Mini Split Sizing GuidE: How to Choose the Right System

Getting the right size mini split is critical. If it’s too small, it won’t keep up. If it’s too large, you’ll waste energy and money. This simple guide explains how to estimate the perfect BTU capacity for your Seattle home.

Step 1: Measure Your Space

Calculate the square footage of the room or area you want to heat and cool.

Step 2: Use a General BTU Estimate

Area Size (sq ft)	Recommended BTUs
150 – 250	6,000 BTU
250 – 400	9,000 BTU
400 – 650	12,000 BTU
650 – 1,000	18,000 BTU
1,000 – 1,500	24,000 BTU
1,500 – 2,000	30,000 BTU +

(Multi-zone systems use multiple indoor units to cover larger spaces.)

Step 3: Adjust for Seattle Conditions

Seattle’s temperate climate means you can choose a slightly lower BTU rating than homes in extreme heat zones. However, older homes with poor insulation may need a bit more capacity.

Step 4: Let a Pro Verify Your Sizing

A certified installer can perform a Manual J load calculation to confirm your exact needs — accounting for windows, insulation, and airflow.

Why Proper Sizing Matters

• Saves energy and reduces bills

• Prevents short cycling and excess wear

• Keeps temperatures consistent

• Ensures longer equipment life

Not sure what size you need?

Contact Mark’s Mini Splits. We’ll recommend the perfect system for your home and budget.