What size AC do I need for a 1,500 sq ft home?

Using the rule of thumb of 400–600 sq ft per ton, a 1,500 sq ft home would need roughly 2.5–3.75 tons of cooling. In hot climates with poor insulation, lean toward the higher end (3.5–4 tons). In mild climates with well-insulated, shaded homes, 2.5 tons may suffice. A Manual J calculation from an HVAC contractor gives the most accurate sizing.

BTU stands for British Thermal Unit. It's the amount of energy needed to raise one pound of water by one degree Fahrenheit. In HVAC, BTU/h (BTUs per hour) measures how much heat the system can add or remove per hour. One ton of cooling equals 12,000 BTU/h — enough to melt one ton of ice in 24 hours.

Is a bigger AC better?

No. An oversized AC cools too quickly and shuts off before removing humidity from the air, leaving the home feeling clammy even at the right temperature. Short-cycling also increases energy use and wear on the equipment. Proper sizing to the actual cooling load is critical for comfort, efficiency, and equipment longevity.

What SEER rating should I buy?

The minimum legal SEER2 is 14–15 depending on your region. For most homes, a SEER2 16–18 system offers a good balance of upfront cost and energy savings. In very hot climates where AC runs most of the year, upgrading to SEER2 20+ can be cost-effective. Premium variable-speed systems (SEER2 20–25) also provide superior dehumidification and comfort.

How often should HVAC equipment be replaced?

Central air conditioners and heat pumps typically last 15–20 years. Gas furnaces last 20–30 years. Annual professional maintenance extends equipment life. When repairs become frequent or the refrigerant is R-22 (no longer manufactured), replacement is usually more economical. Modern high-efficiency systems typically pay back the upgrade cost in 7–12 years through energy savings.

How to Size Your HVAC System: BTU & Tonnage Guide

The Basics: BTU and Tonnage

Air conditioning capacity is measured in BTU per hour (BTU/h) or tons. One ton of cooling equals 12,000 BTU/h. Residential air conditioners range from 1.5 to 5 tons (18,000 to 60,000 BTU/h). Furnaces and heat pumps for heating are also rated in BTU/h, typically 40,000 to 150,000 BTU/h for residential systems.

Quick Rule of Thumb

A commonly used rough guideline is 400–600 square feet of conditioned space per ton of cooling. This means a 2,000 sq ft home might need 3.3–5 tons of cooling capacity. However, this rule of thumb ignores many important factors and should only be used for a very rough estimate:

Climate zone (Arizona needs more than Maine)
Ceiling height (10-ft ceilings need more than 8-ft)
Window area, orientation, and shading
Insulation quality
Number of occupants and appliances
Air duct efficiency and leakage

Manual J: The Right Way to Size HVAC

The industry standard for HVAC sizing is Manual J (a set of calculations developed by ACCA — the Air Conditioning Contractors of America). A proper Manual J calculation takes into account all the variables listed above and outputs the exact cooling and heating loads for each room. Reputable HVAC contractors will provide a Manual J calculation before proposing a system. Be wary of contractors who size systems simply by home square footage or by replacing the previous unit with the same size.

The Danger of Oversizing

Bigger is not better when it comes to HVAC. An oversized air conditioner cools the space too quickly (short-cycles), shutting off before completing a full run cycle. This causes several problems:

High humidity because the unit doesn't run long enough to dehumidify the air
Uncomfortable temperature swings
Higher energy costs due to frequent start-up cycling
Premature equipment wear from constant starting and stopping

An oversized furnace similarly short-cycles, causing uneven heating and excess wear.

SEER and Efficiency Ratings

SEER (Seasonal Energy Efficiency Ratio) measures cooling efficiency. As of 2023, federal minimums are SEER2 14 in the north and SEER2 15 in the south. Mid-efficiency systems run SEER2 16–18; premium variable-capacity systems reach SEER2 20–25+.

A SEER2 16 unit uses 14% less energy than a SEER2 14 unit. In hot climates with high AC use, upgrading from SEER 14 to SEER 18 can save $150–300 per year in electricity. Energy Star-certified systems qualify for federal tax credits of up to $600.

Heat Pumps vs. Traditional HVAC

A heat pump handles both heating and cooling with one system. Modern cold-climate heat pumps work efficiently down to -15°F outdoor temperatures, making them suitable for most of the US. Benefits include:

Single system for heating and cooling
2–4x more efficient than electric resistance heat
Lower carbon footprint than gas furnaces in most US electricity grids
Federal tax credits of up to $2,000 through the Inflation Reduction Act (2026)

In very cold climates (Zones 6–8) or where natural gas is very inexpensive, a gas furnace + central AC may still offer lower operating costs than a heat pump alone.

When to Replace Your HVAC System

HVAC equipment lifespan: central AC 15–20 years, gas furnaces 20–30 years, heat pumps 15–20 years. Signs it's time to replace: frequent repairs (especially refrigerant leaks), increasing utility bills, inconsistent temperatures room to room, R-22 refrigerant systems (R-22 is no longer manufactured), and units approaching or past expected lifespan. The general rule: if repair cost exceeds 50% of replacement cost on a unit over 10 years old, replacement is smarter.