Water Heaters - Hot Water Capacity of a New Gas HW Heater?

Hi,

Last week we had a 40-gallon GE 9-year gas hot water heater professionally installed.

My wife is getting frustrated because, after less than 10 minutes in the shower, the hot water is basically gone. She called Home Depot (where we got it from) and then GE and they had her do a test, filling five five-gallon buckets and taking the temperature of each one. She did this. The first two were 120 degrees, the fifth one was only 98 degrees. GE said that this was an acceptable range. (Actually, the first person she tralked to who told her to try this test said that the range would be 20 degrees before they'd consider invoking the warranty, then the person she talked to AFTER the test said that the range was 25 degrees.)

My question: I have read that dip tube problems can be to blame for low hot water capacity. Does a temperature drop of 22 degrees over 25 gallons sound right for a 40-gallon water heater? We have talked to the installer and they said that they would come out and look at it, but if nothing's wrong then we will end up paying over $100 for a service call.

This was, by the way, mid-day. Could the amount of actual hot water available vary based on time of day? I.e., if the water heater sits in a warmish house for several hours, is there a likelihood that the hot water capacity could be reduced (by not tripping the thermostat that re-heats the water, for example)?

Thanks.

Michael&Maureen, Welcome to the DIY Forums.
40 gallon heater is good for about 29 gallons before the temp starts depreciating noticably. You have to figure that as soon as you turn on the hot water, cold water starts replacing it. Your local water may be much colder than in another area. A shower with a low-flow head uses 25 gallons in 10 minutes (2-1/2 gallon per minute). If you had a dip tube problem, its unlikely you would get 10 minutes out of the shower before you noticed it.
In my Florida home, the water never got cooler than 60° from a 120 foot deep well. My water here in Arkansas from a town supplier is closer to 40°. Hope this helps explain it for you. Good luck.

As the previous post said, a conventional 40 gal WH has a limited amount of hot water and it takes time for it to recover.

Tankless WH's supply a virtually unlimited supply of hot water (up to the gpm for which they are rated. IOW, a 6.9 gpm unit will supply 6.9 gpm of hot water at a constant temperature and never run out. They cost more, but since they don't heat water when it isn't needed they save about 40% in energy cost. Depending on the usage, they will pay for themselves in between 2-5 years and you won't have to deal with your wife getting a cold shower. ;)

BTW, if the clothes washer is being filled or someone is filling a bath tub the shower will get colder a lot faster than 10 minutes with your 40 gallon conventional.

Another thing you can do - but it will likely cause the WH to wear out faster - would be to set the temperature higher. This will mean that when you take a shower you need to use more cold water in the mix to keep the temp down to a comfortable level, thus using less hot water from the tank. IOW, if you mix 60 degree water with 150 degree water in equal amounts you will have 105 degrees. Assuming 2.5 gpm that's 1.25 hot and 1.25 cold resulting in a 20 minute shower using only 25 gallons of hot water. There's another danger to this however and that is that 150 degree hot water is dangerous. At the very least you want to make sure that your shower valve has a temperature control, and you prorbably want to be very careful at the sinks.

Of course, it may not even be possible to turn your WH that high.

Thanks for the advice.

We wanted to go tankless, but money was a major factor at the time. All estimates we had put a tankless WH with installation at about twice what we'd pay for a conventional WH with installation. Maybe next time.

My wife called the parents of friends of ours who run their own commercial mechanical and plumbing outfit. He suggested we crank up the temperature also. We mentioned that we have young children and didn't want to do that as it was dangerous. He then offered to send one of his guys over and install a mixing valve for the house. That way we can turn up the temperature on the WH and not have to worry about really high temps at the faucets. Yeah, it'll end up costing more to run, and will wear out the WH that much faster (though probably not as fast as our limestone-heavy water will choke it up), but then we 'll just get that tankless WH we wanted in the first place. :)

Thanks again.

There is the 70% rule, meaning that a water heater will deliver about .7 X GAL of water above 100º. (40 gal. X .7 = 28Gal.) It seems you are getting this. Variables would include how cold the ground water is and how well the hot pipes in your house are insulated. If you are not using a low flow shower head, or if your pressure is cranked up, these would also contribute to the availability.

Being a curmudgeon, I believe that tankless are less than satisfactory IN THIS COUNTRY because our expectations and demands are a lot different that other countries: large whirlpool tubs to fill, huge washing machines, multi-head showers, 4BR/5BA houses, etc. They are being heavily advertised and will continue to be sold in large numbers. I am also not convinced of the longevity. I worry about scale build-up, given that the average homeowner will NEVER have any preventative maintenance done.
Just my 2 cents. If I'm wrong, I owe you a jelly donut!


My personal choice would be a HiRecovery 50 or 60 gallon.

You will not get much scale build up with a tankless because of the fact that the hot water is not sitting there in a tank. It's the heat that causes the scale to form - particularly when it's just sitting there.

Progress is slow when we fail to give innovation a chance. In this country we tend to use older wasteful technology just because it's tried and true.