How many BTUs do I need to cool my room?

As a starting point, you need about 20 BTUs per square foot. A 300 square foot room needs roughly 6,000 BTUs. However, this varies significantly based on ceiling height, insulation quality, sun exposure, climate zone, and how many people typically occupy the space. A south-facing room with poor insulation in Phoenix needs 30-40% more than a well-insulated north-facing room in Portland.

What size AC unit do I need for my house?

For a 2,000 square foot well-insulated home in a moderate climate, you typically need a 3-ton (36,000 BTU) system. Hot climates may need 3.5-4 tons, while mild climates may only need 2-2.5 tons. An oversized unit is actually worse than undersized — it short-cycles, fails to dehumidify properly, and wears out faster.

Is it better to oversize or undersize HVAC?

Neither is ideal, but undersizing is actually less harmful than oversizing. An oversized unit cycles on and off too quickly (short-cycling), never properly dehumidifies the air, wastes energy, and wears out components faster. An undersized unit runs longer but dehumidifies better and may simply fail to reach the desired temperature on the hottest days. Professional HVAC contractors perform a Manual J load calculation for precise sizing.

HVAC Sizing Calculator

Find the right size air conditioner, heat pump, or furnace for your space

Square Footage

Ceiling Height (feet)

Climate Zone

Insulation Quality

Sun Exposure

Typical Occupants

Why Proper HVAC Sizing Matters More Than You Think

The most expensive HVAC mistake homeowners make is not buying the wrong brand — it is buying the wrong size. A system that is too large for your home is worse in almost every way than one that is slightly too small, yet contractors routinely oversize systems because it is easier to sell "more" and it eliminates callbacks about the house not cooling enough on the hottest day of the year.

An oversized air conditioner blasts cold air into the room, reaches the thermostat setting quickly, and shuts off. Sounds good, right? The problem is that it never runs long enough to pull humidity out of the air. You end up with a house that hits 72 degrees on the thermostat but feels clammy and uncomfortable because the relative humidity is 65% instead of the ideal 45-50%. To compensate, you lower the thermostat to 68, which increases energy costs by 15-20% while still not addressing the underlying humidity problem.

The Manual J Calculation

Professional HVAC contractors use a calculation called Manual J to properly size equipment. It accounts for every factor that affects heating and cooling load: square footage, ceiling height, insulation R-values, window type and orientation, air infiltration rate, ductwork efficiency, number of occupants, internal heat sources (appliances, lighting), and local climate data including both temperature and humidity design conditions.

This calculator provides a solid estimate using the most impactful variables, but a professional Manual J calculation will be more precise. If you are installing a system costing $5,000-15,000, the $200-400 cost of a proper load calculation is the best money you will spend on the project.

Tons, BTUs, and What They Mean

Air conditioning capacity is measured in BTUs per hour (British Thermal Units) or tons. One ton of cooling equals 12,000 BTUs per hour. The name comes from the amount of energy needed to melt one ton of ice in 24 hours. Residential systems typically range from 1.5 to 5 tons (18,000 to 60,000 BTUs). A typical 2,000 square foot home in a moderate climate needs about 3 tons (36,000 BTUs).

For heating, capacity is measured in BTUs per hour for gas furnaces and tons or BTUs for heat pumps. A 80,000 BTU gas furnace is common for a 2,000 square foot home in a cold climate. Heat pumps provide both heating and cooling from one unit, making the sizing decision even more important since the same equipment handles both jobs.

Heat Pumps vs Traditional Systems in 2026

Heat pumps have become dramatically better in cold weather performance. Modern cold-climate heat pumps (like the Mitsubishi Hyper-Heat or Bosch IDS) operate efficiently down to -13°F, making them viable in nearly all US climate zones. The Inflation Reduction Act provides up to $8,000 in tax credits for heat pump installation, which combined with lower operating costs makes them financially competitive with gas furnaces even in cold climates. If you are replacing an aging system, getting a heat pump quote alongside traditional options is worth the phone call.

Red Flags When Getting HVAC Quotes

Be wary of any contractor who quotes a system size without measuring your home or performing a load calculation. "One ton per 500 square feet" is a rule of thumb that ignores insulation, climate, and building characteristics — it is like a doctor prescribing medication based on your height alone. A professional contractor will measure your home, assess insulation and windows, check ductwork, and perform a Manual J calculation before recommending a size. If they skip this step, they are guessing, and their guess will likely be oversized.

How many BTUs do I need per square foot?

The rough starting point is 20 BTUs per square foot, but this varies 30-50% based on climate, insulation, sun exposure, and ceiling height. A 500 sq ft room might need 8,000 BTUs in Portland but 14,000 in Phoenix. This calculator adjusts for these factors to give you a more accurate estimate.

What size AC for a 2,000 sq ft house?

Typically 2.5-4 tons depending on climate and insulation. Moderate climate with average insulation: about 3 tons (36,000 BTU). Hot climate or poor insulation: 3.5-4 tons. Cool climate with good insulation: 2-2.5 tons. Always get a professional load calculation before buying.

How much does a new HVAC system cost?

Central AC: $3,500-7,500. Gas furnace: $2,500-6,000. Heat pump: $4,000-8,000. Full system replacement (AC + furnace + ductwork): $7,000-15,000. Mini-split systems: $3,000-8,000 for 1-3 zones. Tax credits (IRA 2024-2032) can reduce heat pump costs by up to $8,000.

Should I get a bigger unit just in case?

No. Oversizing causes short-cycling, poor humidity control, higher energy bills, and premature equipment failure. A properly sized system runs longer on the hottest days, which is normal and actually desirable — longer run times mean better dehumidification and more even temperatures throughout the house.