How to Size an AC in Pearland.

If your contractor walked your house, asked the square footage, multiplied by some number, and quoted you a 4-ton system in fifteen minutes, they didn't size it. They guessed. And in Pearland's climate, the wrong guess costs you for the next 15 years.

This is the long version of the conversation we have at every replacement quote. Read it before you sign anything.

Why "rules of thumb" don't work in Pearland

The classic rule is "1 ton per 500-600 square feet." That number was published in trade journals decades ago, before SEER ratings climbed past 13, before R-410A, before modern double-pane windows, and before anyone in the industry took humidity seriously. Houston's climate doesn't behave like the climates that rule was written for.

Pearland adds three twists:

• Latent load is huge. The job of an AC isn't just to drop air temperature, it's to remove water from the air. Pearland summers run 70-80% relative humidity outdoors. A correctly-sized system removes 20-30 pints of water per day from a typical house. An oversized system runs short cycles, cools the air without ever dehumidifying it, and leaves you with cold, damp, sticky rooms.
• Solar load varies wildly. Two houses with identical square footage can have 25%+ different cooling loads based on glazing orientation, shade trees, and roof color. The west-facing back wall on a sunny July afternoon is the design hour for most of our jobs, not the square footage.
• Duct leakage is the silent killer. The average Houston attic duct system leaks 20-30% of its air to the attic. If your contractor sizes the equipment to the room load and ignores duct losses, you'll be 25% under-equipped from day one.

What Manual J actually does

Manual J is the ACCA's room-by-room load calculation. It's not a shortcut, it's a real engineering exercise. It takes:

• The square footage of every room and every wall
• Window size, type, and orientation for each opening
• Insulation R-values in walls, ceilings, and floors
• Duct location (attic vs. conditioned space) and leakage
• Infiltration (how leaky the building envelope is)
• Internal gains (people, appliances, lighting)
• The Pearland 1% design conditions: 96°F outdoor / 78°F indoor / 75°F dewpoint

And it spits out two numbers per room: sensible load (how much heat to remove) and latent load (how much moisture to remove). Then we add it all up and pick equipment that matches both.

The "round up to be safe" trap

Half of contractors run Manual J and then round up "for safety." This is wrong. AC equipment runs longest at full design conditions, the hottest, most humid afternoons of the year. The other 95% of the time, it should be running at part load. If you oversize, you guarantee short cycling for almost every hour of the cooling season, which means:

• The system never reaches steady-state operation, where it does its best dehumidification
• The compressor starts and stops 4-5x more often than it should, the #1 cause of premature compressor failure
• Your blower runs in too-short bursts to evenly distribute air, leading to hot/cold rooms
• Energy use is higher per BTU delivered (start-up draws are inefficient)

The right answer is to size to the calculated load and let the system run longer at part load. Variable-speed equipment makes this even better, but even single-stage equipment performs much better correctly-sized than oversized.

Common Pearland sizing mistakes

Here are the most frequent errors we see when we audit other companies' work:

1. Replacing like-for-like without re-sizing. The 4-ton you replaced was probably already wrong. Replacing it with another 4-ton just locks in the mistake for 15 more years.
2. Not separating zones. A two-story home with a single thermostat and a single piece of equipment is almost always undersized upstairs and oversized downstairs. We zone or we add a dedicated upstairs system.
3. Ignoring building improvements. If you've added attic insulation, replaced windows, or added solar screens since the last system was installed, the load has dropped. The new system should be smaller.
4. Treating the bonus room as "free square footage." A garage conversion, sunroom, or attic bonus room has 3-5x the load per square foot of a standard room. Lump it into the same number and you'll never cool it.

"We had a customer in Shadow Creek Ranch who'd been told by three contractors she needed a 5-ton system. We ran Manual J and it came in at 3.5 tons. She was nervous, but we installed the smaller system and her bills dropped 30% in the first month, and her upstairs bedroom finally stopped being humid. The other companies were guessing."

How to spot a real load calc

Ask your contractor for the Manual J report before you sign. A real one is 4-8 pages, has every room broken out, shows window sizes and orientations, and lists the design conditions. If they hand you a one-page summary or say "we did it in our heads," they didn't do it.

What we do on every quote

We run a full Manual J on every replacement and new install. No exceptions. We measure rooms, count windows, and inspect ductwork for leakage. The whole process takes us about 90 minutes on-site, plus 30 minutes back at the office in the software. You get the report with your quote, in writing, with the math.

Then we present three options: a single-stage at the calculated load, a two-stage that handles humidity better, and a variable-speed inverter system that's the most comfortable but the priciest. You pick what fits your budget and comfort priorities.

Bottom line

The right size is the calculated size. Not your old system's size. Not "one ton per 500 square feet." Not "I always upsize for safety." Manual J, every time, on paper, in your hands.

Getting a replacement quote? Ask us for the Manual J. We'll do it free with any replacement bid, and we'll show you the math. 281-992-7866 or book a quote.