14 National Oilheat Research Alliance
Figure 1
Conduction
Draft drop is the difference between the
measured draft over the fire and the draft at
“the breech”—a straight piece of the flue pipe
on the appliance side of and at least 6" from the
draft regulator.
If there are -.04" wc of draft at the breech
and -.02" wc over the fire, the draft drop is
-.02" wc. Figure 4.
As with all settings for Oilheat appliances,
the manufacturer’s instructions must be fol-lowed.
Notice that the draft drop through the appli-ance
is not the same for all boiler sizes. Be sure
to adjust each appliance to the manufacturer’s
specifications. Figure 5
Figure 3: Measuring over-fire draft.
Figure 5
Figure 4
Sections
Draft loss
through
boiler
(in. wc)
2 .020
3 .020
4 .010
5 .015
6 .015
7 .015
8 .025
9 .030