Basics of Heating

According to the U.S. Federal Government heating and cooling accounts for around 45% of Americans’ annual energy bills. They estimate that on average homeowners will spend more than $10,000 for heating and cooling over a 10-year period.

We are a comfort-based society and most of us have high expectations for comfort in our own homes. Nobody wants to toss and turn in a cold house this winter because something has gone wrong with the heating system. When problems hit, it helps to understand how your heating system works and knowing the basics can also help troubleshoot when there’s a problem. Along with understanding how your system works, you should know what different options are available with various systems, what standards or regulations these systems adhere to and lastly, how far these systems have come in what they can do to provide added comfort in your home.

“A heating system is a mechanism for maintaining temperatures at an acceptable level; by using thermal energy within a home, office, or other dwelling.” Heating systems, often part of an HVAC (acronym for “heating, ventilating, and air conditioning”) system, may be centralized or distributed. A central heating system provides warmth to the whole interior of a building (or portion of a building) from one point to multiple rooms.

There are various types of heating systems options that homeowners can utilize. Furnaces fueled by natural gas are the by far the most common heating system for homes in the United States. Furnaces heat your home by circulating heated air through a series of ducts, known as a forced air duct system. As the fuel burns, the hot gases that are generated move through curved metal tubing called a heat exchanger, and then exit your home through a vent pipe. At the same time, the air circulating through the ducts passes over the exterior of the heat exchanger, and gathers heat from the hot metal. This warmed air is then circulated throughout your home.

Boilers, another forced air system, heat water, providing either water or steam for heating. Steam is distributed via pipes to steam radiators, and hot water can be distributed via baseboard radiators or radiant floor systems, or can heat air via a coil.

Heat pumps are another option for heating your home. Like your refrigerator, heat pumps use electricity to move heat from a cool space into a warm, making the cool space cooler and the warm space warmer. A heat pump is an air conditioner in reverse. With an air conditioner, heat is extracted from the building as it is absorbed into refrigerant inside the fan unit in your basement or closet. The refrigerant then carries the heat to an outdoor unit where it is transferred outside. This leaves the air in the building cooler.

In a heat pump, heat is extracted from the air outside and brought into the house. Surprisingly, there is a decent amount of heat to be extracted until the outdoor air gets to approximately 30 to 35 degrees F. Because they move heat rather than generate heat, heat pumps can provide up to 4 times the amount of energy they consumer. Heat pumps work best in climates with moderate heating and cooling needs and offer an energy-efficient alternative to furnaces and air conditioners.

Geothermal heat pumps (GHP) are a very energy efficient way to heat (or cool) your home. Geothermal heat pumps use the constant temperature of the earth as the exchange medium instead of the outside air temperature. This allows the system to reach fairly high efficiencies (300%-600%) on the coldest of winter nights, compared to 175%-250% for air-source heat pumps on cool days. While many parts of the country experience seasonal temperature extremes—from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F (7°C) to 75°F (21°C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger. As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, in some cases, provide you with hot water as a side benefit.

Radiant heating systems involve supplying heat directly to the floor or to panels in the wall or ceiling of a house. This system depends largely on radiant heat transfer; the delivery of heat directly from the hot surface to the people and objects in the room via the radiation of heat, also called infrared radiation.

Radiant heat has a number of advantages; it is more efficient than baseboard heating and usually more efficient than forced-air heating because no energy is lost through the ducts. This has advantages for allergy sufferers. Hydronic (liquid-based) systems use very little electricity and can use a wide variety of energy sources, including standard gas- or oil-fired boilers, wood-fired boilers, solar water heaters, or a combination of these heat sources.

The last type of system is a solar heating system, which utilizes two types of substances – either liquid or air – that are heated in the solar energy collectors. The collector is the device in which a fluid is heated by the sun. Liquid-based systems heat water or an antifreeze solution in a “hydronic” collector, while air-based systems heat air in an “air” collector. Both of these systems collect and absorb solar radiation, then transfer the solar heat directly to the interior space, from which the heat is distributed. Both of these systems (liquid and air) can help supplement a forced air system.

Solar heating systems are most cost-effective when they are used most of the year – in cold climates with good solar resources. They are most economical when they are displacing more expensive heating fuels, such as electricity, propane or oil heat.

AFUE is the ratio of heat output of the furnace or boiler compared to the total energy consumed by a furnace or boiler. An AFUE of 90% means that 90% of the energy in the fuel becomes heat for your home and the other 10% escapes up the chimney and elsewhere. AFUE does not include the heat losses of the duct system or piping, which can be as much as 35% of the energy output of a furnace when the ducts are located in the attic.

Something to note, even though the all-electric furnace or boiler has higher AFUE ratings between 95-100%, due to the high cost of electricity in most parts of the country this is not an economic choice for most. If you are looking for electric heating, you should consider a heat pump.

In the graph below you can see how much money you can save by upgrading your old heating equipment to a new higher efficiency system.