I'm not sure if this applies to Vanagons or
not, since I'm not familiar with the arrangement,
but I'll assume it's the same, and yes indeed,
you need that exhaust.  (I know this from experience)
What's probably happening is that your regular
heater is sucking in "fresh" air that's been
polluted by your gas-heater.  The exhaust needs
to be in place to direct the crap away from
your other intake.

I can also tell you to not go to VW for new,
as the money they want for the heater exhaust
would double the GNP of many small countries...

Mike Wright
Ackworth, Iowa
68 Campter; 79 Bus
wright@storm.simpson.edu