If there is not enough hot water from your gas water heater, either for shower or dish washing, don't immediately call the technician; use the following tips to check is the unit operating properly or not. There are several reasons why there is not enough hot water, but we will use two procedures to check, both of them easy to follow, but time consuming. No need to call the expensive plumber or service personal, just go through these steps. The procedures apply on the residential water heater using the natural gas, either made by AO Smith, Bradford White, Rheem or any other manufacturer.
Lets make two assumptions here; the water heater is a gas-type and it has capacity of 50 gallons.
It is important to say, that according to the heater's manufacturers, 50-gal unit does not use all 50 gallons for the shower (50-gal was used as an example). The unit will actually deliver approximately 70% of the tank's capacity. In our example, 70% of the 50 gallons equals to 35 gallons (0.7*50=35 gal).
Next, if the temperature on the thermostat is set to 120F, the temperature will be between 100F and 120F (approximately 20F difference). If the capacity is unknown, the rating plate found on the heater should be looked at.
This procedure is called the Draw Test
and there are two parts of the test.The water heater should be fully
recovered from the previous use.
First, discharge one cup of hot water by using the TP valve, filling the cup at the free end of the discharge pipe. The temperature of hot water inside the cup should be hotter than the set temperature, at least 10F. If it is colder something is wrong.
Next, use the 5-gallon bucket to collect the hot water from a heater. Do it several times until the capacity reaches approximately 70% of the tank size. After every draw, measure the temperature of hot water. The temperature of hot water in the last draw should be within 20F of the thermostat setting. If it is not, there is a problem.
There are also other reasons for the insufficient hot water such as the undersized water heater (buy bigger one or use the supplemental electric heater for example) or plumbing crossover. Check also the shower head and the flow rate it has been designed for. For the water heater with the capacity of 50 gallons, and after applying the 70% rule, 35 gallons of hot water is available (thermostat set to 120F). Recommended shower head flow rate is around 3 gallons per minute, which gives you approximately 10-15 minutes of shower. So, check the shower head flow rate, before calling the technician.