Let me get right to the point: unvented gas (and kerosene) space heaters and fireplaces are a bad idea. Don't install one.
Last week I described some observations about transportation from a trip I took to Sweden two years ago. While there, I toured two state-of-the-art, wood-chip-fired, combined heat and power (CHP) plants, one in Kristianstad and one in Växjö.
I had the great fortune two years ago to spend a couple weeks in Sweden. In late December 2007 I was visiting my daughter, who was studying at Lund University.
For energy conservation, 'where' you build could matter more than 'what' you build.
Regular readers might remember the toilet-flushing video from March that showed ridiculous quantities of carrots, chess pieces, Gummi bears, hot dogs, plastic letters and numbers, grapes, golf balls, and dog food getting flushed. Fun, but it didn't qualify for GreenSpec because it only met the federal minimum standard for water use.
Thermal batteries can be as effective in load shifting as electrical batteries, without the supply chain issues.