Heaters like this claim to save on energy because they're smaller then an average conventional residential heating system. Smaller means alot less heating capacity which obviously means less fuel to use. They're known as "space heaters" so if you would like to shut off your regular heating system and use one of these you would have to close off pretty much your entire house and just live the space of one room or maybe two connecting rooms.

Our experience, in contrast to Mr. Havac:

While not as impressive as a Natural Gas Rinnai, we've had good luck with a 10 year old, 40K BTU Monitor (virtually identical to a Toyo). Although they have to be cleaned by a professional every couple of years (kerosene burns dirty!) we've had very good luck with ours.

Two floors, 1300 square feet, moderately well insulated, 25 year old duplex condo. This past winter of 07/08, we used less than 300 gallons of K-1. It was our sole source of heat... Portland, Maine, where K-1 is about 15% more expensive than regular heating oil.

We were relatively warm, but you do need to make sure you can have a flow of air to and from the heater, a convection loop as it were. We're installing a few between-the-floors ducts to help our circulation.

I gather the Toyostoves (as they are now called) are very popular on the West Coast, especially in Alaska... while the Monitor seems to be more prevalent here in the East. I think the two companies are related, but I not sure how.