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New Hot water heater (40 gal), how water only last 10 minutes. Is this normal?

New Hot water heater (40 gal), how water only last 10 minutes. Is this normal?

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  #1  
Old 02-05-09, 05:14 AM
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New Hot water heater (40 gal), how water only last 10 minutes. Is this normal?

I just moved in to this place and the old hot water heater only gave me about 5 minutes of hot water. This one only gives me 10 minutes and its brand new. It's 40 gallons and electric with two elements. What would be the causes of only getting a limited amount of hot water? Is this normal for a 40 gallon tank? Ive heard of people with 50 gallon tanks never having this problem. So I wouldnt think 40 gal would have this issue. God forbid two people live in together, theyd have to take showers together and then wait a long while before being able to wash dishes or wash clothes with hot water.
Maybe this is just how it would work with a 40 gallon tank, if that's the case, fine, but it doesnt seem that it would work that way to me.
 
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  #2  
Old 02-05-09, 05:53 AM
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Hi 79,
Not normal, unless your showers are very long. Check your shower head to see if it is a low flow, 3 gallons per minute or less. A mistake that sometimes happens when a new water heater is installed, is the power is turned on with air in the tank. That can kill a heater element. Did you install it or have someone do it? Make sure it is wired to the correct power, most use 220v. 110v would still produce heat, but very slowly, similar to your problems.

let us know,
Bud
 
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Old 02-05-09, 09:18 AM
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I did not install it myself. I can only assume they knew what they were doing.
I will check what the input voltage reading is. And I guess I can put a meter on each element, turn power on and check the current.
I will replace my shower nozzle as it is an old one. I wouldnt think it would make that much of a drastic difference though.
 
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Old 02-05-09, 01:32 PM
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I'm going to disagree with my friend, Bud, and say that what you are experiencing may be completely normal.

A tank-type water heater can only supply about 70% of its rated volume before the outgoing water shows a significant drop in temperature. In your case of a 40 gallon water heater that means that after flowing about 28 gallons there will be a definitely discernible drop in the temperature of the water.

Now if the thermostats are set to 120 degrees or so, which is where they are set at the factory, and you have an old shower head that flows three gallons a minute or more, and you like a hot shower and only mix in a small amount of cold water then 10 minutes may well indeed be the limit of your hot water supply.

I've written quite a bit on this in the last week or so, just read several of the other posts in this forum for some suggestions.
 
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Old 02-05-09, 02:11 PM
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Hi 79 and Furd, I haven't run heat calculations on a tank of water in centuries, but I did raise three kids on a 40 gallon water tank with an old style shower head and far too many long showers (two daughters). That's five people, five showers, dish washer, laundry, and I can't say never, but hardly ever a hot water problem. I've lost thermostats and elements and suddenly we were running out, but not under normal use. And that is with two showers, kids and ours, for over twenty years. (Our shower has had a low flow for a long time.) The last ten years have been just the two of us and one in-law and never a problem. So that is why I feel something isn't right with ONE person trying to take a 10-15 minute shower.

79, if you check your heater, normally only one element will be on at a time, so you may not find voltage on both of them. I don't know your background, but if you have a meter you probably know how to use it, be careful.

Before you replace your shower head, simulate the hot water flow for a typical shower and time how long (in seconds) it takes to fill a quart container. Multiply that time by 4 and divide the results into 60 and you have the gallons per minute you are using. You can then repeat the test with your new low flow and see the difference.

You have another clue, in that the previous heater didn't do much better. I'm going to refresh my memory on hot water heaters and see if I can explain this in Furd language.

I'll be back,
Bud
 
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Old 02-05-09, 02:27 PM
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Thanks to both of you for your responses. Yes I have a meter. I verified there is about 220 volts coming in. But Ive got to run out and wont be able to do some more checking until tomorrow after work.
Ill keep you posted on what i find out from your advice.
 
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Old 02-05-09, 03:14 PM
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Just my $.02. Never had more than a 40 Gal unit (...though all have been gas), and never ran out of water unless the kid had been doing the 25 min thing first thing in the morning. Also never had to set mine past med (?) or just a bit over the factory setting.

Matter of fact...if I waited 10 min after the first shower of the morning...had to add more cold to be my preference.

I think the ratings on WH make sense mathematically...but who showers with full hot water? Maybe if you ran just the hot in the tub with a 3 handle faucet, it would be accurate. I sure wouldn't want to be the lobster who jumps in that pot though.
 
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Old 02-06-09, 06:47 AM
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Ok, let’s see if I can give you some more numbers. Water heaters are rated in “gallons per hour”. I know that number is on the yellow energy tag but may be elsewhere on the heater as it is part of its rating. The number will vary for a 40 gallon tank from the low 40’s to as high as 70 gallons per hour, so check yours and it will help us decide if all is normal or something is wrong. With an 80-20 mix of hot and cold, even a 40 gallon heater should give you 50 gallons of water for your shower. At a terrible 5 gallons per minute old shower head, yes you could run into trouble in 10 minutes. Test your current shower head so you will know if that is the problem. With a new head you should be able to average down to below 2 gallons per minute and thus a 25 minute shower or longer.

Now, I didn’t go into the detailed calculations because some information is not available. Input water temperature, the actual amount of water being held at full temperature (the bottom of the tank is allowed to be colder), and shower temperature. I’m not even sure what output temp is being maintained with the “gallons per hour” rating.

After you locate its rating, if the water supplied still seems to be a lot lower than it should be, do a resistance check on the heater elements to make sure they are ok. The only other parts of the heater are the thermostats and the dip tube. A missing or broken dip tube can certainly cause a shortage, but not sure how that would happen on a new heater.

Furd’s numbers are close enough to say it might just be the shower head. Check your GPH and let us know if a new low flow head makes a big difference.

Bud
 
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Old 02-06-09, 07:19 AM
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There's been a lot of good advice offered thus far. May I add one more item to check, "just in case". Make sure the water heater is plumbed correctly so that the cold water enters the "cold" fitting on top of the heater and that the hot water is exiting through the "hot" fitting. If the piping is reversed, your dip tube will be on the "wrong" side and you will have very little hot water capacity. Perhaps the old water heater was installed wrong (if you only got 5 minutes use out of it) and the new one was simply installed the same way as the old one.
 
  #10  
Old 02-06-09, 08:57 AM
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Good point, Beachboy!

When I bought my first house it had a 40 gallon water heater mounted under the kitchen counter. With the original elements I could barely take a fifteen minute shower without running out of hot water. I ended up installing 3,000 watt elements, wiring it for simultaneous operation of the top and bottom elements AND setting the thermostats for about 140 degrees. That allowed both my wife and I to take fifteen minute back-to-back showers or to take a single shower and run the clothes washer. Within a year I had built a utility room and installed an 80 gallon heater.

I don't like "Navy" showers; the quick rinse, soap up and then rinse, all in five minutes. If this is how a person showers then yes, a 40 gallon electric will do okay for two or three people.

Gunguy, a gas water heater re-heats about five times faster than an electric model so a 40 gallon gas can indeed supply enough hot water for several people IF it has the thermostat set at about 140 degrees and there is a five or ten minute recovery between showers.

Years ago it was common for water heater thermostats to be set at 140 degrees or even higher. I think it was about 20 or 25 years ago that safety groups pointed out how many injuries there were, especially to elderly and children, from excessively hot water in the home and there were many state laws mandating that water heater thermostats in public and rental facilities be set at 120 or 125 degrees maximum. They also required the water heater manufacturers to set at these lower temperatures from the factory.

The problem with these lower temperature settings is that they effectively lowered the amount of hot water any given size of water heater could supply AND they encouraged the growth of harmful bacteria if any such bacteria was present in the incoming water. Because of the potential bacteria problem some authorities are now promoting higher temperatures in hot water production but also mandating that temperature regulating valves (tempering valves) be installed too blend in cold water to lower the temperature of the water to around 120 degrees before it reaches any outlet.

Then there is the energy efficiency factor. Of course it take more energy to obtain higher temperatures and a tank with higher temperatures will lose more heat (energy) to its surroundings than a similar tank (same insulation characteristics) at a lower temperature. Quite simply, it is these factors of desiring lower temperatures for safety and energy conservation that have been behind the big push for tankless water heaters.
 
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