National Oilheat Research Alliance 9
Basically, the test simulates what happens
if all of the air stealing appliances, except for
a whole house exhaust fan, are on at the same
time. To conduct a worst case draft test, the
technician should perform the following tasks:
(1) Close fireplace dampers and fireplace
doors, close all exterior doors and windows in
the building, and close all interior doors in the
building.
(2) Turn on the building’s air exhaust sys-tems,
including clothes dryers, range hoods,
bathroom exhausts, and mechanical ventila-tion
and forced-air heating or cooling system
blowers and operate them at their highest speed
setting. Do not operate a whole-house exhaust
fan.
(3) Operate the burner in the oilheating
appliance with the lowest firing rate first, and
then other appliances in order of increasing
capacity. Measure and record the breech draft
and over-fire draft of each appliance, and check
for flue gas spillage.
(4) Check that the breech and over-fire draft
are at a level that is required by the oilheating
equipment manufacturer as specified in the
installation and operating manuals for the ap-pliance.
Over-fire draft values in oil appliances
are usually negative 0.01 to negative 0.02 in. of
water column (-0.01" wc to -0.02" wc).
(5) If the draft is maintained at the manu-facturer’s
recommended level, the technician
should return doors, windows, exhaust fans,
fireplace dampers, and appliances to their pre-vious
conditions of use.
(6) If the draft is NOT maintained at the
manufacturer’s recommended level, take action
as needed to correct excessive depressurization
of the appliance combustion air zone and return
the flue draft and over-fire draft to the require-ments
of the oilheat equipment manufacturer. If
additional steps are necessary, shut the appli-ance
down until the situation can be corrected.
Notify the homeowner, building owner, or
occupant if combustion air zone depressuriza-tion
impacts the operation of the oilheating
equipment and of all actions and modifications
that are required to allow the flue draft and
over-fire draft to be maintained at the level
required by the oilheating equipment manufac-turer.
Dealing with Confined Spaces and
Other Combustion Air Challenges
In addition to the NFPA recommendations
that address getting additional air either from
the outside or from areas inside the building,
there are two other possible solutions to correct
a combustion air problem.
Additional air can be brought from the
outside into the combustion air zone through
the use of direct or indirect connections to the
outside.
Direct Connection
A direct connection brings in outside air
directly to the oil burner. This can be done by
adding an “air boot” (Figure 10) that con-nects
directly to the oil burner, such as the one
pictured here.
Figure 10