
Any heater powered by liquid or gas fuel burning directly in the atmosphere will cause massive condensation.
Gas heaters are just as bad on the moisture front. Whilst ever the temperature is kept raised, the moisture will stay in the air, (upto a point), but let the temperature drop, and that moisture will condense wherever it can.
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Aye, that's the worst problem with large masses of metal.
That's why I stick with electric options, even though it is just about the most expensive option to run. Solid fuel or electricity are safe heating means, moisture wise. Everything else will eventually give grief around machinery unless there's constant ventilation and airflow, but then you're in a swings and roundabouts situation because you're constantly replacing the heat you're removing/losing.