[gumby79]

The longest our family was able to stay in 1 spot was 3 months, chasing my seniority. Average was 2weeks ,exception was winter lay off. Layoff at Union Pacific Railroad could be hours- months depending on seniority and availability. A 250ga tank would be nice , however not practical as we had to be able to pick-up and go on a moments notice. So we carried a spair tank that got rotated through. Once a week wasn't so bad to fill the gas during the worst weather, 1-2 month in summer. We went to town for food more often than that. 3 people ÷ small RV fridge =frequent store runns.

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How long to plug-in

((W*btu)÷lbs H2O=Delta T per hr) - losses

[Not accounting for thermal loss from lorn block or cooling sys] [not accounting for effect of antifreeze]
1btu= 1°f for 1lbs water
1watt= 3.41btu
1 ga= 8.36lbs
Cummins blockheater=750wh
Late first generation Cummins=4ga coolent

((750*3.41)÷33.44=76.49°f/hr ) - losses
So 1hr will do ~ 50°f/hr

Engine Block Heater
The engine block heater is a resistance heater installed in the water jacket of the engine just above and behind the oil filter. It requires a 110- to 115-volt AC electrical outlet with a grounded, three-wire extension cord. The engine block heater is required only when ambient temperatures are below -20F (-29C), but recommended at temperatures below 0F (-18C). For full capability, once you turn on the engine block heater, it needs to run for one hour before you start your truck.
Ram Turbo Diesel Cold Weather Tips – Geno's Garage

We know its helpful at any temperature below operating °f
I'm using my plug 24/7 now (power bill is upsetting) and at 37below 0°f its a hard start. So I'm going this route http://ecomodder.com/forum/showthrea...ter-34459.html theas are also used a primary Hydronic cabin heater in RVs.