Can I temperature zone an existing HVAC system?
Yes. There are several ways you can zone an HVAC system through its original ducting. The term HVAC temperature zoning is used when each room, section, or floor is individually controlled by a separate thermostat for the same HVAC system. There are many reasons to zone an HVAC system. You have more control of the temperatures in each zoned area or room. Zoned systems can save up to 30% on energy usage. A zoned system tends to deliver more air volume because the airflow is directly concentrated on the room or area it is conditioning and not the entire building.
You may think that because of the many advantages to having a zoned HVAC system; there would be more of them. Traditional air duct systems are designed to the size of the total load (heat loss/gain) it is conditioning. The expression "load", in HVAC terminology, is the amount of heating or cooling it would take to condition a space. The amount of heating and cooling is first determined by the region and climate.
Also included in a load calculation, are the factors of windows and doors, insulation ratings and the type of building materials used to make the floor, walls and ceiling of the space being conditioned. The total air volume delivered by the furnace or air handler (indoor blower unit) is distributed to each room by the size of its load.
For example, a 16' x 12' living room with a large bay window may have 2 to 3 air vents each delivering 90-110 CFM (cubic feet per minute) of air. A 10' x 10' bedroom with a small window may have only one vent with the same CFM volume. A thermostat installed in the hallway and set for 72° would determine the temperature (or close to it) for each room on the HVAC system.
To add zoning, there is an added material and labor cost for extra ducting, a control panel, zone dampers, wiring, and temperature controls. In the world of new construction, budgets and costs are a major factor in determining the design of an HVAC system.
The good news is that a properly sized duct system does not need to be changed to be zoned. This is because if all the dampers were open, the system would still need to distribute its total air volume as designed. New ductwork may need to be added as a by-pass duct to relieve air pressure in the ducting if only a few dampers were open at a time. The excess air is directed back into the system (no loss).
Other advantages to zoning a single HVAC system is that a single HVAC system (properly sized) can be divided. For example, one air conditioning system can be zoned for four apartments, each with its own thermostat. A new addition could be zoned, or even a room that you spend more time in like an office or family room.
You could install programmable or wifi thermostats, and have certain rooms, at certain temperatures, at certain times, on certain days. WOW! There are so many possibilities of having a zoned system. As I stated before, a zoned system can save on energy bills. There could be a payback. Check with an HVAC zoning manufacturer or dealer from our index for more details.
