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Sizing a furnace for this house is not a generic calculation. Homes in Pima County, AZ run heat about five months a year, from November through March. The burner and heat exchanger cycle on and off through that whole stretch, and a unit that is slightly undersized runs longer per call, building wear into those components at a rate a correctly sized unit does not. A contractor working a quote here has to establish actual heat loss for the structure before settling on equipment, because an error in that figure shows up on the heat exchanger first, and shows up predictably.
Existing ductwork is what a furnace installation turns on in this county. Half the homes in Pima County, Arizona were built in 1986 or earlier (2020-2024 ACS 5-year). Ducts sized and routed for equipment that is no longer in those houses were built to move a different volume of air, and a new furnace has to work with what is there or the contractor has to modify it. The electrical is a separate check. Either way, what the house already contains is what sets the scope before any equipment gets ordered.
What a Furnace Installation Covers
The furnace itself sits inside the house, most often in a utility room, basement, or closet. It is the box that generates heat, drawing in air, warming it, and pushing it back out into the home. The flue pipe runs from the furnace to an exterior wall or the roof, carrying combustion gases out of the living space.
The thermostat mounts on an interior wall and is the control point the homeowner touches directly, telling the furnace when to fire and when to stop. A contractor also accounts for the air handler or blower compartment, which moves conditioned air through the home, and the condensate drain line, which carries off moisture produced during operation.
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 Pima CountyPima County, by the numbers
405 severe weather events were recorded in Pima County, Arizona 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 Pima County, Arizona were built in 1986 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesPima County, Arizona holds 479,939 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 65.2% of the occupied homes in Pima County, Arizona (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesFurnace Installation Rules for Pima County, Arizona5 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.
Licensing and Legal Requirements in Pima County, Arizona
Arizona requires a contractor licence in good standing: it is unlawful to engage in the business of contracting, to bid, or to act or hold yourself out as a contractor without one.
Severe Weather Events in Pima County
Weather puts a measurable load on heating and cooling equipment, and that load shapes what a furnace here has to do over its working life. Sizing and installation decisions that ignore local conditions tend to cost more over time, which makes the pattern of weather in this area a practical factor, not a background detail.
405 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.