Water Heaters - Really stupid question about water temp.

My water temp is set lower than the norm; it comes out hot, but I can wash dishes by hand with only the hot water faucet turned on.

I run out of hot water before my big soaking tub fills up. If I raise the temp on the water heater, would the fact that I would then lower the flow coming out of the hot faucet and raise it from the cold give me more or less hot water? In other words, would I be able to fill the tub before the hot water ran out?

Sorry if this has been asked & answered. ( I told you it was really stupid ;-))

Hello Linda431 and Welcome to our Do It Yourself Web Site and the Water Heaters topic.

Water temperature is control solely by the thermostat. Raising the thermostats temperature will not provide more hot water volume. It will only provide hotter water. For all generic purposes.

Hot water volume is controlled by tanks capacity in gallons. The larger the capacity of the tank, the more volume of hot water output in gallons.

It takes the cold incoming water to push out the hot water. Therefore, some dilution of the hot water will occur as a result of the incoming cold water. Dilution is more noticeable in cold weather then in hot weather.

The colder the incoming water is, the faster the dilution happens, less total output hot water volume results. And the longer the time delay will be between recovery.

Recovery means time it will take to reheat the incoming cold water. Recovery rates vary. Usually takes between 1 to 1 1/2 hours for a complete tank to fully recover from all cold water to all hot water.

In order to obtain more hot water in volume capacity in one usage, a larger tank will be needed. A work around temp solution for winter months with cold incoming water, would be to allow more recovery time between demands, less volume demand in the tube and flow volume restriction,etc.

Hope info above helps to understand water heater operations and circumstances.

BTW: (By The Way)
There are no stupid or dumb questions. Asking is a method for learning...:)

Web Site Host, Gas Appliances Topic Moderator & Multiple Forums Moderator. Energy Conservation Consultant & Natural Gas Appliance Diagnostics Technician.

Personal Driving Safety Reminder:
Buckle Up & Drive Safely. "The Life You Save, May Be Your Own."

Thanks Mr. Sharp! I appreciate the reply. I was kind of hoping that setting it higher would allow the tank to reheat the intake water more quickly since the hot water would be going out of the tank more slowly. (Physics & chemistry were never my good subjects!)

So now I'm wondering what would be the best course of action. The only time we run out of hot water is when I use the tub, which is only a couple of times per week. (Yes, I do shower on the other days;-))

Would it be cost effective to install a tankless heater just for the tub? I hate to get a larger tank style heater just for those couple of times a week I need more hot water.

Another but less important issue is the length of time it takes to get hot water at all. We have a raised shotgun type house in New Orleans and the water heater is outside at the very back of the house. All of our hot water use is in the back 1/3 of the house except when we have company in the front room. As you can imagine, it takes a looooooooong time to draw the hot water all the way to the front of the house. In the kitchen, it takes about a minute & a half so we are still wasting a lot of water daily.

Would 2 of these tankless heaters (one for my tub and one for the front bath) work as an adjunct to the present heater? Or any other thoughts on how to get more efficiency? Thank you so much for your time.

I have to disagree with Sharp Advice on this one. While it may not make enough difference to allow filling of the tub, turning up the temp on the water heater will give you more water at a given temperature because you'll be using more cold water to mix. Example: If you want 10 gallons of water at 100 degrees, you won't need as much hot water that's at 125 degrees as you would if your heater was at 100 degrees and had to provide all ten gallons - some of the volume would be cold water to mix with 125 degree water to make 100 degrees.

Is this water heater GAS or Electric and how big ?????

The water heater is gas and I think it's 80 gallons. We went with a larger size than the plumber recommeded. Like I said, it's perfectly adequate for everything except that dang tub.

I would raise the thermostat setting. But use caution with hotter water, especially with children.

Raising the temperature allows you to use less hot water and a little bit more cold water. This reduces the flow rate from the water heater, therefore it will take more time to run out of hot water. The same goes for the tub. With hotter hot water, you will use more cold water to achieve a comfortable bath temperature.

With an 80 gallon gas heater, you should have plenty of hot water. I suspect the temperature is set too low.

If she can stick her hands in the water w/o burning them with only the hot water running, that sounds low to me. 120-125 degrees is a common setting.

Raising the temperature definitely would improve your supply of hot water.
Becuase you would turn the hot tap for a lower volume, to get the same temp water coming out of the spout, then less new cold water is mixing into the tank.

Large commercial properties take advantage of this by setting the WH very hot, and using a tempering valve at the output.

Safety is a big issue here: 140 is the absolute max in a residential situation, but that temp will burn people, especially children and elderly. 125 is a better number if these concerns are pertinent.

NOTE: Anything LOWER than 125 is also not safe, bacterial growth is promoted. There has been some talk that a certain state ( not sure which) is now REQUIRING that WH be installed at a 140º setting, and a mandatory tempering valve installed.

Boy has this turned into a huge thread for something so simple.


for simple math and only for expample look at this.

if you have your water heated to 100 deg and you want to use 100 deg water, you have 80 gallons available.

if you want 100 degree water and you heat your water to 200 degrees and your cold water is 0 degrees (I know it would be frozen but this is for example only), if you add one gallon of the hot to one gallon of the cold, you would then have 2 gallons of 100 degree water, thereby doubling the amount of 100 degree water you have available.

So, as many have suggested, turn the water heater up, DEFINATELY using caution or children or elderly are in the house. Use the cold water to temper the hot water to your liking and enjoy you soaking tub.

Just don't heat it so high as to be unsafe. 594tough has the right plan.

Thank you all so much. I will check that thermostat right away and let you know if that solves the problem.