There are several types of systems used to provide heat in a home, and within each broad type, there are many variations. Some heating systems share components with the home's cooling equipment, and the term HVAC (heating, ventilation, and cooling) is used to describe the overall climate control system in a home.
No matter what system is used, the purpose of all heating appliances is to tap the thermal energy from a fuel source and transfer it to living spaces to maintain a comfortable ambient temperature. Within this general definition, a wide range of fuels and mechanical systems are used to accomplish the task. Some homes may even combine several different systems.
Here is an overview of the most common home heating systems.
By far the most common HVAC system in modern homes is the forced-air system that uses a furnace with an electrically powered blower that moves warmed air to the various rooms of the home through a network of ducts. Forced air systems are very quick at adjusting the temperature of a room, and because air conditioning systems can share the same blower and ductwork, this is an efficient overall HVAC System.
Fuel sources: The furnaces that power forced-air systems can be fueled by natural gas, liquid propane (LP), fuel oil, or electricity.
Distribution: Air that is warmed in by the furnace's burner or heating element warmed air is distributed through a network of ducts. Another system of ducts returns air back to the furnace through cold-air returns.
Forced air systems can be filtered to remove dust and allergens.
Humidifier (or dehumidifier) equipment can be integrated into the forced air system.
Forced air furnaces are relatively inexpensive.
These furnaces can achieve the highest AFUE (Annual Fuel Utilization Efficiency) ratings of any heating system.
Forced air systems can combine cooling with heating capability.
Requires ductwork and takes space in walls.
Furnace fan can be noisy.
Moving air can distribute allergens unless filtered.
Moving air can become dry unless humidified.
Forced air blowers are mechanical systems that wear out; furnaces need to be replaced more frequently than other heating systems.
A precursor to forced air systems, gravity air furnaces also distribute air through a system of metal ducts, but rather than forcing the air by a blower, gravity air systems operate by the simple physics of warm air rising and cool air sinking. A gravity air furnace in a basement heats air, which then rises into the various rooms through ducts. Cool air returns to the furnace heat exchange chamber via a system of cold-air return ducts. The so-called "octopus" furnaces found in many older homes are gravity air furnaces.
Gravity air systems are no longer installed, but in many older homes, they continue to perform effectively.
Fuel source: Forced air furnaces can be fueled by natural gas, liquid propane (LP), fuel oil, or electricity.
Distribution: Conditioned air is circulated through a network of metal ducts.
No moving parts, so these systems are very long-lived and can last for many decades.
Gravity air systems are very dependable and require little maintenance.
Air cannot be filtered effectively.
Energy efficiency is lower than with newer furnaces.
Temperature adjustments are slow since the systems operate by simple convection currents.
While forced air and gravity air heating systems work by heating air at central furnace locations, then distributing that warmed air to various rooms through ductwork, other heating systems work in a much different way. Radiant heating refers to any system in which thermal energy is transferred from warm surfaces to cold in the rooms where the heat is needed. The term can be used to describe such old-fashioned methods as heating a room with a pot-bellied wood-burning stove, or highly modern and sophisticated systems where hot water is circulated through tubes embedded in mortar beneath the floor. It can also refer to systems in which panels powered by electricity are applied to ceilings to radiate heat downward into a room.
For modern homeowners, one of the most common applications is radiant floor heating, in which hot water tubing or electrical wires warm up a mortar or ceramic tile floor to radiate heat into the room.
Distribution: In-floor systems are usually distributed by hot water flowing through plastic tubing.
Radiant systems provide comfortable, even heat.
When heated by boilers, radiant systems can be very energy efficient.
Installation of in-floor systems is expensive.
It is difficult access to hidden piping if maintenance problems emerge.
The most common whole-house radiant heating systems are operated by centralized boilers that circulate steam or hot water through pipes to radiator units positioned strategically around the house. The classic radiator—a cast-iron upright unit usually positioned near windows in older homes—is often called a steam radiator, although this term is sometimes inaccurate.
In reality, there are two types of systems used with these older radiators. True steam boilers actually do circulate gaseous steam through pipes to individual radiators, which then condenses back to water and flows back to the boiler for reheating. These systems can be identified by the fact that the radiators have pipe connections both at the top (steam delivery) and the bottom (condensed water return). These are sometimes called two-pipe systems.
A slightly different type of radiator is used with hot water boilers, in which superheated water circulates through convection to the various radiators. In these systems, there are pipe connections only at the bottoms of the radiators. These are often called ​one-pipe systems.
Fuel sources: Boiler/radiator systems can be fueled by natural gas, liquid propane, fuel oil, or electricity. Original boilers may even have been fueled by coal.
Distribution: Heat is produced by steam or hot water circulating through metal pipes to radiators shaped to facilitate the transfer of thermal energy.
Radiant heat is quite comfortable and does not dry out the air as forced-air heat does.
Radiators can be updated to low-profile baseboard or wall-panel radiators.
When old boilers are replaced, modern boilers have very good energy-efficiency.
Radiator locations may limit furniture placement and window coverings.
Cannot be combined with air conditioning.
Another more modern form of radiant heat is a hot water baseboard system, also known as a hydronic system. These systems also use a centralized boiler to heat water that circulates through a system of water pipes to low-profile baseboard radiators with metal fins that radiate the heat from the water out into the room. This is essentially just an updated, evolved version of the old upright radiator systems.
Fuel Sources: Boilers for hydronic systems can be fueled by natural gas, liquid propane (LP), fuel oil or electricity.
Hot water heated by a boiler and piped to "fin-tube" baseboard units mounted along walls. The fins increase the surface area of heat dissipation making the unit more efficient.
Air is distributed by convection as air rises and is heated by the baseboard unit.
Hydronic systems have excellent energy efficiency.
Hydronic systems are quiet since there are no fans or blowers.
Temperature can be precisely controlled.
Radiator systems are very durable and have little maintenance.
Baseboard radiation/convection units must remain unobstructed and can provide challenges in furniture placement and drape design.
Cannot be combined with air conditioning systems.
The newest home heating (and cooling) technology is the heat pump. Using technology that is similar to an air conditioner, heat pumps extract heat from one source and deposit it in another using an indoor air handler and outdoor pump unit that circulates refrigerant. Some systems extract heat from outdoor air, while ground-loop geothermal systems extract heat from the earth using a ground-loop pipe.
Fuel sources: Heat pumps are usually powered by electricity, although natural gas models are also available.
Distribution: Heat (and cooling) are provided by wall-mounted units that blow air across evaporator coils linked to an outdoor pump that extracts or absorbs heat from the outdoors.
Systems offer both heating and cooling.
Heat pumps are extremely energy efficient.
Individual wall units allow for precise control of each room.
Fans are much quieter than central forced-air systems.
Heat pumps are best suited for relatively mild climates.
Installation costs are higher than ductwork systems.