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Question DetailsAsked on 5/8/2014

Can you replace 2 AC units with a single unit? There are 2 cooling/heating zones in our home.

Approximately 5,300 Sq ft home including basement. We have one AC unit for each heating/cooling zone. The upstairs unit has failed and needs to be replaced. I've noticed other similarly sized homes in our neighborhood have only a single unit (albeit larger).

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2 Answers


If you could, you may would lose the zoning feature you currently have. General rule two floors/stories, two units or a two zone , zoning system for proper temperature controll on each floor.

Trying the two duct systems together may not be possible,due to the construction, ie can't get to there from here.

If the "tonnage/size" required of the two systems together is over 5 tons,there aren't residential units commonly available over 5 tons.

If the size required is 5 tons or under, and ducting can be connected, I would add a zoning system,so you still have two thermostats and two temperature zones. A good two stage unit or the Greenspeed from Carrier is a great choice for this, with Carrier Infinity Zoning.


Answered 6 years ago by BayAreaAC


As BayAreaAC said, depends a LOT on your duct configuration. If both floor's ducts come together (or close together) at one point it may be possible to tie them into one larger unit, with 2 separate zones with a manual or thermostatically controlled damper to balance the airflow between the two zones.

Another possibility, depending on your configuration, is a split unit - one central compressor/condenser unit outside that feeds two separate fan/evaporator units, one for each floor and independently controlled by individual thermostats.

It is also possible that one unit could serve both, with a connecting new duct from the unit to the upstairs - through walls if viable, or in a separate insulated duct chase on the outside wall of the house.

You need a couple of Heating and A/C contractors to look at your house and propose what they would do, then decide which sounds best to you. Of course, whether these A/C units tie into your heating system or are totally independent makes a big difference too, especially if you are not ready to replace that at the same time.

My thought, again depending on the duct configuration, is it is likely to be cheaper to go to one unit IF these are independent A/C units - though obviously at this time would cost more to convert to one larger A/C than to just replace the one you have. If they are part of a central air system that is also used for forced air heating, then that makes it more dubious unless you are looking at replacing the furnace at the same time, and a whole lot more dependent on your ducting layout and accessibility.

One other possible issue - if current upstairs A/C unit is in attic, that one is likely running pretty inefficiently in a hot atrtic environment unless it has dedicated outside air flow paths to and from it, so if that is the case you would likely save a fair amount of energy by getting it out of the attic, in addition to the savings of going with the newer more efficient units.

Answered 5 years ago by LCD

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