It heats the coolant to about 180 F .It is wired to the temperature controls.You control the amount of heat you want like you do when the engine is running. 
It's uses less fuel as a heater than running the engine for heat.Designed to be used when stationary.I don't have any experience with one, I seen them, I don't know if you can use them while driving. 
Robert1982 Westfalia

 
      From: Jeff Palmer <jpalmer@MYMTS.NET>
 To: vanagon@GERRY.VANAGON.COM 
 Sent: Wednesday, January 28, 2015 10:43 PM
 Subject: Re: Gas heaters...was Re: Heater
   
I’m confused.  Is the Webasto BBW46 for heating the cabin or heating the coolant?  
Jeff
85 Westfalia with cabin gas heater

> On Jan 29, 2015, at 12:33 AM, JORDANVW@aol.com wrote:
> 
> In a message dated 1/28/2015 11:38:44 P.M. Eastern Standard Time,
> vwrobb@GMAIL.COM writes:
> 
> Wasn't  there a Canadian option for a gas heater for the cooling
> system (pre-heat  the coolant in the winter)?
> 
> 
> 
> 
> 
> 
> that's the webasto bbw46.
>