Chapter 15 of Mike’s book OnlinePlumbingAdvice.com

Not Enough Hot Water

“Why doesn’t my water heater make enough hot water during cold weather?”

If you notice this problem during freezing weather, often it is due to the extremely cold (ice water) coming in. I call it the “double-whammy affect.” People use a much higher percentage of hot water at the shower because they are mixing with ice water. Meanwhile, the water heater takes longer to heat the ice water. It really is the triple-whammy affect. When you use hot water, ice water squirts down into the bottom of the water heater and dilutes about 25 percent of the stored hot water. This also contributes to the shortage. The amount of hot water required, and the amount of hot water available is directly affected by the temperature of the water supply coming in to the home.
If you suspect that an electric water heater is not working properly, many plumbers will do what I call “the old plumber’s test.” The test must take place only if you are sure no hot water has been used for at least four hours.

The old plumber’s test:

1. He will make sure the proper breaker is off by properly testing the wires (sometimes breakers and fuses are marked incorrectly).
2. He will feel the lower area of the tank (inside the lower access door). If it feels hot, you have a full tank of hot water, and the controls and element work properly.
3. If the lower tank feels cold, he will test the lower element and thermostat (some plumbers will automatically replace the lower element).

Now the old plumber’s test for testing the dip tube (the pipe inside the tank that carries cold water to the bottom to be heated):

1. He will run about ten gallons of hot water from the water heater (running several faucets for about five minutes).
2. If the lower section of the tank (inside the lower door) cools off, the plumber will tell you that the dip tube is doing its job.
3. If the lower section of the tank (inside the lower door) stays hot, the plumber will tell you that you need a new dip tube. (The cold water is not being properly directed to the bottom.) I have electronic equipment to test more precisely, but if your heater passes the old plumber’s test, most plumbers would probably consider it working okay (and it probably is as long as it provides reasonable temperature control).

Explanation(for those that want to try to understand):

Two element water heaters have a thermostat and a heating element for the top section of the tank and a thermostat and element for the bottom section of the tank. This type of setup will normally satisfy the top thermostat (heat the top) before electricity is supplied to heat the lower element. If the top thermostat or the top element is not in working order, the water heater will provide no hot water. In order for the bottom section of the tank to get hot, the upper element and thermostat must be in working order. In order for the lowest section of the tank to get hot, the lower element and lower thermostat must be in working order. If the lower thermostat or the lower element fails, the lowest section of the tank will not get hot (only the top half of the tank will get hot). All electric controls and elements must be in working order before the lowest section of the water heater tank can get hot. This is why the old plumber’s test usually provides satisfactory results.

If the water heater is the single element type (only has a lower heating element), the single element and thermostat must be in working order if the tank is hot; otherwise the water heater would provide no hot water.
The old plumber’s test for gas water heaters is much different than that for electric water heaters. There are too many complicated but necessary safety concerns testing a gas water heater. I shall not even attempt to explain all of these important testing procedures.

One water heater test that is easy for most adults to do:

1. Make sure no hot water has been used for at least four hours.
2. Check the water heater label to determine the capacity (gallons).
3. Using a bathtub faucet or other fast flowing faucet, use a five-gallon bucket to measure the amount of hot water that comes out before the hot water runs out.
4. Make a note of how much hot water you ran before it dramatically cooled down.
5. Make a note concerning how many gallons you ran before the water got uncomfortably cold.

Don’t expect to get the capacity indicated on the water heater label. (Hot water is diluted with cold as the dip tube squirts cold water into the bottom of the tank.) Depending on how cold the water is coming from the water main to the water heater, you will probably only get about 75 percent of the capacity of the water heater in hot water. If you have a fifty-gallon capacity water heater, you will probably only get about thirty-seven and one-half gallons of hot water if everything is working properly. If you test properly and only get about twenty-five gallons, there is probably something wrong. If you determine that your water heater is not operating properly, call a plumber. A trustworthy plumber should perform necessary testing to determine the best course of action to take.

Often I find that people waste lots of hot water

Wasting hot water is expensive and confusing. Efficient use of hot water is the key to providing a reasonable amount of time for showers. I find more cases of people wasting hot water than I find of malfunctioning water heaters.
If you invest a little time testing for wasted hot water you might save lots of money while you enjoy longer showers.

Using a five-gallon bucket, you should go to each showerhead and spray into the bucket for one minute. Keep track of how much water each showerhead sprays per minute (one-half bucket = two and one-half gallons, etc.). If a showerhead is over a bathtub, after testing the showerhead, place the empty bucket under the spout while water is being diverted to the showerhead. Figure how much water is being wasted (if any) by a defective diverter. Doing some simple math should help you understand, what to expect from your water heater. Efficient use of hot water will provide dramatically better results than purchasing a larger water heater.

Factors to consider:
• A wasteful showerhead (adjust or replace)
• A bathtub diverter that wastes water through the spout while you are taking a shower (repair or replace)
• People might have to take showers faster during cold weather
• A trickle down shut-off valve installed on the showerhead, can save lots of hot water (the showerhead only trickles while you are scrubbing)
• Avoid taking a shower within two hours of washing clothes or dishes