Arizona BTU Calculator

Arizona climate zones (quick guide)

Arizona is mostly known for its low desert heat, but elevation changes the picture dramatically. The low desert drives peak cooling load; the high country has real winter heating needs closer to a mountain climate than a desert one.

If you’re between zones, pick the hotter (lower number) for low-desert and southern locations, and the cooler (higher number) for elevations above roughly 5,000–6,000 ft.

Evaporative cooling in Arizona’s dry heat

Standard air conditioners remove heat with a refrigerant compressor. An evaporative cooler — commonly called a “swamp cooler” in Arizona — works differently: it pulls hot, dry outside air across water-saturated pads, and the water evaporating into that air absorbs heat and lowers its temperature before blowing it indoors. It uses a fraction of the electricity of compressor-based AC, but it only works well when the incoming air is genuinely dry.

Where evaporative cooling works

Evaporative cooling is most effective when outdoor relative humidity is roughly below 30–40%. Arizona’s low desert spends much of spring, early summer, and fall in that range — conditions that make a swamp cooler a genuine primary or supplemental cooling option for garages, workshops, covered patios, and even whole homes in much of the state, at running costs well below standard AC.

Where it doesn’t: monsoon season

Arizona’s monsoon season — roughly mid-June through September — brings a sharp rise in humidity and dew point. Once relative humidity climbs into the 40–50%+ range, evaporative cooling loses much of its effectiveness because the incoming air is already closer to saturated and can absorb less additional moisture. This is why many Arizona households run a swamp cooler through the dry pre-monsoon heat and switch over to standard AC once monsoon humidity arrives — and why some homes run both, using the evaporative cooler for supplemental or overflow spaces even after switching the main system to AC.

Sizing an evaporative cooler vs an AC

Standard AC and mini splits are sized in BTU/hr, which is what the calculator above estimates. Evaporative coolers are sized differently — in CFM (cubic feet per minute) of airflow, typically using a rough rule of thumb of 2–4 CFM per square foot depending on ceiling height and how many air changes per minute you want. Use your square footage and ceiling height from the calculator above with that ratio as a starting point, then check the specific unit’s rated coverage area before buying.

Arizona HVAC sizing tips

Shade and radiant heat gain

Arizona’s direct desert sun makes shading and radiant barriers unusually effective. If your room gets strong west or south sun, select “Heavy” sun exposure in the calculator, and consider a radiant barrier in the attic, exterior shade structures, or window film to reduce solar gain before oversizing your AC or evaporative cooler.

Attic and duct losses in extreme heat

Arizona attics can reach extreme temperatures in summer, and leaky ducts routed through them can waste a significant share of cooling capacity. If your ducts are older or poorly sealed, choose “Poor” duct condition to avoid under-sizing, or consider a ductless mini split, which eliminates duct loss entirely.

SEER rating for Arizona

Arizona’s long, intense cooling season means higher-SEER equipment tends to pay back quickly — the Southwest region’s federal minimum is SEER2 14.3. Compare specific ratings for your usage with the SEER savings calculator.

Equipment sizing guide for Arizona homes

Arizona sizing is almost entirely about cooling, with a real choice between standard AC and evaporative cooling depending on the season and your local humidity. Use your BTU result to match common equipment categories:

Cooling equipment

Cooling-specific calculators: AC size · Window AC · Portable AC · Mini split

Heating equipment

Heating-specific calculators: Furnace size · Heat pump · Space heater. All equipment by BTU: equipment guide.