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Last week, I talked about air conditioner efficiency in terms of window air conditioners. In some situations, window air conditioners will work just fine. For some homeowners in Boston, central air conditioning is the preferred solution because it cools the entire house, instead of a single room or selected rooms.
As a brief refresher, the seasonal energy efficiency rating (SEER) compares the output of the air conditioner to the electricity it consumes. The higher the SEER, the more efficient the air conditioner is. A BTU (British thermal unit) is a measure of cooling output. The higher the BTU, the more powerful the air conditioner is.

For a “whole-house” solution, a central air conditioning unit with a BTU output of 60,000 and a SEER of 19.9 (very high efficiency) will consume about 3kW/hr. At $0.05 per kW/hr, assuming that your air conditioning is on for 8 hours daily, you’ll spend about $1.20 per day on electricity to cool your entire house. Over the course of a season (assuming 110 days), you’ll spend about $135 to keep your house cool.

If your central air conditioner had a BTU output of 60,000 but had a SEER of only 10.8 (the same as last week’s window air conditioner), the daily operating cost would be about $2.25 and the seasonal expense would be about $244.

Over the course of 10 to 15 years (the life expectancy of a well-maintained central air conditioner), you’d spend between $1,100 and $1,650 more on electricity to use the low-efficiency air conditioner. If you applied this expenditure to a higher-efficiency air conditioner instead, you’d save money over the life of the unit. You may also qualify for rebates or tax incentives by choosing a high-efficiency unit.
The lesson here is that if you want central air conditioning, install the highest possible efficiency system you can. The up-front expense may be larger, but your expenditure over the lifetime of the system will be lower and it will lower your total cost of ownership.

Also keep in mind that maintenance is a key part of extending the life of your central air conditioner and maintaining its rated efficiency. Without maintenance, an air conditioning system can lose between 5% and 10% efficiency each year. That would effectively transform our example 19.9 SEER unit into a 17.9 SEER unit and increase its electricity cost by $13 in the second season. That doesn’t sound like much, but after 5 years, the seasonal electricity cost would have increased by nearly $70. After 7 years, the high-efficiency unit would cost more to operate than a well-maintained 10.8 SEER unit!

If you have a central air conditioning unit that isn’t working as well as you think it can, contact us at Boston Standard Plumbing & Heating at (617) 362-0377 . We’ll be happy to service your central air conditioning unit and return it to peak efficiency.

DIY Air Conditioning, DIY Blog

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