The big energy hogs in the house are the HVAC, The refrigerator and the water heater.

HVAC in the residentail market simply means a combine furnace and airconditioner that share the same ventilation system. but we will treat them as seperate units for easier detail:

http://www.fypower.org/res/tools/products_results.html?id=100156

Of course it would use natural gas,

 Condensing furnaces contain a second heat exchanger that condenses water vapor in the hot flue gasses, extracting additional heat. The gases are then vented directly outside through a pipe in the wall. Condensing furnaces are the most efficient on the market but they are also the most expensive. Almost all ENERGY STAR qualified furnaces are condensing models.

Efficiency Rating
Furnace efficiency is rated by annual fuel utilization efficiency (AFUE). The AFUE measures the amount of fuel converted to space heat in proportion to the amount of fuel entering the furnace. The federal minimum efficiency standard for furnaces specifies an AFUE rating of at least 78%. ENERGY STAR qualified furnaces must have a minimum AFUE rating of 90%. The most modern and efficient heating systems can achieve an AFUE of as high as 97%.

For a list of the most efficient furnaces in all output categories, visit the American Council for an Energy-Efficient Economy (ACEEE)’s guide to top-rated furnaces.

Efficiency Improvements
Some improvements that have been made to the components of furnaces in recent years are two-stage burners and higher-efficiency blower motors.

Two-Stage Burners — When the heating demand is low, two-stage burners allow you to run your furnace at a lower burn rate most of the time, using less gas than a single stage burner. These use a special gas valve that fires the burners at either the low-heat or high-heat level. When heating needs increase, the burner fires at the high-heat level, increasing the burn rate. These burners save energy by using a smaller amount of gas when demand is low, thereby providing more even heating throughout the day.

Fan Blower Motor — Depending on the size of the furnace, fan blower motors can use between 84 kWh/year for the smallest gas furnaces (25,000 Btu) to almost 550 kWh/year for the largest models (118,000 Btu). Some newer furnaces have an electronically commutated (ECM) fan blower motor that is more efficient than a standard blower motor. Variable-speed blower motors also have been in use in newer models. By using only the power needed for the immediate heating demand, these motors use 75% less electricity than standard motors. They also adjust to changes in air pressure among rooms, heating the space more efficiently.

 http://www.residential.carrier.com/products/furnaces/gas/index.shtml

Gas Furnaces

The smooth comfort of gas heat with the most advanced technology

For the optimal combination of gas heating and impressive energy efficiency, choose Carrier precision-engineered gas furnaces, from the innovative Infinity™ ICS with precision temperature control to the solid Comfort™ 80. The higher the AFUE rating, the more energy efficient—meaning you’ll save more money.

Infinity ICS Gas Furnace

Up to 3.5 times tighter temperature control

          Quietest furnace you can buy

• IdealComfort™ technology
• Lifetime heat exchanger limited warranty

• Infinity 96 Gas Furnace

96.6% AFUE

• Variable speed blower
• IdealHumidity
• Lifetime heat exchanger warranty

Infinity 80 Gas Furnace

80% AFUE

• Variable speed blower
• IdealHumidity
• 20-year heat exchanger warranty

Performance 93 Gas Furnace

93% AFUE

• 4-5 speed blower
• Enhanced humidity control
• Lifetime heat exchanger warranty

 http://www.bryant.com/products/furnaces/index.shtml

Evolution System Plus 95s™ Furnace

• Up to 95 AFUE
• PerfectSense™ functionality
• Up to 73% more consistent temperatures than single stage furnaces
• Quietest furnace that you can buy
• Perfect Humidity
• Perfect Heat technology
• Pilot-free PerfectLight ignition
• Lifetime heat exchanger warranty

• Evolution System Plus 95s™ Gas Furnace

Evolution System Plus 90i™ & Plus 95i™ Furnaces

• Up to 96.6 AFUE
• Perfect Humidity
• Perfect Heat technology
• Pilot-free PerfectLight ignition
• Lifetime heat exchanger warranty

• Evolution System Plus 90i™ Gas Furnace

Evolution System Plus 80v™ Furnace

• Up to 80 AFUE
• Perfect Humidity
• Perfect Heat technology
• Pilot-free PerfectLight ignition
• 20-year heat exchanger warranty

• Evolution System Plus 80v™ Furnace

 

 

 http://www.lennox.com/products/list.asp?type=2

 

ENERGY STAR® Product		Energy Efficiency (AFUE)	Price Guide*

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But then there is the new kid on the block: 

 

Emerging Technology

The MicroHeater, developed by the Pacific Northwest National Laboratory, could redefine the way in which homes are heated. The size of a palm, the MicroHeater is capable of combusting 4,000 to 120,000 Btu of gas per hour. They can be installed in baseboard heaters, and an array of them can efficiently heat an entire house. The MicroHeater can reduce energy loss from a typical central heating system by 45%.

 http://picturethis.pnl.gov/picturet.nsf/All/4A2LDA?opendocument

We have even talked about air conditions yet or geothermal heat pumps…geez