Why One Contractor Says 2 Ton and Another Says 3 Ton

You have two quotes for the same home. One recommends a 2-ton system, another recommends 3 tons. This guide explains why sizing recommendations differ and what questions to ask.

What Tonnage Means

In HVAC, tonnage refers to cooling capacity, not equipment weight. One ton equals 12,000 BTU per hour of cooling capacity. A 2-ton system provides 24,000 BTU/hour, while a 3-ton system provides 36,000 BTU/hour—a 50% capacity difference.

This capacity difference affects equipment cost ($500-1,500), operating efficiency, comfort, and equipment longevity.

Different Sizing Methodologies

Manual J Load Calculation

Proper sizing uses Manual J calculations considering square footage, insulation levels, window quality, orientation, climate, and occupancy. This provides accurate capacity requirements.

Result: Precise sizing based on actual home characteristics

Square Footage Rules of Thumb

Some contractors use simple rules like "400-600 square feet per ton." A 1,200 square foot home might be sized at 2 tons (600 sq ft/ton) or 3 tons (400 sq ft/ton) depending on which rule is used.

Result: Approximate sizing that may over or undersize

Matching Existing System

Some contractors match the existing system size without calculating whether it was properly sized originally. If your current 3-ton system was oversized, matching it perpetuates the problem.

Result: May continue existing sizing errors

Different Assumptions About Your Home

Insulation Quality

Contractors may make different assumptions about insulation levels. One may assume code-minimum insulation requiring larger capacity. Another may assume better insulation requiring less capacity.

Impact: Insulation differences can change required capacity by 20-30%

Air Sealing

Homes with significant air leakage require more capacity to compensate for infiltration. Contractors may assume different air leakage rates.

Impact: Air sealing differences can change required capacity by 15-25%

Window Quality

Single-pane, double-pane, and low-E windows have dramatically different heat gain and loss. Contractors may assess window quality differently.

Impact: Window differences can change required capacity by 10-20%

Different Climate Assumptions

Design Temperatures

Sizing calculations use design temperatures—the extreme temperatures the system must handle. Contractors may use different design temperatures for the same location.

Example: Using 95°F vs 100°F design temperature changes required cooling capacity by 10-15%

Heating vs Cooling Priority

Some contractors size for peak cooling load, others for peak heating load. Heat pumps sized for heating may be larger than those sized for cooling in the same climate.

Backup Heat Assumptions

Contractors planning to use significant backup heat may size heat pumps smaller. Those planning minimal backup may size larger.

Oversizing vs Undersizing Philosophy

Conservative Oversizing

Some contractors prefer slightly oversized systems to ensure adequate capacity during extreme weather. They may add 10-20% to calculated capacity.

Rationale: Ensures comfort during peak conditions, provides margin for calculation errors

Downside: Increased equipment cost, more frequent cycling, reduced dehumidification

Precise Sizing

Other contractors size systems to match calculated loads without safety margins, trusting their calculations and modern equipment capabilities.

Rationale: Optimal efficiency, better dehumidification, lower equipment cost

Downside: Less margin for error, may struggle during extreme weather

Intentional Undersizing

Some contractors in mild climates intentionally undersize slightly, knowing backup heat can supplement during rare cold periods.

Rationale: Lower equipment cost, better efficiency during typical conditions

Downside: More backup heat usage during cold weather

Impact of Existing System Performance

If Current System Struggles

Contractors may recommend larger capacity if your current system can't maintain temperature. However, poor performance may result from maintenance issues, duct problems, or insulation rather than undersizing.

If Current System Cycles Frequently

Short cycling suggests oversizing. Contractors recognizing this may recommend smaller capacity. Others may match existing size without investigating cycling causes.

When Size Differences Matter Most

Significant Capacity Gap

One ton difference (12,000 BTU) is significant. A 2-ton vs 3-ton recommendation represents 50% capacity difference that substantially affects performance.

Borderline Sizing

If calculations suggest 2.5 tons, one contractor may round down to 2 tons while another rounds up to 3 tons. Both approaches have merit depending on other factors.

Equipment Availability

Systems come in standard sizes (1.5, 2, 2.5, 3, 3.5, 4 tons). If calculations suggest 2.3 tons, contractors must choose between 2 and 2.5 tons.

Which Size Is Right?

The "right" size depends on:

• Actual load calculation results
• Your home's insulation and air sealing quality
• Your climate and design temperatures
• Your comfort priorities
• Availability and cost of backup heat
• Your budget for equipment and operation

Contractors using Manual J calculations with accurate home assessments typically provide most reliable sizing recommendations.

Red Flags in Sizing Recommendations

• Contractor can't explain how size was determined
• Size based solely on square footage without home assessment
• Automatic matching of existing system without evaluation
• Significant oversizing "to be safe" without justification
• Refusal to provide load calculation documentation
• Dismissal of concerns about sizing differences