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Old 04-16-2018, 08:41 PM   #31
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City: Anacortes
Country: United States
Join Date: Mar 2016
Posts: 238
Not sure if you're talking in generalities or related to the Dickinson 1200. The Dickinson is a direct vent propane heater. It draws combustion air from the outside, through a double wall stack, uses that for the burner and then exhausts it. There is no mixing or using cabin air. The only way it heats the cabin is by radiant heat. Basically the thing gets hot and then warms the air around it. So it has very little effect on cabin humidity.

Originally Posted by AKDoug View Post
"Dryness" of the air in the cabin is a result of temperature of the heated air and where it is drawn from. Cold air brought inside the cabin and heated will absorb a lot of water since it has very little moisture in it once it's been heated up. Air drawn from inside the cabin and heated already has moisture in it. Think "dew temperature"...

The ventilation air draws in and is then heated causing both dryer air in the cabin and a slight positive pressure inside the cabin. As the cold air heats it is able to absorb and hold a much larger quantity of moisture and a constant stream of freshly heated outside air keeps the ability of the "new" air to pick up moisture from the cabin interior.

Combustion air and ventilation air are two completely different systems.

In my opinion that's the biggest advantage to a forced air system, IF the ventilation air is drawn in cold and then heated.
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