A common complaint about heating and cooling systems is wide temperature differences between rooms and between stories in homes. Heating and air conditioning (HVAC) contractors often refer to correcting temperature differences between areas as balancing the system. An HVAC system that is properly sized and properly installed should require only minor adjustment to achieve a reasonable temperature balance. In practice, HVAC system sizing and installation errors are common and can make balancing difficult.
There are several heating and cooling performance standards for HVAC systems. The International Residential Code (IRC) heating performance standard requires that the system maintain a temperature in the home of at least 68Ës F. The IRC has no performance standard for cooling. The National Association of Home Builders (NAHB) heating performance standard is 70Ës F. and the cooling standard is 78Ës F. or 15Ës F. below an outside air temperature of 95Ës F. The performance standard temperature is often measured near the center of the room and about five feet above the floor.
States or cities may have different performance standards. The Arizona cooling performance standard is 78Ës F. or 30 degrees below the outside air temperature. These national and local standards usually apply to every room in the home. In cooling mode, for example, if the thermostat temperature is 78Ës F., the temperature in every room controlled by that thermostat should be at least 78Ës F. A one or two degree variance from the thermostat temperature is usually allowed.
Balancing is affected by numerous factors that can change based on the time of day and the season of the year. Some factors that affect balancing include: room location (south and west facing rooms can be more difficult to cool), size, quality and location of windows and doors, room size and ceiling height, size and location of supply and return registers, thermostat location, and location of the air handler relative to the room (the air handler must push air further through ducts in unconditioned space).
Because a balancing problem can have multiple causes, solving the problem can require multiple solutions. Here are some simple potential solutions for balancing problems.
- Confirm that all supply and return registers are open and unobstructed.
- Confirm that filters have been cleaned or changed per manufacturer’s instructions.
- Confirm that ducts are sized and installed according to recommended standards.
- Confirm that insulation is installed properly and in the required amount.
- Install sun screens on south and west facing windows in high heat areas.
- Plant deciduous trees on the south and west sides (sun in winter, shade in summer).
- Improve air flow in rooms with doors by providing a return air path if none exists.
If these simple solutions do not produce satisfactory results, other solutions may be required. These solutions may include changing the supply and/or return duct configuration and adding zones that are separately controlled by their own thermostats.