Harvey, et all;
You are all quit right as to leaving the top up and using it as a heater.
The owner's manual for the Wallas 95DP states in a "NOTE: (1) The stove can not be used as a heater without the heater lid closed." This is an insert in my manual for the 'Wallas Safeflame Ceramic Diesel 125DU'.
I don't know if there is a difference other than the heat generated. When I have been doing this it is with the control set very low in the "1-2" range; else I have left the top down.
I must be very fortunate that I don't have any problems. I do start and finish the operation at full heat with the top down . I leave the heat on "6", MAX, for abt 2 minutes+ before I turn the control panel rocker switch 'OFF'. When the LED stops blinking and goes out I know it is safe to do a full power down in the boat.
Do not prematurely turn the unit off if the LED is blinking; either at startup or shutdown.
I hope this helps clarify and I apologize for any confusion I may have set. One interesting note is the left burner runs several times hotter than the right.
Another UBI, for the 125DU is - -
Fuel consumption: 3-5oz/hr
Supply Voltage: 11-14.5VDC
Current- Normal Operation: 0.15A
Current_ Startup: 8A for ~4.5min.
Left heater effect: 3070-6150 BTUs
Right heater effect: 850-2050 BTUs
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