Here is a simple way to think about how an over-sized system can result in higher monthly utility bills. Think about the air conditioning system’s operating efficiency the same way that you think about a car’s miles per gallon (MPG).
Your car may get 35 MPG on the highway but when you are driving in the city, it may only get 28 MPG. The reason for this is because when you are driving in the city, your car is constantly stopping, then accelerating and then stopping again. It takes a lot more gas for your car to accelerate than it does for it to maintain a set speed.
Your HVAC system is very similar but instead of measuring its peak operating efficiency in highway miles per gallon, it is measured using a SEER rating for cooling and an AFUE rating for heating. It’s important to note that there is no city miles per gallon rating for HVAC systems. This is important because an over-sized HVAC system may never operate at its advertised peak efficiency because it may never finish accelerating before the temperature in the space has been reached and the system cycles back off.
The first 12 to 15 minutes after your air conditioning system cycles on, it has to work very hard to build up the correct pressures that are required for the cooling process to take place. During this time, your system is operating at an extremely low overall efficiency (city miles per gallon). Let’s say that your air conditioning system has a SEER rating of 15. If your HVAC system only runs 15 minutes before it cycles back off, that 15 SEER system may have an average operating efficiency of around 10 SEER.

ConsultAir’s HVAC designs are based on the weather and other climate information for your local area. This weather information is reported by hundreds, possibly thousands, of weather data stations which are located across the United States. Each of these weather data stations maintain a 30 year rolling average for temperature (air and ground) and humidity. These data stations also provide other information such as average wind and even the local elevation above sea level.

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A perfectly sized heating and air conditioning system is only as good as the duct system that it is connected to. This is why the Air Conditioning Contractors Association created Manual D.

A duct system that is designed to Manual D standards is going to quietly distribute the correct amount of air to each room. Our Manual D duct design service includes a to-scale drawing of the duct routes and sizes to be installed.

Don’t be fooled by sites offering “Free Manual J Load Calculation Software” or “Free Heat Load Calculation Spreadsheets”. While some of these calculators are likely better than just guessing or using an old-school rule of thumb such as 600 square feet per ton, ACCA’s Manual J 8th Edition is the standard that is almost universally required by local building departments as well as energy efficiency rebates and incentives. ConsultAir only uses ACCA certified Wrightsoft HVAC design software.

International Residential Code – Section M1401.3 Sizing: Heating and cooling equipment and appliances shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methodologies.

Placing your order to have your heating and air conditioning system designed is easier than you may think. ConsultAir’s easy to follow step-by-step questionnaire allows you to quickly gather all of the required information. Once complete, simply forward it to us and we’ll do the rest.