Why am i running out of hot water after only 5 mins?

Question

We recently switched from a gas water heater to an electric one and now I'm running out of hot water in my shower after only 5 mins or so. We have replaced the elements, the thermostats, the anode and dip tube as well as flushed the water heater and cleaned it. It was given to us by a friend so it is an older heater (m.2009). My boyfriend doesn't seem to notice the loss of hot water in his shower (I have but he thinks I'm crazy)but he literally only takes around 7 mins to shower anyways. I do have one of those waterfall showerheads in my shower but it worked perfectly fine with the gas heater. And to note, the gas water heater was as old as this electric one if not maybe even a little older, and we had zero issues with water temp until we switched. He thinks maybe it's the mixing valve on my shower faucet but it doesn't make sense that it didn't have any problems until the switch. What are we missing? Also to note, my boyfriend is an electriction and the water heater was originally set up for electric and he changed it to gas many moons ago. We only switched back to electric to save on tank fills due to some major price increases over the years. Someone please help because I'm tired of taking 5 min showers and not being able to take a hot bath!!!!

Answer 1

So find the capacity of the tank and how much water is used by your waterfall shower per minute.

If you divide the tank capacity by that water use then you get how many minutes of shower you get. Just remember that not all the tank capacity may be hot.

Once you have that then you can consider if you need a new larger tank or other possible solutions like going back to gas etc

Answer 2

First, water heaters have a direction of flow. Cold needs to go down the dip tube. Hot needs to pull off the top.

Now, get a 1 gallon bucket and time how long it takes to fill off the shower head. You need to figure out your GPM (Gallons Per Minute) of the shower. Divide the gallons of tank capacity by that number, and you should get minutes of run time. That might explain your trouble right there.

Now if you want that deluge showerhead, you have several options.

First, if you have anti-scald thermostatic valves on all your faucets, try turning up your hot water heat as high as you can. This means to get your target temperature, you will use less hot water and more cold water. It's a free way to store more energy in the same tank of water. However once you get up over 130F, you start to risk scalding. Conversely below 130F, Legionella and other bacteria will grow in water heaters - we learned that thanks to the Flint water crisis causing a cluster of cases. Before that, people got sick and no one knew why.

You might also consider a drainwater heat recovery system, though the plumbing required is positively daunting. (Might be easy if there's an unfinished basement below the tub). This has waste water run down a long pipe with fresh cold water directly underneath it. The heat of drainwater (probably 80F) transfers to the cold water coming into the spigot, meaning you need FAR less hot water.

If these are not practical, then you need more volume of hot water.

• You can go with a much bigger tank, and that will not require a larger water heater electrical circuit. And here is a good place to think about heat pump water heater tech, which has some drawbacks but saves a fortune on water heat cost. In high cost of electricity territories, the heat pump water heater is practically mandatory, and the water heater can pay for itself in a year.

• you can daisy chain another possibly larger heater and those can be wired to be sequential, so they share the circuit.

• you can go to a gas tankless. Which can deliver as much as 200k BTU/hour. Now here is where we math the math. 1 BTU is the energy needed to raise 1 pound (pint) of water 1 degree F. 8.3 pounds per gallon of water. Now you can figure how many gallons per minute x 8.3 x 60 to get to pounds per hour. Then you figure how many degrees of tempeature rise you need vs street cold water temp. Now you know how many BTU/hr you need to heat that water stream. My cold-climate rule of thumb is 40A == 9600W == 32,000 BTU/hr per GPM, so by that logic, a 200k BTU/hr tankless "should" support 6 GPM.

• An electric tankless is absolutely hopeless. Forget it. Figure 40 amps per GPM and a LARGE household service is 200 amps, so you're probably talking a 400A service upgrade which will cost many thousands.