I'm still here after using my Olympian catalytic heater four four years before I got an additional Plat Cat heater. Now if it gets really cold the Plat Cat vents the Olympian as well.  
The main thing is you have to leave about a two inch opening in a window. H2O and carbon dioxide, the stuff you exhale, are the by-products of combustion. The important thing is to remember is that combustion can only take place with oxygen present, so if the interior is sealed air-tight, a catalytic heater will consume air and and suffocation is the danger .

As long as there is a constant fresh air supply sufficient for heater combustion and breathing, these two brands I know about are safe to use indoors.   

----- Original Message -----
Wrom: WZIDREXCAX
Sent: Tuesday, July 30, 2002 1:53 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Interior heater

> What CO problem Rob? The product of combustion is H�O. All you need
> to do is have a vent to allow fresh air to enter and the excess moisture
> to exit.

Gotta chime in here,

The CO problem that has been responisble for killing many people from
using an unvented catalytic heater in their vans or RV's.  How do you know
how much fresh air needs to enter?  It may be okay to use while you're
awake but sleeping with one of these things on is downright stupid.

Andrew Fox
86 Westy w/ plat cat vented catalytic heater that kept me warm  and
alive camping over 20 nights last winter in sub-zero temperatures.Get more from the Web.  FREE MSN Explorer download : http://explorer.msn.com