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Heating & Air Conditioning

Mixed SEER ratings in a system

16 years ago

I was told that the outdoor heat pump unit (3.5 ton) is failing and both it and the indoor unit have to be replaced. Both are SEER 10. The indoor unit was increased four years ago due to a home addition from 3.5 ton to 4.0 tons. I am told that now the old and the new units have to be increased to SEER 13 ( which I understand). However, I am reluctant to replace the four year old indoor unit. This home is located in coastal SC. No other heating or cooling issues exist with the system. Can the four year old indoor 4.0 ton SEER 10 unit co-exist with a new 3.5 ton SEER 13 unit??

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Comments (8)

plusfour
16 years ago
Usually not. In order to achieve the 13 seer rating, the matching indoor coils have to be larger to handle the increased refrigerant. Failure to change the indoor coil could result in an early compressor failure. Also, without the indoor unit matched to the outdoor unit could result in voiding the warranty. Look thru the matchup charts for the new outdoor unit and make sure the indoor is compatible.
garyg
16 years ago
A matched system is best for performance, longevity, and low operating costs.

It is OK to have a larger evap coil with a smaller condenser unit, but not the other way around.

Have you asked if only the evaporator coil can be replaced, not the entire air handler? Maybe this will save you a few $$.

Good luck.
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Thanks a ton for the fast replies!! ryanhughes "Why does the Carrier unit need to be replaced?" The heat pump(outdoor condensor unit)needs to be replaced as the compressor is going. Started making terribly load noise, making the walls vibrate with this pulsating sound, extremely loud. They checked "everything" else and said it was the compressor. I was told it alone can be replaced for $1500-$1700, and hence figured it may be best to just get a new one, until I found out about all this R22 vs R410, mis-matching etc. The tech who said it needed to be replaced is from my regular AC service company who does my 2 x year prevent. maint. on the units. My parents have a 9 Seer Air handler that is going on 20 years and they replaced their condenser several years back (2002) with a 14 seer, no change to the air handler, he saw huge savings on their electric bill and has had no trouble with the unit. How is that explained? Due to the tight space where this one air handler is and poor lay out up there, it is going to be extremely costly to get down and get a new one in. May need dry wall work and reinforcement up there. Dad is adament that I do not need to change the handler, but hey, he's not an HVAC guy just someone who didn't replace and is seeing great benefit and no problems. The first HVAC guy who came yesterday said he could replace the outdoor unit with a 12 seer max (if he can find one) but not to expect much of any savings, but better to replace with a 10 seer again. ($2400) Why spend that kind of money and see no efficiencies? Having 2 more estimates on Monday. He said he could also replace just the compressor for $1500.00. This is why it seems like it may be best to take a plunge and replace everything, but really I do not have 6K. If I get another R22 outdoor unit, what happens if the air handler goes in 3 years, then what? I have to replace this new 3 year old condenser and an air handler? There went the $2400 out the door. Or are there air handlers that can handle both, just not condensers that can?
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garyg
16 years ago
I just re-read that you have a heat pump, which is a different animal than straight a/c. You need a matched condenser and inside coil for a heat pump. You can still probably use the old air handler, but the coil needs to match.
djpine
Original Author
16 years ago
Thanks. I will explore the option of the new indoor coil. I am also going to get a second opinion on the condition of the outdoor unit as it is not losing refrigerant; just aluminum fins corroded and some rust on outside of accumulator.
trane_man
16 years ago
I doubt you will find a 13 seer evap coil to fit your 4 yr old airhandler.Im sure they did that on purpose.All the above post are correct.
bob_brown
16 years ago
Code tells optimum conditions. Nothing says you have to replace anything. All of the above posts are correct in thier own right, but nothing says you have to match anything to anything. Some techs are not capable of replacing a HP unit. Get a new company to bid the job.
baldloonie
16 years ago
Post your model numbers and we can tell you further.

You can run into problems especially with heat pumps if the indoor coil is too small. Nothing says you have to matching anything to anything but you could need the refrigerant level changed seasonally. Heating mode needs less refrigerant than cooling and that is especially complicated if the indoor coil is too small. You'd have to have refrigerant removed in the fall and added in order to cool when the outdoor coil becomes the condenser.
garyg
16 years ago
A TXV for the inside coil would benefit this mix-matched SEER system, at least in cooling mode.

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