The Water Quality Research Foundation (WQRF) initiated the Battelle study to test devices fed with softened and unsoftened water under controlled laboratory conditions designed to accelerate the waterside scaling in Storage type (traditional) Gas Water Heaters and quantify the performance efficiency.
This portion of the study was conducted to investigate the interaction of water hardness levels on the performance of gas water heaters. They also wanted to quantify the amount of scale formation within the hot water heater due to hard water as well as forming an opinion about the life span of the hot water heater as it is affected by hard water deposits.
Battelle set up and tested ten storage-type gas water heaters of 40 gallon capacity with 38,000 Btu/h burners using an accelerated scaling methodology. Five were tested without any preconditioning of the water supply, and the other five were tested using a water softener to remove hardness. Five units were chosen in order to be able to calculate 95 percent confidence intervals for the results.
At the start of the test, and at approximately one week intervals, the thermal efficiency of each water heater was measured to determine the change in efficiency as waterside scale built up in each water heater. Each water heater
was instrumented to measure the inlet and outlet water temperature at 15-second intervals, the amount of hot water generated, and the amount of gas energy used to produce the hot water. These data were used to calculate the average thermal efficiency of the water heater.
The average efficiency of the gas storage water heaters on unsoftened water dropped from 70.4 percent at the start of the test to 67.4 percent at two years equivalent field service. These data were used to derive equations to predict the efficiency of gas storage water heaters as a function of water hardness and daily household hot water usage. The average annual rate of scale buildup in the gas storage water heaters on unsoftened water was about 528 gm/yr (1.16 lb/yr) while the average rate of scale buildup on soft water was about 7 gm/yr (0.01 lb/yr), which is negligible.
So in summary:
1) Gas storage tank household water heaters operated on softened water maintained the original factory efficiency rating over a 15-year lifetime.
2) With hard water this can lead to as much as a 24% loss of efficiency in water heaters.
3) Each 5 grains per gallon of water hardness causes a 4% loss in efficiency and 4% increase in cost for gas storage tank water heaters. On 15 gpg hard water, like in Midland and Penetang, that’s 12% less efficient than with softened water.