Dishwasher Not Drying

Photo of a dishwasher with wet dishes

As an appliance service company I can't tell you how many times we have heard the customer say, my dishwasher will not dry dishes. This is an extremely common problem with modern-day dishwashers.

It doesn't matter what brand dishwasher you have, aside from perhaps a Bosch dishwasher. Which by the way in addition to being one of the quietest dishwashers on the market, Bosch dishwashers do a fantastic job at drying dishes. And for the record, Bosch dishwashers do not have heaters in the bottom of the tub. They do have a water heater underneath that as you will learn is the most important factor in drying dishes.

Most dishwashers manufactured to be used in the United States have a plastic tub with a heater in the bottom to help maintain the water temperature and supposedly dry the dishes at the end of the cycle. The problem is the plastic tub! The heater in the bottom cannot get hot enough to really dry dishes if the incoming water temperature to the dishwasher is not hot enough.

The most important factor in drying dishes at the end of the cycle is the water temperature that enters the dishwasher. Let me help you understand why. At sea level we all know that water goes from a liquid to a gas at 212 degrees. To the human hand a water temperature of 200 degrees will seem extremely hot. However it will not be hot enough to turn liquid water to a vapor. Everybody that you talk to says hey you want to save energy, turn your hot water heater down to 120 degrees. Well if you don't mind wet dirty dishes, a water temperature of 120 degrees entering a dishwasher will be just fine. That's if you're lucky. A water temperature of 120 degrees leaving a hot water tank will be lower especially if it travels a long way and the pipes are located in a cold environment.

The fact is the water temperature entering a dishwasher today needs to be much hotter than 120 degrees. Ideally you would want the water temperature of 140 degrees entering the dishwasher.

Let us conduct an imaginary experiment to illustrate this point. We have a gas range with two identical burners, and we take two identical size pans and fill both pans with one cup of water. We put both pans on top of the range and turn the burners to high. The only difference is that the water we put in one pan is 120 degrees and the water in the other pan is 140 degrees.

Now ask yourself which one of these two pans of water is going to boil first? Obviously there is a certain amount of time that the water needs to go from its current water temperature all the way to 212 degrees so that it can boil. You would have to agree that the pan with the water temperature of 140 degrees is going to boil faster and turn to a gas AKA steam sooner.

This is the problem with dishwashers. Dishwashers have a very specific amount of time from the end of the wash cycle to when the timer or electronic control reaches the off position. Therefore the heater in the dishwasher has a limited amount of time to do it's job. The main function of the heater at the end of the cycle is to take the water that is on the dishes and heat it to a point where it becomes a vapor and leaves the dishes.

Now you can see if we have a dishwasher with 140 degrees water entering the dishwasher as opposed to a dishwasher with 120 degrees. Which one is going to be able to get to 212 degrees sooner with enough time to do it's job.

It's that simple! Forget all the monkey business about drying agents and soft water etc. The bottom line is if you want dry dishes in your dishwasher at the end of the cycle, turn your water heater up.