Before you sign a contract with an HVAC company to install a new conditioner, insist that they size it correctly first. Your comfort, energy bills and the appliance’s durability depend on proper sizing. Determining the optimal capacity requires a good deal of information about your home’s overall energy efficiency and how you use your home.
Why It Matters
Don’t count yourself alone if you think that a bigger air conditioner is better. In reality, installing a system that’s too large undermines your comfort, energy bills and the appliance’s durability.
A system that’s too large will run in short cycles for brief periods. Because cooling systems use the most power when they first start, your energy bills will climb and the system will turn off before it has a chance to reach its peak operating efficiency. A strong surge of power goes through the equipment’s components that wears them faster, and it’s likely that you’ll experience more frequent repairs or part replacements.
In terms of comfort, a system that’s too large won’t provide the whole-house comfort the new air conditioner promises. Rooms further from the air handler won’t receive enough cooled air before the system shuts off. Humidity levels will be higher throughout your home because the shorter running cycle doesn’t have enough time to condense unwanted humidity, leaving you less comfortable.
Not only does humidity make you feel warmer, it also contributes to the growth of mold, bacteria and dust mites. Dust mites are the most common cause of airborne allergies inside homes. Although not all molds are harmful, a mold colony can destroy anything made from organic materials in your home.
A system that’s too small won’t be able to cool your home as quickly, and on exceptionally hot days, it may run continuously, which taxes the system. If the sizing of the system is in doubt, particularly in hot, humid climates, it’s better to go too small than too large.
How to Size the Air Conditioner
HVAC professionals use a software tool called Manual J to calculate the cooling load calculation for homes to arrive at the optimal size for the new system. Manual J takes into account:
• The home’s cubic footage;
• Insulation levels throughout;
• Window efficiency, their sizes and locations;
• Air infiltration rates;
• Floorplan design;
• Number of heat-producing appliances used in the home;
• Family size and ages;
• Thermal preferences; and
• Landscaping factors.
The software requires inputs for each of these factors on a room-by-room basis. Once the data are entered, Manual J recommends the best size for the system. A reputable contractor will follow the Manual J analysis by using Manual D to determine the ductwork capacity, and Manual S to fine-tune the equipment based on climatic considerations.
Benefits of the Load Calculation
Besides knowing the optimal size of the system, you’ll discover how energy efficient your home is. A home with inadequate insulation, lots of air leaks, or inefficient windows will require a larger system with greater capacity.
Some home improvements, like increasing insulation and sealing air leaks, are affordable projects that reduce the cooling load. You may find that you won’t need as large an air conditioner by making energy efficiency improvements first. You’ll save money initially on the new system and later by lowering ongoing energy bills.
Charlie Teschner started MESA Plumbing, Heating, and Cooling in 1982. Charlie has a journeyman and master plumber’s license. He was raised with a strong work ethic and he now applies those values to tasks such as Longmont, CO heating repair.