Estimate water, utility-cost, and water-heating savings from a shower shutoff valve that restricts flow while you wait.
Usage-based utility rates
Purchase cost
Advanced options
Water-heating assumptions
Calculation details
Table of contents
How to use our Thermostatic Shower Shutoff Savings Calculator
- Enter the normal Showerhead flow rate and time only the unattended Wait time avoided per shower start after the valve restricts flow.
- Enter the number of Shower starts using the valve each day, counting one warm-up cycle when people share it.
- Copy the variable Water usage charge and Sewer usage charge from your bill. Leave out fixed monthly account fees.
- Choose Water heater fuel, enter the matching Selected fuel price, and enter the Installed valve cost.
- Open Advanced options if you know the trickle flow, water temperatures, and heater efficiency. Check that restricted flow is lower than normal flow and that the displayed annual gallons match your expected daily use.
Definitions
Thermostatic shower shutoff valve: A showerhead-mounted device that restricts flow after warm water reaches it, while the person is still away. It is different from a thermostatic mixing valve, which controls water temperature.
gpm: Gallons per minute. This is the flow rate of the showerhead or the small flow that remains while the valve is restricted.
Variable usage charge: The part of a water, sewer, electricity, or gas bill that changes when you use more or less water or energy. Fixed monthly fees are not included.
kWh: Kilowatt-hour, the electricity billing unit.
Therm: A natural-gas billing unit equal to 100,000 Btu.
Water heater efficiency: The percent of purchased fuel energy that reaches the water. A lower percentage means more billed fuel is needed for the same shower-water heat.
Simple payback: The estimated number of months for annual utility savings to equal the entered installed valve cost.
Common mistakes and quick fixes
Mistake: Entering the full pipe warm-up time as Wait time avoided per shower start.
Fix: Time only the unattended minutes after the valve has restricted the flow.
Mistake: Treating Flow while valve is restricted as zero when the valve still releases a trickle.
Fix: Use the valve specification or measure its restricted flow with a container and timer.
Mistake: Including fixed fees in Water usage charge or Sewer usage charge.
Fix: Enter only the part of each bill that changes with gallons used.
Mistake: Entering dollars per kWh for an electric Selected fuel price.
Fix: For electricity, enter cents per kWh; for natural gas, enter dollars per therm.
Mistake: Using the water-heater tank setting as Shower water temperature.
Fix: Enter the mixed water temperature at the showerhead after it stabilizes.
Mistake: Expecting Estimated simple payback to include financing or future utility-rate changes.
Fix: Treat it as installed cost divided by the current annual savings estimate.
Limitations & Key Assumptions / Boundary Conditions
- The estimate covers only unattended water flow after the valve restricts flow. It does not count water used before restriction or during the shower.
- Actual showerhead and restricted flow can vary with water pressure, valve condition, and plumbing.
- Water and sewer savings apply only to usage-based charges. Fixed account fees usually remain unchanged.
- If your utility has tiered rates, use the rate that would apply to the gallons you expect to avoid; an average bill rate can differ.
- The heating estimate uses the entered incoming-water temperature, shower-water temperature, and heater efficiency. Seasonal water temperature and real heater performance can change the result.
- Simple payback excludes financing, maintenance, repairs, rebates, taxes, future price changes, and the time value of money.
Methodology
Water and bill savings
The calculator finds the flow prevented during the unattended wait, then applies that amount to daily shower starts and 365 days. The filled 2.0 gpm showerhead value is an editable US planning value; check your showerhead label or measure its actual flow. [1]
annual gallons avoided = (showerhead flow rate - flow while valve is restricted) x wait time avoided per shower start x shower starts using the valve x 365
Water and sewer savings are calculated separately because their usage charges can differ.
annual water-charge savings = annual gallons avoided / 1,000 x water usage charge
annual sewer-charge savings = annual gallons avoided / 1,000 x sewer usage charge
Water-heating savings
The heat estimate treats each avoided gallon as water that would have reached the entered shower temperature. It uses 8.34 pounds per US gallon, then converts Btu to kWh using 3,412 Btu per kWh.
annual delivered heat in Btu = annual gallons avoided x 8.34 x (shower water temperature - incoming water temperature)
annual delivered heat in kWh = annual delivered heat in Btu / 3,412
For electricity, purchased energy avoided is delivered heat divided by heater efficiency, then multiplied by the entered cents per kWh. For natural gas, the calculator divides delivered heat by 100,000 Btu per therm and by heater efficiency, then multiplies by dollars per therm.
total annual utility savings = water-charge savings + sewer-charge savings + water-heating savings
simple payback in months = installed valve cost / total annual utility savings x 12
Mini-example
With a 2.0 gpm showerhead, 0.05 gpm restricted flow, 2 unattended minutes, and 2 shower starts per day, avoided water is (2.0 - 0.05) x 2 x 2 x 365 = 2,847 gallons per year before utility rates and heating assumptions are applied.
Calculation choices
A zero annual savings result produces N/A payback because there is no savings amount to repay the installed cost. The calculator blocks a restricted flow above normal flow, a shower temperature at or below incoming temperature, and efficiency outside more than 0 percent through 100 percent.