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Sizing a furnace for Denver County starts with understanding what the burner is actually asked to carry. Homes in Denver County, CO run heat about eight months a year, from October through May. The ignition system fires, the heat exchanger flexes with each cycle, and the blower runs through the bulk of the calendar year. A contractor who skips a proper load calculation here is setting up a system that runs near its ceiling for months, and that kind of sustained strain surfaces first in the heat exchanger and the igniter. Those are the components a licensed installer has to spec correctly from the start.
Ductwork laid down for an earlier generation of heating equipment is what a contractor runs into when quoting a furnace installation in much of this county. Half the homes in Denver County, Colorado were built in 1975 or earlier (2020-2024 ACS 5-year). That stock was built around systems whose sizing, routing, and return-air design differ from what a new furnace needs, and what is already in the walls does not always carry the new unit without changes. A contractor who opens the plenum and checks trunk sizing before finalizing a quote is doing the job the house requires.
What Gets Installed With a New Furnace
The furnace itself sits inside the house, most often in a basement, utility closet, or mechanical room. It holds the burner assembly, the heat exchanger, and the blower. The burner is where fuel combustion happens, the heat exchanger is the metal chamber that transfers heat to the air, and the blower pushes that air into the supply side of the duct system.
The flue pipe runs from the furnace to the outside of the house, carrying combustion gases out. Alongside it, a contractor installs the thermostat on an interior wall, which gives the homeowner control over when the furnace fires and at what temperature. A new furnace also comes with a filter housing where the return air enters the unit.
The drawing shows a typical layout, and a licensed contractor determines what applies to the specific configuration of your home.
Get matched in Denver CountyDenver County, by the numbers
243 severe weather events were recorded in Denver County, Colorado 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 Denver County, Colorado were built in 1975 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesDenver County, Colorado holds 359,581 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 48.8% of the occupied homes in Denver County, Colorado (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesFurnace Installation Rules for Denver County, Colorado4 codes & standards
What the Installation Actually Looks Like
Non-weatherized gas furnaces manufactured on or after November 19, 2015 must reach 80.0 percent AFUE.
Non-weatherized oil-fired furnaces manufactured on or after November 19, 2015 must reach 83.0 percent AFUE.
Mobile home gas furnaces manufactured on or after November 19, 2015 must reach 80.0 percent AFUE.
Non-weatherized gas furnaces manufactured on or after December 18, 2028 must reach 95.0 percent AFUE, up from the 80.0 percent minimum that applies to units manufactured before that date.
Severe Weather Events in Denver County
Denver's climate puts real demands on residential heating equipment, and those demands compound over time. A furnace sized and installed without accounting for local weather history will work harder than it should, which is why the record below is relevant to any installation decision.
243 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.