Formula
The guide multiplies floor area by a sun factor:
BTU/h = square feet × 20, 25, or 30
Shaded rooms use 20, average sun uses 25, and sunny rooms use 30. Tons from a known BTU rating, a room with people and windows, and heating fuel each use a different input, so they are separate pages.
Assumptions
- The area is floor area in square feet, for a room with a typical ceiling.
- The factors are a planning guide, not ACCA Manual J.
- Occupants, kitchens, and insulation are not extra inputs.
Worked example
A 300 square foot room with average sun has a cooling guide of 7,500 BTU per hour.
Input definitions
- Floor area
- Length times width of the room, in square feet.
- Sun
- Whether the room is shaded, average, or sunny. That chooses 20, 25, or 30.
Limitations
Do not buy equipment from this number alone. Ceiling height, climate, windows, and insulation can move the real load. Heating fuel cost is an energy-price question, not this sizing guide.
Questions
Is this a Manual J calculation?
No. Manual J measures the building. This page is only area times a sun factor.
Can I enter square meters?
The factors are per square foot. Convert the room to square feet before entering it.