Three heating calculation methods: airside sensible (Q = 1.08 × CFM × ΔT), space rule-of-thumb, and boiler/furnace output sizing.
| Space Type | Rule-of-Thumb (BTU/hr/ft²) | Notes |
|---|---|---|
| Residential (new) | 8–15 | Well-insulated, sealed construction |
| Residential (older) | 20–35 | Pre-1980, minimal insulation |
| Commercial office | 10–18 | Depends on glazing ratio and climate |
| Warehouse / industrial | 8–20 | Large volume, high infiltration potential |
| Retail | 15–25 | High infiltration from frequent door openings |
| School / gym | 12–20 | High OA requirement inflates heating load |
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