Too small, and the diesel heater will not efficiently heat your space. It will use more electricity and fuel.
It may not even keep you warm, even in the highest and noisiest setting.
Diesel heaters can be problematic at high altitudes – above 5-6000 feet above sea level.
The top-end models have features that change the mix of air & fuel, so they still operate at higher altitudes.
Diesel heaters need a 12v electrical supply to get going. As a result, they demand a surge of power on startup and shutdown and a trickle when in use.
Once it’s warm, it runs at around 1 amp per hour.
Diesel fuel is quite a dirty fuel, so the heaters can suffer from carbon build-up over time. To prevent this, give the heater a run for an hour at full blast at least once a month.
Diesel heaters use diesel, of course, though the top-end models now have petrol versions of their products.
The fuel efficiency is fantastic and incredibly low on all diesel heaters.
The top-end models have a high cost, especially compared to a comparable Propex gas heater.
The low-end Russian and Chinese diesel heaters are much, much cheaper..