Which is cheaper: Run the whole house AC to cool 2000 sq feet or use a window unit to cool 200 sq feet?
I was thinking about when I’m sleeping at night, it seems wasteful to cool the whole house. I was thinking about putting in a window AC unit in my bedroom. That way I could turn off the central AC during the night. But then I was thinking that the central AC may be more efficient than the window unit and maybe I’d end up spending more money. That is, maybe it’s more efficient to use the central AC to cool 2000 sq feet instead of use a window unit to cool 200 sq feet.
This is in Texas where the AC will continue to run during the night. For example purposes, say it runs 50% of the time and I’m sleeping for 8 hours. My central AC has a SEER of 9 (it’s 20 years old).
If you are just trying to stay a bit cooler while sleeping consider getting a waterbed.
You lay on a standard foam matress and you can feel your body heating it up. Since you are basically laying on a giant pile of insulation it makes sense.
Now lay on a water bed. It will feel cool. It will STAY cool. As a mater of fact many people have to use low powered heaters to slightly warm the water and insulated padding on their waterbeds because otherwise they get too chilled sleeping on them all night.
Of course you also need a nice hair chest, an open shirt, and a big gold chain necklace to carry off a waterbed sucessfully…
A decent fan in the room might help more than you’d think (and be pretty darn cheap too).
Definately cheaper to cool the one room with a window unit. Just make sure the bedroom door is closed. I also don’t know if I’d fully shut off the whole house AC but you could probably set the thermostat up to 80.
In general, the rule is that central a/c is more efficient per cubic foot cooled, but if you cool a lot less then window units cost less. I don’t know the exact crossover point.
I had a whole house A/C that broke in the hottest part of the summer, went to the big box store and got the largest window a/c that would run on a 15 amp circuit. This unit cools over 1/2 the house including the kitchen, living room, dining room, office (very open design of the house, and why I got the largest one), and spills over into part of the large entrance room and utility room. I also had a small bedroom a/c which I put in for use at night, which also cools the bathroom. My electric bills dropped over $10/month during the cooling season over the last 3 years since I switched from the central a/c. The only rooms not covered is a storage room, a second bedroom and a second bathroom.
How much will you be paying for the window unit? If it saves you $50/month on your electric bill but sets you back $500 to buy & install it’ll take 10 months of use or 2 or 3 years of summers before you’re money ahead.
With 9 SEER it will be cheaper to run a newer window AC unit for one room than the whole house AC. But when you add in the cost of the unit it may not be a savings.
