3 installers--3 different coil sizes recommended. Is more better?

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Old 06-22-16, 10:31 AM
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3 installers--3 different coil sizes recommended. Is more better?

I live in a northern suburb of New York City. I currently have a forced hot air system to which I'm looking to add central air. I've had 3 different installers give me quotes and each is recommending a different size coil with their systems. An American Standard with a 4 ton coil, a Trane with a 3 ton coil and a Lennox with a 2.4 ton coil.

Could it be that, for the same house, different systems would call for different BTU?
 
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Old 06-22-16, 11:03 AM
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The coil size is dependent upon the condensing unit size. The two should match although for better humidity control the evaporator (cooling) coil is sometimes increased in size by about a half-ton.

Did any of these estimators do any kind of a heat gain calculation? Properly, you need a full-blown Manual (manual as in book) J heat gain calculation. This takes into consideration all aspects of the building construction, including insulation, air leakage, number and type of windows, etc. Also site orientation as well as trees or other shading aspects of the surrounding area. As is evident, this calculation takes a couple of hours to gather all the data so it is rarely done UNTIL a contract is signed for the installation.

However, a "quick and dirty" heat gain can be done with just the square footage of the house as well as some prior knowledge of the weather trends. This is usually good enough to make a proposal. Also, if your home is similar to many other homes in the general area it is possible the company has worked on one or more of those other homes and can use that information to make an educated guess on your requirements.

Google heat gain calculation for more information. You can also do your own calculation and if you really want to "get into it" you can lease a computer program that will walk you through the entire procedure. The cost is about $50 and it is good for, as I recall, three months.
 
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Old 06-22-16, 11:27 AM
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I think those 3 installers are just guessing. Ditto on what Furd said.
 
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