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A 12×12 bedroom (144 sq ft) typically needs 3,600–4,300 BTU calculated — retail mini-splits start at 9,000 BTU. Enter your exact dimensions below for cooling load, heating estimate, and recommended ductless head size.

BTU & Mini-Split Calculator

Enter room dimensions. Get cooling BTU, heating estimate, and recommended mini-split size.

Space dimensions

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Sizing settings

Application
Insulation
Sun exposure
Climate

Your sizing estimate

Enter space dimensions to see BTU load and recommended mini-split size.

Room, window & garage calculators

Size window AC units, garage heaters, and multi-room loads — separate from RV and tiny-home mini-split pages.

Mini-split sizing by application

Pre-set insulation and load factors for RVs, tiny homes, backyard sheds, and seasonal cottages.

DIY sizing guides

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RV installs, tiny home insulation, she-shed comfort, cottage heat pumps, and mini-split mistakes to avoid.

DIY install

DIY Mini-Split Project Roadmap — Size, Wire, Mount & Start Up

Plan a ductless mini-split project from BTU sizing and zone selection through electrical work, placement, mounting, startup, and professional handoff.

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DIY install

Mini-Split Electrical Requirements — Breaker, Wire & Disconnect

DIY electrical planning for ductless mini-splits: 110V vs 220V, breaker size, wire gauge, outdoor disconnect, and when to hire an electrician.

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DIY install

How to Install a Window AC Safely — Support, Seal & Power

DIY window air conditioner install: sash support, brackets, sealing gaps, correct outlet circuit, and tipping hazards. Size BTU before you buy.

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Sizing basics

BTU Per Square Foot Explained — Room Sizing Basics

How the 20–30 BTU per sq ft rule works, when to go higher or lower, and how insulation, climate, and sun exposure change your load.

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How it works

  1. 1. Measure your spaceEnter length, width, and ceiling height for each room, RV living area, or shed footprint.
  2. 2. Set application typeChoose RV, tiny home, she-shed, cottage, or standard room — insulation and BTU factors adjust automatically.
  3. 3. Buy the right BTUWe calculate cooling load, heating estimate, and round up to common mini-split sizes (9k, 12k, 18k, 24k).

FAQ

How many BTU per square foot?

Most cooled rooms need 20–30 BTU per sq ft. RVs and uninsulated sheds need more; well-insulated tiny homes need less. Sun exposure, ceiling height, and occupants adjust the result.

What size mini-split for an RV?

Most full-time RVers use 9,000–12,000 BTU depending on length and insulation. A 30 ft RV with 200–250 sq ft of living space often needs a 9k minimum; 12k is common in hot climates.

Can I size a whole tiny home with one calculator?

Yes — add up to five spaces or enter the main living footprint as one zone. Most tiny homes use a single 9k–18k BTU ductless head.

Is this a Manual J calculation?

No. This is a DIY planning tool. For permits and whole-house central HVAC, hire a licensed pro for Manual J and Manual S equipment selection.