Basics
What Is a Manual J Load Calculation?
Stop guessing with your comfort. Discover why Manual J is the gold standard for residential HVAC sizing and how it saves you money.
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Tutorial
How to Calculate HVAC Load (Step-by-Step)
A complete DIY guide to understanding the math behind residential heating and cooling sizing equations.
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Sizing
How Many BTUs Do I Need?
Square footage is just the starting point. Discover the real math behind correct system sizing.
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Equipment
HVAC Tonnage Explained
It's not about how much the unit weighs. Here is the simple math to convert Manual J BTUs into Tons.
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Critical Warning
Why Oversizing Your AC Is a Mistake
"Bigger is Better" is the most dangerous myth in HVAC. Learn about short cycling and mold risks.
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Myths Busted
Manual J vs Rule-of-Thumb
Why estimating based on square footage fails for modern homes. Compare the numbers.
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Efficiency
How Insulation Affects HVAC Load
The secret to a smaller AC isn't a better unit—it's R-Value. See the math.
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Efficiency
How Windows Affect HVAC Load
Windows are thermal holes. Understand U-Factor, SHGC, and Orientation.
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Efficiency
Air Leakage, ACH, and Infiltration
The "Invisible Load." Why drafty homes cost 40% more to cool.
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Professional Advice
When You Should Hire a Pro for a Manual J
Online calculators are great for estimates, but permits require a stamp. Learn about certified reports.
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Example
Manual J Example: 2,000 Sq Ft Home
See the math for a real-world home. 2,000 sq ft doesn't always equal 4 tons.
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Case Study
Old Home vs New Construction
Why a 1950s ranch needs double the AC of a 2024 smart home.
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Modern Design
High-Window Homes & Cooling Impact
Glass walls look great but kill efficiency. How to handle high-solar-gain homes.
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Climate
Hot vs Cold Climate Sizing
Compare the loads of a house in Phoenix vs Minneapolis.
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Checklist
HVAC Replacement Checklist
Don't sign a contract without it. Ensure you aren't buying an oversized unit.
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Code Requirements
Do You Need a New Manual J?
Replacing your equipment? Here's why re-using old sizing is often illegal and expensive.
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How-To
Prepare Your Home for Manual J
Get precise results by gathering these 5 things before the auditor arrives.
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Multi-Family
Manual J for Apartments
Shared walls mean lower loads. Why condo sizing is completely different.
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Cooling vs Heating
Heat Pump vs Central AC Sizing
Why you can't just swap them out one-for-one. The math is completely different.
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Equipment Selection
Furnace vs Heat Pump Sizing
Gas furnaces are often 100% oversized. Do that with a heat pump and you'll regret it.
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HVAC Theory
Manual J vs S vs D: Explained
Load vs Equipment vs Ducts. Why you need all three for a proper design.
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Comfort Science
How Humidity Affects Load
Sensible vs. Latent Heat. Why you can't install a Florida AC in Arizona.
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Efficiency
Air Sealing vs HVAC Size
Stop trying to heat the whole neighborhood. Caulk is cheaper than tonnage.
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The Hidden Factor
Ducts in the Attic?
Why moving or burying ducts is the single biggest upgrade you can make.
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Tools
Are Online Manual J's Accurate?
Is a free calculator enough? Comparing "Rules of Thumb" vs Pro Software.
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Pricing
How Much Does Manual J Cost?
From free quotes to $1,500 engineering audits. What you are actually paying for.
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Troubleshooting
Signs of Improper Sizing
Short cycling? High humidity? Why your "new" AC might be destroying itself.
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Education
Ignorance is Expensive: HVAC Myths
"Bigger is Better." "Like for like." We debunk the top 5 lies contractors tell.
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Glossary
HVAC Terms Explained
BTU, SEER, SHGC, ACH. Don't let the jargon confuse you. We explain it simply.
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Law & Code
Is Manual J Required by Law?
In most states: YES. What you need to know about code compliance.
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