6000BTU

Harry:

The smallest central air unit is 1.5 tons (18,000 btu/hr). The 6000 btu unit would be much cheaper to run to cool a bedroom only. If you run a central air unit, you are cooling every room that has a supply vent. The newer window units are very energy efficient compared to ones from a few years ago.

We do this every night in the bedroom with a 6000 BTU GE unit. It uses about 3.5 kilowatts per night (11 hours run). And this is at a temperature of 71. The central unit would be far more expensive. That's why we do this.

I installed central AC 2 years back and started to ask the same question after a few $150 July electric bills. I found a really cool cost and usage calculator at www.energystar.gov. Apparently, A 7000 BTU room AC in a 400 pk hr zone (SE Michigan) costs $668/yr to run at $.1644/kWh. A 1.5 ton cental AC unit (bigenough for a 1500 sq ft, 1.5 story home)costs $243/yr. This didn't make sense to me. Afterall, I never had $150 bills when I used the window unit. Then I remembered 2 really important facts. One, I rarely used the window unit because I preferred to keep the window available for outdoor air and because to room unit was so noisy. Second, electricity prices have jumped a lot in the recent past and are probably a lot higher than when I used the window unit.

Here is a link that might be useful: Savings Calculator

WHOOPS! Caught a serious error! I was reading the lifetime cost for the window unit, not the annual cost. The corrected stmt would be. A 8000 BTU room AC in a 400 pk hr zone (SE Michigan) costs $37/yr to run at $.1644/kWh. A 1.5 ton cental AC unit (bigenough for a 1500 sq ft, 1.5 story home)costs $243/yr. We had a few hot streaks this summer, so I will probably spend about $300 on summer electricity. I only put the central AC on for a hot streak. Otherwise, I leave it off. I suppose that's the convenience cooling only 1 room; it's not a huge money proposition to use the AC.

Here is a link that might be useful: Savings Calculator