Join Date: May 2005
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Re: Forced air heater duct design
I Have a couple of Espar D-4 units, one on each boat. They both draw combustion and conditioned air from the environment, same source. The “exhaust” air goes out the chimney, the heated/conditioned air goes out the duct into the cabin.
FWIW I’ve never seen any requirement or installation material suggesting that combustion air should be pulled from outside.
Think about a wood stove for a minute. The combustion air comes from the cabin and goes out the chimney. The conditioned air circulates around the hot stove, which is just a poor heat exchanger, and circulates back to mix with the cabin air.
33' Brewer, Murray 33, steel cutter
44' Pape, Steelmaid, cc steel cutter