A/C Tonnage calculator

Is Your New Home’s A/C Underperforming?

Why "New" Doesn’t Always Mean "Correct"

When you move into a brand-new home, you expect everything to be perfect. However, one of the most common issues we find during our inspections is undersized air conditioning units. In an effort to keep construction costs down or due to "rule-of-thumb" estimations rather than precise engineering, builders sometimes install units that lack the cooling capacity (tonnage) required for the home’s actual heat load.

The Hidden Risks of an Undersized Unit

An A/C unit that is too small for your square footage doesn't just mean a warmer house; it leads to a cascade of expensive problems:

• Continuous Running: The system works 24/7 without ever reaching the thermostat’s set temperature, leading to massive energy bills.

• Poor Humidity Control: A/C units act as dehumidifiers. If the unit is constantly "chasing" the temperature, it often fails to properly remove moisture, leaving your home feeling "sticky."

• Premature Failure: Like a small engine trying to pull a heavy trailer, an undersized A/C will wear out its compressor and motor years earlier than a properly sized unit.

• Uneven Cooling: You’ll likely notice "hot spots" in rooms with large windows or high ceilings where the weak airflow simply can't keep up.

How to Check Your Tonnage

"Tonnage" refers to the cooling capacity of your unit. One ton of air conditioning can remove 12,000 BTUs (British Thermal Units) of heat per hour.

Quick Check: Look at the data plate on your outdoor condenser. Look for the model number. You will usually see a two-digit number divisible by 6 or 12 (e.g., 18, 24, 30, 36, 42, 48, 60).

• 24 = 2 Tons

• 36 = 3 Tons

• 48 = 4 Tons

Calculate Your Recommended Tonnage

Use our calculator below to see if your builder installed the right-sized unit for your floor plan.

The Sheldon’s Inspection Calculator

(Note: This provides a standard estimate. A full "Manual J" calculation by an HVAC professional is the gold standard for exact precision.)

Don't Guess—Get a Professional Inspection

If the calculator results show a significantly higher tonnage than what is currently sitting outside your home, you may have a claim with your builder's warranty.

This draft is designed to be professional yet firm, using the technical data from your inspection to hold the builder accountable.

Builder Warranty Request: HVAC Capacity Discrepancy

To: [Builder Name / Warranty Department] From: [Your Name] Address: [Your New Home Address] Date: [Date] Subject: Formal Request for HVAC System Review – Improper Unit Sizing

Dear [Warranty Manager Name or Builder Name],

I am writing to formally request a review and correction of the HVAC system installed at the address listed above. Following a professional evaluation by Sheldon’s Home Inspections, there is significant evidence that the current air conditioning unit is undersized for the total cooling load of the home.

Current Installation Details:

• Unit Size: [Example: 3.0 Tons]

• Home Square Footage: [Example: 2,400 sq. ft.]

The Issue: Based on the square footage, window count, and exterior door exposure, a standard calculation (and our preliminary tonnage assessment) indicates that the home requires a minimum of [Insert Recommended Tonnage from Calculator] tons to maintain a consistent indoor temperature and proper humidity levels.

Currently, the system is experiencing the following symptoms of an undersized unit:

• Inability to reach the thermostat set point during peak daylight hours.

• Excessive run times (short-cycling or continuous operation), leading to inflated energy costs.

• High indoor humidity levels, which pose a long-term risk for organic growth and indoor air quality issues.

Proposed Resolution: Under the terms of the home warranty regarding mechanical systems and habitability, I am requesting that a licensed HVAC contractor perform a formal Manual J Load Calculation for this specific floor plan. If the Manual J confirms the unit is undersized, I expect the builder to replace the condenser and evaporator coil with a system of the appropriate capacity at no cost to me.

I have attached the inspection notes from Sheldon’s Home Inspections for your reference. I look forward to your response within [Insert number, e.g., 5] business days to schedule a secondary inspection.

Sincerely,

[Your Name] [Your Phone Number]

Pro-Tip for the Homeowner:

When you send this, always include a copy of the spec sheet for your AC unit (usually found in your closing documents) and any photos of the thermostat showing the temperature rising inside the house despite the AC running all day.