The Field Controls Draft Control Guide recommends damper placement as close to the furnace as possible (but 12" beyond a stack switch) except for 'forced draft' systems. Is 'forced draft' another name for 'direct vent'?
IMHO direct vent is venting directly to the out side with the manufacture's limited length of vent and temination, with no forced or mechanically assisted venting. Forced draft would be as implyed, a fan assisting the exhaust flow.....
Forced draft is when a fan (ex. combustion blower) is used to create a positive static pressure in the vent pipe to exhaust the combustion gas to the outdoors.
Forced draft is as "mizzo" suggested, a combustion fan used to produce a positive pressure in the flue.
Draft assisted is different; it only induces the draft through the heat exchanger at a preset rate. Yes, it may result in a slightly positive draft neart the outlet of the combustion fan, but natural covection is used in the flue.
A direct vent unit can be a configured as a forced draft. The difference is, a "direct vent" is only with both intake and exhaust taken from outdoors. Without the combustion air intake taken from outdoors, it's just a forced draft.
"The only true wisdom is in knowing you know nothing" Socrates
FYI, all positive vent pressure venting must be listed venting per the IRC. We on the Ul Standards Technical Panel are working on a US version of the Canadian S636 code for listed PVC venting. Stay tuned.
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