Dejanh the espar system is actually THREE seperate systems:
First one is to keep the bunk warm. The "air heater". Espar offers different models:
http://www.espar.com/htm/airheat.htm
If you have a large bunk, or you go up north in the very cold, I recommend the airtronic 4.
My dad did the installation, but I can tell you it's not a couple hour job. There needs to be a fuel line run, wires run to both the battery and inside the bunk. Theres also TWO intakes and TWO exhaust. One of each goes into the bunk(these two are for keeping you warm), the other two stay outside(these two are for combustion). The way mine was done was it was put underneath the bed, in the "tool section". If I were to do it again, it would be right in the bunk. I think this is better, keeps the unit warmer.
These air heaters do NOT keep your engine warm. Read on for those.
Second system is called the "hydronic". For these I would definitely recommend a larger unit, no matter where you are. A larger engine requires more heat.
They are more efficient then most units out there because they do not run all night. You will find those old "run all night" units obsolete. Wabasto comes to mind, now they have a "2 piece" separate air/coolant heaters. Before it was just one unit.
http://www.espar.com/htm/Specs/water/wterheat.htm
I recommend the hydronic 5. With this unit, you run the two coolant heater lines for your bunk heat through it. I recommend having it under the hood, so you don't get as much heat loss. Mine is currently under the bunk, but I may change that.
To install this unit, you need to tap a fuel tank, run electrical to the batteries, run electrical to the bunk to control the unit, and run 2 coolant lines through it. I also recommend running a winter front, as well as insulating the coolant lines.
These units can be equipped with a 7 day timer, very highly recommended. You can leave the truck sunday, set it for wednesday at 5:00 pm, and by the time you show up at 7:00 pm it is warmed right up. This unit will run a MAXIMUM OF TWO HOURS. It sucks a lot of amps(up to 5 amps!)
The third and final "total bunk solution" is an air conditioning unit. I have zero experience with these but I am getting one this spring. I used to park at a terminal every time I slept, so I could just plug in an apartment air conditioner. Not so any more. I will tell you my dad actually runs an apartment air conditioner with his inverter! Batteries don't last long though, a year at most.
The most important thing with these 3 units is that your batteries are in good shape. Also make sure *ALL* of your connections are good. A loose connection running from your alternator won't charge your batteries as good.
That being said, my truck has
*NEVER* failed to start. I've seen -40
before windchill and -52 with the windchill.
However, I do have the small air unit, and sometimes I do get a bit cold. I have insulated my truck, and it definitely helps.