CFM for 3-ton AC?
About 1,200 CFM using the 400 CFM per ton rule of thumb.
Space heater cost = (watts ÷ 1,000) × hours/day × days × $/kWh. A 1,500 W heater at 6 hr/day can add significant winter kWh.
Use the calculator form above with your room size, system capacity, or appliance usage. Results update instantly in your browser — no data is sent to a server.
Concise answers for common searches — definitions, steps, and comparisons.
About 1,200 CFM using the 400 CFM per ton rule of thumb.
12,000 BTU/hr of cooling capacity equals one ton of refrigeration.
Space heater cost = (watts ÷ 1,000) × hours/day × days × $/kWh. A 1,500 W heater at 6 hr/day can add significant winter kWh.
Formula
See calculator inputs and results panel for step-by-step math.Select imperial/metric, rectangle vs area, tons vs BTU, or usage presets as shown.
Type room dimensions, system tonnage, CFM, appliance watts, or electric rate.
Pick climate zone 1–5 and insulation quality for load-based calculators.
Use BTU/hr, tons, CFM, duct diameter, or seasonal cost in the results panel.
Copy results or share a link with your HVAC contractor or energy auditor.
Use Duct CFM, Duct Size, or Energy Cost calculators for a complete HVAC plan.
Input
20×15 ft · 8 ft ceiling · zone 3Output
≈ 7,500 BTU/hr cooling300 sq ft × 25 BTU/sq ft × average insulation × 1.0 height factor.
Input
2.5 tonsOutput
1,000 CFM2.5 × 400 CFM/ton = 1,000 CFM supply airflow rule of thumb.
Common real-world scenarios where this tool saves time.
12×15 ft room, zone 3, average insulation → ~9,000–11,000 BTU/hr cooling load.
2,000 sq ft home, zone 4 → ~3.5–4 tons cooling with average insulation.
3-ton system → 1,200 CFM target → 14" round trunk at 700 FPM velocity.
900 W unit, 8 hr/day, 90 days at $0.16/kWh → seasonal cost estimate for budgeting.
Step-by-step chains that connect related tools for common tasks.
From room BTU to duct airflow and diameter.
Compare portable appliance electricity spending.
| Watts | 6 hr/day × 30 days | Monthly cost |
|---|---|---|
| 750 W | 135 kWh | $22 |
| 1,500 W | 270 kWh | $43 |
| 1,800 W | 324 kWh | $52 |
Rule-of-thumb sizing is a starting point — ACCA Manual J is the industry standard.
Undersized ducts reduce efficiency and comfort even when tonnage is correct.
Include climate zone, insulation, ceiling height, and sun exposure — or request Manual J.
Check heating BTU/hr and balance point, not just cooling tons.
Compressors cycle — actual kWh may be lower than watts × hours suggests.
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At $0.16/kWh running 6 hours/day for 30 days: (1.5 × 6 × 30) = 270 kWh ≈ $43 — adjust watts, hours, and rate for your case.
Most plug-in heaters are 750–1,500 W on high — multiply watts by hours to get kWh.
Sometimes yes if you lower central heat elsewhere — compare to furnace cost per BTU for your fuel and rates.
They cycle on and off at the same watt rating — average kWh depends on thermostat duty cycle, not oil vs ceramic alone.
Still rated in watts — use nameplate watts and actual run hours; efficiency claims do not change the kWh formula.
Follow manufacturer guidance — many models are not for unattended use; this calculator only estimates cost, not safety.
Space heater watts, usage hours, and rate inputs stay local — EverydayTools does not upload space-heater-cost calculator entries.
Estimates only — not professional HVAC or energy audit advice. Verify with a licensed contractor before purchasing equipment.
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Reviewed on 2026-06-28.
Same workflow or intent — pick the next step without leaving the site.
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Typical space heater: 750–1,500 W
30 for monthly, 90 for summer season