Case 3: Furnace Located In A Confined Space, Outdoor Air From Attic Or Crawl Space - Napoleon 9700 SERIES Installation And Operating Instructions Manual

IMPORTANT:
IF AN EXHAUST FAN, FIREPLACE, CLOTHES DRYER OR ANY SIMILAR DEVICE IS PRESENT IN THE
INDOOR AREA FROM WHICH THE COMBUSTION AND VENTILATION AIR WILL BE DRAWN, NEGATIVE
PRESSURE COULD BE A PROBLEM IF NATURAL INFILTRATION FROM THE OUTDOORS DOES NOT
MATCH THE RATE AT WHICH AIR IS EXHAUSTED.
8.1.3 CASE 3: FURNACE LOCATED IN A CONFINED SPACE,
In this circumstance, the free area of each of the two combustion and ventilation air openings is based on
a minimum of 1 square inch per 4000 Btu/hr. In this confi guration, one opening can originate from the fl oor
drawing combustion and ventilation air from the ventilated crawl space.
The other opening may communicate freely with a ventilated the attic. If using the attic air, ensure that the
opening is ducted from the ceiling high enough to be above the insulation. The attic must be adequately
vented with soffi t vents or gable vents (Figure 5).
As an alternative to creating an opening in the fl oor to draw air from a crawl space, a duct may be dropped from
the attic terminating 12" above the fl oor.
The following table shows minimum free areas
and round pipe sizes when drawing combustion air
vertically from the attic or crawl space for the furnace
only. If other fuel burning appliances are present,
their combustion air and ventilation air requirements
must be added to those of the furnace.
TABLE 2 - VERTICAL AIR SUPPLY (CASE 3)
Input Free Area
K/Btu/hr Ea. Opening
60 15 in. ²
80 20 in. ²
100 25 in. ²
120 30 in. ²
IMPORTANT:
IF THE ATTIC HAS AN EXHAUST FAN (POWER VENT), IT MAY CREATE A NEGATIVE
PRESSURE SUFFICIENTLY LARGE ENOUGH TO PREVENT THE ATTIC FROM BEING
AN EFFECTIVE SOURCE OF COMBUSTION AND VENTILATION AIR. POWERED ATTIC
FANS DO NOT CUSTOMARILY RUN DURING THE HEATING SEASON; HOWEVER,
SOME ARE CONTROLLED BY A HUMIDISTAT AS WELL AS A THERMOSTAT, WHICH MAY
ALLOW SOME OPERATION DURING THE HEATING SEASON. THE CHOICES ARE (A)
USE THE DIRECT VENT OPTION; (B) OBTAIN OUTDOOR AIR FROM ELSEWHERE; OR
(C) INTERLOCK THE ATTIC EXHAUST FAN WITH THE FURNACE SUCH THAT THE TWO
CANNOT OPERATE SIMULTANEOUSLY.
OUTDOOR AIR FROM ATTIC OR CRAWL SPACE
Round Pipe Size
5 in.
6 in.
6 in.
7 in.
FIGURE 5 - OUTSIDE AIR FOR COMBUSTION, ATTIC OR
CRAWL SPACE (CASE 3)
19
W415-1064 / 11.11.11