At 03:47 PM 11/3/98 , davidson wrote:
>I don't understand. Can you explain how this can be so? How does an
>unvented catalytic heater (vented with windows open a crack) create more
>water vapor in the van than a vented heater? They are both creating heat,
>they both have air intake from outside and air exhaust to the outside? Have
>you measured this?
>Bill
>90 Westy Syncro
>Lake Tahoe

The "exhaust" from a hydrocarbon fuel is mainly water vapor -- steam.  Propane
is C3H8 (I think) and so C3H8 + 7 O2 -> 3 CO2 + 4 H2O.  Unvented heaters
dump the CO2 and the H2O into the inside of the bus -- lots of H2O.  Vented
heaters dump it out their exhaust pipes.

This is the steam you see from your exhaust pipe one those cool high-dew-point
autumn days as well -- and the water dripping from your tailpipe -- gasoline
is also hydrocarbons, and so produces lots of water when burned.

In your camper, the propane stove does the same thing -- think of the flames
you see as hot carbon dioxide and steam -- mostly steam!

Malcolm H.