December 5th, 2014

Furnace and Heat Pump Replacement Tips

Home Owners Network

Sooner or later you will replace your heating and air conditioning system. Furnace and heat pump air handler (the inside unit) service lives vary between 16 and 25 years. Air conditioning condenser (the outside unit) service lives vary between 12 and 15 years. Here are some tips to ensure that your new system provides many years of safe and energy efficient operation. 

 HON Furnace

Comply with all local building codes and manufacturer’s instructions when installing your new equipment. You should obtain a permit and have the new installation inspected, if required in your area. A licensed contractor should know and comply with local building codes and with manufacturer’s instructions.


Install new equipment that has the highest energy efficiency rating that you can afford.  The energy savings from a high efficiency system will often save you more over the system’s life than the additional cost. Higher efficiency systems add value to your home. They may also qualify for government and utility rebates.


  • Replace both the air conditioner evaporator coil and the condenser, even if one unit still works. An air conditioner condenser and evaporator coil (the inside and outside units) are designed to work best as a system. You may not receive the full energy efficiency of the new condenser if it is connected to an old evaporator coil. An improperly matched condenser and evaporator coil may be highly inefficient and result in higher than necessary energy use. In many cases, you should replace the furnace or air handler while you’re at it.


  • Use mastic to seal all joints and seams. Do not use duct tape. You may use foil tape at joints and seams, but mastic is better. These joints and seams include where: the evaporator coil connects to the air handler, the supply plenum connects to the evaporator coil, the return plenum connects to the air handler, and the air ducts connect to the plenum. Supply and return plenums are rectangular metal boxes where the ducts connect to the air handler. Joints, seams, and ducts that leak air can significantly reduce the energy efficiency of your system and increase operating costs.


  • Connect flexible air ducts to the plenums using both foil tape and plastic straps.  Improperly secured air ducts may leak and may work loose from the plenum.


  • Do not bend a flexible air duct so that it reduces the diameter of the duct. An air duct is like a garden hose. If you kink a garden hose, the water flow is reduced. If you kink a flexible air duct, the air flow is reduced. Reduced air flow can cause the system to work longer to heat and cool your home. Reduced air flow can also cause comfort problems in rooms. Improperly installed flexible ducts are a common problem.


  • Install an overflow pan or condensate cutoff switch under air handlers with evaporator coils located in attics and anywhere else inside the home where leaking water could cause damage. Extend a ¾ inch diameter pipe from this pan to a visible location outdoors. If you see water coming from this overflow pipe, there is a problem. Call a qualified contractor to locate the problem.


  • Install a ¾ inch diameter drain pipe from the evaporator coil to the outside or to a plumbing drain. Slope the pipe down toward the discharge point over its entire run. Insulate this pipe if you live in a warm and humid climate. Water that flows in this pipe is cold and can cause condensation on the pipe’s exterior. This condensation can damage materials and provide moisture for mold.


  • Replace the circuit breakers for the condenser and air handler if the recommended circuit breaker rating for the new equipment is different from that of the old equipment. It is common that new equipment is more energy efficient than the old equipment and needs less power to operate. More energy efficient equipment usually needs a circuit breaker with a smaller rating.


  • Confirm that the air ducts are the proper size to work with the new system if you are adding air conditioning to a home without air conditioning or if you are changing from one type of system to another. For example, air ducts sized for an old oil-fired furnace may not be properly sized for a high efficiency gas-fired furnace. Improper air duct sizes may affect system energy efficiency and may cause comfort problems.


The Bottom Line


A new furnace or heat pump can provide many years of safe and energy efficient service when properly installed. By using these tips you can ensure proper installation of your new system.


We’re here to help at Home Owners Network. Use our ‘Ask The Experts’ service if you need help.  Please include as many details as possible about your situation so we can provide you with our best advice.


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