|
Part 1 of 2
The days of the old galvanized flue
pipe vented into a masonry chimney lined or unlined are quickly
fading away. It will not be long unit even Type “B” double wall gas
vent will be a thing of the past.
With increased efficiencies in equipment the requirements for
“special venting” are now in place, and venting requirements for 90+
efficiency products are likely to continually change.
Warnings like this in Installation and Operation manuals are
commonplace:
WARNING
FAILURE TO VENT THIS BOILER IN ACCORDANCE WITH THESE INSTRUCTIONS
COULD CAUSE FLUE GAS TO ENTER THE BUILDING RESULTING IN SEVERE
PROPERTY DAMAGE, PERSONAL INJURY, OR DEATH:
• Do not
attempt to vent this boiler with galvanized, PVC, or any other
vent system not listed in the instructions.
• Do not attempt to mix components from different approved vent
systems.
• Do not obtain combustion air from within the building.
• Do not install a barometric damper or drafthood on this
equipment.
CAUTION
Moisture and ice may form on the surface around the vent
termination.
In talking to manufacturers reps about problems they discover on new
installations they tell me that most are improperly vented due to
failure to read the installation directions. We all know what
INSTALLATION INSTRUCTIONS are…we use them to set our coffee cups and
soda cans on so we don’t mark the equipment!
I am not going to attempt to teach Category IV 90+ Modulating
Condensing venting here. I simply want to point out some of the
typical things to watch out for. It is first of all imperative that
directions be followed. Here are some of the things most
manufacturers have in their instructions.
A lot of equipment today will list several different ways to vent
their product:
1.
Horizontal Side Wall Concentric Vent – the vent exits the
building through the outside wall. Concentric pipe is a “pipe
within a pipe”. Flue gas exits through the inside pipe, air for
combustion is drawn in around the space between the inner and
outer pipe.
2. Horizontal Side Wall Double Pipe (Separate flue gas pipe out
and another pipe for air in)
3. Vertical Double Pipe vent exits the building through the
roof. (Separate flue gas pipe out and another pipe for air in)
In some
cases they may be direct vent or they may be classified mechanical
exhausting. There are different requirements for those as to
termination outside the building. We will cover some of those later
in one of the other parts of this article.
Two basic categories:
1.
Concentric
2. Double Pipe (Separate flue gas pipe out and another pipe for
air in)
There are
usually requirements for maximum vent and air intake lengths as well
as in some cases minimum lengths.
Vent terminals vary with manufacturers and are not interchangeable
from manufacturer to manufacturer.
The most difficult and often the most troublesome is the vent
termination itself. This will be covered next month in Part 2 of
Venting Today – A Complex Subject.
These technical manuals are now available:
•
Circuitry and Troubleshooting Volume I and Volume II. $75.00 for
Volume I and $35.00 for Volume II + $10.00 S/H.
• New Edition of FUNDAMENTALS OF GAS VOLUME I. $75.00 + $10.00
S/H.
• FUNDAMENTALS OF GAS Volume II, which covers “Air for
Combustion” and “Venting” it is up to date with the latest
changes to the Fuel Gas Code Book. $75.00 + $10.00 S/H.
We also
conduct seminars on the following topics and many others:
•
Fundamentals of Gas
• Circuitry and Troubleshooting
• Hydronic Controls
• Electric Ignition Systems
• Advanced Electric Ignition Systems
• Powerpile Systems
• NEW COMBUSTION TESTING DESIGN GAS EQUIPMENT
For
information call Tim McElwain at 401-437-0557, email him at
gastc@cox.net,
or write to:
Gas Appliance Service Training and Consulting
22 Griffith Drive
Riverside, RI 02915
Venting Today - A Complex Subject
by Tim
McElwain
Part 1 of 2
One of the most difficult and often
troublesome aspects of the new venting when venting out the side of
buildings or even through the roof is vent termination or vent
location. When we go to the code books it gets very detailed for
example in the National Fuel gas Code ANSI Z223.1/NFPA 54 section
12.3.5 for direct vent appliances and concerning termination of
direct vent section 12.9.3.
For Mechanical Exhausting the rules for termination are different as
per section 12.4.3.6 concerning no vent terminating less than 7 feet
above grade where located adjacent to public walkways.
Many times the Direct Vent rules and the Mechanical Exhausting rules
get mixed up and incorrect venting termination occurs. Section 12.9
Through the Wall vent Termination covers all aspects of both direct
vent (12.9.3) and mechanical exhausting (12.9.1 and 12.9.2) We will
address those in Part Three of this article.
Some of the typical requirements:
-
Vent
terminal must be at least 1 foot from any door, window, or
gravity inlet into the building.
-
The
double pipe (Example: The vent and air intake terminals must be
at the same height and their center lines must be between 12 and
36 inches apart. Both terminals must be on the same wall)
-
All
terminal bottoms must be 12 inches above normal snow line or no
less than 12 inches above grade. (Note: it is often difficult to
determine normal snow line)
-
7 feet
above public walkway
-
Do not
install directly above windows or doors
-
The
bottom of the vent terminal must be at least 3 feet above any
forced air inlet located within 10 feet.
-
A
horizontal distance of at least 4 feet between the vent terminal
and gas meters, electric meters, regulators and relief
equipment. Do not install vent terminal over this equipment dues
to condensate.
-
Do not
locate vent under decks.
-
Top of
vent terminal must be at least 5 feet below eves, soffits, or
overhangs. Maximum depth of overhang is 3 feet.
-
Vent
terminal must be 6 feet from an inside corner.
-
Be aware
that condensate may freeze and cause damage to structures
nearby.
-
Install
vent termination away from prevailing winds in excess of 40 MPH.
-
Air
intake must not be near possible combustion air contaminants.
These are some of the termination
rules for sidewall venting. When vertical termination is allowed
there are other rules these will be covered in Part Three in next
month’s Sales Bytes.
We are now offering our latest manuals Circuitry and Troubleshooting
Volume I and Volume II. They are selling for $75.00 for Volume I and
$35.00 for Volume II + $10.00 shipping and handling.
We have two OTHER NEW manuals in their second printing. The first
one is titled FUNDAMENTALS OF GAS VOLUME I it is priced at $75.00 a
copy + $10.00 shipping and handling. In addition we also have
FUNDAMENTALS OF GAS Volume II, which covers “Air for Combustion” and
“Venting” it is up to date with the latest changes to the Fuel Gas
Code Book. It is also being offered at a price of $75.00 + $10.00
shipping and handling.
We also conduct seminars on the following topics and many others:
-
Fundamentals of Gas
-
Circuitry and Troubleshooting
-
Hydronic
Controls
-
Electric
Ignition Systems
-
Advanced
Electric Ignition Systems
-
Powerpile Systems
-
NEW
COMBUSTION TESTING DESIGN GAS EQUIPMENT
If you are interested in information
call 401-437-0557 or write to:
Gas Appliance Service Training and Consulting
22 Griffith Drive
Riverside, RI 02915
E-mail
gastc@cox.net
Venting Today - A Complex Subject
by Tim
McElwain
Part 3 of 5
This is the final article on the
minimum venting including requirements and exclusions.
As was mentioned in Part two we want to address the code
requirements for vent termination. We are looking at the National
Fuel Gas Code ANSI Z223.1/NFPA 54 2006 version and also the
International Fuel Gas Code 2006 version.
This section will cover some of the code requirements, which must be
addressed by manufacturers when setting down the rules for
installation. The code rules can be added to but never made less
severe in their application. It is however important note that
manufacturers installation requirements have precedence.
In the NFPA 54 code this is addressed in Section 12.9 on page
54-102. In the IFGC section 503.8 page 85. There is also a reference
to and Appendix “C” which is an illustration showing the application
of some of these rules.
To keep it simple we will refer to the NFGC section 12.9, keep in
mind the international code in this instance is exactly the same as
the national. I have also removed the metric measurements for
simplicity.
12.9 Through the Wall Vent Termination.
Section 12.9 provides requirements for separation of the
termination point of the venting systems from the building openings
for venting systems that terminate through the side of the building.
The concern is for recirculation of products of combustion back into
the building. There is also the possibility of cross contamination
of the fresh intake air for combustion to the equipment.
12.9.1 A mechanical draft venting system shall terminate at least 3
feet above any forced air inlet located within 10 feet.
Exception No. 1: This provision shall not apply to the
combus¬tion air intake of a direct-vent appliance.
The intent of 12.9.1 is to prevent gases from being drawn back into
the building. This requirement recognizes that vent gases are
lighter than air. Exception No. 1 recognizes that direct vent
appliance inlets do not communicate with air in a building.
Exception NO.2: This provision shall not apply to the separation of
the integral outdoor air inlet and flue gas discharge of listed
outdoor appliances.
Exception No. 2 to 12.9.1 prevents confusion in the installation of
outdoor gas appliances. Some authorities have misinterpreted the
code to prohibit such appliances or to require them to be modified
in the field, which is not the intent of 12.9.1. An example of this
type of appliance is a packaged rooftop air conditioner, which
incorporates a gas vent and a circulation air inlet used for
building air supply.
12.9.2 A mechanical draft venting system of other than direct-vent
type shall terminate at least 4 feet below, 4 feet horizontally
from, or 1 foot above any door, operable window, or gravity air
inlet into any building. The bottom of the vent terminal shall be
located at least 12 inches above grade.
A question that often comes up concerning section 12.9.2 is do
the separation requirements for exit terminals apply to windows that
do not open? In the 1992 revision to the code the word “window” was
replaced with “operable window”. This came about as a question
pertaining to picture windows, which do not open. So the section
does not apply to any windows, which cannot be opened.
12.9.3 The vent terminal of a direct-vent appliance with an input of
10,000 Btu/hr or less shall be located at least 6 inches from any
air opening into a building, and such an appliance with an input
over 10,000 Btu/hr but not over 50,000 Btu/hr shall be installed
with a 9 inch vent termination clearance, and an appli¬ance with an
input over 50,000 Btu/hr shall be at least a 12 inches vent
termination clearance. The bot¬tom of the vent terminal and the air
intake shall be located at least 12 in. (300 mm) above grade.
Sections 12.9.1 and 12.9.2 are concerned with preventing equipment
combustion products from being drawn into a building through fresh
air inlets, including operable windows (windows which can be
opened).
Subsection 12.9.3 permits the vent terminals of direct vent
appliances to be located much closer to air inlets than is provided
for with mechanical draft equipment. There is often a mis
application of rules for mechanical draft to direct vent equipment.
The vent gases from direct vent equipment disperse rapidly upon
leaving the vent terminal, even when the terminal is located under
an open window. However, a window is unlikely to be open when heat
is needed.
12.9.4 Through-the-wall vents for Category II and Category IV
appliances and noncategorized condensing appliances shall not
terminate over public walkways or over an area where condensate or
vapor could create a nuisance or hazard or could be detrimental to
the operation of regulators, relief valves, or other equipment.
Where local experience indicates that condensate is a problem with
Category I and Category III appliances, this provision shall also
apply.
Subsection 12.9.4 provides for the protection of persons and
equipment, including gas meters. It places responsibility on the
installer to locate vent termination for Category II and Category IV
appliances away from walkways and gas equipment. It also recognizes
that any appliance can present a condensation problem in a cold
climate.
High-efficiency condensing appliances have a seasonal efficiency of
90 percent or higher, which reduces vent gas temperatures to a point
where the water vapor produced as a product of combustion condenses
to liquid water in the appliance or in the vent. These condensing
appliances carry a vented appliance category of Category IV. This
type of appliance produces much cooler vent gases, resulting in
water condensing in the vent. Venting must be accom¬plished with a
fan, because the vent gases are not hot enough to operate the
natural draft vent. Water will condense in the vent and will
dissolve some of the gases produced during combustion, which are
slightly acidic. The vent materials used with these appliances must
be able to resist the acidic condensate. For many of these Category
IV appliances, plastic vent material is acceptable and preferred for
corrosion reasons. The appliance manufacturer specifies the vent
material for use with Category IV appliances.
The advantage of high-efficiency appliances is that they
significantly reduce the amount of gas consumed with no loss in
output. A mid-efficiency appliance uses one-third less gas than a
conventional appliance, and a condensing appliance uses only
one-half of the gas of a conventional appliance. The savings in fuel
are offset by higher first cost and the higher maintenance
requirements of high-efficiency appliances, as well as the added
cost of the electricity to operate the fan.
In the next part (Part 4) we will
address other requirements for venting in particular vertical
venting.
In part 5 we are going to address the venting categories mentioned
in this article.
We are now offering our latest manuals Circuitry and
Troubleshooting Volume I and Volume II. They are selling for $75.00
for Volume I and $35.00 for Volume II + $10.00 shipping and
handling.
We have two OTHER NEW manuals in their second printing. The first
one is titled FUNDAMENTALS OF GAS VOLUME I it is priced at $75.00 a
copy + $10.00 shipping and handling. In addition we also have
FUNDAMENTALS OF GAS Volume II, which covers “Air for Combustion” and
“Venting” it is up to date with the latest changes to the Fuel Gas
Code Book. It is also being offered at a price of $75.00 + $10.00
shipping and handling.
We also conduct seminars on the following topics and many others:
• Fundamentals of Gas
• Circuitry and Troubleshooting
• Hydronic Controls
• Electric Ignition Systems
• Advanced Electric Ignition Systems
• Powerpile Systems
• NEW COMBUSTION TESTING DESIGN GAS EQUIPMENT
If you are interested in information call 401-437-0557 or write to:
Gas Appliance Service Training and Consulting
22 Griffith Drive
Riverside, RI 02915
E-mail
gastc@cox.net
Venting Today - A Complex Subject
by Tim
McElwain
Part 4
With this continuing discussion on
venting of Modulating/Condensing equipment it is once again not the
purpose of this article to define exact installation requirements.
The attempt here is to address some typical types of requirements
for venting this equipment.
When vertical venting is an option on this equipment it is important
to follow manufacturers rules as to EQUIVALENT LENGTH as it relates
to air intake of vent. An example would be:
90-degree concentric elbow 4.5 feet
45-degree concentric elbow 4 feet
A 3” 90 degree elbow 5.5 feet
A 3” 45 degree elbow 4 feet
Many times failure to observe these equivalent lengths in
calculating the maximum length of the vent can result in inadequate
air supply or problems with the pressure switch not making. It is
often a good idea if the system will not work with the vent
connected to remove the vent temporarily and see if the equipment
will operate with it disconnected. If it will and it will not work
with it connected you obviously have a problem with the vent. One of
the things to address is length and also equivalent lengths of
fittings. There may also be other problems such as blockage or
damage to the vent.
There may also be other requirements addressed in the following
examples:
Permitted Terminals for Vertical Venting - A straight
termination is installed in the end of the vent pipe. The air inlet
terminal consists of a 180-degree elbow (or two 90 degree elbows)
with a rodent screen. Vent manufacturer part numbers for these
screens vary.
Vertical Vent Terminal Locations - Observe the following
limitations on the location of all vertical vent terminals.
• The
top of the vent pipe must be at least 2 feet above any object
located within 10 feet.
• The vertical distance between top of the vent and air inlet
terminal openings must be at least 12".
• The bottom of the air inlet terminal must be at least 12"
above the normal snow accumulation that can be expected on the
roof.
• The air intake terminal must be located on the roof and must
be no further than 24" horizontally from the exhaust pipe.
Wall
thimbles - Wall thimbles are often required where single wall
vent pipe passes through combustible walls.
Pitch of Horizontal Piping - Pitch all horizontal piping so
that any condensate, which forms in the piping, will run towards the
boiler:
• Pitch
horizontal concentric venting 5/8" per foot
• Pitch Stainless steel venting 1/4" per foot.
Supporting Pipe - Vertical and horizontal sections of pipe must
be properly supported:
•
Support concentric venting near the female end of each straight
section of pipe.
• Support stainless steel venting as called for by the vent
manufacturer's instructions.
The next
article on this topic will cover some of the code requirements,
which must be addressed by manufacturers when setting down the rules
for installation. The code rules can be added to but never made less
severe in their application. It is however important to note that
manufacturers installation requirements have precedence.
We are now offering our latest manuals Circuitry and Troubleshooting
Volume I and Volume II. They are selling for $75.00 for Volume I and
$35.00 for Volume II + $10.00 shipping and handling.
We have two OTHER NEW manuals in their
second printing. The first one is titled FUNDAMENTALS OF GAS VOLUME
I it is priced at $75.00 a copy + $10.00 shipping and handling. In
addition we also have FUNDAMENTALS OF GAS Volume II, which covers
“Air for Combustion” and “Venting” it is up to date with the latest
changes to the Fuel Gas Code Book. It is also being offered at a
price of $75.00 + $10.00 shipping and handling.
We also conduct seminars on the following topics and many others:
•
Fundamentals of Gas
• Circuitry and Troubleshooting
• Hydronic Controls
• Electric Ignition Systems
• Advanced Electric Ignition Systems
• Powerpile Systems
• NEW COMBUSTION TESTING DESIGN GAS EQUIPMENT
If you are
interested in information call 401-437-0557
or write to:
Gas Appliance Service Training and Consulting
22 Griffith Drive
Riverside, RI 02915
E-mail
gastc@cox.net
Venting Today - A Complex Subject
by Tim
McElwain
Part 5
You can use the chart below to
determine the equipment’s venting category. Look at the equipment’s
rating plate and then proceed down that column to determine
requirements and perimeters for venting that particular category.
For example, a listed Category I appliance can be vented using a
Type B gas vent, chimney, single-wall metal pipe, chimney lining
system that is listed for gas venting, or a special gas vent listed
for the appliance. The chart refers to appliance Category I through
Category IV. The categories are based on vent temperature and
pressure.
The term non-positive vent (negative pressure) means that even if
fans or blowers are used in an appliance or vent system, venting is
accomplished by natural draft. Natural draft is created by
temperature difference (delta T) and the height of the vent. (The
vent pressure is lower than atmospheric).
The term positive vent pressure means that fans, blowers or other
means are used to propel vent gases through the vent at above
atmospheric pressure.
Note that the definitions reference "a vent gas temperature that may
cause excessive condensate production in the vent.") A specific
temperature is not provided, because it is not the same for all
appliances. The ANSI Z21 standards for appliance categorization can
be referenced for this information. Annex L contains a complete list
of the ANSI Z21 standards. Note that the installer should not need
this information, since the appliance vent category is included in
the appliance manufacturer's installation instructions and on the
appliance nameplate. The criteria in the ANSI Z21 standards are
based on a flue loss of 17 percent of total energy. The 17 percent
flue loss is the same flue loss built into the vent sizing tables
for fan-assisted appliances. In this way, the standards ensure that
the appliance will work properly with the vent system. The term
nonpositive vent pressure means that the pressure in the vent
will be lower than the surrounding atmosphere if the vent system
meets the requirements of the National Fuel Gas Code Chapter 12 and
Chapter 13. The incorporation of a fan into the appliance does not
always mean that the vent pressure is positive. If unsure, check the
appliance nameplate or manufacturer's instructions for the venting
category, or check the vent pressure with a manometer or other
pressure gauge when the appliance is operating.
|
VENTING
CATEGORIES: |
GAS-FIRED EQUIPMENT |
|
Operating
|
|
|
|
|
|
|
characteristics |
Category I |
Category II |
Category III |
Category IV |
|
Pressure in
the vent |
Negative |
Negative |
Positive |
Positive |
|
Temperature
of |
Above |
Below |
Above |
|
Below |
|
vent gas
(4) |
275°F |
275°F |
275°F |
|
275°F |
|
Annual
efficiency |
Below 84% |
Above 84% |
Below 84% |
Above 84% |
|
Condensation |
Not acceptable |
Possible |
Possible |
In heat |
|
|
(1)
|
(in vent) |
(3) |
|
exchanger |
|
Design requirements
|
|
|
|
|
|
Gas (air)
tight vent |
No |
No |
Yes |
|
Yes |
|
Corrosion-resistant |
No (1) |
Yes |
Possible |
(3) |
Yes |
|
vent (water
tight) |
|
|
|
|
|
|
Vent into
|
Permitted |
No |
No |
|
No |
|
masonry
chimney |
(1) and (2) |
|
|
|
|
|
Combined
venting |
Permitted |
No |
No |
|
No |
|
Condensate
drain |
No |
Ask |
Possible |
(3) |
Yes |
|
|
|
manufacturer |
|
|
(At |
|
|
|
|
|
|
equipment) |
|
Source of
|
N.F.G.C. |
Manufact. |
Manufact. |
Manufact. |
|
information
|
Fuel gas code, |
literature |
literature |
literature |
|
heating equipment
|
|
|
|
|
|
|
and vent system |
|
|
|
|
|
|
manufacturers |
|
|
|
|
NOTE 1 Usually, there is no problem when high vent gas
temperature equipment is vented into double-wall vent or into a
lined masonry chimney; but condensation could occur if
mid-efficiency (80% to 84%) mechanical draft equipment is vented
into a vent that has highly conductive walls, cold walls, or massive
walls. In this case, design a vent system that minimizes the wall
losses (use double-wall pipe for the whole run and avoid long runs
through cold spaces).
NOTE 2 Install either a rigid or flexible metal liner inside
of the masonry chimney and use a double-wall connector when venting
mid-efficiency (80% to 84%), me¬chanical draft equipment.
NOTE 3 Condensation in the vent is posing on the ambient
temperature and the conductivity of the vent walls. In this case,
design a vent system that minimizes the wall losses (use insulated
pipe and avoid long runs through cold spaces). A corrosion-resistant
flue and a drain may be required if condensation cannot be prevented
- refer to the manufacturer's recommendations.
NOTE 4 The dewpoint of the vent gas depends on the fuel
(natural or LP gas), the amount of excess air and the amount of
dilution air. The limiting case occurs when the dewpoint of the vent
gas is at a maxi¬mum, which is about 135°F. This maximum is produced
when natural gas is burned with no excess air or dilution air.
There¬fore 275°F = 135°F dewpoint + 140°F
It is a good rule of thumb when looking at vent temperature that any
temperature from 300° (F) down is a concern for condensing and needs
to be addressed in the case of Category I and III venting.
We are now offering our latest manuals Circuitry and Troubleshooting
Volume I and Volume II. They are selling for $75.00 for Volume I and
$35.00 for Volume II + $10.00 shipping and handling.
We have two OTHER NEW manuals in their
second printing. The first one is titled FUNDAMENTALS OF GAS VOLUME
I it is priced at $75.00 a copy + $10.00 shipping and handling. In
addition we also have FUNDAMENTALS OF GAS Volume II, which covers
“Air for Combustion” and “Venting” it is up to date with the latest
changes to the Fuel Gas Code Book. It is also being offered at a
price of $75.00 + $10.00 shipping and handling.
We also conduct seminars on the following topics and many others:
•
Fundamentals of Gas
• Circuitry and Troubleshooting
• Hydronic Controls
• Electric Ignition Systems
• Advanced Electric Ignition Systems
• Powerpile Systems
• NEW COMBUSTION TESTING DESIGN GAS EQUIPMENT
If you are interested in information
call 401-437-0557 or write to:
Gas Appliance Service Training and Consulting
22 Griffith Drive
Riverside, RI 02915
E-mail
gastc@cox.net
Venting Today - A Complex Subject
December 2007 issue
by Tim
McElwain
Part 6
Plastic Piping:
• The Code
• Product Recall
• The Effects of Temperature on PVC pipe
National Fuel Gas Code specifies that plastic piping used for
venting appliances listed for use with such venting materials shall
be approved.
Before the introduction of high-efficiency (90 + percent efficiency)
gas utilization equipment, plastic piping was prohibited as a vent
material. High-efficiency (Category IV) appliances reduce vent
temperatures, resulting in condensate formation. As accumulation of
condensate can become a source of corrosion of metal vents, plastic
piping became the preferred material. Paragraph 12.5.2 of the
National Fuel Gas Code requires that plastic vent materials be used
for listed gas utilization equipment only when specified in the
manufacturer's instructions.
Section 12.5.3 of the National Fuel Gas Code Special Gas Vent
Special gas vent shall be listed and installed in accordance with
the special gas vent manufacturer's installation instructions.
All special gas vents are listed vent materials. Special gas vents
are listed in accordance with UL 1738, Standard for Venting
Systems for Gas-Burning Appliances, Categories II, III and IV.
Installation instructions for special gas vents include limitations
on operating temperature, categories of appliance to be used with
each vent, clearance to combustible materials, types of fittings and
joint sealant to be used, and vent termination requirements.
Special attention should be given to the following areas:
1. Proper support for the special gas vent to prevent sagging and to
allow for expansion, contraction, and condensate drainage
2. Proper cutting and cleaning of joints and fittings, and the use
of recommended joint sealants (substitutes are not usually
permitted)
3. Construction of a condensate trap (see the appliance
manufacturer's instructions for special requirements)
4. Wall penetrations (the pipe should not be secured at a thimble,
because the pipe must be allowed to move to accommodate expansion
and contraction)
5. Insulation [the vent pipe or the fittings of the inside of a wall
thimble must not be insulated when polymeric (nonmetallic) vent
materials are used]
Product Recall
More than 15 years ago, a class of special gas vent known as "high
temperature plastic vent" (HTPV) was introduced to the market for
use with mid-efficiency appliances. Field experience has shown that
these vent systems are prone to failure. The failure may occur
because of improper installation practice and/or corrosion from
acidic condensate. At this time an active product recall is still
under way, with the cooperation of the U.S. Consumer Product Safety
Commission, appliance manufacturers, and the vent pipe
manufacturers. The product recall covers furnaces that are
horizontally vented, as well as all boiler installations. Those who
encounter one of these vent systems should call (800) 758-3688 for
information on how to proceed. This number is operated by the
product manufacturers and will be in operation until the recall is
substantially complete. If the number is not in operation, questions
can be referred to the furnace, boiler, or water heater
manufacturer.
To determine whether the installation has an HTPV pipe system that
is subject to this program, the vent pipes attached to the natural
gas or propane furnaces or boilers should be checked. Vent pipes
subject to this recall program can be identified as follows:
• The vent pipes are plastic.
• The vent pipes are colored gray or black.
• The vent pipes have the names "Plexvent," "Plexvent II," or "Ultravent"
stamped on the vent pipe or printed on stickers placed on pieces
used to connect the vent pipes together.
The location of those vent pipes should also be checked. For
furnaces, only' HTPV systems that have vent pipes that go through
the side walls of structures (horizonta1 systems) arc subject to
this program. Other plastic vent pipes, such as white PVC or CPVC
are not involved in this program.
The Effects of Temperature on PVC Pipe
Polyvinyl Chloride (PVC) is a thermoplastic, and as such, its
physical properties change with temperature variations Dimensions,
pressure capacity, and stiffness are all affected by temperature
changes. The published dimensions and performance ratings for PVC
pipe and conduit products are usually applicable only for 73°F. The
following will help to explain how PVC pipe and conduit products are
affected by operating temperatures other than 73°F.
Dimensions
Like all materials, PVC expands with increasing temperatures and
contracts with decreasing temperatures.
The coefficient of thermal expansion for PVC is: 3.0 x 10-5 in/in/°F
Because the length-to-diameter ratios of PVC pipe and conduit
products are generally very large, length change from temperature
variation is the most noticeable. A good rule of thumb in design of
PVC pipe and conduit systems is to allow 3/8" length variation for
every 100 feet of pipe for each 10°F change in temperature. (This
rule is independent of pipe size.) Table 1 can also be used to
determine the effects of temperature changes on the length of PVC
pipe and conduit.
NOTE:
THE MAXIMUM RECOMMENDED OPERATING TEMPERATURE FOR PVC PRESSURE PIPE
IS 140° (f)
FOR CPVC IT IS 200° (F)
This is reason enough to pay very close attention to flue gas
temperatures on a lot of 90+ condensing equipment.
We are now offering our latest manuals
Circuitry and Troubleshooting Volume I and Volume II. They are
selling for $75.00 for Volume I and $35.00 for Volume II + $10.00
shipping and handling.
We have two OTHER NEW manuals in their second printing. The first
one is titled FUNDAMENTALS OF GAS VOLUME I it is priced at $75.00 a
copy + $10.00 shipping and handling. In addition we also have
FUNDAMENTALS OF GAS Volume II, which covers “Air for Combustion” and
“Venting” it is up to date with the latest changes to the Fuel Gas
Code Book. It is also being offered at a price of $75.00 + $10.00
shipping and handling.
We also conduct seminars on the following topics and many others:
• Fundamentals of Gas
• Circuitry and Troubleshooting
• Hydronic Controls
• Electric Ignition Systems
• Advanced Electric Ignition Systems
• Powerpile Systems
• NEW COMBUSTION TESTING DESIGN GAS EQUIPMENT
If you are interested in information call 401-437-0557 or write to:
Gas Appliance Service Training and Consulting
22 Griffith Drive
Riverside, RI 02915
E-mail gastc@cox.net
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