oil instead of water

Yes, but you need to build it from the get go for oil, due to the different physical properties.

emesine said:

Can you run a hydronic system with oil instead of water? What boilers lend themselves to this?

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An oleic system? In principle, sure. Growing up there was a neighbor that was too [del]cheap[/del] frugal to buy antifreeze and he used kerosene in his tractor's cooling system. It was an atmospheric pressure thermo-siphon system, stank pretty bad when he went down the road. And of course big transformers are oil cooled.

Specific heat of oil is about half that of water, and the density is lower, so you'd have to move more that twice the gpm to get the same btu per hour. Maybe a problem with gaskets and whatnot.

Seems like any pressurized boiler would as suitable as any other as long as you can pump oil through it fast enough to transfer the heat away and not get coking on the heat exchange surfaces.

Of course your insurance agent would drive up in a vehicle with a tank of fifteen or twenty gallons of gasoline behind the back seat and she'd tell you it was a fire hazard.

There are silicone oil based transfer fluids which are/were used in solar heating systems.
They tend to seep from packings and threaded joints more than water or antifreeze and they are quite expensive.

I believe they were a Dowtherm product.
They did have a very high flashpoint, which made them safe for solar systems, but I would wonder about wood systems.

I would expect boiler manufacturers would not be accepting of the use of oil.

Wouldn't have to worry about rust !

IF water were not so common, we would marvel at its physical properties- including its tremendous ability to move thermal energy- which exceed nearly any other substance unless, maybe, one gets into the truly exotic. Look out for dihydrogen monoxide cross-contamination, though: www.dhmo.org