Here are some ballpark numbers for operating outdoor heaters, based on rates in the San Francisco Bay Area, keeping in mind that rates vary for commercial and residential utility users, winter and summer, and in some cases peak and off-peak hours.

• Propane patio heaters: $1.50 to $3 per hour 
• Natural gas patio heaters: $0.25 to $0.75 per hour 
• 240 Volt electric patio heaters (2000 watts to 6000 watts): $0.32 to $2.75 per hour 
• 120 volt electric patio heaters (1500 watts): $0.24 to $0.68 per hour