Did you know furnaces come in several different sizes? This equipment isn’t one size fits all – the right furnace for your Montgomery home can differ from other houses nearby. Determining the right furnace size for your home involves many factors that vary from one home and household to the next. The HVAC technicians at Hans Heating & Air explain how to determine furnace size and why a perfect fit is important.

Furnace Sizing with Manual J

Manual J is a standard of the Air Conditioning Contractors of America (ACCA), used to determine a home’s heating and cooling load and how to determine furnace size, as well as capacity for air conditioners and heat pumps. When sizing a new furnace, Manual J allows your contractor to determine how much heat the system needs to add to your home to keep temperatures comfortable.

Manual J calculations are very comprehensive, looking at several different aspects of the home that impact its heat load. How to determine furnace size takes into account:

  • Winter design temperature, which is the outdoor temperature the area stays above for 99 percent of all hours in a year. This temperature is set by ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) and based on a 30-year average.
  • The number, size, and location of all windows, glass doors, and skylights in the home, as well as any shading or overhang that may impact solar heat gain.
  • The location of ducts, the insulation R-value of the duct wall material, as well as air leakage in the duct system.
  • The home’s orientation and number of walls exposed.
  • The home’s floor plan, whether it is open or closed.
  • Ceiling heights, insulation R-value, roofing material, and the color of the roof.
  • Square footage of the home.
  • Air infiltration throughout the home.
  • Ventilation equipment within the home.
  • Floor and wall insulation.
  • Internal sources of heat gain, including appliances and number of occupants.

The findings of Manual J tell your contractor how many BTUs of heat output are required to heat the home. BTU/h stands for British Thermal Units per hour, the measure used for the amount of heat a furnace creates in one hour. Once the necessary heat output is determined, your contractor can help you select a furnace that offers the needed capacity as well as the energy-efficiency rating you desire, measured as AFUE (annual fuel utilization efficiency) for furnaces.

Why Accurate Sizing Is Important

When you’re looking to buy a new heating system for your Alabama home, be sure your contractor performs a Manual J calculation, which is critical in determining the right size furnace for your home. If a contractor only asks for the square footage of your home and recommends a furnace size based on that alone, it’s not guaranteed to be the correct size.

If your contractor fails to follow the correct process of determining the correct furnace size, the furnace you receive may be too small or too large for your home. Both undersized and oversized equipment will cause you problems.

  • An undersized furnace won’t be able to keep you home comfortable and maintain temperatures correctly. It will run longer in attempts to do so, burning excess energy. This drives up your heating bills and wears out the equipment faster.
  • An oversized furnace will also struggle to properly maintain temperatures in your home. The correct temperature will be achieved quickly, causing the system to short cycle, which increases wear. There are typically noticeable temperature swings between rooms and poor humidity regulation. Larger furnaces cost more to purchase and use more energy than needed to heat your home.

Let Hans Help You Find the Right Size Furnace

When you need a new heating system, don’t risk wasting money on an incorrectly sized unit. Make sure you work with a contractor who knows how to determine furnace size and uses Manual J. Count on Hans Heating & Air to find the perfect fit for your home – contact us today to request an estimate for your new furnace.