Ok, so I did some calculating yesterday at work.
It costs ~12¢ per day to run the heater. That's running from 6am8am and then from 2pm4pm 5 days a week. 400Watt heater run for 4 hours = 1600Watts or 1.6kWh. 1.6kWh = 12.32¢. So now it only takes my car ~1 minute to hit operating temp as indicated by temp gauge instead of ~6 minutes it takes without the heater. I'm not completely sure of the mileage I get while the car is in rich mode warming up, but I'll assume 25MPG and normal operating temp mileage will be 45MPG let's say (due to me not putting in the WAI again for winter). Assuming Gasoline is $3 per gallon it costs me 12¢ per mile during warmup as opposed to only 6.6¢ per mile cost during normal operating temp. So I'm saving almost 6 cents per mile for roughly ten minutes each day (2 x 5 minutes...once in the morning and once in the afternoon) in that ten minutes I cover ~10 miles. That means I'm saving 60¢ in gas every day or $3 every week that I use the heater (which is also one gallon of gas). In order to recoup the cost of the heater, I need to use it for ~13 weeks. Please correct me if any of my math is wrong.
So a block heater is a great investment for the DIY'er or even the type of ecomodder that wants to save gas without cost being an issue (i.e. having a shop install the heater).
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