It is not safe to use a unvented catalytic heater
in a enclosed space.
A unvented catalytic heater will work ok for those who camp
in a relatively warm place and use it more like a campfire, with
lots of ventilation.
I found that a unvented catalytic heater can give me a terrible
headache if it stays on all night, even with a window partly open.
In addition one loses almost as much heat as you gain from
the necessary cross-ventilation.
Basically if one is serious about winter camping in a northern
climate, any unvented heater is a pretty useless health hazard.
Discovered this by trial and error.
The only vented catalytic heater on the market, the platinum
cat,  is totally safe and comfortable to use in a small closed and
insulated space, since it does not release any combustion
by-products into the surrounding air.
The forced-air ventilation from the platinum cat does not
create any cold drafts. I found that enough air enters the
camper through the front dashboard vents, for the platinum cat to
operate safely.
To compare a unvented catalytic heater with a vented catalytic
heater is kind of like comparing a smoky campfire with an
airtight modern wood stove. Which one would you
prefer in your living room?
I am probably somewhat biased, since my platinum cat
vented heater has given me more than 10 years of faithful
service in several vanagons.
Harald
90 westy.