Common Approaches to Heating and Cooling Your Home: Part II

The Traditional Furnace and Air Conditioner Approach

Part I of this article can be found here.

The traditional furnace burns fossil fuel, either electricity or gas to create heat. The air conditioner is a one way heat pump. Air conditioners are almost exclusively powered by electricity today. It has not been that long since there were many gas powered air conditioners and refrigerators. Burning fossil fuel; either coal or natural gas is the primary source of electricity in Kansas. Less than 10% of our power is nuclear or wind generated, as of 2010.

The efficiency loss of a gas furnace can be as much as 50 percent of the heat literally going up the chimney. The most efficient gas furnaces are sealed combustion types. They utilize a condensing flue to achieve an extremely high efficiency. These units usually do not have a chimney through the roof. They exhaust out the wall near the ground. The temperatures are low enough, to allow plastic flue piping.

Their efficiency rates from 92 – 95 percent. In 2011, the Federal Income Tax Credit allowed home owners that purchase a 95 AFUE condensing furnace. An added feature of these furnaces is the sealed combustion chamber. They require no make up air from inside the home, and they cannot back draft deadly flue gasses into the home.

Electric furnaces are generally considered to be 100% efficient in the home. The electrical transmission system, does see a loss that amounts to about 35%. The generator burning fossil fuel also has less than 100% efficiency.

Air conditioners, available at this time, at a minimum are rated at 13 SEER. Most existing units vary from 6 – 11 SEER. You can purchase units with a rating of 18 – 20 SEER. A rating 15 SEER is the most common available High Efficiency Unit. Some manufacturers have a 14.5 SEER that is certified to use less power than a 16 SEER unit.

CompressorWhat is that trick? It is not a trick, but is part of the tool kit available for selling heating and ac units. An air conditioner consists of two parts. The outside unit, referred to as the compressor or the condenser, and the inside unit referred to as the evaporator. These must be matched correctly each other and the furnace (the blower fan is there) to achieve a specified SEER Rating. SEER is Seasonal Energy Efficiency Ratio.

For a user friendly description on the magic of Air Conditioning, a link to Energy Vanguard’s Blog Post on the subject.

The American Heating and Refrigeration Institute (AHRI) certifies furnaces, and air conditioners. Here are 3 entries with the same condenser/evaporator match with different furnaces.

AHRI Number      Model No Cond.        Model No Evap        Furn No              SEER

4137591                 24ABC630A**30       CNPV*3621A**        58HDV040–12        15

3630546               24ABC630A**30       CNPV*3621A**       58CV(A-X)090-16    16

3630606              24ABC639A**30        CNPV*3621A**       58CV(A-X)0110-16  15.5

As you can see here are 3 different furnace units partnered with the same outdoor unit and indoor coil. They are rated for different efficiency levels.

If you would like to look up your units, the information is on the data plates. You need the model numbers.

  • The evaporator coil plate is on the inside unit, usually the easiest to find. The evaporator will be either above or below the furnace, appearing to be in the ductwork.
  • The condenser unit is on the outside unit, usually it is on the side by the copper tubing. The furnace data plate is usually found in the burner compartment of the furnace.
  • If you have the original paperwork for your units, the model numbers may be there. After collecting these numbers go to AHRI Directory

If you are buying a new HVAC system, ask your contractor for the AHRI certification numbers and look up for your self, the efficiency ratings.  Unfortunately I have seen many new systems the Home Owner was told is a High Efficiency Unit, only to find the matching process did not meet the Sales Hype!  If you would like some help in this process, The Energy Guy can help. Contact me for details.

For Part III

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