How Many BTUs for 1200 Sq Ft House?
Warning: At 1200 sq ft, layout is more important than power. Buying one giant unit is a recipe for hot bedrooms and a freezing living room. Here is the Multi-Zone strategy.
The Engineering Load Range
Standard Home
Average Insulation
36k BTU
Efficient Build
New Windows/Foam
24k – 30k BTU
⚠️ Stop! Do not buy a single unit unless it’s an open loft. Check the Master Sizing Guide.
Why One Big Unit Will Fail
If you have a 1200 sq ft house with 3 bedrooms, installing one 36,000 BTU unit in the living room is a $3,000 mistake.
Airflow Does Not Turn Corners
The thermostat in the living room will hit 70°F and shut off the compressor. meanwhile, the bedrooms down the hall (behind doors) will remain at 80°F.
The Multi-Zone Fix
You need to distribute the BTUs. Instead of one 36k head, you need a Multi-Zone System (e.g., 18k Living + 9k Bed + 9k Bed).
Single vs Multi-Zone: Read the comparison →Choose Your Layout Strategy
Standard 3-Bedroom House
The most common layout. Requires individual comfort for sleeping zones.
- Zone 1: Living (18k)
- Zone 2: Master (9k)
- Zone 3: Guest (9k)
Open Loft / Shop
No walls, high ceilings. Air can flow freely.
Hidden Ducted Mini Split
Using a “Slim Duct” unit in the attic to feed vents in bedrooms.
Consider Ceiling Cassettes too →Fixing a 1200 Sq Ft Heat Trap
The House: 1200 sq ft, 1980s build, poor insulation.
The Challenge: The old central AC died. Quotes for new ductwork were $12,000.
The Goal: Cool the whole house for under $5,000.
The Engineering Solution
FAQ: Whole House Sizing
How many tons is 1200 sq ft?
Generally, 1200 sq ft requires 2.5 Tons (30,000 BTU) to 3 Tons (36,000 BTU). In very well-insulated homes in mild climates, you might get away with 2 Tons (24,000 BTU), but that is risky.
Is it cheaper to run one big unit or multi-zone?
Multi-Zone is cheaper to run. Why? Because you can turn off the units in the bedrooms during the day. With one big central unit, you are forced to cool the entire 1200 sq ft even if you are just sitting in the kitchen.
How much does a 3-Zone system cost?
For a DIY MrCool 3-Zone system (36k), expect to pay around $4,500 – $5,000 for equipment. For a professional Mitsubishi install, expect $12,000 – $15,000. See our Cost Breakdown here.
One House. Multiple Zones.
Don’t guess the zones. Use our calculator to size each room individually before you buy the outdoor unit.
