Size Your System

Quickly Size Your Mini-Split Heat Pump System

Use our mini-split heat pump sizing calculator to build your ductless system, whether it's a single room or multiple rooms.

When you're sizing a multi-room system, click "Save & Calculate Additional Room." If you have a more complicated set-up and need sizing help, send in your request to

Room Name
Naming the rooms will help you keep track if you are calculating the BTU of multiple rooms. Naming examples: "Living Room"
Room Width (ft)
Measure the width of the room you would like to install the ductless indoor unit. Enter that measurement below.
Room Length (ft)
Measure the length of the room you would like to install the ductless indoor unit. Enter that measurement below.
Number of Windows
How many windows are in the room that you will be installing the ductless system into. Enter the number below.
Number of Occupants
How many people on average will occupy this room? Enter the number below.
Room Location
Select an option below to help us understand where & the type of room the unit's going to be installed in in your home.
House Insulation
Select the current condition of the room you will be installing your ductless system.
Cooling BTU's Required:
Heating BTU's Required:

Recommended Unit: 0 BTU

Saved Rooms:

  • Why BTUs need to be calculated?

    If you don't size your ductless system properly, you run the risk of your unit not effectively cooling or heating the space (or under or overcooling it). An undersized system will be working too long or non-stop. And if you the system is oversized - the system will use too much energy and short-cycling.

    In both ways, you'll spend more money than necessary causing high electrical bill.

  • What is BTU?

    British Thermal Units or BTUs are a measurement of the energy required to raise the temperature of one pound of water by one degree. In other words, the amount of heat that the system needs to remove from the space in summer, and the amount of heat that the system needs to bring to space in the winter season.

  • Professionally Sizing Your Ductless System

    Our sizing calculator is based on over ten years of industry experience. If you have a more complicated set-up, you might need a professional load calculation. Professional load calculations take many factors into account, not just the dimensions of your rooms.

Mitsubishi Size Your System

Sometimes, the rule of thumb calculators can be misleading. When you're getting an in-home ductless system consultation, your ductless designer takes into account:

  • What climate you're in?

    Mini-split heat pumps are sized differently in hotter or colder climates because of the environment.

  • How many windows the room has?

    Windows impact the size of your heat pump because aren't insulated and leak air. 

  • How many doors the room has?

    Doors are the same as windows. They're not insulated like your walls are and leak air through the cracks between the door and frame.

  • Direct sunlight, how much does the room get?

    Direct sunlight will heat your room. The amount of sunlight your room gets can affect the size of the system that room needs.

  • How well insulated the room each evaporator is going in?

    The better insulated a room is, the less energy it will take to heat/cool the room.

  • If the room is a kitchen or close to the kitchen

    Kitchens are wide open, and ductless units near them usually need to be sized bigger to account for the open space.

  • Square footage of the room, excluding space?

    The more space inside the room that needs to be heated or cooled, the larger the system your room will need.

  • How high the ceilings are?

    Ceiling height affects the room size. Taller ceilings make the room larger, meaning you'll need a bigger ductless system.

  • Any additional heat sources that might be in the room?

    Other sources of heat can help take the load off your mini-split.

  • The type and amount of lightbulbs there are in the room?

    Lightbulbs generate heat and certain types of lightbulbs generate more heat than others. If the room has a lot of lightbulbs, it could affect the size of your system.

  • The usual number of occupants in this room?

    People generate heat and can affect the size of the ductless units you need.

  • If your floor is carpet or hardwood?

    Carpet is a lot more insulating than hardwood is and it could have an effect on your ductless system's size.

Mitsubishi Primary Source of Heat

Some Other Factors

Some of the factors affect the size of the system more than others. For instance, a tall ceiling (8 feet or more) could increase the BTU output by 20%. A poorly insulated room can increase the BTU output by 30%. Your climate could increase the estimated BTU output by 30%.

Reach Out

Reach out to our team if you need assistance sizing your system! We are more than happy to assist on new construction, retrofits, single zone applications, and all other projects. Submit your request here or call us.