FAQs

System size, or cooling capacity, is measured in British Thermal Units (BTUs). Determining the right sized HVAC system requires performing a calculation. There are different calculations but basically you want to know the size of the room in square feet, and multiply it by 25 BTU. For example, a 12- by 15-foot room requires an air conditioner of at least 4,500 BTU, but an experienced technician can perform a load calculation to get a more precise value. If you’re A/C is oversized or undersized, it may run constantly, cycle too frequently, or create uneven heating or cooling.

It is not better to install a system that has more capacity than you need. People oversize their HVAC systems all too often, which can cause humidity problems. A larger system cools the house too quickly, before it can effectively remove humidity. This can lead to indoor air quality issues. If your furnace is oversized, then your home may be filled with hot air that, even during the winter, can make it too hot in some spots and too cool in others.

Air conditioners operate via heat transfer and the compressor enables this function. This component compresses the refrigerant, raising its temperature and pressurizing it to form a liquid. It runs on the principle that heat flows from higher temperature areas to lower temperature ones and that gases flow from high to low pressure zones. As a result, excess heat is released into the cooler atmosphere. A blower fan is often used to help remove excess heat from the condenser coil. The compressor also manages the entire cycle, as hot pressurized refrigerant is pumped to the condenser and refrigerant in vapor form is pulled in from the evaporator.

Two-stage cooling allows an air conditioner or heat pump to operate at different capacities depending on environmental conditions. A single-stage unit will run, at 100% capacity, until the preset temperature is reached, and turns off; but with two-stage cooling, a system can then run at partial capacity to maintain a set temperature. It may also run at lower capacity if it is cooler outside and less energy is required, so the compressor and circulating fan may operate at a reduced speed. Benefits include energy efficiency, more consistent comfort, and dehumidification.

Variable speed air conditioners can run from 30% to 100% capacity, which is controlled by a variable speed compressor or, in the case of an air handler or gas furnace, a blower motor. The technology allows the system to run at different levels depending on how much cooling you need. It reduces energy usage during the start/stop cycle and helps maintain the desired temperature, so it doesn’t need to compensate for temperature swings. Variable speed cooling also helps improve the temperature/humidity balance and allows more time to filter circulating air.

The Air Conditioning, Heating, & Refrigeration Institute, or AHRI, is a trade association that represents manufacturers of HVAC equipment. It oversees leading performance certification programs for indoor comfort and commercial refrigeration equipment. These include ARI Performance Certified for A/C and refrigeration equipment and components, GAMA Efficiency Rating Certified for space and water heating systems, and I-B-R for hydronic heating products. If a product is certified, it typically meets Energy Star standards. The AHRI also provides a source for education, research, workforce information, and industry shipment data.

There are many types of ventilation. Mechanical ventilation may be driven by exhaust-only systems, which use small fans to create negative pressure that removes stale air and moisture, or supply-only systems. These draw in fresh air, but stale air must escape through cracks and other points of air leakage. A balanced ventilation system controls inlet and exhaust airflow. You can ventilate your home naturally as well. While exhaust fans in a kitchen or bathroom may be necessary, opening a window can let fresh air in to cool your home, or let warm air out. Ventilation influences air quality, so remember to clean/change your air filter and install a dehumidifier if your HVAC system doesn’t completely remove moisture from your home.

You can save energy and reduce utility costs by purchasing energy efficient heating and cooling appliances and installing programmable or smart thermostats. These let you set your HVAC system according to when demand is higher, so less energy is used when, for example, you are at work or on vacation. Insulating your home, sealing air leaks, and installing energy efficient windows can also help you control energy costs. But not all strategies involve an investment. You can lower energy costs by replacing older lightbulbs with LEDs, or adjusting your habits by turning off electrical fixtures and appliances when not using them, hang-drying clothes, or washing dishes by hand.