HVAC System Sizing Calculator Find the Right Cooling & Heating Capacity
Estimate the right cooling (BTU/hr & tons) and heating (BTU/hr) for your home. Use Simple for a quick ballpark, or Advanced for a more precise recommendation.
System Sizing Calculator
This tool gives realistic estimates. For design-grade results, ask for a Manual J/D/S.
Recommended Cooling Capacity
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Recommended Heating Capacity
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Rounded to common furnace sizes.
Duct Loss Applied
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Occupancy & Internal Gains
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Ceiling Height Factor
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Safety Margin
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Method & assumptions
- Baselines (cooling/heating BTU per sq ft) based on climate band (CDD).
- Multipliers: insulation/age, window quality, window area, solar exposure, infiltration, ceiling height.
- Internal gains: ~600 BTU/hr per person + 3.412 × watts from appliances/lighting.
- Duct losses: scaled by 1/(1 − loss%).
- Safety margin: +% to cover extremes & unknowns.
- Use this as a planning estimate; confirm final size with a Manual J/D/S.
Why Proper Sizing Matters
Comfort & efficiency
Undersized systems struggle on extreme days; oversized systems short-cycle, waste energy, and leave rooms uneven.
Lower bills, longer life
Right-sized equipment runs steadier, lasts longer, and keeps utility costs manageable.
FAQ
What does “tonnage” mean?
Tonnage is cooling capacity. 1 ton = 12,000 BTU/hr.
How many BTUs per square foot?
Rules of thumb vary (~15–30 BTU/sq ft) by climate and build quality. Advanced mode refines this with your inputs.
What is a Manual J?
The industry’s detailed load calculation method. Our results guide planning; your installer should confirm with Manual J/D/S.