Posted: 7/27/2015 6:17:35 PM EDT
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My home was originally 1500 sq ft and had a 20 year old 10 seer 2.5 ton central air. I added a 400 sq ft room on that is open to the kitchen. Kitchen supply air was moved to the addition and two 10" round return air ducts installed at the end of the addition. 2.5 ton is undersized for 1,900 sq ft. (northern Indiana). I have a 12,000 btu window unit i bought last year to use while building the addition. Will it be more efficient to use the window unit to supplement cooling, or just use the central unit? |
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Quoted:
My home was originally 1500 sq ft and had a 20 year old 10 seer 2.5 ton central air. I added a 400 sq ft room on that is open to the kitchen. Kitchen supply air was moved to the addition and two 10" round return air ducts installed at the end of the addition. 2.5 ton is undersized for 1,900 sq ft. (northern Indiana). I have a 12,000 btu window unit i bought last year to use while building the addition. Will it be more efficient to use the window unit to supplement cooling, or just use the central unit? You're not that undersized. A very rough Man J shortcut says you need 30,400 BTU's of cooling for that space, you have 30,000 with the central air. Those returns will help a ton, but it does come back to the true Man J as far as windows, insulation and building materials are concerned as to dictate the efficiency of anything. You're already behind the 8 ball with the older more inefficient unit, adding a craptastic window shaker would just worsen the electric bill. Id say try it both ways, but with the weather that we in the midwest have been getting you wont be seeing a true comparison as the weather is all over the fucking map. To me the little bit of extra run time the primary central may need vs the loud ass window unit make it an easier decision. Make sure your filter as well as outdoor coil are nice and clean. |
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Never size AC based only on square footage. If someone does that don't hire them to do the work.
Having an undersized AC is actually not a bad thing. The unit runs longer, but dehumidifies better because of the longer run times. Which means you can keep the temperature higher and still be completely comfortable. You're probably only undersized only a couple of months during the summer, but when the temperature outside drops you'll be fine. If it really bothers you you can look at adding better insulation. |
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You may want to check your unit. Some have three speeds. If you have a 2.5 ton unit it should be about 1000cfm. Some you could put on high speed and get 1200 or so.
The returns will also help and if you do use the window shaker the returns will pull the air and move it throughout the house. Do you know how many grills and what size they are? A 6 handles 100-110, 8 is 220-230, 10 is 390-400. If you have volume dampers in your ducts to each grill you can close them some to push more air to other grills. |