Enter both values to calculate btu per hour
Watts (W)
Efficiency (%)
Common:
BTU per Hour (BTU/h)
Result will appear here
Understanding Heating & Cooling Power
BTU and watts measure the same thing - energy transfer rate:
- 1 BTU/h = 0.293071 Watts
- 1 Watt = 3.41214 BTU/h
- 12,000 BTU/h = 1 ton of cooling
For Solar-Powered HVAC
Understanding these relationships helps you:
- Size your solar - Know the wattage of your AC unit
- Calculate runtime - Determine battery requirements
- Compare efficiency - Higher SEER means lower watts per BTU
- Plan for peak loads - AC startup draws extra power
Real-World Solar Examples
Solar Panel Heat Output
A 400W panel converts ~20% of sunlight to electricity. The remaining ~1,600W becomes heat — 5,459 BTU/h. This is why rooftop panels provide a shading benefit, intercepting heat that would otherwise enter the roof.
Inverter Waste Heat
A 5,000W inverter at 95% efficiency loses 250W as heat — 853 BTU/h. Over 8 hours, that is 6,824 BTU, roughly a small space heater. Adequate ventilation is necessary in equipment rooms.
Battery Charging Heat
A lithium battery charged at 3,000W with 97% round-trip efficiency generates 90W of heat — 307 BTU/h. In a sealed battery enclosure, this thermal load must be managed to stay within 0–45°C.
When You'll Need This Conversion
- Ventilating a Solar Equipment Room — An installer needs ventilation for a room with a 5 kW inverter, charge controller, and batteries. Converting total waste heat to BTU lets them select the right exhaust fan size.
- Winter Battery Protection — In cold climates, battery enclosures need heating. If 2,000 BTU/h is needed to stay above freezing, converting to watts (586W) tells you the heater size and how much solar to reserve.
- Solar-Powered Heating Assessment — A 2,000W ceramic heater produces 6,824 BTU/h. Comparing to a home's 20,000–60,000 BTU/h heating load shows resistance heating alone is insufficient — but a heat pump multiplies this by COP 3–4.
Solar Tips & Common Mistakes
Heat Pumps vs Resistive: Not a 1:1 Ratio: For resistive heating, 1W = 3.412 BTU/h is exact. But heat pumps with COP 3.5 deliver 3,500W of heating from 1,000W input = 11,942 BTU/h. Always check whether equipment is resistive or heat-pump based.
Inverters Derate in Hot Environments: Inverters reduce output above ~45°C. A 5,000W inverter in a hot attic might derate to 3,500W, reducing available power for connected loads. Calculate equipment room thermal load and ensure adequate ventilation.
Battery Thermal Safety: Lithium battery safety sheets express thermal runaway energy in BTU. A 10 kWh battery in thermal runaway can release ~34,120 BTU in minutes — roughly equal to a gallon of gasoline. This informs enclosure design.
Solar Calculators
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Last updated: January 5, 2026
