Here’s What a Load Calculation is

You need a heating and cooling load calculation to make sure a new furnace or air conditioner is the right size for your specific house. “Size” refers to the BTU capacity of the unit. In the case of a furnace, capacity means the amount of BTUs of heat energy it adds to the house per hour. For an air conditioner, it means the BTUs of heat energy the unit extracts from the house.

An oversized furnace or A/C consumes too much energy and functions erratically. A unit that’s undersized, on the other hand, doesn’t produce enough heat or cooling for adequate household comfort. How much BTU capacity is too much and how much is too little for your house? Only a professional load calculation can determine that for sure.

Every house is different. Calculating the load can’t be left to old fashioned guesswork nor rough estimates based on similar homes in the neighborhood. Today’s high energy costs require a standardized procedure performed by a qualified HVAC technician utilizing Manual J software, the accepted industry load calculation program. Here’s how the process works:

In a room-by-room survey, the technician gathers a variety of data including:

• Year of construction and total square footage.
• Orientation of the house to sun exposure.
• Type and depth of installed insulation.
• Estimated amount of air infiltration.
• Condition of weatherstripping and caulking.
• Duct leakage.
• Number and total square footage of windows.
• Light fixtures and large appliances installed in the house.
• Usual number of occupants.

Also included in the factors entered into Manual J are details of the local climate such as typical average high and low temperatures as well as relative humidity. After all data is entered, Manual J calculates the precise BTU per hour capacity of the furnace or air conditioner required for optimum comfort and energy efficiency. An accurate load calculation allows your HVAC contractor to select the furnace or air conditioner with capacity specifications that match the specific BTU requirements of your home.

If you’re thinking about a new furnace or A/C, ask the professionals at Rinaldi’s Energy Solutions about a professional load calculation.
Our goal is to help educate our customers in Orlando, Florida and surrounding areas about energy and home comfort issues (specific to HVAC systems).

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