Home Heating Alternatives to Traditional Forced Air
Nationwide, about 85% of homes have central heating systems installed. Most of these systems are gas forced air systems, which use a gas furnace with a fan to circulate warm air throughout the home. Despite its ubiquity, gas forced air heat is not necessarily the best option for all homes. If you are considering upgrading your heating, cooling, or hot water heating systems, various heating alternatives may provide better service while reducing your energy consumption and cost. Here is how a traditional forced air system works:
Gas Forced Air System
Air is pulled from a return grille inside the home, through a return duct into a forced air furnace. The forced air furnace consists of an electric air distribution fan and a gas burner inside of a heat exchanger. The fan blows return air from the house across the heat exchanger, and the warm air is circulated into various rooms of the home through a network of supply ducts and grilles. The heating system is controlled by a central thermostat, usually located in the main living area. The furnace and ductwork are usually located in either the crawl space, basement, or attic. The main drawback to most forced air systems is that the heat is created and transmitted outside of the heated space, and often 30% of the hot air – or more – is lost to the attic or crawl space before it even gets inside! Additionally, poorly insulated ducts can result in the air cooling off before it gets inside. Considering that most existing gas furnaces are 70% to 80% efficient, the overall system efficiency can be 50% or lower once distribution losses are factored in. These furnaces also frequently suffer from high carbon monoxide output, poor flue gas exhaust systems, and/or leaks in the gas supply, which can be major safety hazards.
A new duct system sealed to 6% leakage or less with continuous R-8 ducting can have an overall distribution efficiency of 90%. Condensing, sealed combustion gas furnaces dramatically reduce the safety risks associated with traditional gas appliances, while achieving 95% or higher combustion efficiency.
Alternatives to the gas furnace are becoming increasingly popular. The hydronic air handler and the electric heat pump are still considered forced air systems, though the equipment and fuel sources are completely different.
Heating Alternative #1: Hydronic Air Handlers
Hydronic Air Handlers replace a traditional gas burner with a heat exchanger connected to a water heater.
This is a popular system because it reduces the number of gas appliances and the complexity of the gas system. Also, since tank water heaters keep 50 gallons of hot water on hand, it makes sense that this heat would serve a purpose instead of just sitting in the tank being reheated over and over. Installing a hydronic air handler makes the most sense when the water heater is also being upgraded so that both the heat and hot water systems receive a major efficiency improvement, equipment costs are lower than buying separate mechanicals for both systems, and the demand on the water heater will likely be higher.
Heating Alternative #2: Electric Heat Pumps
Electric Heat Pumps replace a traditional gas burner with a refrigerant coil.
The coil is linked to an outdoor condenser via a refrigerant line. All the equipment is similar to air conditioning equipment, but a reversing valve allows the system to transfer heat from outside to inside rather than from inside to outside when in cooling mode. Just as an air conditioner can make a house cooler even when it is hot outside, by capturing and concentrating heat in the condenser and releasing that heat at the coil, a heat pump can heat a home even on a cold day. Whereas traditional electric heat is considered to be 100% efficient since it turns all the electricity it consumes, heat pumps are 250-300% efficient because they use energy to move heat, rather than to create it. This can yield substantial reductions in energy costs in homes where the heat comes from electric baseboards, and can even be cost-competitive with natural gas heat in most utility markets. In fact, when installed in conjunction with solar PV electricity, your home can be brought to or near net-zero energy consumption
Still, all forced air systems do make compromises:
- In most cases, the entire house is heated to the same temperature, regardless of which rooms are occupied
- Smells and moisture can be transmitted throughout the house
- Some noise will be present, even with a well-designed and well-installed system
- Pressure imbalances inside the house can pull doors open or closed and enable problems with moisture, air leakage, and even carbon monoxide
Heating Alternative #3: Ductless Minisplit
In the last five years, ductless minisplit heat pumps have increased in popularity due to increased performance and features, combined with falling prices. Although minisplits often serve as “add-on” systems that supplement heating or cooling in an area that is difficult to keep comfortable, more and more builders and homeowners are choosing minisplits as their primary heat source. Ductless minisplit heat pumps work on the same principles as ducted heat pumps: refrigerant draws heat from an outdoor condenser coil and moves the refrigerant to an indoor evaporator coil, also called a “head”, which distributes the heat into the home. As with ducted heat pumps, most ductless minisplits provide both heating and cooling.
Many newly constructed homes, especially those designed with an open floorplan on a single floor, are being heated and cooled solely with a single ductless minisplit unit, in climates from southern California to Maine. However, most existing homes will need multiple heads in different locations in order to provide comfort throughout the home. Multi-zone systems like the Fujitsu Halcyon use a single outdoor condenser to provide heating and cooling to as many as eight indoor heads, each of which can be individually controlled. Heads are available in a number of configurations that mount on the floor, wall, or ceiling.
A ductless minisplit heating and cooling system offers many benefits:
- Each zone can be kept at a different temperature, so occupants only heat the areas they are in. Why heat the bedrooms if everyone is in the family room? Each zone can also be put on a programmed schedule
- Ductless minisplits work by moving, not creating, heat, so they often exceed 300% efficiency. Compare that to a 95% efficient gas furnace, or a 100% efficient electric baseboard.
- Ductless minisplits are all-electric. You can avoid all the potential hazards of having a gas appliance in the home. You can also install a solar PV electricity system to offset the energy consumption of the heating and other uses in the home to wean the home off of fossil fuels and sell excess power back to the grid, while still having the reliability of grid electricity.
- Since ductless minisplits don’t have duct systems, they avoid many of the indoor air quality issues associated with forced air systems.
As solar PV gains ground in California and elsewhere in the country, electricity becomes cost-competitive with gas. Add in 300%+ efficiency and zoning flexibility, as well as rebates for solar and electric heat pumps, and ductless minisplits become a cost-competitive option that slashed heating energy consumption by half or more while increasing livability.
Heating Alternative #4: Hydronic Heating
Hydronic heating systems have existed alongside forced air systems for decades, primarily in multifamily, institutional, and commercial buildings as well as large residential homes in cold climates. Hydronic systems typically use a gas boiler to heat water that is circulated through pipes to either radiators or heat exchangers mounted under floors.
A number of different fuels can provide the heat source for a hydronic system, from fossil fuels and electricity to solar thermal. Often, these systems work in tandem, such as a solar thermal system with gas backup. Some systems are even powered by on-demand water heaters that also provide domestic hot water!
Hydronic systems have many benefits. Zoning works more effectively with a hydronic system than with a forced air system. Since hydronic systems radiate heat onto our bodies, comfort is often achieved at lower heating temperatures than forced air heating systems. Hydronic heating is virtually silent, and does not dry out the air in a home. It does not move air, so it is not subject to the indoor air quality problems associated with forced air systems. However, hydronic heating is generally more expensive than other heating systems, both to install and service. It does not respond to temperature changes quickly, making it difficult to save energy with programmable thermostats. For these reasons, hydronic heating remains a niche in residential heating.
Forced air systems are much better than they used to be, and keep getting better. They remain popular due to the ease and low cost of replacement. However, other options may meet your current and future needs better. Consider other options before settling on replacing your forced air system – you will likely live with the decision for 20 years or more.
Sources : EIA http://www.eia.gov/todayinenergy/detail.cfm?id=14771
Home Energy Magazine http://www.homeenergy.org/show/article/id/1197 forced air graphic
Energy Trust of Oregon http://energytrust.org/residential/incentives/info/heat-pump-optimization.aspx heat pump graphic
naturalgasefficiency.org http://naturalgasefficiency.org/residential/Heat-Combi_Space-Water.htm hydronic air handler graphic
wiki http://en.wikipedia.org/wiki/Zero-energy_building net zero link
wiki http://en.wikipedia.org/wiki/Solar_thermal_energy solar thermal link
Copyright September 2014 by Advanced Home Energy
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