 degree. When else is one required? Virtually all water heaters that I see have no expansion tanks. Only boilers.
 

Jadnashua

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Water expands when you heat it. It has to go somewhere. Often, it just pushes back out into the supply mains, back into the street. That means that if you polute that supply, you could be polluting everyone else connected to that supply. This could come from having a garden hose sitting in a puddle and there's a hiccup in the supply pressure, a handheld shower sitting in the tub without a working vacuum breaker, or other problems. Some cities put in a check valve to prevent that. Some places need a pressure reduction valve to bring the supply pressure back down to reasonable levels. Each of those create a 'closed' system...water can come in, but can't go back out. So, when that hot water expands, it could break something, leak past worn seals, or drip out the T&P valve protecting the WH. To prevent issues when the city periodically replaces water meters, or does other service, some places madate that an expansion tank be installed. This gives that water someplace to go without stressing all of the fixtures, pipes, and hoses in the house and often discharges from the T&P valve. So...it's not a bad idea to have one, regardless.
 

GabeS

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So there can be no harm in installing an expansion tank at all?

How come in NYC, I barely see them on water heaters? Even on new installs I don't see them?
 

SewerRatz

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Gabes: You defiantly need an expansion tank installed if there is any kind of backflow device IE a checkvalve on the cold water supply, an RPZ or duel check valve at the meter.
 

GabeS

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Got it. I justed wanted to say got it, but it wouldn't let me, said my message was too short. Must be at least 10 characters. :cool:
 
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