Enter both values to calculate watts
BTU per Hour (BTU/h)
Efficiency (%)
Common:
Watts (W)
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
High-Efficiency 12,000 BTU Mini-Split
A 12,000 BTU (1-ton) mini-split with SEER 20 draws only 600W continuously — well within a modest solar array's output during peak sun hours.
Standard 18,000 BTU Unit
An 18,000 BTU (1.5-ton) unit with SEER 15 draws 1,200W continuously. Over 10 hours, that is 12 kWh — roughly 3,000W of panels with a dedicated 5 kW inverter.
Efficiency Comparison
A 24,000 BTU mini-split at SEER 25 draws 960W vs 1,600W at SEER 15. The high-efficiency unit saves 640W continuously — 5.1 kWh/day over 8 hours, or roughly $190–280/year.
When You'll Need This Conversion
- Sizing an Off-Grid Solar Array for Cooling — An Arizona homeowner wants to run a 12,000 BTU mini-split on solar. Converting BTU to watts determines panel count and inverter size. The AC's startup surge (3–5× running watts) also sets minimum inverter capacity.
- Adding AC to an Existing Solar System — A DIYer with a 3 kW solar system wants to add a mini-split. A 12,000 BTU / SEER 20 unit at 600W might fit; an 18,000 BTU / SEER 15 at 1,200W might not.
- Comparing Heating Systems for Solar — A 12,000 BTU resistive heater draws about 3,500W, while a 12,000 BTU heat pump draws 600–1,000W. This reveals why heat pumps are far more solar-friendly.
Solar Tips & Common Mistakes
SEER Is an Average, Not a Constant: On the hottest days, actual EER is lower than SEER. A SEER 20 unit might operate at EER 13–15 during peak heat, meaning real watt draw is higher than SEER-based calculations suggest.
Startup Surge Can Trip Inverters: Standard compressors surge 3–5× their running wattage at startup. A 600W unit can spike to 1,800–3,000W. Look for inverter-driven (variable speed) compressors with soft-start capability.
BTU Ratings Are Output, Not Input: A 12,000 BTU AC removes 12,000 BTU of heat while consuming only 600–1,200W of electricity, thanks to the refrigeration cycle. Do not confuse this with resistive heaters where watts and BTU relate directly.
Solar Calculators
Related Conversion Calculators
Last updated: January 5, 2026
