I have to buy a new AC, Should I purchase a new furnace at the same time?

Like most other appliances and equipment inside a home, home heating, ventilation and air conditioning systems must be periodically replaced. This is just a natural fact. Of course, the air conditioner and furnace, although generally run through the same vents, are two separate entities and must be purchased, or replaced separately. Due to this, when someone is considering a new air conditioner, they may wonder if they should purchase a new furnace along with it. Well, it isn't typically as simply as just saying yes or no, as a residential HVAC may not need an upgrade for both systems at the same time.

The main factor anyone considering a new furnace along with the air conditioner must take int account is the overall age of the two appliances. If the house is on the newer side, chances are both the air conditioner and the furnace were both installed at the same time. This means, theoretically, both systems are going to wear down in roughly the same amount of time, possibly give or take a year or two. However, if the house has had multiple owners in previous years, the air conditioner may actually be several years older than the furnace. When replacing both systems, it makes sense to do so if both are roughly the same age. However, if the furnace is five years or more newer than the air conditioner, it still has plenty of life in it, making it rather pointless to install a new air furnace at the given time. New furnaces and air conditioners are now Energy Star efficient, so less electricity and gas are used to run the equipment, but the cost of a new furnace far surpass possible savings when there is still life left in the equipment. So, if the furnace is considerably newer than the AC, only installing a new AC into the residential HVAC is the most logical and cost effective option.

If the furnace isn't running ragged, despite being the same age as the AC unit, a valuable option is to bring in a home HVAC inspector to see if the furnace is serviceable for an extended period of time. These professionals are able to make recommendations as to if a new furnace is necessary, or if the current equipment is able to function further into the future. 

A rather large upside to installing both a new AC and furnace into a residential HVAC system is a cost reduction. Most service provides reduce the total equipment and installation cost when both devices are installed at the same time. This way, the warranty for the two devices runs out the same time, the equipment both is able to run energy efficient, not to mention a home owner doesn't have to worry about having their utility space or basement under minor construction at two different points in time. This by far is the more convenient method to go about improving the heating and cooling of the house. 

Often times this just comes down to a personal preference. If a home owner believes they will be staying in the house for an extended period of time and the furnace does not need replacing, than installing just the AC unit is cost effective and corrects any current problem in the residential HVAC system. However, if the home owner is considering selling the house, upgrading and installing a new furnace, along with the AC, looks good to possible interested house shoppers, not to mention the new equipment improves the overall value of the house, making it easier to sell the house for a desired price.