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A contractor quoting a central AC install in Washtenaw County has to size the system against what this climate actually delivers, not against a catalog average. 166 severe weather events were recorded in Washtenaw County, Michigan between 2015 and 2024. At that rate, severe weather is part of the normal season here, and a system undersized or poorly matched to the load will run harder and longer than the equipment was built to sustain. Getting the install right the first time means specifying for a place where that kind of load is expected, not exceptional.
Existing ductwork is what a contractor prices around, not what they price after the unit is selected. Half the homes in Washtenaw County, Michigan were built in 1978 or earlier (2020-2024 ACS 5-year). In housing of that vintage, the duct layout was designed around equipment whose airflow and static pressure characteristics differ from a modern central AC system, and whether those runs can carry what a new unit delivers is something a contractor has to measure, not assume. If the ductwork needs rerouting or resizing, that work sets the schedule and the budget. The electrical service gets the same look, since the load a current system draws may exceed what the original panel was wired to handle.
What Goes Into a Central AC Installation
The outdoor condenser unit sits outside the house, usually on a concrete pad beside the foundation, and holds the compressor and the condenser coil. Inside, the air handler or furnace-mounted evaporator coil sits in a mechanical room, basement, or utility closet, and is the piece the cooled air passes through before it moves into the home.
The refrigerant line set runs between the two units, connecting the outdoor and indoor sides through a small penetration in the wall. A thermostat mounts on an interior wall and gives the homeowner control over when the system runs and at what target temperature.
The drawing shows a typical layout, and a licensed contractor determines exactly what applies to your house and its existing setup.
Find a contractor in Washtenaw CountyWashtenaw County, by the numbers
166 severe weather events were recorded in Washtenaw County, Michigan 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 Washtenaw County, Michigan were built in 1978 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesWashtenaw County, Michigan holds 159,782 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 61.6% of the occupied homes in Washtenaw County, Michigan (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesRules & Standards for Central AC Installation in Washtenaw County, Michigan10 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.
Licensing and Legal Requirements in Washtenaw County, Michigan
Michigan issues the mechanical contractor’s licence by classification: HVAC equipment, ductwork, refrigeration, hydronic heating and cooling, and limited or unlimited heating and refrigeration service are each a separate classification a contractor has to hold.
Michigan requires a mechanical contractor’s licence: nobody may install, alter or service the regulated mechanical work unless they, or an employee, hold a licence from the department that has not been revoked or suspended.
Severe Weather Events in Washtenaw County
Weather puts a measurable load on cooling equipment, and that load varies by where you live. A contractor sizing and installing central AC here is working against Washtenaw County's specific climate record, not a national average.
166 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.