AC Sizing Guide & Climate Zone Map: Choose the Right Cooling Power by Region

Leaving Lake Breezes Behind: Why Ohio AC Rules Don’t Work in Texas Heat

Moving day feels exciting—until your first August afternoon in Dallas reminds you that 90 °F in Texas hits harder than 90 °F back in Cleveland. Ohio’s shorter cooling season lets a modest system coast along. In Texas, the sun stays fierce well into October, so your air conditioner runs marathon miles instead of Ohio’s daily sprints. Picture the extra wear on bearings, refrigerant pressures, and your electric bill. Right away, we’re facing a different equation: more run‑time + higher outdoor temps = larger capacity need. You don’t have to guess; we’ll solve it step‑by‑step together.

Meet Your New Climate Zone (and Map)

Ohio sits in a mixed‑humid zone; much of Texas sits in zones with far higher cooling degree days. That shift bumps the recommended BTUs per square foot from roughly 20–25 up to 25–30. Knowing your zone lets you narrow choices before a contractor even visits. Pro tip: Print the map, circle your new ZIP code, and jot down the zone number; every HVAC calculator, rebate form, or energy‑code chart will ask for it. 

Having it handy speeds up design calls, especially if you hop on The Furnace Outlet’s free Design Center chat.

From Frosty Nights to Triple‑Digit Days: How Temperature Swings Change Load

Ohio’s January lows dip into the teens, but summers peak briefly. Texas flips that script: mild winters, then long runs above 95 °F. That wider hot‑season window raises “cooling degree hours,” the metric engineers use to size coils, fans, and compressors. Think of it like filling a bucket: In Texas, the faucet (heat gain) runs longer and harder, so the bucket (your home) needs a bigger drain (your AC). Skip the math headaches—just remember the takeaway: longer, hotter season = more BTUs required.

BTUs, Tons, and Texas Sun: Sizing Basics Made Simple

Here’s the plain‑English formula many pros start with:

• 20–25 BTU per ft² for moderate climates (Ohio).

• 25–30 BTU per ft² for hot zones (Texas).

For a 2,000 ft² home:

1. Ohio: 2,000 × 22 = ≈44,000 BTU → 3.5‑ton unit.

2. Texas: 2,000 × 28 = ≈56,000 BTU → 4.5‑ton unit.

That’s a full ton jump! Still, these are ballpark numbers. Shading, attic insulation, and window orientation all tweak the final size. Never order equipment without a Manual J—but this quick math tells you to expect a bump.

Real‑World Case Study: A 2,000‑Square‑Foot Home Goes South

Last summer, we helped a family moving from Columbus to Houston. Their 3‑ton Ohio unit struggled: indoor temps drifted to 78 °F, humidity stayed above 60 %, and the compressor ran non‑stop. After a Manual J load calc, the fix was a 4‑ton R‑32 condenser paired with a matching coil. We also added radiant‑barrier decking and Solar‑Screen window film. Net result: 18 % lower runtime and a home that held 74 °F in a 96 °F heatwave. 

Curious about equipment? Browse our R‑32 residential condensers to see the models they chose.

Avoiding the Oversize Trap: The Manual J Safety Net

Bigger isn’t always better. An oversized unit short‑cycles—it blasts cold air fast, then shuts off before pulling humidity out. You feel clammy, and parts wear out prematurely. That’s why every reputable pro runs a Manual J: a room‑by‑room heat‑gain calculation considering walls, windows, occupancy, and even kitchen appliances. Ask for the printout; it’s your proof the system fits. 

Insulation, Shade, and Smart Upgrades That Shrink Your Load

Before you sign off on a larger compressor, knock down your heat gain first:

• Add R‑38 attic insulation (often a weekend DIY under $1 / ft²).

• Plant fast‑growing shade trees or install patio covers on the west side.

• Upgrade to low‑e windows or apply reflective film.

• Seal duct leaks with mastic—Texas attics hit 130 °F, so every leak hurts.

These tweaks can shave 0.5 ton off your load—money you can re‑allocate to a higher‑efficiency SEER2 unit or smart thermostat.

Picking the Right Equipment: Condenser, Coil, or Packaged Unit?

Texas homes vary: slab foundations in Houston, attics in Austin, crawl spaces in older Hill Country cottages. Choose gear that fits the structure:

• Split systems: Most common; match a new R‑32 condenser with a properly sized coil.

• Packaged units: Great for rooftops or tight yards, see our residential packaged systems.
  
  

• Ductless mini‑splits: Perfect for garages turned game rooms; explore DIY kits.

Swapping refrigerant lines? Flush with nitrogen and pull a deep vacuum,skipping this step wrecks efficiency and voids warranties.

Pro Tips From the Field: What Installers See Every July

After 20+ Texan summers, we’ve logged the same top issues:

1. Clogged condensate lines cause ceiling leaks—add a float switch.

2. Undersized return ducts starve airflow—verify sizing during the load calc.

3. Outdoor units buried by hedges lose 15 % capacity—keep 24 in. clearance.

4. Dirty attic filters in April spike runtimes in June—set phone reminders.

A small investment in preventative care beats emergency calls when every HVAC truck in town is booked.

Must‑Have Features for Humid Gulf Summers

Humidity control matters as much as temperature. Look for:

• Variable‑speed blowers: Longer, lower‑speed cycles wring out moisture.

• TXV (thermal expansion valves) for precise refrigerant flow.

• High‑SEER2 ratings—lower watts per BTU means smaller bills during long seasons.

Pair these with a whole‑home dehumidifier or smart thermostat that includes humidistat logic

Budgeting and Buying: When to Replace, When to Retrofit

Replacing a still‑running 10‑year‑old Ohio system feels painful, but freight‑shipping a too‑small unit south is worse. Use this rule: If the load calc shows more than a 0.5‑ton shortfall or your current SEER is under 13, replace. 

Financing? Many customers bundle equipment and labor through their utility’s low‑interest loans—ask your installer. 

Simple Checklist Before You Sign the Contract

1. Print your climate zone map and highlight your ZIP.

2. Schedule a Manual J with a local Texas pro.

3. Audit insulation and ductwork; fix leaks first.

4. Compare equipment options—split vs. packaged vs. ductless.

5. Get at least two bids and verify licensing.

Follow this list and you’ll land in your new Texas home cool, dry, and confident you chose the right system—without paying for more BTUs than you truly need.

Ready to size your new Texas system the right way? Start with our free Design Center at The Furnace Outlet, no guesswork, just expert help.