The majority of American oil-fired boilers, and many gas-fired ones as well, use the single-pass heat exchanger type, whereas,  European boilers like Buderus, use a triple-pass heat exchanger. What this means is an American oil-fired single-pass boiler may have a 400-500 degree stack temperature (temperature of the flue gas going up the chimney), while a Buderus triple-pass design will have between 250 and 350 degrees going up into the atmosphere. That’s approximately 30% less heat going up the chimney and instead going into the space heating water.

What you don’t have as much of going up the chimney with European designs is C02 and a lot of other “nasties”. American-made boilers of the oil variety spew a lot more greenhouse gasses and S02 (the key ingredient in acid rain) into the atmosphere.

Interestingly enough, you don’t see many American fuel oil companies selling efficient European boilers, because that would reduce the amount of oil they would sell to their customers. I’ve often wondered if there is a further ‘cozy’ relationship between the fuel oil industry and American boiler manufacturers. American fuel oil consumers, you gotta wake up! In my opinion (from someone who started his career as an oil burner technician for fuel companies in the early 80s) you should never hire your fuel company to install your heating equipment, or service it either. That’s the same as letting the fox guard the hen house. Certainly, there are some ethical fuel dealers who do offer high-efficiency equipment and who employ decent technicians and sales staff.

The worst American oil-fired boiler types are the kind that utilize a “tankless coil” to heat domestic hot water. These boilers are so in-efficient that they have been banned in some states, like New York, unless it can be shown that the appliance has “an acceptable standby loss”. In my opinion, there is no acceptable standby loss with a boiler that heats potable hot water with a tankless coil, as the boiler must maintain temperature 24/7/365, and much of the heat generated goes right up the chimney. Of course, a stack damper would help, but not eliminate that heat loss up the chimney, not to the room the boiler is installed in.

Here is a video of a Burnham V73 boiler with a tankless coil – this equipment really eats up the fuel!

The better way to heat potable hot water is with a triple-pass boiler design like the Buderus G-series, and an indirect-fired water heater like a Triangle Tube Smart series. But then your fuel company will hate you if you switch from the American Oil Eaters they love to sell to their customers.

The only American boilers I buy are steam boilers, because the Europeans don’t heat with steam, they heat with predominantly forced hot water, because they know better than to heat with the least efficient of all heating technologies – steam and, therefore, don’t make steam boilers as a rule.