[dumass]

I've got a hot water recirc system in two apartments and in ten years I've only had 1 pump failure (due to the tenant running it continuously for a couple monts with the heat off) using the old radiators (1927 4-plex). fwiw have you considered a loop with your engine (with isolation ball valves of course) and a propane fired heater plumbed like the camp showers? You could embed the water lines into foam insulation in the floor and if you really worked at it the thermal flow would help the recirc pump.

http://www.espar.com/
I have one of these in the Volvo and they also make diesel fired coolant heaters which would work for this kind of application I think.

 

[dumass]

I've got a hot water recirc system in two apartments and in ten years I've only had 1 pump failure (due to the tenant running it continuously for a couple monts with the heat off) using the old radiators (1927 4-plex). fwiw have you considered a loop with your engine (with isolation ball valves of course) and a propane fired heater plumbed like the camp showers? You could embed the water lines into foam insulation in the floor and if you really worked at it the thermal flow would help the recirc pump.

http://www.espar.com/
I have one of these in the Volvo and they also make diesel fired coolant heaters which would work for this kind of application I think.

http://www.espar.com/htm/Specs/water/wterheat.htm
When heat is called for by the switch or timer, a control unit signals the units integrated Coolant pump to start circulating the coolant.