| Calculations |
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Basis for calculations:
1 therm = 100,000 BTU
Cost per therm estimated for use on this page April 2017/ $.69 at
residential retail price with taxes.
1 BTU will raise 1 lb of water 1°F at sea level, but requires more BTUs
for higher
elevation.
Cost of
hot water for 1
bath using Tank gas water heater:
Assume 17 gallons of water for typical bath x 8.34 lbs per gallon = 142
lbs
Raise 142 lbs water 1° = 142 BTU
Assume incoming water supply is 60° F and tank thermostat is set to
120°F, or 60° rise in temperature. Incoming water temperature varies by
season, latitude, elevation and other factors.
Raise 142 lbs water 60°F = 142 BTU x 60 = 8520 BTU
1 BTU = .00001 therm
Example
1:
typical 2012 50 gallon gas water heater efficiency .55, and this is
generous efficiency for older water heater with dirty combustion parts
and build up of sediment on heat transfer surface.
Calculation
for 2102 50 gallon: 8520 BTU ÷ .55 efficiency = 15490 BTU
for 1 bath
15490 BTU x.00001 therm = .15490 therms per bath x .69 per therm =
10.7¢ per
bath
So 10.7¢ per bath, at sea level, depending on cost of therms.
Same
calculation
for 2012 30 gallon with .58 efficiency = 10.1¢
per bath
Example
2:
typical water heater manufactured after April 2015, for 50
gallon
heater, and let's say new heater still has full
efficiency of .60.
Calculation
for 2015 50 gallon: 8520 BTU
÷ .60 efficiency = 14200 BTU
for 1 bath.
14200 BTU x .00001 therm = .14200 therms x .69 per therm = .098¢ or 10¢
per bath.
Cost 10¢ per bath, at sea level, depending on cost of therms.
Same
calculation
for 2015 30 gallon with .63 efficiency
= 9.3¢
per bath.
Buy:
EKM gas meter
Resources:
Troubleshoot Gas water heater
\Cost to operate gas water heater .pdf |
| Conclusions |
-This webpage can only apply simple
1-or-2-dimensional math to a complex multidimensional problem
encompassing a huge swath of usage patterns,
conditions, etc, making
the gas meter shown at top of page the most reliable answer for any gas
appliance.
-The analysis on this page shows .7¢
(almost a penny) per bath improvement
with new water heater vs old water heater.
-If
your water heater has 2% increase in efficiency, and your house takes 3
baths per day x 365 days x 1¢ = $10.95 per year
savings for
baths.
-Other hot water usage for home is not estimated, but the
numbers show 2015 efficiency standards provide a savings (if
manufacturer's product actually meets the standard).
-It also shows
household can save money by reducing hot water consumption and
installing the smaller, more efficient water heater Resources:
calculate peak demand
9 ways to save with water heater
Which is best gas water heater
-250 million people in US x 1 bath per day x 1¢ = 250 million ¢ = $2.5
million saving per day?
Why
the new energy standard is suspect:
-Aside
from reliability of self-tested products, the older
2012 energy standard is based on 135° thermostat setting. The new 2015
energy standard uses lower setting of 125° to achieve the higher
efficiency. A lower thermostat setting means you have less hot water in
the tank. It reduces first
hour delivery, so the water heater
might run longer to keep up with
demand. This factor might eliminate the expected
savings shown on this page. Calculate first hour Ways to increase amount of hot
-All
costs are energy. The new heaters are larger, use
more materials to manufacture, arrive in larger boxes, take up more
space and cost
more to buy. On the back end, they cost more to replace. What is the
real energy savings if a heater saves $12 per year, lasts 12 years for
a total saving of $144, but
consumes more raw materials to manufacture and costs
$300+ more to buy just to claim higher efficiency? Moreover, larger
heaters create an installation challenge for tight locations, resulting
in remodeling expense to expand area, move gas line, and vent.
-The
new water heater standards illustrate an effort to preserve the heyday
of
consumption by using 'more efficient'
products. Since most of the design difference between pre-and-post 2015
30-40-50
gallon water heaters is thicker insulation, why not sell a cheap add-on
insulation kit?
-My
observation: Relying on 'the marketplace' to solve problems
has usually resulted in higher prices, and not more efficiency.
Our economic system awards 'energy stars' to 4-person, 5000
square foot home because the massive windows are triple-pane, while
overlooking inherent efficiency of a 6 person mobile home.
Perhaps
more do-it-yourself decisions, and
less reliance on 'somebody inventing a new product' might be correct
solution.
Protect your investment:
How to maintain water heater
The future of water heating is solar panels: Convert AC water heater to DC |
| General information: |
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Gas
water heaters with power vent or flue damper consume 120 volt to
operate flue damper or power vent. Power vent models have 1/4 HP motor.
The cost of electricity is a
consideration, as is the need to install dedicated outlet and surge
protection. Troubleshot power vent water heater
Figuring
cost ACCURATELY is a considerable task as seen above: Age, type of gas,
cost of local
gas supply, seasonal fluctuations in prices and temperatures, elevation
above sea level, incoming air supply,
efficiency, efficiency decline over time, cold water temperature,
thermostat setting etc play a role in
calculation.
All numbers for efficiency, BTU rating etc, are based on new heater
under ideal
conditions rarely attainable in real world.
Showing approximate cost of fuel consumption per bath does not take
into consideration the
cost of the heater. For example, 75 gallon condensing gas heater shows
74% efficiency
but the total cost is misleading because of the increased cost of
purchase, maintenance and
repair for high tech heaters. Same with residential heaters, the
purchase cost, maintenance and replacement cost have not been
calculated, but they affect the real cost of heating water. How to maintain water heater
Each
water heater has a BTU rating seen on the label that says how many BTUs
are burned. For example commercial gas water heaters have large burners
and are rated for higher BTU than residential heater. Installing
commercial gas heater in home might consume so much gas that the
household gas meter cannot keep up, starving other appliances of fuel
and causing malfunction.
Resource:
How to install gas water heater
Maintain water heater
Which is best gas water heater
|
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Resource:
Troubleshoot Gas water heater |
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Resource:
Troubleshoot Gas valves with manuals |
