A Manual J load calculation ensures that the cooling capacity of your new central air conditioner closely matches the requirements of your specific home. It’s critical to get this right. Over-sized air conditioners—those with too much cooling capacity for the home—consume excessive energy and tend to short-cycle, resulting in noticeable indoor temperature swings and high indoor humidity. Under-sized units, conversely, don’t provide enough cooling capacity and run almost constantly, boosting electricity costs, increasing system wear and tear, and yet still not keeping the house comfortably cool.
Calculating Performance And Efficiency
A Manual J load calculation is a survey by a qualified HVAC contractor to determine your home’s unique cooling load, expressed in BTUs. This load figure is then compared to the cooling capacity specification of available new air conditioners. In this way, the unit you select can be a perfect match to your home—not too big, not too small.
Guesswork’s Not Good Enough
Every house is different. Informal estimates of cooling load—or a quickie comparison to other houses—aren’t accurate. Installing a central A/C without a Manual J survey before can increase monthly energy costs and provide disappointing cooling performance for as long as that unit’s installed.
Here’s the sort of information the survey gathers:
- Climate district where the house is located.
- Seasonal climate specifics.
- Size of the structure in square feet.
- Direction the house faces.
- Typical daily hours of sun exposure.
- Count of windows plus type of glass.
- Estimated outdoor air filtration into the house.
- Type and quantity of insulation.
- Number of light fixtures and type of bulbs.
- Major appliances installed.
- Number and ages of occupants.
Crunching The Numbers
After the survey, data is is entered into load calculation software developed by the Air Conditioning Contractors of America. The program computes the home’s optimum BTU cooling load figure. With that information, your HVAC contractor can present makes and models of air conditioners with the appropriate cooling capacity to choose from, as well as various available options.
Ask the professionals at Detmer and Sons for more about the advantages of a Manual J load calculation when upgrading your central A/C.