Oddly enough, Carrier Corporation...one of the biggest American air conditioning companies used Riello burners exclusively on their oil fired equipment (boilers and furnaces)
Back in the pre central-air conditioning days here in the USA...well, at least in my hometown of Richmond, and parts further northeast, oil fired hot water heat was the way to go for both simplicity and minimal building expense. This was the system employed by many mid-century developers and architects such as William Levitt, who built in New England and mid Atlantic areas, and by Henry Eichler who built even more modern style homes on the west coast. Many other builders used these systems as well.
Oil fired systems used in many mid-century homes have baseboard radiators in wood-frame homes, which is basically a finned pipe behind a metal cover at the bottom edge of the floor. If the home is built slab-on-grade, the pipes are simply buried in the concrete slab when the house is built. The heating pipes are imbedded in the slab heat the floor of the home. The radiant floor system is really nice for giving out comfortable draft-free heat that many users say is comfortable at a lower thermostat setting than forced-air heating. The baseboard systems have almost the same comfort level as the radiant floor systems as well. Domestic hot water is heated by the same boiler by using a hot water loop within the boiler's heating water tank. If Domestic hot water is needed when the home does not need heating, the boiler's burner will kick in, but the circulator pump for the heating system does not run.
Oil fired hot water heat was cheap for the builder and developer because gas lines did not need to be installed when the infrastructure of the new subdivision was put in place. It was also more inexpensive for the builder, since it elimintates one mechanical system, the hot water heater, due to the fact that the boiler is doing double-duty providing water for both systems. There is also the advantage that the home's frame does not need to be constructed to accommodate the extra "tin" needed for large ductwork in a forced-air system. It's much easier to hide a 3/4 inch pipe behind a wall than a 12 inch round air duct. There's also the advantage that another tech was not needed for the installation. The same plumber that hooked up the bathrooms and sinks can be used to install the heating system.
For a breif while around here, electric baseboard heat, with separate hot water systems got slightly popular, but quickly faded as electricity prices in the seventies got high...Oddly enough, oil caught back on until the late 70's when heat pumps came on the scenes, and homeowners started demanding central air conditioning in new homes. Nowadays, heat pumps seem to be the defacto standard in new homes. I imagine this is done for the same reasons hot-water baseboard systems became popular...because of minimal building expense and to mimimize mechanical equipment the builder needs to install. The other factor is that homes are much larger now than they were back in the 50's and 60's (1200 sq/ft versus 2500 sq/ft0, and the ductwork is easier to accommodate in the larger rooms. If a hot-water system is used, the new home buy is still going to want air conditioning, which will require ductwork, and a separate mechanical system. Elecric hot water heaters today are much cheaper than a separate central air conditioner. For that reason the heat pump is used, which will serve the purpose for both heating and cooling with a separate electric water heater for domestic water. The problem is that while air conditioning provided by the heat pump makes the home very comfortable during the summer, the heat pump provides cool, drafty, minimal heating comfort during the winter months. Most people end up upgrading their heat pumps after the home is built with a gas backup system fueled by natural gas if the lines come through their neighborhood, or by propane bottles, if there are not gas lines.
