Recommended Electric Furnace for 1400 Sq FT

Incorrect Furnace Sizing

• Incorrect sizing for furnaces results in inefficient operation and unnecessary costs. Many factors are analyzed to determine the correct size furnace for the size space. Some improper methods include simply using the existing furnace BTU capacity and getting the same size new furnace, called reading the nameplate, or using a “rule of thumb” that assigns a certain BTU load per square feet for the total capacity. The U.S. Department of Energy reports that these simplistic methods are not accurate for selecting a size of furnace.

Proper Sizing

• A competent HVAC contractor estimates furnace size using room volumes after measuring walls, ceilings, windows and floor space, and taking into account the number of occupants. A building’s air leakage also should be inspected and figured into the calculations, and can be tested. A competent HVAC contractor uses Manual J, an industry standard for heating and cooling systems design, and provides the results of a heating and cooling load calculation. The Air Conditioning Contractors of America recommends not accepting rule of thumb or nameplate estimates for furnace sizing.

Manual J, Manual D and Manual S

• Factors affecting furnace sizing include local climate, size and shape of the building, insulation, window sizes, location and type, air infiltration rates, number of building occupants, and lights and appliances. Correct sizing calculations are acquired by using "Manual J Residential Load Calculation," published by ACCA, the Air Conditioning Contractors of America. A competent contractor uses Manual J to properly size heating and air systems. The ACCA also publishes "Manual D Residential Duct Design," for sizing heating and air ducts, and "Manual S Residential Equipment Selection" for choosing heating and air systems.

DIY Furnace Sizing

• You can inspect and measure your home and complete a Manual J worksheet by following the instructions, entering the measurements and doing the math. Many Manual J software programs may make calculations easier. Many municipalities and home improvement centers offer the use of planning tools at little or no cost.