If your hot water heater is delivering less hot water than it used to, there are several things that can be causing your problem, depending on what type of water heater you have.
If your tank is electric, a lower element could be defective, or the dip tube could be missing.
If you have a gas model, it would most likely be the dip tube (see our FAQ section regarding dip tubes).
And, sometimes we find there is nothing wrong at all. In the winter, incoming water temperature is much colder, which causes the remaining hot in the tank to dilute much faster (the cold water coming in is what pushes the hot out to your shower). Another possibility is if you recently changed your showerheads to a higher flow rate model.
Here are a few things to consider. A water heater will only give you 2/3 of it’s capacity as usable hot water. If your tank is a 50 gallon model, that would be about 33 gallons. If your showerheads are limited to 2.5 gallons per minute (GPM), then your shower time should be close to 15-20 minutes before you notice a temp drop. However, if you have 5 GPM showerheads, simple math says you’ll have 8-10 minutes of hot water.
Here’s a test you can perform to see what is happening. Start with a completely recovered tank (no hot water has been used for several hours). You’ll need a 5-gallon bucket and a thermometer that has a range up to 160 degrees. With the thermometer in the stream of hot water, fill the bucket from the tub spout and record how many times you fill the 5 gallon bucket before you see a 20 degree temperature drop. Do the math to see how much hot water your tank is producing. If it is not 2/3 of the tank’s capacity, it’s time for service or replacement.
Another test will help you determine what the GPM rate of your showerhead is. Just hold the bucket up to the showerhead and have someone turn on the shower. Fill the bucket for 30 seconds and then determine how much water is in the bucket. Double that amount and you have your GPM. If your bucket fills more than 1/3 of the way in 30 seconds, it may be time to consider low flow showerheads. They conserve water and help “stretch” your usable hot water supply.
Check out the Model & Serial Number page to determine how old your tank is. If it’s more than 7-8 years old, it may not be worth spending money to repair the tank.