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RE: High Efficiency HVAC -
the Good, the Bad, and the Uncomfortable

Dear Website Customer:

Just because they sold you high efficiency doesn’t mean that it really is. Well before the Department of Energy developed any standards for rating the output and efficiency of HVAC equipment, consumers asked for higher efficiency, and manufacturers competed for industry leadership by racing to be first to the table. Contractors have installed these products in many cases without any regard for the subtle requirements of these systems, and subsequently, many of these systems never obtain the expected efficiency or comfort.

First, let’s discuss the key rating systems in place by the Department of Energy.

    AFUE - Annual Fuel Utilization Efficiency is a measure of the percentage of heat output to the space versus the amount of fuel that is burned. (80% is average, 96% is the highest)

    SEER - Seasonal Energy Efficiency Ratio is a measure of the percentage of cooling output to the space versus the amount of power that is consumed. (10 SEER is average, 12 SEER is extremely good, 16 SEER is the highest)

In determining AFUE, SEER, or any one of the other various efficiency ratings in our industry, each test in done in strict accordance with extensive published test procedures. These laboratory conditions are impossible to recreate in your home or business, but with strict adherence to installation guidelines we are able to get imperceptibly close. The following is a short list of the considerations we must examine in order to best provide the comfortable, high efficiency system you paid for:

  • System size - Higher efficiency equipment is not as tolerant to the old rule of thumb sizing estimates once used in our industry. It is very easy to undersize when moving up to higher efficiency, this will obviously result in poor comfort and longer running hours of your system. If the system is oversized, many times the space will feel humid and muggy, and system efficiency may be compromised.
  • Ductwork - You can put the best system in the world on old, leaking, or poorly designed ductwork and never obtain comfort or efficiency. Ductwork is always a factor in system replacement or installation. Don’t let your HVAC company overlook it.
  • Matched Equipment - Mixing and matching different components on a system are not by definition a problem. But, it is imperative to perform the engineering to verify that the sizing of each component are designed to work with each other for maximum comfort and efficiency. Although there is no published data on mixing a Lennox cooling coil with a Carrier condensing unit, many times we can determine the viability of the match. To be 100% sure, always use all components of the same manufacturer with certified ratings.

Of course this is just a short list of the major items. We must always pay attention to the special requirements of each specific product as described in the original installation, service and operation documentation provided with the equipment.

If you would like data on your specific HVAC equipment or a reprint from any of the efficiency rating articles we have in our library please do not hesitate to give me a call at 214-631-1010. I look forward to hearing from you.

Sincerely,

KAHN MECHANICAL CONTRACTORS

Josh Kahn

TACL A16607C

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