Air conditioning systems are just that - several components designed to work together in order to provide the best possible cooling for an application. Manufacturers purposely design condenser coils and evaporator coils to work together, in order for end users to obtain the best possible efficiency, reliability, and operation out of their system.

So why would anyone consider replacing one coil and not the other? The answer isn't as simple as you think, and the 13 SEER transition has brought the ongoing mismatched coil debate to a head. At the heart of the debate is what should contractors do if they replace an existing, lower-efficiency condensing unit with a 13 SEER unit. Should the existing indoor coil automatically be replaced as well? Or can they simply install a thermal expansion valve (TXV) on the existing coil to increase its efficiency?

Manufacturers differ in their responses to this question, so it's no surprise that contractors have different approaches as well.


Henry James, owner, Suburban Heating and Cooling, Franklin, Tenn., doesn't think he'll be faced with the mismatch problem too often because he usually finds that the indoor coil is the first component to fail. "If one piece has to be replaced, it's usually the indoor coil because it's leaking," said James.

During the past several years, if an indoor coil has failed, it has been James' policy to replace it with a 12 SEER coil with a TXV in the hopes that it will functionally match a future 13 SEER condensing unit.

"The system may not reach 13 SEER, but that's not my main concern. I don't think customers can tell the difference in their electric bill between a 12 SEER or 13 SEER system. I'm more concerned with whether or not the system is going to operate normally. Will it have the latent and sensible Btu capacity that the system is supposed to have?"

He noted that he wouldn't consider replacing an indoor coil with another 10 SEER coil because if the condensing unit subsequently fails, the customer will not want to replace the indoor coil yet again. "Our assumption is that if we install a 12 SEER expansion valve coil, we will be able to put a 13 SEER condensing unit on there and it will work."

That being said, if a condensing unit goes out, he insists that customers with anything less than a 12 SEER indoor coil replace that as well. "That's our approach going forward," said James. "If the condensing unit goes out, we will replace it with a 13 SEER unit, and we will replace the inside coil too. Period."

Why the hard line? Because James does not believe in installing components that are not intended to work together. "If we don't replace the indoor coil at the same time as the condensing unit, the system can become operationally and functionally mismatched. When this happens, the system will not deliver the sensible or latent Btu that it's supposed to because it's a fixed orifice device. You can hook up the gauges and see them creep all over the place because they're not right. And there's nothing you can do to make things right. We want to avoid that."

Another reason to only install matched systems, according to James, is that manufacturers don't always respond well to problems with mismatched systems, and sometimes there are warranty issues.

"Sometimes it's hard to get answers to questions about systems they built. If it's a ‘Frankensystem,' tech support is simply not going to be available. Not to mention that we already see 10 SEER systems that are mismatched. They don't work well, are hard to diagnose, and impossible to charge correctly."

James added that customers are more than welcome to call someone else who will only change out the condensing unit and not the indoor coil.

"We lay down the law pretty strongly in what we will and will not do. That's based on our experiences in the past. When we've done it the customer's way, no matter what they've told us up front, it turns out to be a mess. We will only do jobs where we are confident that we control the variables, and then we are responsible for its performance."

Contractors continue to debate when the indoor coil has to match the outdoor coil.


Bob Barnes Jr., vice president and general manager, Western Heating and Air Conditioning, Boise, Idaho, stated that his company would take each potential mismatch scenario on a case-by-case basis.

"If the unit's not very old, and if you're matching a factory brand coil like a Carrier indoor coil with a Carrier outdoor unit, you should be able to find out from the factory what you can do," said Barnes. "For example, maybe you can install an externally exposed TXV on the indoor unit to get the efficiencies up. I'm sure there are going to be some cases where it's not going to be necessary to change the indoor coil."

If the inside coil is over 10 years old or if it's not possible to obtain information from the manufacturer, then Barnes said it would be necessary to change out the coil, although he would leave the final decision to the customer.

"We will explain everything, but if the customer chooses to not replace the indoor coil, we will have the customer sign a waiver stating that he understands that the efficiencies may be less than expected."

Barnes is adamant that his salespeople be upfront with customers, telling them all about the efficiencies they may or may not achieve. "I will not allow our salespeople to go out and misrepresent the company or the customer by telling them that this is going to be a 13 SEER unit if they leave the old inside coil in," said Barnes.

"As long as customers understand, then it becomes their choice. We will have a disclaimer because I'm not going to have somebody come back on me and say we didn't tell them about this."

Over the last three years, the technicians at Western Heating and Air Conditioning have received training, so they can accurately estimate a consumer's bills and usage with a new, matched higher-efficiency system. They quote this system compared to one in which the indoor coil is not changed out, so customers will know how their energy usage will differ based on what's installed.

The quotes may also reflect the higher costs associated with replacing the indoor coil. As Barnes noted, it's going to become more difficult and more expensive because in many cases it will be necessary to tear out the furnace in order to remove the old coil and replace it with the new, larger coil. Not to mention that there may have to be modifications made to the flue, gas piping, electrical system, and ductwork.

"It's going to be a big process," he said. "Just going out to the customer's house and setting an air conditioner and being out of there in three or four hours is just not going to happen anymore. It's going to become a whole day job to do an air conditioner changeout. This is going to change the way we do business."


Mike Roy, senior service technician, Alicia Air Conditioning and Heating, Lake Forest, Calif., stated that his company is taking its cue from the manufacturers regarding indoor coil replacement.

"The manufacturers recommend replacing the indoor coil, and so do we," said Roy. "But not everyone can afford it, so we're not going to require that customers replace the coil. We strongly recommend it, and we explain the differences in efficiency, but the manufacturers have told us they will not void the warranty if the indoor coil isn't changed out."

Even though Roy's company may suggest replacing the indoor coil, it doesn't plan on asking customers to sign any kind of waiver if they decide not to replace it.

"The manufacturers are telling us we won't have any operational or warranty issues. It just has to do with efficiency. We don't want to use scare tactics. We'll just tell customers they'll have a lower efficiency if they don't replace the indoor coil."

If an indoor coil needs to be replaced, Roy only sells high-efficiency coils with TXVs. He pointed out that the higher efficiency coils cost only a little more than 10 or 11 SEER coils, but customers will definitely need them in the future to work with 13-plus SEER condensing units. If the indoor coil is newer, Roy might consider installing a TXV on it, but "on some of the older coils, it's impossible. There's just no way to attach a TXV. Honestly, though, when you have to start soldering, it's not worth the money. Just replace the coil," said Roy.

Replacing the coil may be difficult in certain applications, though, such as condominium complexes. "The size of the new coils will definitely be a problem for some condos," said Roy. "We work in some complexes that have very tight spaces."

The manufacturers also have not given contractors much information regarding what they plan to do with their 10 SEER package units, which are often found in condominium complexes. This type of equipment can technically be manufactured until 2010, but the DOE regulations are unclear, and there are a number of conditions and size limitations.

Early in 2005, Roy notified all his condominium customers that the changes were coming and if they had older equipment, they might want to consider replacing it. He even went before the board of a condominium association to discuss the issue and to let them know the expense and difficulty involved with replacing the equipment at a later date.

The result? The condos decided to wait and see. "We've done our due diligence," said Roy. "They were all informed."

Contractors will ultimately have to decide whether or not to require the replacement of an indoor coil when they are replacing the outside condensing unit. Whatever the decision, it is incumbent upon the contractor to explain all efficiency issues to customers, so they can be fully informed about their air conditioning system.

Publication date: 04/10/2006