Inputs
BTU per Hour result
Understanding heating & cooling power
Key formulas
BTU and watts measure the same thing — energy transfer rate:
Resistive vs heat pump
Resistive heating
1:1- 1,000W = 3,412 BTU/h exactly
- Space heaters, baseboard heaters
- Efficiency is always 100%
Heat pump
COP 2–5- 1,000W at COP 3.5 = 11,943 BTU/h
- Mini-splits, central heat pumps
- 3–5× more BTU per watt
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
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.
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.
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.
