The factor is an input, not a hidden constant
Measure the conditioned floor, not the whole footprint with garages and porches. 30 BTU/ft² is a mild-climate start. Cold rooms, single-pane glass and leaky villas need a higher factor — type the number you were given. An 8 ft ceiling is the basis; taller rooms scale the load.
A 36,000 BTU/h planning load is about 3 tons as a conversation number. It is not a 3-ton furnace on a spec sheet.
CFM is airflow, not this page
Room airflow from volume and air changes lives on the CFM calculator. Neither page is Manual D or a duct size. In Qatar and the GCC this is still only a planning start — cooling-dominated villas need a designer, not a square-footage rule.
Do it in order
- Enter conditioned length, width and average ceiling height.
- Replace the 30 BTU/ft² default with the factor you were given.
- Read the planning load and approximate tons, then talk to the HVAC designer before buying equipment.
Worked example — 40 ft × 30 ft, 8 ft ceiling, 30 BTU/ft²
Floor area is 1,200 ft². Height factor against 8 ft is 1. Planning load is 36,000 BTU/h, about 3 tons. A 9 ft ceiling is not this ticket — the height factor rises and so does the load.
Planning boundary
This is a planning load. It does not design equipment, ducts, refrigerant charge, combustion air or a code path.
Is this Manual J?
No. It is a square-footage planning factor. Manual J needs insulation, glass, infiltration and orientation.
Can I buy a furnace from 3 tons?
No. Equipment, refrigerant and combustion air stay with the designer.
Where does CFM fit?
Open the CFM calculator for room airflow from volume and air changes. That is also not a duct size.