Being a homeowner is not just a financial responsibility. Sometimes, you will need to make decisions about things that you’re not very familiar with. While some decisions such as replacing fixtures can be made purely based on your aesthetic tastes, others such as your HVAC system need to be considered in terms of efficiency, performance, and cost. This decision can be made even more complicated because of the unfamiliar heating and cooling terms often used to describe and rate systems. Fortunately, you can make more educated choices when you have a basic understanding of many of the common terms. 
SEER:
SEER is a very common term in the HVAC industry. It is an abbreviation for the Seasonal Energy Efficiency Ratio. SEER is used to rate the seasonal efficiency of heat pumps and air conditioners. The greater the SEER rating, the more efficiently the appliance or unit will run. In the United States marketplace, all heat pumps and air conditioners sold are required to meet a minimum SEER rating of 13 but it is possible to purchase systems rated at 20 or more.
MERV:
The Minimum Efficiency Reporting Value (MERV) is used in rating the efficiency of air filters. The greater the MERV rating, the greater the number of particles the filter has the capacity to successfully capture. The MERV scale was established to measure captured particles that are less than .03 micrometers and larger than 10 micrometers. Opting for a higher rating on your chosen unit can provide lower energy costs but you can expect a higher initial cost. Choosing the right rating for your home will depend on your budget, the energy savings you are looking to achieve and the time you are planning to run the unit when you are purchasing your new system.
AFUE:
The Annual Fuel Utilization Efficiency (AFUE) is the method used to determine the efficiency of heaters and furnaces. It is calculated by measuring how efficiently the heat source is used by the particular appliance or unit. The greater the number of AFUE, the greater the efficiency. For example, a furnace that is rated at 90 AFUE uses 90% of the fuel burned for heating the home, while the remaining 10% is lost. New furnaces installed in the United States today must be rated at least 80 AFUE.
BTU:
The British Thermal Unit or BTU was once a common method of measurement in England. In recent years, this has been replaced by the joule, but the BTU is still commonplace here for heating and cooling equipment. One BTU is calculated by measuring the amount of energy needed to increase the temperature of one pound of water by only one degree Fahrenheit. For heat pumps and furnaces, a larger number represents a larger capacity of heat production. In air conditioners, a larger number represents a larger capacity of removing heat from the air.
While it may appear complicated, failure to understand heating and cooling terms would end up wasting energy, costing you more on your utility bills in the long term. If you are unsure about which appliance or system would be best suited to the specific needs of your property, it is a good idea to speak to a professional and experienced HVAC company.