Of all the things I could spend $8,800 to buy, a new central air-conditioning system is not near the top of my most-wanted list. But that’s what I did this week, and I actually feel pretty good about it.

Department of Energy

I am happy about the $1,500 tax credit I am going to get for buying a very efficient system, one that is going to save me hundreds of dollars a year. To sweeten the pot, the manufacturer offered a plan that allows me to pay for the system over three years with no interest. My installer told me that the financing deal was unusual for this time of year, but business has been slow in these recessionary times.

Of course, I am happy about the fact that I am going to reduce my family’s carbon footprint. But as I think about the process I went through to buy my new air-conditioner, the economics really came first. And right now, possibly for a limited time only, the economics and green thinking coincide.

My air-conditioner story begins with my old system, 17 years old and leaking Freon, that organic compound linked to ozone depletion. Over the last two years, my regular air-conditioning service guy would pour in some Freon, and I would be good to go for another year. $175 was a small cost to put off replacing my old system.

This year, he came back again when a Houston heat wave overwhelmed my air-conditioner. But this time the Freon refill didn’t do the trick. He returned to tell me that now I needed a new evaporator coil, at a cost of $1,675. I still didn’t need to replace my air-conditioner, he said.

I said O.K., but then I stopped to think. That’s a lot of money to invest in an old clunker. He came back with a proposal to replace the system with a 13-Seer unit that would cost $3,925. I stopped to think again. Would that qualify for the tax credit under the stimulus package? The SEER rating, the Seasonal Energy Efficiency Ratio, was too low — even though the new system would be at least a third more efficient than my leaky clunker.

So I went up the price scale to a much more efficient and expensive system. My new system, which is rated at 16-SEER, should be 50 percent more efficient than my old system and should save me well over $500 a year. (We would save more, but we keep our thermostat at 77 during the day and 79 at night.) We may not stay in the home enough years to pay for the system, but my real estate agent tells me prospective buyers will be impressed with our efficient new air-conditioner.

Good thing my clunker broke down when it did. A few months from now, the tax credit will be history. I probably would have bought the less efficient system. Chalk it up as one small victory for government climate change policy.