Central Air Conditioning

If you’re considering replacing your central air conditioning system – or if your contractor has told you that you need to replace your A/C – the first thing you should know is that replacing can mean many different things. Sometimes, it refers to the entire system, everything that is both inside and outside of the house, including duct work, condenser, fans, heat pumps, thermostats, etc. Or it could just mean replacing the condenser and leaving everything else in place.  The former is a huge, expensive project, while the latter is far less expensive and far less obtrusive.

Let’s take a minute to review how your air conditioning actually works (essentially the same technology as your fridge):

  • Your air conditioning system draws heat out of your home and dumps it outside.  This is done by using two separate components (heat exchangers), one outside the home and one inside the home.  The cold indoor coil that does the cooling (heat extraction) is called the evaporator, while the hot outdoor coil that dumps the heat outside is called the condenser.
  • A pump transports the heat via a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils, and it is also compressed and expanded at certain stages.  The cool air is then delivered throughout the house using some sort of duct work. Voila, you have a cool house.

central air condition unitsWhat does it mean when you need to “replace” your  A/C?  In most cases it simply means replacing the outside condenser. While not inexpensive, this is straightforward project is a great opportunity to save money and energy going forward – as long as you know what to look for.

When replacing A/C equipment the most important metric you want to use is the Seasonal Energy Efficiency Rating (SEER).  SEER indicates the relative amount of energy needed to provide a specific cooling output. Many older systems have SEER ratings of 6 or less. The minimum SEER allowed today is 13, but consider using air conditioning equipment with higher SEER ratings for greater savings.  Frequently, there are tax credits or other incentives for equipment with a SEER rating of 16 and above.

Even if you discover that it’s time to replace your entire system, including both heating and cooling, you have options.  This could be an opportunity to completely re-engineer the biggest energy hog in your house, your HVAC system, which can account for up to half of all your energy use.  Under these circumstances you may want to investigate renewable energy sources, such as solar and geothermal, to provide the power for your heating and cooling needs.

Behind the Walls
Innovation Center
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Cambridge, MA 02142