Central AC

To start a project, check the picture below to get familiar with the system

  • Central A/C has two main components: Coil sitting on top of furnace, Condenser sitting outside

  • It relies on the blower of furnace since blower push air through coil to become cool air

  • Lineset connects coil and condenser


Main features to be considered when buy central air conditioner:

1. Cooling capacity ( for residential )

  • In Ontario, the Rule of Thumb is for every 1000 sqf you need one Ton (12,000 BTU) of cooling capacity.

  • If house insulation is poor or it has big sun exposure , add extra half ton.

  • Basement shouldn't be included in the square footage calculation.


2. Efficiency

  • It's usually rated as SEER ( Seasonal Energy Efficiency Rating). The bigger number, the more efficient.

  • Energy Star rated product starts at 13 seer.


3. Dehumidification

  • Central air conditioner also functions as dehumidifier. Hot and humid air is pushed through coil to become cool and dry air.

  • The blower of furnace is very important to central air conditioner because it relies on blower to push air through the house. Since DC variable speed blower provide longer air circulation cycle, it can enhance dehumidification function of air conditioner.


Factors related to installation:

1. Location of condenser

  • Condenser should be close to furnace room where the coil is installed. Ideally it's not directly under sunlight

  • When in use, condenser needs big volume of air to exchange energy. Top and sides of condenser should be wide open.  The side next to wall should have at least 4" clearance.

  • Condenser makes vibration so it should be placed on the ground. If it has to be mounted on wall, it's better to be mounted on concrete wall.


2. Power supply

  • If it's a replacement, new A/C can simply use the old electrical wire.

  • If it's a new installation, a dedicated power line has to be run from electrical panel to new A/C. Make sure electrical panel has at least 2 empty spot for breaker since A/C needs 220V to run


Further factors to be considered:

1. Insulation

  • Sunlight cast on roof generates tremendous heat. Good attic insulation will prevent that heat from transferring into house

  • Upgrading insulation on wall and windows will decrease A/C hydro consumption


2. Cooling air distribution

  • Air inside duct is pushed from furnace by blower with biggest volume

  • As duct extends and branches take away part of air, the airflow is getting less and less

  • The farthest room from furnace gets the least airflow. This is the born problem with this kind of forced air system

  • DC variable blower will improve the situation by keeping air moving. So more or less cooling air will be delivered into even farthest room