About ACCalculator.com
Free HVAC sizing tools and expert guidance for homeowners, contractors, and energy auditors.
Our Mission
ACCalculator.com exists to solve a simple but costly problem: most air conditioners are incorrectly sized. Industry studies show that 60-70% of residential HVAC systems are oversized by 25% or more, leading to:
- 20-40% higher energy bills
- Poor humidity control and discomfort
- Frequent cycling that shortens equipment life
- Thousands of dollars in wasted equipment costs
We created free, accurate BTU calculators and educational resources based on ACCA Manual J principles to help homeowners and contractors size HVAC equipment correctly from the start.
What We Offer
Free BTU Calculator
Our flagship tool calculates cooling loads using Manual J-inspired methodology. Unlike simplistic "square footage only" calculators, we account for:
- Ceiling height and room volume
- Insulation quality (R-values)
- Window orientation and solar exposure
- Climate zone and design temperatures
- Occupancy and internal heat gains
Specialized Tools
- Multi-Room BTU Planner - Size mini-split zones and whole-house systems
- BTU to Tonnage Converter - Translate between rating systems instantly
- Climate Load Adjuster - Fine-tune for extreme temperatures and humidity
Educational Guides
13+ in-depth guides covering:
- Manual J load calculations simplified
- Climate zone impacts on AC sizing
- Insulation and air sealing effects
- Contractor bid evaluation
- Heat pump vs central AC comparisons
Expert Blog
Evidence-based articles on HVAC efficiency, sizing mistakes, new technologies (SEER2), and cost-saving strategies.
Who We Serve
Homeowners
Get accurate BTU requirements before requesting contractor quotes. Verify proposals, avoid oversizing, and make informed equipment decisions with confidence.
HVAC Contractors
Use our tools for quick load estimates during site visits. Share calculator results with customers to explain sizing recommendations and differentiate your service with data-driven proposals.
Energy Auditors
Supplement Manual J software with fast checks. Identify obviously oversized systems and quantify potential savings from right-sizing during retrofits.
Our Approach
Accuracy First
We use ACCA Manual J methodology adapted for homeowner accessibility. Our calculators include envelope multipliers, internal gains, ventilation, and climate factors—not just square footage guesses.
Transparency Always
Every calculation shows its work. We explain why a result is what it is, cite industry standards (ASHRAE, ACCA), and link to supporting guides. No black boxes, no hidden assumptions.
Free Forever
No accounts, no credit cards, no gated content. We believe accurate HVAC sizing information should be freely accessible to everyone.
Why Trust Us?
Manual J Alignment
Our calculators follow ACCA Manual J principles—the industry standard for residential load calculations. We incorporate the same envelope factors, internal gains, and climate adjustments that professional HVAC design software uses.
Conservative Estimates
When uncertain, we err on the side of slightly oversizing (10-15% buffer) rather than undersizing. However, we explicitly warn against the 25-50% oversizing common in the industry.
Continuous Improvement
We update our tools and guides regularly based on:
- User feedback and questions
- New ASHRAE climate data
- Equipment efficiency standards (SEER2, HSPF2)
- Emerging HVAC technologies
What We're NOT
Not a Substitute for Manual J
Our calculators provide accurate estimates for typical homes, but they don't replace a full Manual J calculation performed by licensed HVAC professionals. Use our tools for initial sizing and verification, then hire qualified contractors for final design and installation.
Not Equipment Sellers
We don't sell HVAC equipment, installation services, or lead generation. We have no financial incentive to recommend oversized (more expensive) systems. Our only goal is accurate information.
Not "One Size Fits All"
Every home is unique. Our calculators handle the most common variables, but unusual construction (strawbale walls, earth-bermed homes, extensive skylights) requires professional engineering.
Our Commitment
We Promise To:
- ✓ Keep all tools free forever
- ✓ Never sell your data or email
- ✓ Update content with latest standards
- ✓ Respond to questions and feedback
- ✓ Cite sources and show methodology
- ✓ Admit limitations honestly
Get Involved
Feedback Welcome
Found an error? Have a suggestion? Want us to cover a specific topic? Contact us—we read and respond to every message.
Share Our Tools
If ACCalculator.com helped you avoid an oversized system or save money, please share with friends, family, or online communities. Word-of-mouth is our only "marketing."
Professional Use
HVAC contractors and energy auditors: feel free to use our calculators with clients. We only ask that you clearly explain the difference between our quick estimates and full Manual J calculations.
The Bottom Line
Air conditioning is expensive—both the equipment and the electricity to run it. A correctly sized system costs less upfront, runs more efficiently, lasts longer, and keeps you more comfortable. Our mission is to give you the knowledge and tools to get sizing right.
Whether you're a homeowner researching your first AC purchase, a contractor looking for quick load checks, or just someone curious about HVAC—welcome. Let's make the world a little cooler (but not too cool).