Heating and Cooling
Sizing and Installation of Cooling Systems
Your new cooling system should be a custom fit for your home. Sizing and installation practices can dramatically affect how well your new equipment will deliver comfort. Expect to pay a little more for a good contractor who follows these practices.
Calculate the size of the equipment.
For starters, your air conditioner should be sized to fit your home. You should request a copy of the design load calculation used to determine the right size of equipment. A good contractor will not size your equipment solely on the square footage of your home or assume existing equipment was sized properly in the first place.
Proper equipment sizing is based on your heat gains during warm weather. To complete the design load calculation the contractor will need to take measurements during the initial visit to your home and ask you some questions. The calculation is usually done using software and should be based on professional guidelines such as Manual J from the Air Conditioning Contractors of America (ACCA) or similar method.
Oversized or undersized equipment.
Oversized equipment can cause reduced comfort and excessive "air" noise. Oversizing will shorten the life of the equipment by causing it to cycle on and off more frequently than a properly-sized unit. Undersized equipment, with airflow that is too low, can reduce the efficiency of the air distribution and accelerate wear on system components, leading to earlier failure.
After the design load calculation is completed, ducts, supply registers, and return grilles can be sized and selected using professional guidelines in ACCA's Manual D or similar method.
Check and correct airflow.
For central air conditioners or heat pumps there is an optimal air flow for comfort and savings.
- If airflow is too high, duct leakage increases and the temperature at the register is not sufficient for optimal home comfort.
- If airflow is too low, distribution efficiency drops and accelerates the wear on system components leading to premature failure.
A good contractor will test the airflow of your cooling system and make adjustments for optimal performance. The test consists of measuring the airflow at the indoor coil, a component that is installed in the ductwork at or near the furnace or air handler that heats or cools the room air. Typically, testing and adjustments should be done after duct leakage repairs have been completed.
Proper refrigerant charging.
If you are installing a new central air conditioner or heat pump you should know that recent field studies suggest that approximately 75% of installed cooling equipment may have incorrect amounts of refrigerant. Incorrect refrigerant levels can lower efficiency by 5 to 20% and can ultimately cause premature component failure, resulting in costly repairs that could have been prevented. A good contractor will use one of three methods, recommended by equipment manufacturers, to verify the correct refrigerant level. These methods include super-heat, sub-cooling, or weight. Ask your contractor how they verify the refrigerant level is correct.
In addition, you should know that since 1992, in order to protect the Earth's atmosphere (ozone layer), all technicians must be certified to handle refrigerant. Ask them to show you proof of refrigerant handling certification.
Equipment placement.
Placement of new equipment is unique for every home, but a good contractor should follow manufacturer's installation instructions for best results. For example, indoor equipment should be installed in a conditioned space, or a space that is well insulated. The outdoor compressors should be placed out of the sun and kept free of debris. Equipment should be installed in an accessible area for easy maintenance. Allow plenty of room for free airflow on all sides of the equipment. Thermostats should be placed away from direct sunlight, drafts, doorways, skylights and windows.
- The contractor should be able to verify that equipment placement is in accordance with manufacturer's installation instructions and local codes.
Duct Sealing
Your new or existing cooling equipment is only as good as the system that delivers air to every room. Central air conditioners and heat pumps rely on a system of ducts to circulate air throughout your home. To maintain comfort and good indoor air quality, it is important to have the proper balance between the air being supplied to each room and the air returning to your cooling equipment. Leaky ducts can cause an unbalanced system that wastes energy. Sealing your ducts is one solution that can improve your system's ability to consistently cool every room in your home.
In some instances, your contractor may advise you that it is necessary to replace or add ducts. If there are insufficient supply registers or return air grilles in your home, it may be necessary to install additional ducts to accommodate the need for registers or grilles. When possible, ducts should be located within conditioned space. If the ducts must be in unconditioned space (attic or crawlspace) they should be insulated.
Whether you're having new equipment installed or working to improve the performance of your existing cooling system, you should have your duct system checked.
Most duct improvement repairs require the assistance of a contractor. A good contractor will:
- Identify any duct leaks with diagnostic equipment.
- Seal your ducts with mastic, metal-backed tape, or aerosol sealant. Duct tape should not be used because it can not withstand high temperatures and will not last.
- Test airflow after ducts are sealed.
- Insulate your ducts where it counts to keep the air at its desired temperature as it moves through the system. The contractor should use duct insulation material rated at R-6 to insulate ducts located in unconditioned spaces such as an attic or crawlspace.
- Conduct a combustion safety test after ducts are sealed to be sure all gas or oil-burning appliances are working properly.
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