Some of those fake fireplaces and mantles look great. But I agree with the others -- forget about them as a heat source.

There are a number of "ventless" gas heaters on the U.S. market. They use an extra-efficient burner system, a catalytic converter, and a low-oxygen shutdown sensor. But I'm skeptical of them, at least in a sealed house and sleeping area. They still vent tiny amounts of carbon monoxide, and the moisture from combustion stays in the house. They'd be great in an unheated sunroom, though.

To my knowledge, ventless gas heaters are neither legal nor available in Canada.

I believe there are stand-alone gas fireplaces (with a wall vent) that will operate without electricity.

My parents installed a couple of these gas fireplaces, one in a sunken living room and one in their basement. They are surprisingly effective as heaters, and not half bad to look at either.