The squat caframo style ones are almost impossible to tip over, and with main air intake on top and a smaller one on the bottom they work well. I have considered adding mesh over the top air intake so that air can get in even if it gets covered.
I always run the thermostat as low as will keep the cabin warm, that way if the heater vent is blocked it turns off right away.
If it fails, it is OFF. the oil heater tipped over is still hot, even assuming the tip over sensor works. I've already damaged 2 things and burnt myself on the oil heater.
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