On Sunday, April 1, 2012 8:46:10 AM UTC-4, wrote:


I'm no expert on draft regulators, but thinking about
the location issue, the following occurred to me.
The draft regulator is basicly a door that swings open
against a spring so that as the chimney draft increases
it will open to let more air in and try to keep the draft
to the furnace constant. If that door is in a horizontal
section of flue, the combustion gas stream is only hitting
the edge of the thin metal door and it will have very little
interaction
with the door. The gases pretty much go right by it.
If the regulator is inserted in a vertical
section of flue, when the door opens, the combustion
gas stream is hitting directly against the door and
exerting pressure against it.

That may be the key issue. How big of a difference it
makes, I don't know.
_____________
Most are now counter-weighted: http://ecx.images-amazon.com/images/...500_AA300_.jpg So depending upon how much draft is needed the weight can be turned in or out so it takes more or less draft to open the door.