February 1,2000 -Arlington, V A- 1999 sales statistics for vent-free gas
products continue to increase and vent-free gas heating products are in more
than 8 million U.S. homes. The immense popularity and the acceptance of
vent-free products in most states have inspired a strong demand for information
about these "smart technology" gas appliances. To help provide the
where's, why's and how's of vent-free gas products, here is a list of
commonly-asked questions and their answers. This "Q & A" has been
prepared by the Vent-Free Gas Products Alliance, a coalition of members of the
Vent-Free Gas Products Division of the Gas Appliance Manufacturers Association (GAMA).
A. ABOUT THE PRODUCT:
1. What exactly are "vent-free" gas products?
gas products are gas appliances that are designed to be installed and operated
without the addition of a vent or chimney. They are intended to provide
supplemental heat to a home. Because there is no vent, flue, or chimney
required, all of the heat generated by the product goes directly into the home.
That's why vent-free products are 99 percent energy efficient.
2. What types of vent-free gas products are available?
Vent-free gas appliances are available as gas space heaters, gas
logs, gas stoves, gas fireplaces, and gas fireplace inserts. They operate on
natural or propane gas.
3. Can I use vent-free logs in any wood-burning fireplace---masonry
Vent-free logs are certified for installation in the following enclosures:
o A masonry fireplace with a suitable chimney;
o A listed factory-built fireplace, assembled with a working chimney, in
accordance with the terms of the listing, and not including a marking
prohibiting use with unvented gas logs;
o A vent-free firebox enclosure, tested and certified to accept any ANSI
Z21.11.2 approved vent-free gas logs; or
o A vent-free firebox enclosure specifically tested and approved for use with
the vent-free gas logs being installed.
o Wood-burning stoves are not tested to allow for conversion to gas
Customers need to follow individual manufacturers'
instructions on the fireboxes that they purchase.
4. In an existing wood-burning
fireplace with vent-free logs, in what circumstances do I need to use a hood?
A hood is used to allow deeper mantels to be installed
at lower heights above a fireplace opening and to reduce wall temperatures above
the fireplace opening. A hood should only be used in accordance with the
manufacturer's installation instructions and in accordance with the
manufacturer's specified clearances from combustible construction.
5. If I have
a wood-burning fireplace and I put vent-free logs in it can I seal off the flue?
What is the best way to do it?
No, we do not recommend any modification to a
wood-burning fireplace in which vent-free gas logs are installed, other than
closing the flue damper. If the logs give off too much heat and cause
discomfort, the damper can be slightly opened.
6. Most feel that in order for an
appliance to be vent-free it must have a blue flame. If that is so, why do so
many units have a yellow flame?
Historically it has been believed that only a
hard, blue flame is allowable on gas appliances. However, recent technology has
emerged to enable yellow flames that have clean combustion. Several hearth
products incorporate this aesthetic feature.
7. The general rule has been that
there is not to be any flame impingement on the logs, yet several manufacturers
have impingement on the front log on their sets. How can they do this?
technological developments have made flame impingement on (contact with) the
front logs possible. Vent-free appliances with front log impingement typically
utilize both blue flame and yellow flame burner design technologies. The blue
flame burners impinge and provide a significant source of radiant heat and a
glowing effect or charcoal appearance. The yellow flames in the rear of the
appliance do not normally impinge on the logs, but rather burn between the logs
and twigs, completing the "wood-burning" aesthetic effect of the
8. Some units now incorporate a catalyst. How does a catalyst work in
a vent-free appliance?
The catalyst used on a vent-free appliance is similar in
concept to that used on a wood stove, with only slight differences. With a
vent-free catalyst, flue gases passing through the combustion module heat up the
catalytic material to the minimum conversion of "light off'*
temperature. Once this temperature is reached, the catalytic material combines
any CO with O 2 from the catalyst (a noble metal) forming CO2.
* "Light-off" is the activation
temperature of the combustor catalyst.
B. SAFETY ISSUES:
I. Are vent-free gas products safe to
use in the home?
Yes. There is a national safety standard for vent-free
gas appliances, ANSI Z21.11.2, which requires the products to satisfy numerous
construction and performance requirements. The safety standard is approved by
the American National Standard Institute (ANSI) and is developed by an
independent Committee comprised of representatives from various interests
including state and federal regulatory authorities, utilities, manufacturers,
consumers and general interests. Vent-free gas products are certified for
compliance with this standard to assure their safety.
2. Is it safer to use a vented
model instead of an unvented one? The fact is, both vented and
unvented gas products are safe provided they have been certified to their
appropriate product safety standard and they are installed and operated in
accordance with manufacturers instructions. In addition to the Oxygen Detection
Safety-Pilot (ODS), every vent-free gas appliance is equipped with:
o an automatic shut-off valve, which shuts off the gas
flow if the pilot extinguishes or the gas flow to the main burner is interrupted
in any way;
o burners that are precision-engineered to produce the
cleanest, most complete gas combustion, with no lift-off or flash-back when
subjected to low input rates, low gas pressure, or drafts;
o a non-adjustable pressure regulator that
prevents overfiring in case of increased gas pressure;
o an automatic ignition device, usually a Piezo
igniter, which eliminates the need for matches in starting the appliance;
o design features that limit cabinet temperatures for
wall- or floor-mounted heaters;
o instructions for minimum clearances to combustible
o safety grills for heaters and fire screens for gas
3. How does an ODS work?
An Oxygen Detection Safety-Pilot CODS) system reacts to
a decrease in a room's oxygen supply in a manner that shuts off the gas supply
to the appliance. The gas pilot burns normally when it is exposed to normal air
(22- 22.5 percent oxygen). In the rare case when the oxygen level in a room
starts to drop to an 18- 18.5 percent level, the pilot flame lifts off of the
thermocouple, which causes the gas valve to close. In other words, it shuts off
the gas supply and "fails safe." This unit was introduced to the U.S.
in 1980 - 1981. All ANSI certified vent-free gas products incorporate an ODS.
Based upon data available from manufacturers of the ODS, manufacturers of
vent-free gas appliances and data available via legal data bases, there are no
documented deaths associated with emissions from vent-free gas products that
incorporate an ODS. This data covers a 20 year history during which more than
eight million units were sold in the U.S.
4. How can you ensure the
vent-free gas product you purchase operates safely?
You should verify that the product has been certified
to ANSI 221.11.2. This can be done by locating the product's certification mark
from an accredited safety certification testing agency ( e.g., American Gas
Association Blue Star Seal). The installation of vent-free gas products should
always be performed by a qualified technician who is able to ensure that all
manufacturer instructions have been followed during installation and all local
code requirements have been satisfied. Also, the manufacturer is required to
provide operating instructions for the consumer to ensure safe operation of the
5. Are vent-free gas products
safe in terms of indoor air quality?
Yes. This has been verified by research conducted by
the American Gas Association Research (AGAR) laboratories. AGAR is the research
arm of the International Approval Services, a nationally recognized testing
agency, and the most renowned independent research body for gas products. This
laboratory has been certifying gas appliances since 1928 to ANSI safety
standards. (In 1997, AGAR was purchased by Energy International, Inc. ) The AGAR
research shows that when the product is properly sized and installed, vent-free
gas heating products meet applicable emissions requirements, even when used over
extended time periods, among sensitive populations, and with oversized units. In
fact, using oversized appliances actually results in lower average emissions
because the unit operates for a shorter period of time. The researchers
concluded that under "worst case" conditions, vent-free gas heating
products perform well within nationally recognized guidelines for indoor air
quality. For instance: When tested for Nitrogen Dioxide (NO2), the vent-free gas
products tested by AGAR produced less than one-half of the parts per million (ppm)
level of NO2 recommended by the Occupational Safety and Health Administration (OSHA)
for a 1 hour period. Also, when tested for carbon monoxide (CO), vent-free gas
products emitted less than 20 percent of the current recommended guideline level
set by the Consumer Product Safety Commission (CPSC) for an 8 hour period.
C. SIZING AND OTHER INFORMATION:
1. Where in the home do people
install vent-free gas appliances?
Vent-free appliances may be installed in any room in
the home. It is important to remember that the appliance should be sized to fit
the area in which it is to be installed. However, ANSI Z21.11.2 limits
products installed in bathrooms to an input rating no larger than 6,000 Btu/hr and
products installed in bedrooms are limited to an
input rating no larger than 10,000 Btu/hr.
2. How do I find the correct size of
vent-free gas appliance for my home?
The Vent-Free Gas Products Alliance has
published an easy to use set of sizing guidelines that allow the consumer to
determine the appropriate size unit that should be installed in their home,
depending on the size of the area to be heated, the construction of the home,
and the home's geographical location. Because there are broad temperature ranges
in all regions of the country, the desired heat output from a vent-free gas
appliance will vary dramatically based on the season and usage patterns of the
household. All vent-free gas products offer a range of heat settings, whether
manually or thermostatically controlled. In terms of indoor air quality, any
size of product can be chosen based on personal preference in all applications
other than in DOE's region v. The Vent-Free Gas Products Alliance has printed
these guidelines, including sizing guidelines for DOE's region V, in a
publication entitled Consumer Guide to Vent-Free Gas Products. For a free copy,
see the end of this article.
3. What consideration should I give
if my home is an extremely tight one?
A home is considered to have tight
construction if :
o Walls and ceilings exposed to the outside atmosphere
have a continuous water vapor retarder with a rating of 1 perm or less with
openings gasketed or sealed; and
o Weather stripping has been added on operable
windows and doors; and
o Caulking or sealant are applied to areas such as
joints around window and door frames, between sole plates and floors, between
wall and ceiling joints, between wall panels, at penetrations for plumbing,
electrical, and gas lines, and at other openings.
In tightly constructed homes, additional provisions for
combustion and ventilation air must be provided using one of the methods defined
in the National Fuel Gas Code, ANSI Z 223.1/NFPA 54.
D. OPERATIONAL ISSUES:
1. What causes the odor when the unit
is turned on for the first time? What causes odors during operation? N
Many manufacturers do not require an initial
burn-off time, however, some units do emit an odor when operated for the first
time due to burn off of excess paint and machine oil. Odors during operation
should not be apparent. If there are odors, the cause is best determined by a
qualified service person. Homes with many animals, new carpeting, or hobby
chemicals sometimes do have odor concerns. The service person can usually
identify the problem.
2. Should I place a limit on
the operation of my vent-free gas product to no more than two hours at a
stretch, as a rule?
It is important to recognize that vent-free gas
appliances are supplemental heating units. They are not to be used as a central
heating system but to assist in heating the home. Many units have thermostats
and remote controls that will regulate the amount of heat needed based on each
individual's comfort levels. A major AGAR research project proved that vent-free
products perform well within nationally recognized guidelines for indoor air
quality ( see Section B, Safety Issues, Number 5, above). The AGAR research was
based on "worst case" operating conditions. Worst case operating
conditions consisted of a maximum sized unit (40,000 Btu/hr) emitting the
vent-free products' maximum levels of combustion for a minimum of four hours of
continuous operation. Even at these extreme operating conditions, the vent-free
gas products met all applicable emission requirements, with the exception of a
confined space in DOE heating region v. However, this one exception is accounted
for in the sizing guidelines, as detailed in the publication Consumer Guide to
Vent-Free Gas Products. For a free copy, see the end of this article.
3. Is it necessary to leave at
least one window open in the space where the vent-free gas appliance is
No. This is an obsolete requirement that no longer
applies to products manufactured today which comply with the current safety
standard, ANSI 221.11.2. This requirement was based on outdated information that
was developed from pre-1980 vent-free units and kerosene heaters. Vent-free gas
products now come with an ODS and many other built-in safety features as
standard equipment (see Section B, Safety Issues, above). Additionally, in order
to satisfy combustion air requirements for vent-free products, ANSI 221.11.2
requires that all vent-free products be installed in accordance with local
codes, or in the absence of local codes, the National Fuel Gas Code. These codes
specify the appropriate measures to take for ensuring an adequate supply of
combustion air for all gas appliances. The ventilation requirements are the same
for both vent-free gas products and vented gas products.
4. How about vent-free
appliances in homes at high altitude?
Vent-free gas appliances installed at high
altitudes can operate safely and satisfactorily. Many manufacturers have taken
advantage of the International Approval Services and Mountain Fuel Testing
Laboratory high altitude testing capabilities to investigate and ensure proper
performance of vent-free appliances at high altitudes. The state of Utah decided
to allow vent-free equipment throughout the state on January 1, 1999. Because
high altitude reduces available oxygen, at extreme elevation, nuisance
"fail-safe" shut down may occur. Currently one manufacturer has 123
vent-free gas products working in Vail, CO.
1 . How much moisture does a
vent-free appliance put out?
The amount of moisture is dependent on the gas Btu
input. A 100,000 Btu/hr gas input produces about a gallon of water per hour. A
25,000 Btu input heater would produce about a quart of water as vapor per hour.
It is important to keep this issue in perspective. When a typical consumer sees
condensation on a window, it does not trigger an immediate alarm regarding
allergenic organism growth or structural damage. The relative humidity in
residential indoor air results from many contributing factors: cooking, showers,
dishwashing, humidifiers, etc. The American Society of Heating, Refrigerating,
and Air Conditioning Engineers (ASHRAE) recommends a maximum relative humidity
value of 60 percent for human comfort. The AGAR research project (see Section B,
Safety Issues, Number 5, above) demonstrated that, even under "worst
case" conditions, the highest relative humidity produced by vent-free gas
heating products was only 49 percent, well below the recognized comfort level of
60 percent. In fact, during very cold weather, the air is dry, so many consumers
use humidifiers to increase the relative humidity for greater comfort. In this
context, vent-free gas heating products serve a useful function by providing
some water vapor.
6. What specifically needs to be told
to a customer about product usage and care in their home?
As with all gas appliances, the customer should read
and follow the instructions and safety warnings provided on all gas appliances
and included in the manufacturer's instruction manual for the proper
installation, use, and maintenance of the appliance.
7. What maintenance is needed on
As with all gas appliances, vent-free appliances should
be inspected for proper operation at least annually by a qualified service
agency. The burners should be visually inspected and cleaned in accordance with
the manufacturer's instructions. The area in which the appliance is installed
should always be kept clear and free of combustible materials, gasoline, and
other flammable vapors and liquids.
E. COMMON CONCERNS:
1. Do the building codes in my area
allow for the installation of vent-free gas products?
Most building codes throughout the U.S. now allow for
the sale and installation of vent-free gas products. This includes Winston -
Salem ,Forsyth County and surrounding counties. In fact, vent-free gas products
are allowed in 47 states. However, since this is not the case in some regional
or local areas, you should always check with your local code authorities before
purchasing and installing a vent-free appliance.
2. Do people need to install a CO
alarm when they install a vent-free appliance?
It is a good idea to install a CO alarm in every
home, regardless of an upcoming vent-free appliance installation or whether a
home is heated using electricity , oil, or gas. Home-related CO incidents are
caused by many sources; some examples are automobiles in attached garages,
portable grills or hibachis used indoors, improper use of a gas range for
heating, and malfunctioning gas appliances. Whether vented or unvented,
following the manufacturers' instructions and having all gas appliances
inspected and properly maintained by qualified service personnel will reduce the
chance of a CO incident occurring from a malfunctioning gas appliance. CO alarms
are recommended by the Consumer Product Safety Commission.