
While it is our intention to give you the best calculations possible,
these calculations have
many factors that will influence accuracy.
Your results may vary based on water temperature, cost to heat, flow
rate and other factors. The calculators are for information purposes
only.
Cost to heat a gallon of water:
We
fill in this box in the calculator but you can change it to whatever you
want. When we researched national averages we saw numbers all over the
place for heating shower water. Therefore we decided to create a
calculator just for estimating costs of heating shower water. That can
be found at
Water Heat Cost Calculator. This calculator
will estimate the cost of heating a gallon shower water to
100^{o}F (gcost). It does this by calculating the energy required to
heat water to 100^{o}F from the inlet temperature (T_{i}). Then
based uses the efficiency factor (ef) and price per kilowatt hour (pk) or price per therm (pt).
Here are the formulas used:
For Electricity:
hcost = (((100  T_{1}) X 0.00245) / ef ) X pk.
For Gas:
hcost = (((100  T_{1}) X 0.0000837) / ef ) X pt.
We fill in $0.02 which is based on heating the water with an
electric water heater where rates are $0.15 per kilowatt hour and inlet temperature
is 50^{o}F.
Cost of water:
Usually you are charge per 100 cubic feet of water that comes into to
your home or business. Nationally, the price you will pay is about $2$3
per 100 cubic feet (748 gallons). Many cities will also base their sewer
rate on your consumption of water. You can find the calculator for water
at our Water Cost Calculator. In that calculator you
you simply put in the total cost for your water (water and sewer) per
100 cubic feet and it will tell you how much you pay for each gallon of water.
The formula is simple. Input your total water rate (twr) into the calculator
(this should be the sum of your water rate plus your sewer rate if applicable).
Hit "Calculate".
The calculator shows you a number for cost per gallon (gcost).
gcost = twr / 748.
We fill $0.005 into the box on the calculator. This assumes $2 per
100 cubic feet for the water rate and $1.75 per 100 cubic feet
for your sewer rate.


Shower Calculator formulas:
In this calculator you put in the number of showers per day taken (sn_{1} and sn_{2}),
flow rate of two different shower heads (fl_{1} and fl_{2})
and the time for each shower (ti_{1} and ti_{2}).
You also put in your costs to heat a gallon of water (hcost) and your cost for a gallon of water (gcost).
You also select if you are going to take a cooler shower and how much
you are spending to make changes (setcost) by buying a new shower head
or Waterpebble or even hiring a plumber.
We set up the calculator this way so that you can mix and match the
three different options we explain in the write up (low flow, shorten
shower and lower temperature shower). The calculator will provide
before and after water use and cost estimates for the changes you are
looking to make.
To calculate the before (g1) and after (g2) annual gallons use
we use:
g1 = sn_{1} X fl_{1} X ti_{1} X 365.
g2 = sn_{2} X fl_{2} X ti_{2} X 365.
To calculate the before (c1) and after (c2) annual cost
we use:
c1 = g1 X (hcost + gcost)
c2 = g2 X (hcost + gcost)
To get the "return on investment" (roi) estimate in months we
convert the annual savings into a monthly savings rate (mr). Next, we take
the set up costs (setcost) and find calculate how many months of
the savings it would take to make back the set up costs.
mr = (c1  c2) / 12
roi = setcost / mr
For the option to take a cooler shower, we reduce the heating cost (by 3%)
for c2 and make all the other calculations as normal.
c2 = g2 X ((hcost X 0.97) + gcost)
Shower dynamics:
Your shower use habits may change a bit when using a lower flow shower head. It may
take a little longer for the shower to get up to the desired temperature
because less water is going through the shower head. Therefore, your shower time
might increase a little bit (2030 seconds).
Some people report that they run the shower a little
warmer because it is cooler when standing outside the water stream.
Other people report that they need a little more time to rinse off.
These factors may contribute a little to the accuracy of the estimates obtained
from the calculator.


Water conserving shower products in our Amazon.com store.
