Understanding the Cost of Hot Water Usage with Water Heaters
When it comes to hot water usage in a shower, the cost can vary significantly depending on the type of water heater you use: tank or tankless. This article aims to break down the cost analysis, energy efficiency, and operational differences between these two systems, as well as the average temperature and flow rate for a typical shower.
Typical Shower Conditions and Heating Requirements
According to a Quora answer, the preferred shower temperature is around 105°F. A standard showerhead uses 2.5 gallons per minute (gpm), which translates to 150 gallons per hour (gph). Starting from a ground water temperature of 55°F, the water needs to be heated by 50°F. Given that water weighs approximately 8.3 pounds per gallon, the total weight of water heated is about 1245 pounds. The sensible heat of water is 1 BTU per pound per degree Fahrenheit, so the energy input required is 62,250 BTUs.
For natural gas water heaters, this energy is approximately 100k BTUs, which can be roughly equivalent to 1 therm of natural gas or about 1 gallon of LPG. For electric water heaters, the required energy is 18.25 kWh. These figures provide a glimpse into the amount of energy needed to heat the water for a typical shower.
Energy Efficiency and Cost Breakdown
When considering the cost of hot water usage, it's crucial to evaluate the energy efficiency of the water heater. A standard natural gas water heater is around 60% efficient, but let's assume it's 100% efficient for simplicity. This means that the actual usage in terms of natural gas or electricity will be higher.
In terms of cost, the average cost of natural gas in the United States is about $1.15 per therm. Therefore, the cost of heating the water with a natural gas water heater would be approximately $0.115 per therm. For an electric water heater, the average cost per kWh is about $0.13 in the United States, making the cost of heating the water approximately $2.37 per 18.25 kWh.
Tank vs Tankless Water Heaters: Operational Differences
A standard tank-type water heater cycles on and off to maintain a constant temperature, 24 hours a day. This means that there is always a standby loss, i.e., heat loss even when the water is not being used. On the other hand, a tankless water heater operates only when hot water is needed, providing a continuous flow of hot water.
The primary advantage of a tankless water heater is the endless supply of hot water. However, it's important to note that both systems require cold water to enter and be heated, meaning the user may experience cooler water flow if the heater cannot maintain a fast enough reheat of the incoming cold water. Gas tank water heaters are typically better for fast reheating of incoming water, making them a preferred choice for many.
Conclusion
While the cost of heating a typical shower is minimal, the choice between a tank and tankless water heater affects the overall efficiency and the amount of energy used. Tankless water heaters provide a more sustainable and on-demand hot water solution, but they come with higher upfront costs. Ultimately, the decision should be based on your specific needs and the cost of energy in your area.