A friend asked me about choosing a replacement air conditioner. He wonders about what SEER rating to choose in order to get best payback for the added cost of a higher SEER efficiency.
Until about 3 years ago, the minimum standard was 10.0 SEER. New minimum requirement is 13.0 SEER. It is a linear scale, so 13.0 is 30% more efficient than 10.0. You can get them as 16, 18, even 20 or more.
Typically, the highest efficiency units are a Hybrid Heat Pump which will run the AC summer & in the winter to provide heat. It runs "forward" in summer, and "backward" in winter. Then when it gets too cold in winter for the heat pump to be efficient, the gas furnace kicks on. The combination of the electric heat pump and the gas furnace is what makes this a Hybrid system.
Now, to analyze efficiency. If you use the AC a lot, then the quicker it will pay back for you, and the higher the SEER you should get. If the AC is running almost constantly, then the more money you are saving with a high SEER unit every hour it runs! The money you save goes toward paying back the higher upfront cost.
But if you don't use the AC often, then the efficiency hardly matters at all. Think about it - if you only drive 5 miles to work, then the gas mileage of your car hardly matters. On the other hand, if you drive 60 miles each way, the savings of an efficient car really pays off. The same goes for AC: the more you use it, the more important efficiency is.
And, if you are going for a high SEER AC then it might make sense to also get the Hybrid Heat Pump version of it. The heat pump will generally save you money on winter heating bills, and it gives you the flexibility to fine tune your gas and electric use in case of a massive fluctuation in the price of one or the other.
My own house uses a 14 SEER AC unit, and it was built 4 years ago when 10 SEER was still standard. So it was an upgrade at that time, but now it is just slightly more efficient than the minimum standard. We are not heavy AC users. But even though we don't use the AC too much, if I was building a house now I probably would use a hybrid heat pump. The extra expense would be justified by the winter savings, and as a added benefit I would save on the summer AC costs as well.