This is purely speculation, as I have never owned one, but I would guess these to put out very very little heat. Per their site these fireplaces are described as "decorative", not so much for heat.

In my space I have one of these, they REALLY pump out the heat if it could be something you could fit into your place. I run my whole house off two 100# tanks, but you could run this for cold occasions only on a 5lb tank.

Alternatively, I also have two of these, which REALLY pump out the heat, but you need to make sure you crack a window as they are not externally vented and do use oxygen.