# 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 units

Cook-Tops

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.

Clothes Dryers

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.

Electric Dryer

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.