When a furnace replacement tops your home improvement list, give yourself plenty of time to do the research that will help you choose the system you need based on your home’s heating requirements. Your budget, safety and comfort are at stake, so making an educated decision about the system you choose will improve your satisfaction for the years ahead.

The primary considerations include:

  • System size
  • Energy efficiency
  • Options
  • Installation

Sizing the System

The HVAC contractors from whom you get a quote should do a careful heating load calculation of your home to determine the best size. Too small a furnace won’t tackle the coldest weather in the winter and if the system is oversized, it will turn on and off frequently, short cycling.

When a furnace short cycles, it won’t keep your home as comfortable and will drive up energy costs and increase the wear on the furnace’s parts. Your home will heat too quickly and the air won’t circulate as thoroughly, which means that locations in your home may never warm adequately.

Contractors use software called Manual J that takes these aspects of your home into account to determine the best size:

  • Insulation levels in the walls and attic
  • Energy efficiency of windows
  • Air infiltration rates
  • Layout of your home
  • Number of home occupants and ages
  • Preferred indoor temperatures
  • Amount of heat you generate indoors
  • Landscaping factors.

These factors lead to the correct size for your furnace replacement. Going through the load calculation will also help you learn where energy inefficiencies in your home exist. If you have significant air leaks and lack enough attic insulation, adding more and sealing the leaks could help you choose a smaller heating system. Not only will you save money on the initial purchase, you’ll use less fuel throughout the winter, which lowers energy costs.

Energy Efficiency

Heating systems carry AFUE (annual fuel utilization efficiency) ratings that indicate how much of the fuel the system actually converts to heat for your home. The minimum AFUE stands at 78 percent, which means that 22 percent of the fuel it consumes is wasted. In our climate, selecting a furnace replacement with a high efficiency system makes sense, since our winters are cold. New heating systems carry AFUE ratings as high as 98 percent, which means that the furnace wastes just 2 percent of the fuel it consumes.


Engineers have made significant improvements in furnace technology over the last decade. These are options that will increase your comfort and lower the cost of heating your home:

  • Variable-speed blowers. The motor in a variable-speed blower uses much less electricity than a single-speed motor. The electronically commutated motor (ECM) runs more quietly and slowly, which eliminates much of the noise when the furnace is running. Since it runs more slowly, it mixes the air throughout your home better, increasing comfort. 
  • Variable-heat output. This feature is often combined with the variable-speed blower and cuts fuel consumption by adjusting the amount of fuel the system uses based on the heating load indoors. When the difference in temperature between the thermostat and your home is slight, it won’t use as much fuel. This upgrade improves the AFUE of furnaces.
  • Dual-heat exchanger. Furnaces with this option are called condensing furnaces, the most efficient on the market. Gas creates water vapor as it burns that contains a lot of heat. A condensing furnace uses the second heat exchanger to extract the heat from the vapor, using it to heat your home instead of sending the vapor up the chimney.


The installation process during the furnace replacement has an impact on the overall efficiency of your new system. The contractor needs to assess the configuration and size of your current ductwork and closely check it for leaks, using special equipment to evaluate the amount of leakage. The ducts need to be sealed with mastic or metal tape. 

Depending on your home’s layout and size, you may need a return duct in every room. This duct will return that room’s air to the furnace and the supply duct blows back the heated air. Homes without adequate return registers can have uncomfortable rooms and if your family members habitually keep their doors closed, the return duct improves comfort in those rooms.

The best way to go about a furnace replacement is to work closely with an HVAC contractor from the start of the process. To learn more, contact Griffith Energy Services. We provide outstanding HVAC services for the Baltimore region from 12 convenient locations. 

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