[Greenbuilding] Advice on heating in Tucson

[Racheli Gai]

Hi,
I live in a cohousing community in Tucson AZ.
Part of our common house is a building which doesn't benefit
from winter solar gain.
It has a kitchen, and when people congregate there to eat after a meal
was cooked, it's warm enough.  However, there are times when people
meet there (in the winter) and it's cold - at least by Tucson standards 
:)
What kind of heating would people recommend for a space which
needs only intermittent heating, and not for long durations?  - I'm
interested in both energy conservation, and minimizing pollution.
Additionally, it should probably be something which doesn't take too
much space (unless it's moveable).

Thanks,
Racheli.