I have a portable propane catalytic mfg by Coleman in the 60s  4800BTU and will 
keep the frost off yer punkin.  These use the Olympian mesh technology for the    
catalytic burner and have flame off safety valves.  You can sometimes find 'em
at used things places.  I bagged mine at a yard sale for $20US.  

For an accumulator type heater for using on the stove you'll want the following
properties.

medium conductivity, smooth surface, high specific heat and thermal mass.  An anvil fits the bill but of course has other drawbacks.   For a radiant heater try a 
simple 8" flower pot inverted over the flame.  Works pretty well but of course has 
virtually no thermal capacity so the 'carry over' effect when you turn off the 
fire is pretty limited.

It does do handwarming and space heating pretty well though.

BTW the flower pot does get HOT! so appropriate caution and handling techniques are
advised.

Anyone know how the desert flower season is progressing?
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         ___  / __   __/   ____/         Al Knoll HP Performance Technology /
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      /           /     /             email:  alf@hpptc38.rose.hp.com    /
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