engine block heater Return on Investment ROI What is the payback or breakeven point when its worth it to install an engine block heater? Scenario#1 ========== Suppose a 400wh engine block heater ( let's ignore any installation cost for now and look at only energy cost ) was installed on a 2010 Toyota Prius hatchback which normally get 65 mpg in the summer and about 50 mpg in the winter. Electricity after taxes is costing about 18 cents per kilowatt hour, from what I understand the engine block heater needs about three hours to warm up the prius ( total electric need per session 1.2kwh which translates to about 22 cents per session) Suppose gasoline cost about 3.40 per gallon. Let's estimate that prewarming up the Prius will give a 15 mpg improvement during the winter (that is, the engine block heater brings the Prius to its summer time fuel efficiency during the winter time). Without an engine block header the Prius can get up 50 mpg with just grill blocking in the winter (which last about 4 months) on a 16 mile commute. If one warmed up the Prius for only *to* work trip each month (20 workday per month) only 320 miles per month would be affected by the ICE warmup procedure which burns about 24kwh per month to achieve about a 1.48 gallons (6.4 gallons used vs 4.92 gallons used ) of gas saving per month. The cost of the electricity = $4.32 per month was used to save 1.48 gallons of regular 87 octane gasoline (@3.40/gallon of E10) = $5.03 month. The saving per month would be 71 cents per month for four months - plus you get MPG bragging rights...
My rule of thumb -- which needs refinement -- is that engine warmup normally costs about 2 miles of extra fuel, or 0.04 gallon. Maybe 0.06 gallon if frost is on the windows. But this is very coarse, and includes more heat than the EBH can provide, and catalyst warmup that is beyond the reach of the EBH. This limits the EBH value to something less than $0.15 to 0.22 of gasoline saved ($3.80/gal locally) per warmup cycle. But I welcome more precise measurements. I don't want to characterize the benefit in terms of MPG improvement because that will vary drastically with commute distance. And I don't imagine that it can boost your winter MPG to match your summer MPG because there are many other winter losses that the EBH does not help.
3hr to warm up in MD?? this sounds overly excessive. 1/2hr more then enough neighbor Yeah the savings are negligible, you probably save more by applying anti-fog on windshield.
At the risk of hijacking this thread, what is anti-fog? Is it applied to the inside of the windshield? I'd love for a way to avoid the irritating and at times dangerous fogging-up of the windows in cold weather.
All the anti-fog stuff I've seen is applied to the inside of the windshield. It's supposed to help prevent fogging of the window. I think years ago I tried using some of it, and didn't really notice a big difference. Of course, every situation is different, and maybe there's better products out there.
I know my estimates/numbers in scenario#1 were wanting - and that even how it frames the ROI is simplistic and dearly flawed - but I thought it might be useful as an initial starting point as to how one might try to approach and frame the answer/solution. My interest in the Engine Block Heater(EBH) is not to improve the efficiency or performance of the Prius windshield defroster system (albeit a EBH probably would do that) but to improve overall fuel efficiency of the Prius warm-up cycle when starting up in operating temperatures below 50F which ultimately impacts the overall winter time MPGs. That being said - I concide that the uniform EBH 3 hour warmup session cycle is probably way too long for my situation here in MD and that depending on climate the length of a EBH warm up session should vary with the outside temperatures. It makes sense to run the EBH only as long as it is necessary to get the ICE running at its most optimum temperature range is the quickest manner. Would it be fair to say that an EBH needs only 30 minutes to warm up the Prius when the outside temperatures are above 50F? Could the EBH warm up a Prius when the outside temperaturesare from 50F to 32F in about 60 minutes? Would running EBH about 90 minutes be sufficient to warm up the Prius if the outside temperature is between 32F to 10F? Without checking the local weather records - I'd say that there are less than 30 days per year in MD where a morning (8am) commute temperatures are less than 32F.
Anti-fog is a chemical applied on the inside of the windshield that inhibit fogging (condensation). It is sold in bottles or as towelettes. here are two brands that I have ------------------------------ Rain-X Anti-Fog (UnelkoCorp, Scottsdale, Az) Never Fog (North American Oil Company, Atlanta Ga) IMHO - They work best when the temperatures are above freezing(32F/0C). hope this helps Walter Lee mileage log on Cleanmpg.com under "HyperDrive 1" 2010 Toyota Prius Type3, Blue Ribbon/Dk Grey, oem floormat Yokohama Avid S33 (50/48) ScangaugeII ( FwT, SoC, GPH, RPM) 100% grill blocking Odeometer = 16750 miles, overall +60 mpg
