If the P4 is a typical vented heater with heat exchanger and the rating is on
the burner, there's your answer: the rating is on the burner and the heat
exchanger is not 100% efficient.

I can heat my house much more efficiently (near 100%) when running an unvented
gas fireplace than my house heater.  There are many factors involved, but my
heating bills (i.e. gas use) went down when using the fireplace.  You'll notice
that the exhaust of a vented heater with heat exchanger is still hot.  That's
lost heat, i.e. it's not 100% efficient.

BUT the big drawback of direct heating of unvented appliances is that they use
oxygen inside the living space and give off CO2 and H2O (lots of it).  That's
not safe or desirable in the long run.

-Karl

> >  At 19:08 10/17/2000, S Sittservl wrote:
> >  >If I turn the 5200 BTU/hr Westfalia stove on full (both burners) on
> >  >a 40 degree day, the van's interior temperature will be about
> >  >80 degrees in 10 minutes.  But if I turn the 7500 BTU/Hr P4 on full
> >  >on the same day, I might make it to 70 degrees after an hour.  That
> >  >seems like a lot more gas for a lot less heat.
> >
> >  2x5200 = 10,400, or 40% more than the P4...
>
> I thought  the 5200 BTU/Hr was for both burners.  I assumed that
> the label applied to the appliance as a whole, with everything
> turned on.  No?
>
>                                                       -Steven Sittser
>

Karl & Kristina Bloss - Trexlertown, PA
'00 Wannabusser "Julia"
'87 Westy Weekender "Bev" - 201K Miles
'85 Westy Camper "Fred" - 39K Miles
http://www.enter.net/~bloss/vw - vanagon@makarov.com
US West Trip 2000: http://www.enter.net/~bloss/vwtrek
PA/NJ/DE/MD area VW bus "group" http://www.enter.net/~bloss/vw/pavanagon
LINUX - for IQs higher than 98