Check out the Bock water heater at www.bockwaterheaters.com. Fuel oil contains more BTU's than either natural gas or propane and with a well engineered unit like a Bock, oil can be an excellent fuel source.
Bock also manufactures an amazing variety of gas water heaters, all with great recovery rates, excellent efficiency, power venting capabilities, and some models with BTU/hr. ratings of up to 600,000!
If you have a few minutes to download a PDF file and you want a detailed look at the inner workings of the Bock water heater, see their Literature page.
A note about alternate fuels
This information doesn't apply to oil-fired Bock water heaters, but Biodiesel, a product made from virgin soy or waste vegetable oil, is now commonly processed into a fuel that in many cases can outperform petroleum products. Biodiesel is cleaner, renewable, contains no sulphur and would be well worth investigating for use in a heating appliance.
In fact, as a real world example of how effective even pure vegetable oil can be, our web designer collects used fryer grease from restaurants, filters it, and then pours the straight oil directly into the fuel tank of her diesel Volkswagon Jetta! She estimates her fuel costs at $.10 per gallon (the filters cost a few pennies each).
Actual biodiesel is vegetable oil processed to more closely resemble the No.2 heating oil used in oil-fired water heaters and boilers and could very well serve as an alternative to a petroleum based fuel source. Several "waste oil" boilers currently on the market would happily burn biodiesel and so would many conventional oil-fired boilers and water heaters.
But needlessly to say, always check with the manufacturer of your chosen heat source before using biodiesel and, should you go that route, always use a biodiesel blend that carries the ASTM certification.
For more details about biodiesel, follow this biodiesel link.
American ProLine Series
If your BTU requirements are moderate, it may not be practical to spend $2,300 to $4,000 dollars on a high-efficiency water/space heater. The Polaris and the Bock are powerful units. But, if they're oversized for your application, you end up with a lot of expensive, highly efficient heating capacity sitting around doing nothing much of the time. This is especially true if your system utilizes a secondary heat source such as solar panels or an outdoor wood boiler. In these two cases, the water heater is mainly a back-up and it rarely makes sense to own a four thousand dollar storage tank.
The American Water Heater Proline Series units come in a wide range of storage capacities (30 to 75 gallons), heating capacities (between 40,000 and 75,000 BTU's/hr) and are available in either gas or electric models.
American even offers Direct Vent and Power Vent models, and some have extra side taps for easy installation of a heat exchanger loop when secondary heat sources are part of the heating system. Quality wise, they are a level above most "standard" water heaters. Their efficiency rating is 78%.
