TEC DG-700 User manual

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Using the DG-700 and TECLOG3 to Measure Worst Case Fan
Depressurization and Appliance Draft
Buildings with natural draft combustion appliances should be routinely tested to ensure that the
spillage of combustion products into the building is unlikely. Combustion safety testing is critical
because of the potential for severe health effects from spillage susceptible appliances, including
carbon monoxide poisoning. Building depressurization, caused by exhaust fans, dryers,
unbalanced forced air distribution systems, and duct leakage can be a major cause of appliance
spillage. As buildings (or combustion appliance rooms) are made tighter, these problems can be
made worse, although very leaky buildings can also have venting problems related to
depressurization. One way to determine how the combustion appliances respond to changes in
building pressures is to perform a worst case depressurization test, along with an appliance draft
test.
If you have a DG-700 gauge (or a DG-500 or APT data acquisition box) and a laptop computer,
you can easily perform and graphically document these important tests. All you need is a copy of
our TECLOG3 software (available for free at www.energyconservatory.com) and a
communication cable (USB or 9-pin serial), or TEC WiFi Link to connect the DG-700 gauge to
your computer. Using TECLOG3 along with your DG-700 gauge you can capture and record the
two best indicators of venting performance, namely the pressure in the Combustion Appliance
Zone (CAZ) and the appliance draft pressure. (Consult Chapter 10 of the Minneapolis Blower
Door Operation Manual for more details on combustion safety testing.)
Getting Started/Example File
Below is a quick summary of what is involved in performing these tests. This summary uses an
example test file recorded on a house with a natural draft water heater (the furnace was sealed
combustion). The DG-700 gauge is located in the CAZ for this test.
1. Set up your DG-700 gauge to measure both the CAZ pressure and the vent pressure for a
natural draft appliance. Since we want to measure the CAZ pressure with reference to
outside, you will need to connect the Channel A Reference tap to the outside using a long
piece of tubing. Leave the Channel A Input tap open to the CAZ. Connect the Channel B
Input tap to a static pressure probe installed in the appliance vent. Leave the Channel B
Reference tap open to the CAZ.
2. You will need to create a communication link between the DG-700 gauge and your laptop.
You have two options to create this link.
•Physically connect the laptop to the DG-700 gauge using a USB or 9 pin
communication cable. This will typically require the laptop to be in the CAZ. Note:
go to http://www.energyconservatory.com/support/user-tips#1 for information on
using the DG-700 communication ports.
•Or, use a TEC WiFi Link to create a wireless communication link between the gauge
and the laptop. This will allow the laptop to be almost anywhere in the house. Note:
see documentation that came with the WiFi Link.
3. Start TECLOG3 and open the Configuration Settings
window (click on Configuration….Settings). Enter 1.0
seconds into the Sample Interval field (this tells
TECLOG3 to take one second average pressure readings).

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4. In the Device Settings part of the Configuration Settings
window, you will need to enter the Device Type and
Serial # of the gauge on the top line. Choose the Device
Type from the drop down list, enter the device Serial #,
and a Device Label of your choice. Note: You can use the
Scan for Ports/Devices button to confirm that you can create a communication link with the
gauge – the gauge must be “on” to be detected.
5. Now open the Channel Settings window (click on the
View and Edit Channel Settings button). In the Label
fields, type in appropriate labels for Channels A and Bon
the DG-700. These labels will appear on the graph
generated by TECLOG3. Leave the Channel Type set to
Pressure. You can choose the graph color that will be displayed for each channel by clicking
on the color square. Exit the Channel Settings window.
6. Begin data recording using the
Recording….Start Recording menu item.
After entering a filename, data collection
and recording will begin. TECLOG3 will
display a graph showing the CAZ pressure
and the appliance draft pressure. In the
graph to the right, the baseline CAZ
pressure (green) is approximately –2 Pa
(typical cold climate wintertime pressure)
while the baseline water heater vent
pressure (red) is about –1 Pa.
7. Turn on exhaust fans one at a time. Each
time an exhaust fan is turned on, TECLOG3
graphically displays the change in both the
CAZ pressure and the vent pressure. In this
case, a dryer, a kitchen fan and a bath fan
were turned on. The CAZ becomes more
depressurized with each successive fan,
until the CAZ pressure was about –4.5 Pa
with all fans running. This represents a
measured worst case fan depressurization of
-2.5 Pa (from –2 Pa baseline to –4.5 Pa with
all fans running). The graph also shows that
the water heater vent pressure becomes
slightly positive with all fans running,
indicating that outside air has begun to
come down the water heater venting
system. Note: The air handler fan did not
cause a change in CAZ pressure.

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8. Now turn on the water heater with all
fans continuing to run. In this case,
the water heater immediately begins
to spill into the house due to the
downdraft in the vent (note the
positive vent pressure). The water
heater continues to spill for about 90
seconds at which time the venting
system finally warms up, suddenly
reverses and begins to operate
properly. Once the venting system
overcomes the downdraft, the water
heater draft is a strong –4 Pa.
9. Stop data recording using the Recording….Stop Recording menu item.
Although this testing can certainly be done without TECLOG3, using TECLOG3 gives you better
documentation of what you found, more definitive measurement of the pressure changes and a
more professional way of reporting the results to your client.
Other Hints
If you are using the TEC WiFi Link to wirelessly communicate with you laptop, try using our
mobile iTEC-700 app instead of the laptop to monitor changes in pressures real-time while
walking around the house with your mobile device, turning fans on and off.
When using TECLOG3, create a configuration file which stores all of the channel and
configuration settings needed to do your testing. Then simply load the configuration file
using the File….Load Configuration menu item and you are ready to go.
Use a notebook to jot down the times at which you turned on or off the exhaust devices and
air handler. Make sure to synchronize your computer clock with your watch before starting.
These “events” can then be added to your test file by using the TECLOG3 Event Marker
tool (as shown in the graphs above).
Use the Region Select Tool to quickly determine the average pressure reading for any
selected portion of the graph.
Example Test File
The example test file illustrated above has been installed on your computer along with the
TECLOG3 program. The file (named cstest.TeclogData) is copied to the TECLOG installation
folder. Test files can be loaded into TECLOG3 using the File….Load Data File menu item.