What size mini split do I need? A real Texas sizing guide
Getting your mini split size right in Texas heat
Let's be honest - sizing a mini split for Texas isn't like sizing one for Ohio or Michigan. When it's 105°F in Dallas and your electric bill looks like a mortgage payment, you need to get this right the first time.
I've been selling and installing Comfort Temps mini splits across Texas for years, and I can tell you that those generic sizing calculators you find online? They don't work here. They weren't made for Houston's swamp-like humidity or Austin's blazing sun beating down on your roof all day.
This guide will walk you through exactly how to size your mini split for Texas conditions. No fluff, just the real numbers and adjustments we use every day.
The basics: BTUs and tonnage explained
What's a BTU actually mean?
A BTU (British Thermal Unit) tells you how much heat a system can move in an hour. When we say a mini split is 12,000 BTU, it means it can pull 12,000 BTUs of heat out of your room every hour. Simple as that.
The tonnage thing
Old-timers still talk in tons - one ton equals 12,000 BTUs. So a 12,000 BTU unit is a "1-ton" system. It's leftover from the ice house days, but HVAC guys still use it. A 1-ton mini split typically handles 500-600 square feet in normal conditions. But Texas isn't normal conditions, which we'll get to.
Base sizing chart - your starting point
Here's the standard chart everyone uses. Remember, this is just where you start - we'll adjust for Texas reality in a minute.
| Room Size (Sq. Ft.) | BTU Needed | Where You'd Use It | Real-World Notes |
|---|---|---|---|
| 150-400 | 9,000 | Small bedroom, office | Add more for kitchens |
| 400-550 | 12,000 | Master bedroom, den | Check ceiling height |
| 550-1,000 | 18,000 | Living room, large master | Texas sun adds load |
| 1,000-1,250 | 24,000 | Open concept area | Great for open plans |
| 1,250-1,350 | 30,000 | Bigger spaces | Insulation matters here |
| 1,350-1,500 | 36,000 | Large areas | Consider your usage |
| 1,500-2,000 | 48,000 | Really big spaces | May need multiple units |
| 2,000+ | 60,000 | Huge rooms, commercial | Call us for this |
The Texas reality check - city by city
Now here's where those online calculators fail you. Texas isn't just hot - it's different kinds of hot depending on where you are. And that changes everything about sizing.
Houston: the humidity monster (+20% to your BTU)
Houston isn't just hot, it's wet hot. That humidity makes everything harder. Your mini split isn't just cooling air - it's wringing water out of it like a sponge. A system that's too small won't run long enough to actually dry out your air, so you end up with that sticky, swampy feeling even with the AC blasting.
Real example: That 500 sq ft bedroom that charts say needs 12,000 BTU? In Houston, multiply by 1.20. That's 14,400 BTU, which means you're buying an 18,000 BTU unit. Trust me on this - I've replaced too many undersized units in Houston to count.
Why it matters: If your system doesn't dehumidify properly, you get mold. Period. Houston humidity doesn't play around.
Dallas/Fort Worth: the furnace (+15% to your BTU)
Dallas heat is different - it's dry and brutal. When it's 105°F with low humidity, your body can't cool itself through sweat evaporation. The sun here is relentless, especially on west-facing rooms after 3 PM. Plus, Dallas gets those weird temperature swings where it's 95°F one day and 65°F the next.
Real example: Same 500 sq ft room needs 12,000 BTU base × 1.15 = 13,800 BTU. Round up to 18,000 BTU. Yeah, it's the same as Houston but for different reasons.
Why it matters: That dry heat penetrates everything. Your walls, your roof, your windows - they all radiate heat into your space long after the sun goes down.
Austin: the tech city variable (standard or +10%)
Austin's interesting because half the homes here are brand new with great insulation, and half are older homes that leak air like sieves. The newer builds with good windows can often use standard sizing. But if you've got those big architectural windows facing south? Add 10% minimum.
Real example: Well-insulated 500 sq ft room might actually work with 12,000 BTU. Same room with floor-to-ceiling windows? 13,200 BTU minimum, probably safer with 18,000.
Why it matters: Austin's educated buyers often over-research and under-buy. Don't be that person sweating in August because you thought you'd save $200 on a smaller unit.
San Antonio: the marathon summer (+15%)
San Antonio's problem isn't peak heat - it's duration. Summer here starts in April and doesn't quit until November. Your system runs more hours per year than anywhere else in Texas. That means it needs headroom to stay efficient over the long haul.
Real example: 500 sq ft × 12,000 BTU × 1.15 = 13,800 BTU. Get the 18,000 BTU unit and thank yourself in October when it's still 95°F.
Why it matters: A system running at 100% capacity for six months straight will die young. Size it right and it'll run at 70-80% capacity and last twice as long.
Your house matters too - adjustment factors
Beyond just your city, here's what else impacts sizing:
| What You're Dealing With | How Much It Matters | What to Add |
|---|---|---|
| Ceiling over 8 feet | Every foot counts | +10% per 2 feet |
| Crappy insulation | Heat pours in/out | +15-20% |
| Great insulation | Holds temp well | No adjustment |
| Big south windows | Solar oven effect | +10-15% |
| Room under attic | Heat from above | +10-15% |
| Kitchen | Oven, stove, fridge | +10-20% |
| Typical Texas summer | Over 90°F daily | +15% minimum |
| Garage conversion | Basically outside | +20-25% |
How to actually calculate your size
Let me walk you through this like I would if you called me:
Measure the damn room
Length × width = square feet. Don't guess. Measure it. If it's an odd shape, break it into rectangles and add them up.
Get your base number
Look at the chart. Find your square footage. That's your starting point.
Apply the Texas tax
Houston? Multiply by 1.20. Dallas? Multiply by 1.15. Austin? Good insulation = 1.0, bad or big windows = 1.10. San Antonio? Multiply by 1.15. Somewhere else? Use Dallas numbers.
Add your house's personality
Got vaulted ceilings? Add percentage. Garage? Add percentage. Basically outside? Add more. Stack these adjustments - they're cumulative.
Buy the next size up
Mini splits come in these sizes: 9,000, 12,000, 18,000, 24,000, 30,000, 36,000, 48,000, 60,000. Whatever number you calculated, go up to the next size. Never down. This isn't the place to save fifty bucks.
Real customer examples from Texas
Let me show you some actual jobs we've done:
Houston master suite nightmare
Customer had a 500 sq ft master bedroom. Previous company installed a 12,000 BTU unit "by the book." Room never got below 78°F and felt like a swamp. Here's what they actually needed:
- 500 sq ft = 12,000 base
- Houston humidity = × 1.20 = 14,400
- 10-foot ceilings = × 1.10 = 15,840
- Installed: 18,000 BTU Comfort Temps
- Result: 72°F and dry as you want
Dallas home office disaster
Guy working from home, 240 sq ft office, massive window facing west. Afternoon sun made it unusable even with a portable AC running.
- 240 sq ft = 9,000 base
- Dallas heat = × 1.15 = 10,350
- Huge west window = × 1.15 = 11,903
- Installed: 12,000 BTU Comfort Temps
- Result: Comfortable even at 4 PM in August
Austin open-concept challenge
Modern home, open kitchen/living/dining, 1,050 sq ft with 14-foot ceilings. Architect said "standard sizing is fine." Architect was wrong.
- 1,050 sq ft = 18,000 base
- Austin (good insulation) = × 1.0 = 18,000
- 14-foot ceilings = × 1.25 = 22,500
- Installed: 24,000 BTU Comfort Temps
- Result: Whole space stays perfectly comfortable
San Antonio garage conversion gone right
Customer converted 360 sq ft garage to man cave. First quote was for 9,000 BTU. We knew better.
- 360 sq ft = 9,000 base
- San Antonio long summer = × 1.15 = 10,350
- Minimal insulation = × 1.25 = 12,938
- Installed: 18,000 BTU Comfort Temps
- Result: Cool cave even with garage door cracked for ventilation
Why getting size wrong costs you big
When you go too big
People think bigger is always better. Wrong. An oversized unit is like driving in stop-and-go traffic - inefficient and hard on the equipment. Here's what happens:
The system cools the room super fast then shuts off. Sounds good? It's not. It never runs long enough to pull moisture out of the air. In Texas humidity, that means you're cold but clammy. Plus, all that starting and stopping kills the compressor early and jacks up your electric bill. You'll feel the temperature swing up and down all day long.
When you go too small
This is worse. The unit runs 24/7 trying to keep up and never quite makes it. Come 3 PM when the sun's cooking your house, you're sweating despite the AC running full blast. Your electric meter's spinning like a slot machine, and the poor compressor never gets a break. I've seen units dead in two years from this. Two years!
Getting it just right
A properly sized mini split runs in cycles - on for maybe 20-30 minutes, off for 10-15. It pulls the temperature down, removes the humidity, then takes a breather. Your house stays comfortable, your bills stay reasonable, and the system lasts 15+ years easy.
Working with multiple rooms? Here's what to know
If you're thinking about cooling multiple rooms, each room needs its own properly sized unit. Don't try to cool two bedrooms with one oversized unit - it doesn't work that way. The room with the unit will freeze while the other room stays hot.
Each space needs individual attention:
- Size each room separately using all the calculations above
- Consider how you use each space (bedroom vs living room vs office)
- Remember that doors being open or closed changes everything
For larger projects covering multiple rooms or whole homes, it's worth getting professional guidance to ensure each space gets exactly what it needs.
Why Comfort Temps works in Texas
Look, we sell Comfort Temps exclusively because they actually work here. Not all mini splits are equal when it's 105°F outside. Here's what matters:
- They maintain efficiency in extreme heat. Most units' SEER ratings tank when it gets over 95°F. Comfort Temps keeps trucking at 20-30 SEER even at 105°F.
- The dehumidification actually works. Special dry mode that Houston customers love. Pulls moisture without overcooling.
- They're quiet as a church mouse. 20-40 dB is quieter than your refrigerator. You forget they're running.
- Built for the long haul. Corrosion-resistant coils handle our humidity. Variable-speed compressors that don't burn out from our long cooling season.
- Installation flexibility. Multiple indoor unit styles mean we can put them anywhere without tearing up your house.
When you should call a pro
This guide covers 90% of situations, but sometimes you need professional load calculations:
- Open floor plans with cathedral ceilings
- Houses with basically no insulation
- Multiple rooms needing individual units
- Any commercial application
- Historic homes with weird construction
- If you're making a significant investment
We do free consultations at Mini Split AC Texas because we'd rather size it right the first time than replace it later.
Ready to pull the trigger?
Alright, now you know your BTU number. You've adjusted for Texas heat. You've accounted for your house's quirks. Time to actually buy something.
Mini Split AC Texas has been doing this for years. We know every Comfort Temps model, what works where, and what doesn't. We're based here, we live here, we sweat here just like you.
Whether you need a simple 9,000 BTU for a bedroom or something bigger for your living space, we'll make sure you get exactly what you need. No overselling, no undersizing, just right.
Give us a call or check out our Comfort Temps lineup online. Summer's coming whether you're ready or not.
Common questions we get
Chart says 500-600 sq ft. Reality in Texas? 400-500 sq ft if you want it actually comfortable. Less if it's Houston humid or Dallas afternoon sun.
Always up. Always. Saving $200 on a smaller unit costs you thousands in discomfort and early replacement.
Yeah, all Comfort Temps units do heating. Honestly, they're overkill for Texas winters, but nice to have when we get that random freeze.
Garages need 20-25% more BTU than indoor spaces. No insulation, concrete slab, metal door - it's basically outside. Size accordingly.
If it runs constantly and never quite cools, it's too small. If it cycles on and off every 5-10 minutes, it's too big. If you're comfortable and your bills are reasonable, someone sized it right.
100% yes. Houston humidity and Dallas dry heat are completely different animals. What works in Austin might fail miserably in Houston. This isn't marketing - it's physics.
Each room needs its own properly sized unit. One big unit won't cool multiple rooms evenly - you'll get hot and cold spots. Size each space individually for best results.
Bad idea. An oversized unit for your current space will short-cycle, waste energy, and won't dehumidify properly. Buy what you need now, add more later when you actually need it.
Bottom line from Mini Split AC Texas
Listen, we've been doing this long enough to know what works and what doesn't. The formulas in this guide? They're based on thousands of actual installations across Texas. Not theory - real houses, real heat, real results.
Want to make sure you get it right? Give us a call. Free consultation, straight answers, no sales BS. We'll size it right the first time.
Because when it's 105°F outside, the last thing you want is to wonder if you bought the right size AC.
Mini Split AC Texas - Serving Houston, Dallas, Austin, San Antonio, and every hot spot in between.