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Sizing a central AC system for this house starts with knowing how hard the compressor actually works each year. Homes in Montgomery County, MO run cooling about three months a year, from June through August. The compressor, the condenser fan, and the contactor each cycle through a concentrated run before going quiet for the rest of the calendar. Equipment that is undersized or installed with duct leaks or a mismatched refrigerant charge does not get enough runtime to reveal those faults gradually. The contractor who does the load calculation here has to account for that pattern, because the first call of the season is often the first sign anything was wrong.
Ductwork laid out for an earlier generation of equipment is what a contractor prices around on an installation job here. Half the homes in Montgomery County, Missouri were built in 1978 or earlier (2020-2024 ACS 5-year). A system put in decades after the original build draws on ducts that were never spec'd for it, and whether those ducts can carry the load a new central AC unit requires is a question the contractor answers by opening registers and measuring, not by reading the permit. Electrical service is the second variable: a panel sized for a lighter load may need an upgrade before the new unit can be connected. The ductwork assessment comes first because it is the part of the quote that changes most.
What a Central AC System Includes
The outdoor condenser unit sits on a concrete pad beside the house and holds the compressor and condenser coil. Inside, the air handler or furnace cabinet mounts in a utility space, attic, or basement and moves air through the system. These two units are the core of what a contractor puts in place.
A copper refrigerant line set runs between the outdoor and indoor units, and a new thermostat mounts on a wall where the homeowner controls the system. A condensate drain line also connects to the indoor unit to carry away moisture that collects during operation.
The drawing shows a typical layout, and a licensed contractor determines exactly what applies to this house.
Get matched in Montgomery CountyMontgomery County, Missouri, by the numbers
59 severe weather events were recorded in Montgomery County, Missouri 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 Montgomery County, Missouri were built in 1978 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesMontgomery County, Missouri holds 5,832 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 73.4% of the occupied homes in Montgomery County, Missouri (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesRules & Standards Governing Central AC Installation in Montgomery County, Missouri8 sourced rules and standards
What the installation looks like in Montgomery County
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 Montgomery County
Weather puts real hours on heating and cooling equipment, and what the sky does in Montgomery County shapes how hard a system has to work over its life. That load profile is a local fact, and it belongs in any honest conversation about what to install here.
59 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.