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I am getting quotes for a new R410A condenser unit/evaporator coil from several HVAC contractors. A salesperson refused to give me a quote unless I purchase a new furnace as well. He said that he has seen problems using a new evaporator coil on top of an older furnace. My furnace is an old natural gas Trane furnace from the mid 80's. My current evap/condenser is about 7 years old.

I live in south Texas, so the furnace isn't really used enough to justify replacing it if I don't have to. I had it checked out when I bought the house about 4 years ago and it passed a health check. Is there any truth to what this salesperson is telling me? Are there any issues that can arise from using an old furnace with a new coil?

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The only technical reason that this isn't possible is that the coil needs a specific amount of air to flow through it when it's cooling. So to select the correct coil, you need to know the CFM of the air moving through the air handler. Not impossible to figure out or measure, but might not be easy for an air handler as old as yours.

However, if I was a professional HVAC installer, I would not want to put a new coil on a furnace that old, either. The installer only touches a small portion of your system, but in the eyes of the owner easily becomes responsible for the whole thing. So if I wasn't comfortable with my assessment of the existing air handler, I would probably decline to replace just the coil, too.

tl;dr: find a different installer if you don't want to replace the whole thing.

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  • The installer should be measuring the air flow as part of the installation, to determine what speed the blower should run at.
    – Tester101
    Aug 12, 2015 at 21:02
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    I had a problem a few years ago and my HVAC guy replaced the coil and the outside unit. He gave me a rough quote on a full furnace/air handler replacement - and the new venting requirements, etc. - and told me to save up and do it eventually but that there was no rush. Since then a couple of repairs on the furnace but still WAY ahead of where I would be if I had replaced everything.
    – manassehkatz-Moving 2 Codidact
    Jan 23, 2018 at 22:03
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    I do agree with longneck , I don't do much residential HVAC but people think if you touch any part of the system and something else breaks it is your fault. The last one I did I replaced the compressor and failed condensing coils , they did not want a new evaporator I flushed and told them it may limit the life 3-1/2 years later they were upset because the evaporator was failing now... Can't make a silk purse out of a pig's ear and people always have complains when they have no clue of what the right way to do something is.
    – Ed Beal
    Jan 23, 2018 at 23:37

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