HVAC365 Sizing Calculator
Energy Efficiency Matters
Actionable guidance to reduce load and operating cost—tailored to your selections.
Weather & Region
Pick your climate zone to calibrate per-ft² loads.
Envelope & Insulation
Upgrade attic insulation and air sealing to reduce runtime 10–20%.
Usage & Controls
Smart thermostats & schedules curb waste during peak hours.
Estimated Cooling Cost
Enter values and click Estimate Cost. We’ll use your calculated cooling BTU.
Maintenance & Care
Simple routines to keep your system efficient, quiet, and reliable all year.
Installation Requirements
Electrical & Location
- Dedicated breaker; correct wire gauge
- Outdoor pad, 12–24" clearance around coil
- Service disconnect within line-of-sight
Refrigerant & Airflow
- Line set sized per OEM; nitrogen purge & deep vacuum
- 350–400 CFM/ton; verify external static pressure
- Proper condensate trap and float safety switch
Cold-Climate Notes
- Balance point & auxiliary heat sizing documented
- Defrost control verified; condensate management
- Consider dual-fuel in very cold regions
Electrical & Airflow
- Strip heat breaker sizing; wire gauge per kW
- Airflow checked for both heating & cooling modes
- Thermostat supports staging & lockouts
Furnace + AC
- Combustion air & venting per code; gas leak test
- Proper furnace orientation & condensate routing
- Match AHRI with outdoor AC for SEER2 compliance
Duct & Controls
- CFM/ton verified; filter sizing for low static
- Thermostat wiring (C wire), stage configuration
- CO safety confirmed; heat rise within spec
Single-Zone
- Indoor head sized to room load; line set limits
- Wall bracket/pad; condensate drain routing
- Remote placement & Wi-Fi pairing
Multi-Zone
- Outdoor capacity ≥ sum (with diversity)
- Branch box/headers; line set sizing & maximums
- Per-zone control; condensate for each head
HVAC Sizing: Frequently Asked Questions
How accurate is this calculator?
It’s an informed estimate using region factors plus adjustments. For permit-grade design, hire a pro to perform ACCA Manual J/S/D.
Should I oversize “just in case”?
No—oversizing short-cycles and hurts humidity control. Right-size and consider variable-speed.
What if I’m adding insulation or windows?
Envelope upgrades can cut loads 10–25%. Re-run after improvements; you may step down a size.
When should I split into two systems?
Around/above 60,000 BTU/h cooling, two systems generally win on comfort and humidity control.
How do ceilings affect the load?
Higher ceilings increase volume and cooling load. We scale results when ceiling height differs from 8 ft.
Do extra people in the home change sizing?
Yes—each person beyond two adds sensible + latent load. We add ~600 BTU/h per additional person.
What about sun exposure and shading?
High exposure boosts heat gain; we add ~10% for “High” sun and reduce ~5% for “Low.”
Can this replace a Manual J?
No—this is a fast estimator for shopping guidance. Use a pro Manual J for design and permits.
Need additional support?
Questions about sizing, duct design, or equipment matching? We’ll guide you.
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