How to Calculate What Size Central Air Conditioner You Need

Your old central air conditioning unit has called it quits. Maybe it’s just showing signs of age and is no longer as efficient as it used to be. Or perhaps you’re considering a central AC installation as a first time-ever investment.
Whatever the reason for installing a central air conditioner, it’s crucial that the system is properly sized for your home by an HVAC professional. Many homeowners don’t know that central air conditioning units come in different sizes meant to deliver properly functioning cooling with the appropriate load (how much cooling the home needs) and capacity (how much cooling the AC unit can deliver). As we noted in a previous article, HVAC units that are not the correct size for the space make it difficult to maintain indoor air comfort, lead to higher energy costs, and shorten the equipment’s lifespan.

Calculating the proper size
The only way to size a house (for any HVAC system) is to measure the conditioned space room by room and perform a series of mathematical calculations:

• A Manual J is an industry-standard residential load calculation to determine the home’s HVAC capacity, which in turn informs the size of the central air conditioning unit we recommend. The formula considers the home’s total square footage to be cooled and heated, its location (for example, in a humid climate), insulation R values, and how the space is used.
• A Manual S is done to determine correct equipment sizing. This nationally recognized standard prevents issues that arise when equipment is either oversized or undersized. You want to make sure your HVAC contractor performs Manual S to ensure indoor air comfort and energy efficiency, protect the equipment from undue wear and tear, and avoid excessive humidity in the home. Manual S is also a requirement under the International Residential Code.
• If new ductwork is to be installed, a Manual D is required to make sure the proper duct sizing is fabricated. This calculation is the industry standard for sizing HVAC return and supply duct systems and registers by distributing the optimal amount of cooling and heating to every room. Because Manual D helps contractors develop the right duct blueprint, the residential Manual D duct design system is not only essential to a correct installation, but many municipal building departments require this before issuing a permit.

If an HVAC contractor does not perform these, even on replacement units, this is cause for concern.

NOTE: Many homeowners make energy-efficient improvements to the house such as installing new windows and doors or adding insulation in the attic or walls. Others may add rooms or remove trees on the property that used to shade the house, leading to the need for more air conditioning. These other factors all contribute to calculations of the correct central AC equipment sizing.

What happens if HVAC ductwork is the wrong size?
When the ductwork is too large for the home, rooms may become uncomfortably cold. Ductwork that is too small forces the central AC to overwork, making it inefficient and increasing utility bills. In short, a properly designed HVAC duct system:

• improves system efficiency (the AC unit runs less frequently and for shorter times).
• maintains adequate airflow and even temperature distribution.
• keeps energy costs in check.
• protects the compressor and coil from breakdowns that happen due to improper duct design and size.

Although many homes are suited for prefabricated HVAC ductwork, at Bloomfield Cooling, Heating & Electric we have our own sheet metal workshop where our team fabricates custom ductwork as needed…so you are always assured of having the right ductwork installed in your home.

Contact Bloomfield Cooling, Heating & Electric for your central air conditioning needs
From brand-new installations to system upgrades, Bloomfield Cooling, Heating & Electric is here to provide the best central air conditioning equipment, backed by industry-leading warranties and excellent customer service. Call our office at 973.237.0505 to schedule a consultation. If you need routine spring maintenance on your existing equipment, be sure to book an appointment before June 30 to get our maintenance discount.