We are renting, so I don't want to install anything permanently... but I need a way to warm my garage so I can work out in it during the cold months. And, since the house has no fireplace, I can use whatever I get as an emergency indoor heater and I realize that we would need to crack a couple of windows to make sure there's enough oxygen. It would be nice to have a unit that has a safety cut off for low oxygen and I'd like for it to be able to operate without needing electricity in the event power goes out during the cold months as this may be our only heat (the house has gas heat, but will have no fan if power is out to move warm air around). And, I'd need it to be somewhat portable or at least able to be moved around with a dolly or be in a cabinet with it's own wheels. Any suggestions on where to find options? I found one thing on Amazon HERE that uses what looks like BBQ tank (which should be able to be rented locally), but it doesn't have a fan to move the air. Please let me know if any of you guys know where to find stuff like this.