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Sizing a central AC system for this house starts with what the compressor will actually be asked to do, and a contractor has to establish that before anything else on the quote makes sense. Homes in Johnson County, KS run cooling about four months a year, from June through September. The compressor and condenser fan start and stop on every warm day across those months, and a system that was undersized at installation runs longer cycles to keep up, putting extra wear on the contactor and the refrigerant circuit with every season. A contractor doing an installation quote here will want to run a proper load calculation against the house's envelope, not carry over a unit size from the previous system, because an undersized replacement shows the error quickly.
Ductwork in a house does not get replaced every time the equipment does, and in Johnson County that gap is where most installation decisions get made. Half the homes in Johnson County, Kansas were built in 1989 or earlier (2020-2024 ACS 5-year). A central AC unit sized and selected for a house means nothing if the ducts it has to push air through were laid for a different system and never touched since. A contractor will open the supply and return runs, check the trunk sizing, and find out whether the existing layout can carry what the new unit delivers before the equipment order is finalized.
What a Central AC System Includes
The outdoor condenser unit sits outside the house, usually on a concrete pad at ground level, and is the piece most homeowners recognize on sight. Inside, the air handler or furnace coil assembly lives in a utility space, basement, or closet, and is where the system meets the air that moves through the house.
The refrigerant line set runs between those two units, carrying refrigerant through insulated copper tubing that passes through an exterior wall. The thermostat mounts on an interior wall and is the control point that tells the whole system when to run.
The drawing shows how these pieces relate in a typical installation, and a licensed contractor determines exactly how they fit the layout and existing infrastructure of your home.
Get matched in Johnson CountyJohnson County, Kansas, by the numbers
367 severe weather events were recorded in Johnson County, Kansas between 2015 and 2024.
NOAA National Centers for Environmental Information, Storm Events Database, bulk CSV export, events 2015-01-01 through 2024-12-31.Half the homes in Johnson County, Kansas were built in 1989 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesJohnson County, Kansas holds 259,655 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 68.5% of the occupied homes in Johnson County, Kansas (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesCodes & Standards Governing Central AC Installation in Johnson County, Kansas8 sourced rules and standards
What the Installation Actually Looks Like
Split-system central air conditioners rated below 45,000 Btu/h manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Split-system central air conditioners rated at or above 45,000 Btu/h manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Split-system central air conditioners manufactured between January 1, 2015 and December 31, 2022 had to meet 13 SEER, the metric that preceded SEER2.
Single-package central air conditioners manufactured on or after January 1, 2023 must meet a federal minimum of 13.4 SEER2.
Space-constrained central air conditioners manufactured on or after January 1, 2023 must meet a federal minimum of 11.7 SEER2.
Federal efficiency standards for split-system central air conditioners and heat pumps are set on each certified combination of outdoor unit and indoor coil rather than on the outdoor unit alone.
Residential and light commercial air conditioning and heat pump systems assembled in the field, including mini-splits and unitary systems, may not be installed on or after January 1, 2025 using a refrigerant with a global warming potential above 700.
A field-assembled system whose specified components were all manufactured or imported before January 1, 2025 carries no installation compliance date under the refrigerant restrictions and may still be installed.
Severe Weather Events in Johnson County
Weather puts a load on HVAC equipment, and that load is shaped by what actually happens in this area. Knowing the local pattern helps a contractor size and install central AC to handle what the climate here asks of it.
367 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.