How do oil filled radiators work?

Updated April 10, 2017

An oil-filled space-heater radiator is a freestanding version of what was under each of Grandma's windows, connected to a boiler for hot water or steam. Like Grandma's radiators, it's actually also mislabelled.

Convection, Not Radiation

Both freestanding and system "radiators" actually heat by convection --- the heat from inside the coils or fins is transmitted to the outside surface by conduction, and as cool air contacts that hot outside surface, it rises into the room and draws more cool air into contact. In practice, this means these heaters don't need fans to distribute the air they've warmed.

Heating What's Inside

The oil inside a freestanding radiator doesn't burn. It's used because it doesn't need to circulate through a boiler to be heated, so it can be heavier, and because it's thicker than water, it holds heat longer. Electrical circuits warm the oil by actual radiant heat.

Slow Start, Long Finish

It takes some time for the oil to get warm enough to get the convection going, so an oil-filled unit isn't the way to take the chill off a room fast. On the other hand, once the oil is warm, convection will continue for some time even after you've turned off the power.

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About the Author

Barbara Kellam-Scott has written since 1981 for print publications including "MassBay Antiques" and the award-winning corporate science magazine "Bellcore EXCHANGE." She writes as an advocate and lay Bible scholar in the Presbyterian Church. Kellam-Scott holds a Bachelor of Arts in intercultural studies from Ramapo College of New Jersey and conducted graduate work in sociology, theology and Biblical Hebrew.