Models central fuel cost per delivered BTU, space heater kWh, and thermostat setback savings to find your tipping point.
Central Heating System
AFUE-style furnace efficiency
Home & Space Heater
Each 1°F setback reduces central heating cost by 1%.
Cost Comparison
Tipping point: calculating…
Central heat only (full temp)—
Space heater + setback—
Space heater share
—
Central @ setback
—
Cost per 100k BTU
—
Zone % of home
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Practical tips & common mistakes
Setback strategy
Zone heating wins when you can drop central thermostat 4°F+ for many hours. Mild setbacks erase portable heater savings.
Comparing peak kW only
Central heat distributes BTUs; space heaters concentrate them. Compare annual dollars at your real thermostat schedule.
Safety and placement
Keep 3 ft clearance, never on extension cords, and shut off when leaving the room — efficiency means nothing if fire risk rises.
Heat pumps change the math
If you have a modern heat pump, portable resistance heat is almost always more expensive per BTU than central mode.
Note: Simplified energy model for planning — actual savings depend on insulation, climate, duct losses, and how low you set the thermostat. Space heaters are 100% efficient (1.0 COP) at point-of-use.