Thank you for all your replies.
After long thinking and making mocks I decided to go for blow air system. The reasons for me were:
-Blow air heats boat faster then radiant type,
-It takes air from outside, so with proper installation
all air will be replaced in the boat even from bilges.
and electricity nearly same
-No issues with back pressure
-Easier to find place on the boat for the unit (I made mocks of them for trying different places)
-Easier to light up (just matter of pressing button)
-It cost more , but by the time price
will be forgotten and in general I think it will be cheaper to run air forced heaterin relation fuel consumption
vs speed of heating boat
So now Iím I progress of ordering Wallas 30DT.