Choose the right type of central heating

The best time to choose a new heating system is before you hear your boiler emit its final death rattle on the coldest day of the winter — in which case, you'll be buying whatever furnace or boiler your local fuel dealer likes to install. Building a new house, you'll have a wide range of options, but even if you're replacing an existing system, your choice can have a big impact on your home heating's cost to you — and the environment.

How to choose the right type of central heating

The first step in choosing a new central heating system is to learn basic terminology and to understand the differences between the most common types of systems.

Is it a furnace or a boiler?

Most heating systems in the US today are fueled by natural gas or home heating oil. Heat is generated in a gas- or oil-fired system in either a furnace or a boiler.

A furnace heats air, which is distributed by blowing it through air ducts and out into the rooms in your house through registers.Wilson, Alex and Morrill, John (1998) Consumer Guide to Home Energy Savings. Washington, D.C.: American Council for an Energy-Efficient Economy: 54 A boiler heats water or steam, which is circulated through copper pipes attached to baseboard radiators or older-style cast iron radiators in your rooms.Wilson, Alex and Morrill, John (1998) Consumer Guide to Home Energy Savings. Washington, D.C.: American Council for an Energy-Efficient Economy: 54

Is it hot air or hot water?

Heating systems that use furnaces are called hot air or warm air systems, or else forced air or forced hot air systems.Trethewey, Richard, (1994) This Old House Heating, Ventilation, and Air Conditioning. Boston: Little, Brown, & Company: pageWilson, Alex, "Your Best Heating & Cooling Options" Mother Earth News (Summer 2007): 99 Hot air systems are most commonly fueled by natural gas, but they can also be fueled by wood, propane, oil, or electricity.Wilson, Alex, "Your Best Heating & Cooling Options" Mother Earth News (Summer 2007): page

Heating systems that use boilers are called hydronic systems, more commonly referred to as hot water or forced hot water systems.Wilson, Alex and Morrill, John (1998) Consumer Guide to Home Energy Savings. Washington, D.C.: American Council for an Energy-Efficient Economy: 54 Hot water systems are usually fueled by gas, propane, or oil.Wilson, Alex, "Your Best Heating & Cooling Options" Mother Earth News (Summer 2007): 100 A less-common form of hot water heating is radiant heating, in which water runs through plastic tubing in the floor. Radiant heating systems aren't usually a good green choice: besides being expensive, in a well-insulated house or a house with passive solar elements, overheating is a problem.Wilson, Alex, "Your Best Heating & Cooling Options" Mother Earth News (Summer 2007): 100

Which is better: A furnace or a boiler?

In general, boilers have the upper hand, due to the following advantages:Wilson, Alex, "Your Best Heating & Cooling Options" Mother Earth News (Summer 2007): 100

• They're quieter than forced hot air systems.
• They require less energy to distribute the heat.
• They're more adaptable to zone heating (so you can set the temperature separately in different parts of the house, which saves energy).

What about electric?

Electric heat falls into two categories: electric resistance heat and electric heat pumps. Electric resistance heat turns household electricity directly into heat. Aside from being expensive, it usually isn't considered a good green choice, given that in 2007, 48 percent of electric power in the US was generated by coal-fired plants.[1] One exception might be if you have a super-insulated home and live in a warm climate with a very small heating requirement. In this case a $10,000 system isn't worth it if you only need to generate $100 worth of heat every year.Wilson, Alex, "Your Best Heating & Cooling Options" Mother Earth News (Summer 2007): 101

An electric heat pump is a better choice if you live in a warm climate and have a moderate heat load, since heat pumps produce more heat per kilowatt hour of electricity. They also do double-duty as they are also used for air conditioning. An air-source heat pump uses the outside air as the source for its heat, as well as for a heat sink (where unwanted heat is disposed of). In a colder climate, using a ground-source heat pump, or geothermal is a better choice, since it uses the ground — which maintains a more constant temperature — as the heat source and sink. (And air-source heat pumps have to shift over to electric resistance heating if the outside air temperature dips down to about 30 °F or 40 °F).Wilson, Alex, "Your Best Heating & Cooling Options" Mother Earth News (Summer 2007): 101

Should I switch distribution systems?

If you have an existing hot air system it rarely makes sense to switch to a hot water system, and vice versa, as the cost of adding new piping or air ducts would be much too expensive. Upgrading a steam heat system to a hot water system might be a viable option, however, and worth asking your heating technician about.Wilson, Alex and Morrill, John (1998). Consumer Guide to Home Energy Savings. Washington, D.C.: American Council for an Energy-Efficient Economy: 60

Picking the most efficient system

The efficiency of an oil- or gas-fired heating system is determined by how well it converts fuel into heat. One measure is combustion efficiency, which tells how your system performs while it's running. An even better measure is AFUE which stands for annual fuel utilization efficiency. While combustion efficiency is equivalent to the miles per gallon your car gets zipping down the highway, the AFUE measures start-up, cool-down, and other operating losses as well — more like measuring your car's mileage for both city and highway driving.Wilson, Alex and Morrill, John (1998) Consumer Guide to Home Energy Savings. Washington, DC: American Council for an Energy-Efficient Economy: 58

Find it! Energy-efficient heating products

Choosing the right type of central heating helps you go green because…

• Home heating accounts for about two-thirds of the energy used in most homes in cold climates.Wilson, Alex and Morrill, John (1998). Consumer Guide to Home Energy Savings. Washington, D.C.: American Council for an Energy-Efficient Economy: 53
• Reducing the energy you use for home heating is the single-most effective action you can take to reduce your home's contribution to global warming.[2]

The Union of Concerned Scientists analyzed the ecological costs of the most common consumer activities and products and ranked "home heating, air conditioning, and water heating" fourth in its list of the "seven most harmful human activities" the environment.[3]

Glossary

• annual fuel utilization efficiency (AFUE): A measure of heating-appliance efficiency that includes heating system start-up and cooling time and any other losses associated with its normal operation during the entire year.Pahl, Greg,(2003) Natural Home Heating: The Complete Guide to Renewable Energy Options. White River Junction, VT: Chelsea Green Publishing Company: 263
• baseboard radiator: Baseboard radiators have a copper tube inside that runs the length of the unit and is ringed with fins. They heat primarily by convection. The fins increase the surface area of the radiator and promote air movement.Trethewey, Richard, (1994) This Old House Heating, Ventilation, and Air Conditioning. Boston: Little, Brown, & Company: 124
• boiler: An enclosed heat source (usually located in a basement, but sometimes outdoors) in which water is heated and then circulated for heating a house. Boilers can burn a wide variety of fuels. Pahl, Greg,(2003) Natural Home Heating: The Complete Guide to Renewable Energy Options. White River Junction, VT: Chelsea Green Publishing Company: 264
• electric resistance heating: Electric resistance heating turns household electricity directly into heat.[1] Electric resistance heat can be supplied by centralized forced-air electric furnaces or by heaters in each room.[4]
• furnace: An enclosed heat source (usually located in a basement) in which heat is produced to heat a house, usually via hot air. Furnaces can burn a wide variety of fuels. Pahl, Greg,(2003) Natural Home Heating: The Complete Guide to Renewable Energy Options. White River Junction, VT: Chelsea Green Publishing Company: 267
• geothermal: In the context of heating systems, geothermal refers to systems that pump heat either from or into the ground or outside air in order to heat or cool your home.Pahl, Greg,(2003) Natural Home Heating: The Complete Guide to Renewable Energy Options. White River Junction, VT: Chelsea Green Publishing Company: 267
• heat sink: A component — such as masonry, concrete, stone, or water — inside a structure that absorbs heat and then radiates heat slowly when the surrounding air falls below its temperature. Pahl, Greg,(2003) Natural Home Heating: The Complete Guide to Renewable Energy Options. White River Junction, VT: Chelsea Green Publishing Company: 268
• heat pump: A unit that heats or cools by moving heat. During the winter, a heat pump draws heat from outdoor air and circulates it through your home's air ducts. In the summer, it reverses the process and removes heat from your house and releases it outdoors. [5]
• hydronic: A system of heating or cooling that involves the transfer of heat by a circulating fluid in a closed system of pipes.Pahl, Greg,(2003) Natural Home Heating: The Complete Guide to Renewable Energy Options. White River Junction, VT: Chelsea Green Publishing Company: 268
• radiant heating: A heating system that works by heating surfaces (usually floors, panels, or ceilings), from which heat eventually radiates into the living space.Pahl, Greg,(2003) Natural Home Heating: The Complete Guide to Renewable Energy Options. White River Junction, VT: Chelsea Green Publishing Company: 270
• radiator: Radiators may be baseboard radiators or older style, upright cast iron radiators. Most radiators use a combination of convection and radiation to heat a room.Trethewey, Richard, (1994) This Old House Heating, Ventilation, and Air Conditioning. Boston: Little, Brown, & Company: 123
• register: A grille often with shutters for admitting heated air or for ventilation.
• zoning: With zoning, a house is divided into two or three zones, each controlled by a separate thermostat. This means more comfort for a lot less money. Trethewey, Richard, (1994) This Old House Heating, Ventilation, and Air Conditioning. Boston: Little, Brown, & Company: 94

External links

• American Council for an Energy-Efficient Economy - Heating Systems: Furnaces and Boilers Get the skinny on how to select a new furnace or boiler, including purchasing tips for each type of system, in this excerpt from the book Consumer Guide to Home Energy Savings.
• US Department of Energy - Selecting and Replacing Heating and Cooling Systems Find out more about all types of heating system options, including electric resistance heating and heat pumps.
• ENERGY STAR - Heating & Cooling Find out how to choose an ENERGY STAR boiler, furnace, air-source heat pump, or geothermal heat pump, including tips on system sizing and finding a contractor.

Footnotes

1. Energy Information Administration - Electric Power Monthly (December 2007)
2. American Council for an Energy-Efficient Economy - Heating Systems: Furnaces and Boilers
3. San Francisco Chronicle - Group's Surprising Beef With Meat Industry
4. US Department of Energy - Electric Resistance Heating
5. Lennox ‰ÛÒ Glossary