Saving Money Cooking and Washing
Question: It’s about time I updated my cooking and washing appliances and I know there are a number of different options. I also expect energy costs to continue to rise over time so I want to select the most economic products to own. How do I know which is the best solution?
As with heating and cooling and hot water systems, it is important to investigate other in home appliances that can operate using different fuels. For instance there are electric and gas cooking appliances and electric and gas clothes dryers. Many people opt for electricity because it seems an easier appliance to deal with. However, when selecting any new appliance considering the cost of operation is important, especially as these units should last beyond 10 years.
Cooking appliances use the same analysis as a water heater; if you boil water in a saucepan then:
The energy required to heat the water in BTUs
= (Volume in gallons x Water weight) x Temperature change ΔT
Where the volume in gallons is 1
The weight of water is 8.345 pounds per gallon
The temperature rise from cold to hot is 160°F (50°F to 210°F)
Efficiency Factors (EF) supplied by the Department of Energy (DOE)
1 Therm of gas is $1.13 and 1KWh of electricity is $0.118
Gas burner Average gas cook-top has a 40% efficiency factor (EF)
(1 x 8.33) x 160 = 1332.8 BTU
1332.8 x EF = Total BTU
1332.8 x 40% = 3332 BTU
3332/100000 = 0.033 Therm x $1.13 = $0.037
Electric ring burner Average electric cook-top has a 70% efficiency factor
1332.8x 70% = 1904 BTU
1904/3412 = 0.558KWh x 0.118 = $0.066
Induction burner Average induction cook-top has a 90% efficiency factor
1332.8 x 90% = 1481BTU
1481/3412 = 0.434KWh x 0.118 = $0.051
Summary based on DOE numbers a gas burner cost 44% less than an electric burner and 28% less than an induction burner even though the device efficiencies would lead you to believe the opposite.
Gas oven Average gas oven has a 6% efficiency factor (EF)
1332.8 x EF = Total BTU
1332.8 x 6% = 22213 BTU
22213/100000 = 0.222 Therm x $1.13 = $0.251
Elect oven Average electric oven has a 13% efficiency factor (EF)
1332.8 x 13% = 10252 BTU
10252/3412 = 3.0KWh x 0.118 = $0.354
Convection oven Average electric convection oven has a 23% efficiency factor (EF)
1332.8 x 23% = 5795BTU
5795/3412 = 1.698KWh x 0.118 = $0.2 + 2W fan
In summary and based on the DOE numbers a gas oven is 31% more operationally cost effective than an electric oven, but 20% less than an electric convection oven. Another factor to consider is the time it takes to boil the water, boiling time is based on the amount of heating capacity in BTU available and the efficiency of the heat transfer.
Example: The gas burner above has a 10,000 BTU element. It needs to supply 3332 BTU to boil the gallon of water. The time needed is 10,000/3332 = 3 and 60/3 = 20 minutes. A 50,000 BTU burner would take just 4 minutes and both would cost the same in energy.
The Department of Energy has set standards for electric and gas clothes dryers; they are rated by an efficiency factor based on the number of pounds of clothes dried per KW of energy. For electric dryers its 3.01 pounds and for gas units it 2.67 pounds; this looks like a no brainer the electric unit must be more efficient.
Now if we consider that Energy Star has established that the average household completes 416 dryer cycles a year and the energy used is 967KWh for electric units and 1091KWh for the gas units again the electric unit looks more efficient.
The electric unit is very straight forward 1KWh of electricity costs $0.118 and we use 967KWh per year.
967KWh x $0.118 = $114.40
Natural Gas Dryer
The natural gas unit is specified in KWh, but must be converted into BTU or Therms. 1KWh equals 3412 BTU and a Therm equals 100,000 BTU. A Therm costs $1.137
Therefore 1091KWh x 3412/100000 = 37.2 Therms
37.2 Therms x $1.137 = $42.32
In summary the gas unit costs $72.00 a year less to operate than the electric unit and proves that in spite of the figures above is more cost efficient. The gas units additional $50 upfront cost is paid back within a year. However, if you need a gas line connection installed it will take longer to break even and this should be taken into account.