An oversized coil can help with efficiency in hot, dry locations. But usually only 1/2 or 1 ton, not 2.

(Its usually not done in humid locations as it can impair dehumidification some)

that makes sense. what is the risk if having a 2 ton difference in size? is there a risk our evaporator coil might freeze? we hadn’t heard that before so not sure that is correct. we are wondering what to be on the lookout for… or whether we should replace the evaporator.

The model numbers of the furnace, condenser, and coil? We may be able to go on the AHRI directory to see if the manufacturer lists it as a allowed match. A 5 ton coil is unusual but it may be listed as correct. If the coil has not frozen then I would not worry about it. The efficiency is usually higher with a bigger coil.

that makes sense. what is the risk if having a 2 ton difference in size? is there a risk our evaporator coil might freeze?

IMHO the biggest risk you face is lack of proper oil return to the compressor, as the coil is bigger... the oil that runs thru the system has a larger area to pool.

Freezing of the coil, just because it's larger or smaller? uh- no. To freeze there has to be some other reason beside that. Typically an AC evap coil is going to run around 40F with some designs in the mid 40's to low 50's. At those temps it's impossible to freeze unless there is some other problem, running with clogged filter, in operable blower motor, improper refrigerant charge, clogged or restricted meter device or running the system with no load and ambient temps 55F or lower outside *(without the proper controls to do so).

What's the manufacturer of your system? Is your system working? If it is -- I wouldn't worry about it until it does. They all break. Worry about the things you can control, like changing filters regularly, system maintenance checks performed by licensed tenured techs if you can find one.

Some companies will lay into you for a wide variety of reasons because they are looking for reasons to get you to decide you need a new one, or some reason to do an expensive repair you likely do not need.

What's the reason you've been talking to people about this? Is the system working or not?

Provide a picture of your e-coil data plate info with model / serial number clearly visible. I'll tell you what it is.

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In terms of dehumidifying a larger than necessary e-coil for a hvac system will hold water, that water can be reintroduced back into the home as the humidity it tried to expel. This is typically a design issue.

With all that being said it was a verbal rule not to go any higher than 1 ton difference from that of the out door condenser, that was 20 years ago when each coil design was seperate and coils were smaller then in physical size all of them. In the search for higher government mandated efficiency requirements I've seen larger differences than that 1 ton. Not typically 2 tons though.

*However it should be noted that some manufacturers 4 ton / 5 ton e-coils are interchangeable... meaning that if you have a 4 ton system, the E-coil is the same as a 5 ton e-coil. If larger coils were known to freeze, would a mfg do this? uh-no.

The mfg's are after your e-coil money... selling you a 5 ton coil when what you really need is 4 ton? LOL. yeah it's all about money. It's cheaper for the Mfg to make just one coil for two different configs than 2 separate ones. Eventually the waters here could get even murkier due to a wide variety of problems coming to a hot town near you. 2023 is the year, for some it might not be felt until 2025. It's coming, you've been warned. ;-)

So a 3 ton condenser paired with one of those e-coils? If that is the case? It's not going to mean much, unless the condenser is 2 ton paired with a 4 ton/ 5 ton e-coil. Because? they make plenty of 3 ton e-coils, unless there's a mfg supply problem or it was an installer mistake.

I service the Katy, Texas area.

What is happening in 2023?

There can be a number of undesirable effects caused having an oversized evaporator and would basically be the same problems you have with an undersized condenser.

The amount of heat absorbed by the evaporator would be more than the condenser could remove at times and some of the gas wouldn't condense to a liquid in the condenser. So the condenser isn't big enough to provide enough subcooling and some liquid is prone to saturation in the liquid line just from absorbing heat through the copper tube and into gas.

This will cause poor oil circulation, poor expansion valve operation, lower efficiency, excessive power consumption and can ruin your system. It may work fine on mild days when load is low but on warmer days the condenser just can't remove the load absorbed by the evaporator and when you'll see problems.

Can you explain how this happened?

The load calcs show only a 3 ton system is needed. we believe the engineer put in a 5 ton evaporator to improve the efficiency. however, he has since passed away so we can’t ask him to confirm.

What is happening in 2023?

R22 has been in phase out mode for well over 12 years now. The current refrigerant that replaced R22 known as R410a is going to be phased out.

California enters this phase first. No new R410a installations in CA starting in 2023. R410a begins it's phase out with strict rules than the aformentioned R22 Freon. (no dry units like with R22). Texas is likely to enter this realm in 2025 at the latest.

The refrigerants replacing R410a isn't much better than that of R410a. Two competing versions R32 & R454b both of which are mildly flammable. How flammable? mildly. If you choose R32 solution, that is likely to be phase out sooner because it is mildly more offending than R454b. But either of these choices shelf lifes will be short. Maybe 15 years, maybe 20.

R22 is cost prohibitive now. If you have a unit that uses R22 --9 times out of 10-- and you spring a leak -- you buy a R410a unit now. Because? The new units have yet to arrive! ( this is assuming you can even find what you want now.)

So in short order anything you buy now will essentially be obsolete "over night". This primarily will only effect you if you spring a refrigerant leak. BUT, refrigerant leaks nowadays are more common than 20 years ago.

If you're curious what, where, how and why this is happening? I made a video about it embedded below for your convenience. Note: this video is only a starting point... Part 1.

Thanks for the cartoon break, Ray. And now, back to our regularly scheduled program...

The OP asked "What are the potential risks (or benefits) to having an oversized evaporater coil?"

The capacities of your evaporator and condenser coils should be matched. A higher capacity evaporator coil will operate at higher temperature. That will increase run time (it will take longer to cool the space) and decrease dehumidification. That's a decrease in efficiency--not an increase.

"evaporator and condenser coils should be matched" Matched how Tim? The old saying size doesn't matter but how it's used, also applies to A/C coils. The 5 ton Evaporator coil can easily be used with a 3 ton condensing unit by adding a 6" long "liquid to suction heat exchanger" to control flash gas and oil migration and tweak the TVX.

Capacities of the two coils have nothing to do with working together, it's how the refrigerant cycle is controlled and the refrigerant properties. A typical refrigerator has an evaporator 2 to 3 times the capacity of the condenser coil, and a walk in cooler or freezer have evaporators 4 + the size the condenser size, it's how the refrigerant is controlled.

Wondering if the evaporator coil can freeze up? If the installer raised the Blower speed to 1500 to 2000 Cfm's the answer is NO way ever. If the install set the blower speed at 1200 Cfm's for a 3 ton coil, it would depend on how well he tweaked the TVX valve to set superheat, but highly doubtful it would. If the TVX was set rich, on a mild day with above average humidity, maybe.

Hi, Kevin,

The context here is a residential HVAC system as designed and manufactured--not some field modified version.

Manufacturers design evaporators and condensers to work together as components of a system and to be able to guarantee the system performance. Substituting coils with capacities different from what the OEM supplied as part of the original system is likely to both degrade performance and void the warranty. Here's a link to an article from the Heating Air Conditioning and Refrigeration News which provides a good overview:

https://www.achrnews.com/articles/92710-mismatched-coils-can-really-mess-things-up

Thanks Charles, the response was to the original poster that actually read what I wrote and responded with an additional question. It wasn't for you.

So your response is to post an outdated recommendation from 2003? Gee how many things have changed since then? We were still using R22 Freon, coils as I referred to further up were actually made in each individual size, unlike the MFG processes of today.

This is the problem of trying to gather info on the internet... you don't read let alone understand exactly what it is you are reading. Just as you failed to see the original author of this thread ask for additional info for what's coming in 2023 and beyond.

Stick to building homes Charles.

click to enlarge pictures if you can't read them.

The video posted in regards to what is happenining in 2023 is chocked full of information. Mock it all you want, it changes nothing for me.

@Austin Air Companie,

You threw out a teaser, Ray, and somebody took the bait. I can't imagine why you would divert the discussion except for an excuse to promote one of your not-ready-for-prime time cartoons. It's no more timely nor accurate then when you posted it in a discussion five months ago and the inaccuracies in the content were aired:

https://www.houzz.com/discussions/6172337/the-future-of-r-410a#n=26

I've said repeatedly Charles where the info was derived from, that the video is a "starting point" part 1.

Contrary to popular myth, HVAC contractors do not contain any psychic abilities what so ever.

Yet we are often asked how long we think a repair a replacement a certain brand over another brand will work? How long will it last? If I had a nickel every time I was asked that I would have retired years ago.

Time doesn't stand still in HVAC land. The info is a starting point... as in you have to start somewhere. There were changes to the rules of the R22 Freon phase out as well.... after the fact due to lawsuits etc. So can things change?

Yes. Refer to the 2003 article that the Builder posted. But he's trying to change the argument from his lapse of judgement of posting inferior information himself. Ironic +1 --- skip your 1 a day +iron Charles. No irony over doses on my watch. LOL.

Ray,

Unlike policy and regulations, the principles of engineering don't have a shelf life. Based on the quality and content of your posts, it's obvious your expertise includes neither.

LOL Charles.

28 years doing HVAC in a high heat climate in which AC is needed here upwards of 10 months of the year here.

1 man operation. How many repairs, mods to equipment, replacement equipment, zoning, inverters, 2 stage communicating systems have I done in 28 years time?

Yet I still have the time to waste responding to you and your "myths"? Charles?