How Many BTUs for 800 Sq Ft?
800 sq ft sits right on the border between 1.5 Tons and 2 Tons. Choosing the bigger unit isn’t “safer”—it often creates a cold, clammy swamp. Here is the math.
The Engineering Range
Apartment / ADU
Insulated space
18,000 BTU
Garage / Shop
High heat load
24,000 BTU
⚠️ Don’t assume you need 24k. Read our Master Sizing Guide first.
Why “Bigger” is NOT Better
The “Safety” Myth
Contractors love installing 24k units in 800 sq ft spaces “just to be safe.”
Result: Short Cycling
The unit turns on, blasts ice-cold air for 5 minutes, and shuts off before removing humidity.
Insulation Quality
An 800 sq ft insulated apartment only holds ~15,000 BTUs of heat. A 24k unit is overkill.
Layout (Open vs Closed)
Is it one big room (Studio) or divided rooms? Single Zone vs Multi-Zone matters here.
Occupancy Load
Is this a workshop with machines running? Or a guest house used twice a year?
Sensible vs Latent
In humid climates, you need run time to remove moisture. Smaller is better.
Select Your 800 Sq Ft Scenario
Accessory Dwelling Unit (ADU)
Standard 8ft ceilings, modern insulation, residential use.
3-Car Garage / Workshop
Concrete floor heat sink, uninsulated doors, tools running.
Why garages kill efficiency →The “Oversized” Nightmare
The Space: A brand new 800 sq ft guest house in Los Angeles.
The Problem: The general contractor installed a 24,000 BTU unit because “more is better.”
The tenants complained the air felt “sticky” and cold. The unit would run for 4 minutes and turn off. It never ran long enough to dehumidify.
The Engineering Fix
FAQ: 800 Sq Ft Sizing
Is 24000 BTU too big for 800 sq ft?
If the space is well-insulated (like an apartment), YES, 24k is too big. It will short-cycle. However, if it is a poorly insulated garage or has high ceilings, 24k might be correct. Context is everything.
How many tons is 800 sq ft?
800 sq ft typically requires between 1.5 Tons (18,000 BTU) and 2 Tons (24,000 BTU) depending on your climate and insulation.
Can I use two smaller units instead of one big one?
Yes, and it’s often better. Installing two 9,000 BTU units (one in the bedroom, one in the living area) provides better zoning and comfort than a single 18k unit blowing from one spot. Compare Single vs Multi-Zone here.
Don’t Buy Until You Verify.
Are you an “Apartment 18k” or a “Garage 24k”? Use the calculator to find your exact number.
