Application Note

6 Fluke Corporation Carbon monoxide: A mechanic’s approach
Fluke Corporation
PO Box 9090, Everett, WA 98206 U.S.A.
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. [phone] or
Fax [phone]
In Europe/M-East/Africa [phone] or
Fax [phone]
In Canada (800)-36-FLUKE or
Fax [phone]
From other countries [phone] or
Fax [phone]
Web access: http://www.fluke.com
©2010 Fluke Corporation.
Specifications subject to change without notice.
Printed in U.S.A. 1/2010 3611250A A-EN-N
Modification of this document is not permitted
without written permission from Fluke Corporation.
Fluke. Keeping your world
up and running.
®
Combustion air tips
Any return ducts located in
the same space as the fossil
fuel equipment must be sealed
airtight.
Filter access panels must be
sealed airtight.
Returns and filter access
panels located in garages must
be sealed airtight, airtight,
airtight.
When combustion air open-
ings to the outdoors are used,
always use two: one high, one
low. If ducts are used to connect
to the outdoors, use two ducts,
one for each opening. If only one
combustion air supply or duct is
used, it may act like a vent in
the space and try to remove air,
rather than make it available.
Add a small register to the
supply trunk in the equipment
room and make sure there are
no return leaks. This will make
available in the equipment room
the same air that’s available to
the entire structure. Supply-
ing 33 cfm per 100,000 BTU
input allows for 50 % excess air.
Footnotes
(1) LEED-EB IEQ
LEED = Leadership in Energy Efficiency and Design
EB = Existing Building
IEQ = Indoor Environmental Quality
(2) Rate of CO
2
generation per person = 0.0084 cfm x met rate
Resting met rate = 1.0
Light activity met rate = 1.2
Cooking met rate = 1.8
House cleaning met rate = 2.7
Calisthenics met rate = 3.5
Basketball met rate = 6.3
(3) Calculating CO Air Free
(Oxygen in Air/(Oxygen in Air - Oxygen in Vent Products)) x
CO in Vent Products
(21/(21 - O
2
Sample)) x CO Sample
(Ultimate CO
2
/(Ultimate CO
2
- CO
2
Sample)) x CO Sample
Natural Gas: (12/(12 - CO
2
Sample)) x CO Sample
LPG: (13.7 / (13.7 - CO
2
Sample)) x CO Sample
#2 Fuel Oil: (15.6/(15.6 – CO
2
Sample)) x CO Sample
O
2
example: (21 % O
2
/(21 % O
2
– 6 % O
2
Sample)) x 100 ppm
CO Sample = 140 ppm CO Air Free
CO
2
example: (15.6 % CO
2
/15.6 % CO
2
– 12.5 % CO
2
Sample))
x 100 ppm CO Sample = 124 ppm CO
(4) Values based on National Comfort Institute recommendations
developed from many years of research data
(5) Gas Engineers Handbook
When natural draft venting is
used, double this amount. While
you’re at it, add the poor man’s
ventilation system. A duct with
a balancing damper between a
hood installed outdoors and the
return duct will ensure an “on
demand” pressurizing whole-
house ventilation system.
Remember that any outdoor
air access must not use a screen
covering with less than ¼”
mesh. Smaller mesh screens can
become lint traps which block
the supply of outdoor air.
Various after-market combus-
tion air systems are available for
quick and easy installation.
A heat recovery ventilator
could satisfy the requirement
for combustion air, along with
providing healthy indoor air.
See how much money is
available for ensuring adequate
ventilation, venting, and com-
bustion air; then see how much
is left over for the furnace or
boiler purchase. If we didn’t
think our brakes would work,
we wouldn’t even want to start
our car. Don’t even think about
starting a fossil fuel product
until you’re sure that there is
adequate ventilation air.
One would think that direct
vent gas and oil products would
not have combustion air prob-
lems. Yet improper design and
installation or poor location can
cause exhaust gas recirculation
into the air intake and create
elevated CO and even sooting.
Chances of lingering direct-vent
exhaust gasses increase with
low velocity discharge, mild
weather, dampness, low baro-
metric pressure conditions, or
any combination thereof. Follow
the manufacturer’s direct-vent
application and installation
requirements very carefully and
don’t use one manufacturer’s
guidelines for another manufac-
turer’s product.