3

It's difficult to find a consistent straight answer on this. I asked earlier today on Reddit, and was told "It’s common to upsize the indoor (evaporator) coil to get greater efficiency".

When I search "next size up evaporator greater efficiency", these are the top results:

  1. "Yes, it’s bad if your evaporator coils are sized bigger or smaller than your condenser coils."
  2. People arguing 9 years ago on a forum about whether you want the condenser smaller or larger. Little agreement suggests people don't know what they're talking about.
  3. "Matching Evaporator and Condenser Coils – An Absolute Must"

Number 6 says "Mismatched Coils Can Really Mess Things Up". Number 5 says "I usually go a half ton larger on the evap coil. The added surface area slows airflow and you get better heat and dehumidification.", while the answer to "Can you Oversize an evaporator coil?" says the exact opposite: "After extensive research, we have found that having a matched or oversized evaporator coil will not control humidity enough. Rather it increases the humidity level in the home, especially at night. The reason is that the evaporator cannot get cold enough to properly dehumidify the air, causing your air to feel sticky and humid."

I've tried other search phrases, and the results are generally the same: all over the place. I think this is a representative sample, so I won't bother exhaustively listing them all.

What's the truth? Is there any evidence to back up the claims of a particular side?

2

You have done a fair amount of research as you can see this an art and depending on what you want lower operating cost or dryer air the answer can be different.

To me I like much dryer air for 2 reasons the first is how much cooler and comfortable it feels, the second reason cool high humid conditions are a great mold factory in the ducts I found this out later on industrial systems.

The control of your system also has some affect where the sizes are exact and a very high efficiency throttle valve system setup it may not get as cold and not remove as much moisture unless set on a less efficient setting, again it is a power savings vs comfort to get in the mid to upper 20 seer the coil is not as cold so not as much moisture is removed, but down around 18 seer the coil gets really cold and removes a bunch of moisture. So even with a exact match there can be trade offs.

My split I think 23 or 24 seer has a dehumidifier setting that we cycle on 2-4 times a day depending on how humid it is.

Sorry to add another variable into your research but almost every system I have installed is slightly different so there is not a one size fits all unless you have a system that can vary it’s pumping rate then an equal match is best so you have efficiency for most of the day and dehumidifier for a couple of hours.

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  • Interesting stuff. + – JACK Jun 10 at 19:30
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A simpler answer to this may be that IF the A/C manufacturer could have made it more efficient by simply changing the coils, don't you think they would have? On something like an AC unit, having a higher efficiency rating than a comparable competitive product is like printing money for a manufacturer. If it would make a difference, they would have already done it. There is no advantage to their design in having a less efficient model, in fact it would be a distinct DISADVANTAGE and would not save them any discernible costs.

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  • But I think the sizing question is valid many outside units only state the tonnage and that MFG may not have the appropriate coil shape for a particular unit, this is what I see why some change size, for fit in the air handler, that’s what the question is all about. – Ed Beal Jun 10 at 21:36
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Some matches are compatible and some aren't. The Air Conditioning, Heating, and Refrigeration Institute (AHRI), an industry group, keeps a directory of known-good matches that can be searched, by condenser or evaporator model number, at https://www.ahridirectory.org/Search/SearchHome. Every result will have a reference number. If a particular match you're considering does not show up in the results, that is if it doesn't have a reference number, then it is not a good match.

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