Find answers to your questions about your furnace, air conditioner & more.

Heater and Air Conditioner FAQ

We hope the answers to the following frequently asked heater and air conditioner questions will take some of the mystery out of selecting, using and maintaining your equipment. The purpose of our HVAC FAQ page is to offer the HVAC knowledge that can help you make the most informed decisions about your home comfort system.

What is an HVAC system?
HVAC stands for heating, ventilation, and air conditioning. An HVAC system is an indoor comfort system that provides heating, cooling, and air quality control functions. While HVAC systems can consist of a variety of different components — such as a furnace, heat pump, air conditioner, humidifier, dehumidifier or other air processing unit — these systems fall into two main categories: local, or zonal, systems and central systems.

Local systems are designed to treat a single room or zone. They are often self-contained units and may include such equipment as window air conditioners, window fans, evaporative coolers, portable heaters, woodstoves, and fireplaces. Another type of zonal system is called a split system, which is designed for locating one unit outside the home and a second unit inside the room or zone to be treated. The two units are connected by a refrigeration line. A ductless AC or heat pump system is an example of a split system that provides local heating and/or cooling, with the former providing cooling only and the latter providing both heating and cooling.

Central HVAC systems can either consist of a furnace for heating and a central air conditioner for cooling or a heat pump for both heating and cooling. Other combinations can be used as well, including supplementing a heat pump system with a furnace to provide greater warmth and energy efficiency in colder climates. A central HVAC system differs from a zonal system in that it generally uses an air distribution system consisting of a network of air ducts to deliver heating and/or cooling throughout the home.

How does an HVAC system work?
A central HVAC system either uses a heat pump exclusively or combines a furnace with an air conditioner or heat pump to provide heating and cooling, as appropriate, depending on the season and the climate in which they are used. A humidifier is also often added to monitor the relative humidity of the air and add moisture when the air begins drying out, which can easily occur during the heating season. Cooling systems generally provide dehumidification, removing the excess moisture from the air during the cooling season. HVAC systems deliver the warmed and humidified or cooled and dehumidified air into every room of the home through supply vents that open into each room via the air duct system. Return-air registers then draw the air back through the return ductwork to the central unit to be reheated or re-cooled, adjusted for humidity and redistributed throughout the building.
How is an HVAC system controlled?
The system is controlled through a wall-mounted thermostat that can be set to control the temperature at which the system switches on and off. The user sets the temperature desired for the space. Once the temperature strays too far from the mark, the system switches either on or off, as required to maintain the target temperature. When the preset temperature has been reached, the system turns itself off until the temperature again drops below the target temperature during heating or rises above the target temperature during cooling. The system then turns itself back on automatically.
What is a Zoning System for HVAC?
A Zoning System allows you to install multiple thermostats throughout your home to ensure that all areas, or zones, enjoy equal comfort. With this system, each thermostat controls a different zone, with a main control panel coordinating the overall process. The system works by facilitating communication between individual thermostats and opening and closing the dampers inside your HVAC system’s air ducts to heat or cool each zone as needed to reach the desired temperature setting. A Zoning System gives you unprecedented control over even the hardest to treat areas of your home, regardless of their differing heating, cooling and air-quality control requirements.
How does an air conditioner work?
Your air conditioner, whether it is a central or a portable AC unit, uses a liquid refrigerant that is pumped through a refrigerant line between an evaporator coil and a condenser coil. Partly because the refrigerant flowing toward the indoor coil is colder than the air inside your home and partly because the liquid refrigerant evaporates and turns to a gas by the time it reaches the indoor coil, the refrigerant absorbs heat from the inside environment and carries that heat to the system’s outdoor coil, after compressing it and causing it to turn back to a liquid. When the refrigerant returns to the liquid state, it releases its heat to the outside air and flows back toward the evaporator coil to repeat the process again. This process repeats itself over and over, allowing your air conditioner to provide ongoing cooling to your home during the hottest weather.
What size air conditioner do I need?
The size of the air conditioner that will work best for your home is based on a number of factors, including the size of the area you need to cool, the layout and structural features of your home, and the climate in which you live. Selecting an air conditioner that’s large enough to cool your home but isn’t larger than you need is important since an oversized air conditioner won’t run long enough to remove sufficient humidity from the air. This can contribute to significant discomfort — particularly if you live in a humid climate. The best way to ensure that you choose the right size AC system for your needs is to consult a professional HVAC contractor, who can evaluate your home, do the calculations needed to determine the system capacity that will work best for your application, and advise you on the most appropriate size air conditioner to buy.
What is a heat pump?
A heat pump is a “reversible” HVAC system that works like an air conditioner when run in cooling mode and reverses the process to provide warmth when run in heating mode. Like an air conditioner — or a refrigerator, which works on the same principle — a heat pump uses a liquid refrigerant, which is pumped between an evaporator coil and a condenser coil, through refrigerant lines, to absorb heat from the air in one location and transfer it to the air in another location.

In summer, the indoor coil serves as the evaporator coil, absorbing heat from the indoor air, moving that heat to the outdoor unit and releasing it outside through the condenser coil. In winter, this process is reversed: The outdoor unit serves as the evaporator coil, absorbing heat from the outdoor air, compressing that heat and moving it indoors to the condenser coil where it is released to heat your home. The refrigerant that flows through the system at all times is the medium that absorbs and transfers the heat to the required location as it turns from a liquid into a gas and vice versa. This ingenious invention uses the laws of Thermodynamics to provide a single heat transfer process that can be used for both heating and cooling.

What is a variable-speed furnace?
A variable-speed furnace features low and high blower speeds to provide more consistent temperatures and greater comfort. The system automatically adjusts airflow based on its intelligent monitoring of conditions. While variable-speed technology is energy-efficient, its main benefit is improved comfort.
What are furnace ratings?
The unit of measurement used to rate furnace efficiency is known as AFUE, which stands for Annual Fuel Utilization Efficiency. AFUE is used to rate both furnaces and boilers. It measures the percentage of fuel the unit burns that is actually converted to usable heat — meaning heat that is available to warm your home, rather than escaping through the chimney flue. AFUE does not, however, measure your furnace’s electricity usage. As of May 1, 2013, the minimum AFUE ratings required for new gas furnaces are 75% to 83%, depending on the type of furnace, though many modern high-efficiency furnaces boast up to 98% AFUE ratings.
What do all those air conditioner and heat pump ratings mean?
Seasonal Energy Efficiency Ratios, or SEER ratings, are used to rate the cooling efficiency of air conditioners and heat pumps. New cooling products are required to meet a minimum SEER rating of 13.0, though ratings above 20 are possible for higher-efficiency systems, with some mini-split ductless AC units achieving 27.2 SEER. Minimum SEER rating for ENERGY STAR-qualified systems is 14. SEER measures cooling output, in BTUs, over the course of a season, dividing that by the electrical energy, in watt-hours, used that season, and thus providing a ratio of cooling power to energy consumption. On January 1, 2015, new regional SEER minimums will take effect.
Where are the different types of HVAC systems available?
Most industry leading HVAC manufacturers offer a complete line of systems through their factory-authorized dealers, who are located throughout the U.S. We are proud to be a factory-authorized dealer offering all the latest system types and models to allow you to choose the one that best meets your needs.
What is involved in humidifier installation and maintenance?
A humidifier can easily be installed by your HVAC professional by attaching it to your new or existing furnace or air handler. For your central humidifier, make sure the damper is open during heating season and closed during cooling season. Replace the core or clean the foam pad at the beginning of each heating season. See this link for other humidifier use and maintenance tips.
Why is it important to have regular maintenance on my home comfort system?
Your HVAC system works hard to heat and cool your home, and the system requires regular upkeep to maintain energy efficiency, provide optimal comfort, continue functioning properly year after year, and achieve its maximum potential lifespan. Just like any other piece of mechanical equipment, your HVAC system has moving parts that can wear out or malfunction if not properly maintained. In addition to changing or cleaning your system’s air filter monthly, a semi-annual tune-up by a qualified HVAC professional will help you get the most from your system.
What is a Precision Tune-up, and how much does it cost?
A Precision Tune-up is a thorough inspection, cleaning and lubrication of your HVAC equipment. The cost of this service varies by contractor and location but generally ranges from $59 to $159. Before scheduling a precision HVAC tune-up, be sure all three of the above services are included and that all critical system components will be serviced. Your contractor should be able to provide a list of the specific issues that will be addressed by the precision system tune-up.
What causes my ductwork to pop when the furnace starts or stops?
A loud pop or bang when your furnace kicks on or off is caused by changes in air pressure inside the ductwork that occur when the furnace fan starts or stops. These sounds can indicate ductwork that was installed close enough to your home’s wood framing that the duct makes contact with the wood as the metal expands each time a blast of hot air enters the duct. The pop is then repeated as the metal cools down. These sounds can also indicate inadequate or undersized ducts, closed or blocked vents, or a clogged air filter. If you’ve checked to make sure the system’s vents are open and the air filter is clear, you may need to call an HVAC technician to inspect the ductwork and determine whether the ducts are large enough to handle the volume of air the system is sending through them. This inspection can also determine whether another duct-related issue might be causing the problem, in which case the technician should be able to correct it. For example, in cases where the duct makes contact with wood, the technician can add insulation or install a rubber pad between the duct and the wooden surface.
Why is my HVAC system freezing up?
If your HVAC system is freezing up, the first things to check are the air filter, supply vents, and return-air registers. An excessively dirty or clogged filter or registers/vents that are closed or blocked can inhibit air flow, preventing the system from working properly. If these checks show no problem, you’ll need an HVAC specialist to inspect the system to determine whether a malfunctioning blower motor, low refrigerant level, or dirty evaporator coil may be responsible.
How do I know if I have an existing warranty on my furnace, air conditioner or HVAC system?
If you purchased your equipment within the past five years, you likely have an active warranty. You’ll find the date of manufacture on the equipment label. If you have trouble locating or deciphering the date, try calling the manufacturer for help. The company should also have a record of your warranty registration on file if you completed one after purchase. If you didn’t register your warranty, your HVAC dealer should be able to help you determine the age of your equipment and let you know whether or not your warranty is still active.
When replacing the outdoor unit, should the indoor unit also be replaced?
There are a number of good reasons for replacing both units at the same time:

  • You’ll have a complete system with fully compatible components that were designed to work together.
  • The entire system will be new, meaning that all parts should perform optimally.
  • Being more modern, a completely new system will be more energy-efficient than a partly new and partly old system.
  • The other unit may be ready to fail at any time.
  • You’ll receive a warranty on the entire system.
What should I know about changes in refrigerants?
New, safer refrigerants have been developed to replace older, less-environmentally friendly refrigerants that are known to damage the earth’s ozone layer. As a result of the Montreal Protocol, and the 1990 Clean Air Act that followed, the EPA (Environmental Protection Agency) began phasing out these older refrigerants and regulating their use until the phase-out is complete. R-22 is one such refrigerant that is used in many older residential and commercial air conditioners and other refrigeration applications. These CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons) have been recognized as harmful to the environment and are being replaced by R-410A.

No newly manufactured AC equipment uses R-22, and a limited amount of the refrigerant is available for use in currently-owned equipment. As supplies dwindle, R-22 prices are expected to rise. Replacing your older AC equipment with newer, R-410A models can help you avoid the rising costs and increasingly stringent regulations of R-22 refrigerants. Visit the EPA website for more information about the R-22 phaseout.

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