Division of Energy
Residential Energy Efficiency - Heating
Heating is the largest energy expense in most in most homes. Reducing the energy used for heating is the single most effective way to reduce the utility bill.
A combination of conservation efforts and a new, high-efficiency heating system can cut fuel bills in half without lowering your comfort level.
The heating system replaces heat that is lost through the envelope of the house. How much heat is needed depends on how big the house is, how cold and windy the winter is, the efficiency of the heating system and the habits of the family.
If there is a choice of heating fuels, the decision is generally based on economy of operation. The cost of operation is not only based on the fuel cost but the efficiency of the heating system. Other factors that should be considered are the system cost of fuel delivery (installing natural gas mains).
Forced-air Systems (Gas-fired)
Forced-air furnaces that deliver heated air to all parts of the home operate from a thermostat that signals burners to ignite. When the air surrounding the heat exchanger in the plenum reaches a preset level, the electric-powered blower comes on. Air from inside the house is pulled into the furnace cabinet through the return air duct. The air passes through a filter and is circulated over the outside surface of the heat exchanger. The heat is transferred to this circulated air through the heat exchanger walls and does not come in contact with the fuel or the products of combustion. A blower forces the heated air circulating around the heat exchanger out of the furnace, through the ductwork, out the registers and into the living space. Return air ducts carry the cooler room air back to the furnace where it is reheated. Both delivery and return air ducts should be well
When the desired room temperature is reached, the thermostat signals the burners to shut off. The blower continues to operate until the furnace cools to a preset level and then shuts off. The plenum thermostat that controls the blower can be set to come on at a lower temperature and stay on longer to move more heat into the home.
It is very important with forced-air systems to clean or change the filters monthly during the heating and cooling season. Older, natural gas forced-air systems have a continuously burning pilot to ignite the gas-air mixture. New, high-efficiency furnaces have electronic ignition devices.
It is not a good idea to spend money for repairs on an older furnace. Existing forced-air furnaces may have a seasonal efficiency of about 60 percent; new systems have a seasonal efficiency of 80 percent to 95 percent. Changing an older system to a new, high-efficiency system, instead of investing in repairs, should be done; however, replacing a working furnace with a new high-efficiency model has a long pay-back time.
Hydronic (hot water boiler) systems are less common. In this system, hot water from the boiler is circulated through pipes to radiators in each room, then back to the boiler to be reheated. There is a pump at the boiler which circulates the hot water from the boiler to the radiator. The thermostat usually controls the pump and burner and turns it on when the house needs heat. The water starts circulating and continues until
This type of heating system is a radiant system and does not have fans, which eliminates the chilling factor of moving air. The system is more efficient because it does not have duct losses. For more efficient operation, a control can be added to measure outside temperature and adjust the boiler temperature hotter as the outside temperature cools. Boilers can be fueled by gas, electricity or even wood.
The need for combustion air for gas-fired heating appliances must not be overlooked. Failure to provide adequate combustion air will ultimately result in the production of carbon monoxide. Overall tightening of a dwelling could make a home so tight that adequate combustion air would not be provided to the gas-fire appliance.
If your furnace draws combustion air from the crawl space, and you seal and insulate the crawl space, you need to be sure adequate combustion air is provided by running a combustion air duct from a crawl space opening to the furnace.
When your existing gas furnace or boiler fails, you will need to replace it. There are a number of replacement furnaces to choose from, including many high-efficiency models. Over the lifetime of the heating system, the pay-back in energy savings can be substantial.
How do you know which one to buy? First of all, check all the models available before you decide. We suggest getting bids from several contractors.
EnergyGuide fact sheets are available from heating contractor or dealer. These fact sheets will help you compare models. Be sure to ask the heating contractor who replaces your furnace to run a heat loss calculation on your home. This is needed to size the new unit correctly. A new furnace will probably have a lower Btu input rating.
If you replace your furnace, you will usually need a permit from the local building authority. Also, any time you have work done on your furnace by a contractor, be sure he/she is licensed and has taken out all of the necessary permits.
Old coal stoker furnaces that have been converted to natural gas should be replaced as soon as possible, as they are highly inefficient.
Electric Heating Systems
Electricity is a more expensive fuel than natural gas, so it is important to choose the most efficient electric heating system you can afford.
Forced-air electric furnaces, employing resistance heating coils, are sometimes used in small homes and apartments because they are less expensive up front, however, they cost more than twice as much to operate as electric heat pumps.
Baseboard resistance heaters use a metal element to convert electricity to heat. Almost all of the electricity that passes through the element is converted to heat.
The units are located in each room and usually have individual thermostats. By zone-heating, keeping only the room you are using at a higher temperature, this type of heating cost can be reasonable.
Radiant panel heating may be located in the floor, walls or ceiling and may use electric resistance heating or hot water from a central boiler. The heat is transferred by radiation and convection to the surrounding room.
If the radiant heating is located in the ceiling or floor, be sure the attic or foundation is adequately insulated. By the same token, walls should be insulated behind the radiant panels to keep the heat inside the home. Radiant panel systems can be slow to respond to temperature changes.
Electric heat pumps have been available for home heating for more than thirty years. Essentially an air conditioner running in reverse, heat pumps produce two to three units of heat energy for each unit of electrical energy consumed. A seasonal efficiency rating for heat pumps has been devised by the U.S. Department of Energy (DOE). This rating, known as the Heating Season Performance Factor (HSPF), equals the average heating capacity in Btu-per-hour divided by the power consumption in watts. The efficiency of a heat pump increases with higher outdoor temperatures, therefore, seasonal efficiencies are higher in warmer climates.
Most heat pumps employ the same basic layout and components as the equipment of 30 years ago. With the emphasis in the last decade on energy efficiency, and with the advent of solid state controls, today's heat pump offers marked improvements in efficiency and reliability. Because heat pumps also provide cooling in summer, consideration should also be given to their cooling-efficiency rating or Seasonal Energy Efficiency Ratio (SEER). New developments in heat pumps, including variable speed compressors and new compressor designs, are improving the HSPF's.
Air-to-air heat pumps are effective in winter at temperatures down to about 30oF. Supplemental heat is necessary at temperatures below that.
Ground source heat pumps are the most efficient and most expensive in initial cost of electric heating systems. These units use the ground, or ground water, as a heat source for warming, or a heat sink for cooling. Generally, ground source heat pumps are installed at the time of construction or when retrofitting an existing air-to-air system.
Living with a Heat Pump
The heat pump delivers air at temperatures closer to room temperatures than conventional gas or electric furnaces. Because a heat pump does not deliver hot blast of air, some people will feel cool until they adjust to a heat pump-conditioned environment.
The effectiveness of a heat pump is diminished by closing off unused rooms. Thus, the homeowner must heat all of the home instead of only rooms used on a constant.
Special automatic thermostats must be purchased if you want to set back temperatures at night and during periods the home is unoccupied. Without the special thermostat, the immediate several degree jump in the heating when the thermostat is turned up requires the backup heat source (usually electric resistance heating), so the heat pump savings are reduced.
If you are replacing an existing system with a heat pump, be sure to ask the contractor if your present ductwork will have to be modified or replaced. Heat pumps require large ducts, and there should be several air returns. Both ducts and returns should be insulated in all systems.