How to Install A Vent Free Gas Heater

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A vent-free gas heating appliance operates without a chimney, flue or vent, so you can install one just about anywhere.

A variety of vent-free gas products are available including space heaters, fireplaces, stoves, fireplace inserts, and gas logs. Modern vent-free gas heating appliances:

Plaque burner

  • are inexpensive and have low operating costs;
  • are 99 percent energy efficient;
  • provide warmth during power outages;
  • are Design-Certified to the latest national safety standards (ANSI Z21.11.2);
  • do not exceed 40,000 Btu/hr of heat output; and
  • are a source of pleasure that will serve your family for years to come.

Nine million American homes — and more than 45 million households worldwide — already enjoy the comfort and convenience of vent-free gas heating products. In fact, more Americans are buying vent-free gas appliances than any other type of supplemental gas heating product.

Blue-flame burner

How do Vent-Free Gas Heaters Work

Vent-free supplemental gas heating products operate on natural or propane gas — most models require no electricity.

The flame is fueled by natural or propane gas through a permanent line that is connected to a blue-flame/yellow-flame burner or ceramic plaque burner within the heating appliance.

Indoor air quality

The primary gas combustion byproducts that can affect indoor air quality are carbon monoxide, carbon dioxide, nitrogen dioxide, oxygen and water vapor (humidity). Today’s vent-free heating products operate well within nationally recognized standards and recommendations for all five byproducts. These low emission levels are confirmed by American Gas Association Research Division.

Oxygen Detection Safety-Pilot

Since 1980, vent-free gas heating appliances have been equipped with a unique safety-pilot system called an oxygen detection safety-pilot, or ODS. The ODS is the proven technological innovation that revolutionized the safety of vent-free gas heating appliances.

The ODS automatically shuts off the gas supply in the rare event that the oxygen level in the room falls to 18 percent.

Until recently, questions remained about the long-term effect of vent-free gas product emissions on indoor air quality.

In 1995, the Vent-Free Gas Products Alliance of the Gas Appliance Manufacturers Association (GAMA) commissioned a study on indoor air quality as it relates to vent-free gas heating products in the home. The results proved that vent-free gas heating products meet or exceed the most current and applicable nationally recognized standards and guidelines for indoor air quality.

See: How Safe are Ventless Gas Fireplaces

Cost and Efficiency of Vent Free Gas Heaters

With a vent-free gas product, there’s no chimney or vent allowing heat to escape. And if there’s no heat escaping, you’re saving money. All the heat stays in the room, right where you want it.

A vent-free gas heating product literally costs only pennies per hour to operate, because no heat is wasted through an open chimney damper and flue. Compare that to heating with wood.

Vent-free gas heating appliances operate on natural gas or propane, and both are considerably less expensive than electricity. The cost to heat a room with gas is less than the cost to heat the same space with electricity.

Even homeowners with electric heat can often benefit from vent-free gas heating appliances because they may already be on natural gas lines or can be connected to propane.

According to the American Gas Association, natural gas remains a good energy value because it is a clean, highly efficient, easy to use a form of energy found in abundance in North America.

More than 70 percent of all new single-family homes nationwide are heated with natural gas, demonstrating that an increasing number of Americans prefer natural gas heat to any other source of energy.

In areas where natural gas is not available, be sure to ask for propane gas. All vent-free gas products are available for natural or propane gas use.

No chimney? No problem.

You don’t need one, so you’re spared the costly expense of having a vent or chimney installed.

In fact, the installed cost of a vent-free gas fireplace can be as low as one-third the cost of a wood-burning fireplace.

An added bonus: You don’t have to deal with any smoke, soot, burning embers, ashes, or chopping, stacking and carrying wood. A vent-free gas heating product offers the most affordable solution when adding a fireplace to your home.

Use your old masonry fireplace

If you have a traditional fireplace, you’re already aware of how inefficient they are, and the associated mess and inconvenience. Simply put in a log set, or install an insert if your fireplace is damaged or inoperable.

Heat Where You Need it

You can lower the thermostat of your central heating system by adding supplemental heat in a primary gathering area of your home, such as the:

  • living room
  • kitchen
  • family room
  • dining room
  • home office

Vent-free gas heating products are available in various styles to suit every application and location in your home. From glamorous to functional, from modern to traditional, there’s a vent-free appliance that fits your needs.

Limited use areas

A vent-free gas heater also can be used to warm limited use, hard-to-heat areas such as a basement, garage, room addition, sun porch or greenhouse.

Install them almost anywhere

Because you don’t need a chimney, a vent-free gas heating product can be installed almost anywhere — even an inside wall. In contrast, installing a traditional wood fireplace is a major (and costly) construction project.

With a vent-free gas fireplace or heater, you have complete flexibility in designing or redesigning your room.

Is Vent-Free Gas Heating Right for Me?

While most states allow installation of vent-free gas heating appliances, a handful of states still prohibit residential use. Very often, that’s because a state’s building codes haven’t caught up with vent-free gas technology.

Because counties and municipalities may adopt different codes than state agencies, please check with your salesperson, installer or local codes officials to determine the current code in the city where you plan to install the appliance.

Other considerations

Also double-check with your retailer before installing a vent-free
heating appliance in:


    • an extremely tight home — if your home shows symptoms of an inadequately ventilated home (moisture on inside of windows, mildew, and shower or bath humidity lingers), additional ventilation may be required prior to adding additional vent-free gas appliances. Also, if you have an extremely tight new home, talk with your builder or contractor to make sure your home is properly ventilated;


  • homes at high altitude (i.e. homes at 4,500 feet above sea level or higher) — homes in higher altitudes may experience nuisance pilot outage and flame shutdown due to lower atmospheric pressure.

Who sets the standards?

The American National Standards Institute — known as ANSI — maintains a strict national safety standard for vent-free gas heating appliances. The standard, called ANSI Z21.11.2, is reviewed and updated regularly to address product safety and performance.

How do I know that a gas product meets ANSI standards?

When shopping for your vent-free gas products, always be sure the models you are considering are Design Certified to the ANSI Z21.11.2 standard by a nationally recognized laboratory.

The following six model building codes permit the installation of listed vent-free gas products:

  • National Fire Protection Association (NFPA)
  • Building Officials and Code Administrators (BOCA)
  • Southern Building Code Congress International (SBCCI)
  • Council of American Building Officials (CABO)
  • International Mechanical Code (IMC)
  • International Fuel Gas Code (IFGC)

What Size (Btuh) Vent-Free Gas Heating Appliance Should I Choose?

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 the exception described in heating Region V.



House Construction

Heating Region




Appliance Operation







Minimum Input Rate Needed to Maintain Comfort Btuh/ft3






































House Construction

Heating Region




Appliance Operation







Maximum Input Rate Needed to Maintain Indoor Air Quality Btuh/ft3









  1. Loose construction (high heat losses and infiltration rate): little insulation, no storm doors and windows, no vapor barrier, undampered fireplace, and an ACH of about 1.0.
  2. Average construction (typical heat losses and infiltration rate): insulated, vapor barrier, loose storm doors and windows, dampered fireplace, and an ACH of about 0.5.
  3. Tight construction (low heat losses and infiltration rate): well insulated, vapor barriers, tight storm doors and windows with weather-stripping, dampered fireplace, and an ACH of about 0.35.

(ACH=Air Changes Per Hour)

If you live in the state of New York, be sure to ask your dealer to give you a set of sizing guidelines for New York State. If not available, contact the Alliance office.

Installation of vent-free gas products must meet the guidelines of the National Fuel Gas Code ventilation requirements, as is the case for all gas appliances.


  1. Information that the Consumer Must Provide:
    1. Determine the volume of space to be heated in cubic feet. This space may be a single room, or it may be connecting rooms or areas.
    2. Select the house construction: loose, average or tight.
    3. Select the type of heater control system desired: thermostatic or manual operation.
    4. Determine the region of the country where the house is located.


  2. Heater Sizing Calculation
    1. Find the heater input rate (in Btuh/ft3) from Table A according to the above information from 1b, 1c and 1d.
    2. Multiply this value from Table A by the volume of space from 1a. This result will provide a minimum heater input (in Btuh) to ensure human comfort under a range of operating conditions.


Exception: In heating Region V, if the heater is to be installed in a room that can be isolated from other rooms by doors, find the heater input rate (in Btuh/ft3) from Table B. Multiply this value from Table B by the volume of space from 1a. This result will provide a maximum heater input (in Btuh) to ensure acceptable indoor air quality. However, it may not supply enough heat under certain operating conditions. Alternatively, if you increase the ventilation to this isolated room — e.g., by installing a permanent opening to an adjoining room or area at least 40 percent greater in volume than the isolated space — this exception does not apply.

Consumer Knowledge

In early 1996, when scientists at the American Gas Association’s Research Division (AGAR) set out to test the effects of vent-free gas product emissions on indoor air quality, they ran trials with real vent-free products in a real home — the AGAR research and demonstration house.

With this unique facility, AGAR researchers have the capability to model and measure variations in indoor air quality based on the operation of various gas appliances.

Testing the air

AGAR scientists tested the levels of all five major contributors of indoor air quality — oxygen, carbon monoxide, carbon dioxide, nitrogen dioxide and water vapor (humidity) — against the latest IAQ guidelines and recommendations:

  • Recommended maximum levels of carbon monoxide (CO) are set by the Consumer Product Safety Commission (CPSC), with sensitive populations — such as children, pregnant women and the elderly — as the benchmark.
  • Nitrogen dioxide (NO2) levels are defined by the Occupational Saftey and Health Administration (OSHA) and gas industry experts.
  • Carbon dioxide (CO2) maximum emission levels are defined by Residential IAQ Guidelines/Canada.
  • The oxygen (02) standard is established by the National Institute for Occupational Safety and Health (NIOSH).
  • National recommendations for water vapor are set by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE).

In their testing, AGAR researchers also considered a wide variety of operating conditions such as Btu output, space to be heated, air change rates and outdoor temperatures.





Combustion byproduct


Specifying agency


National IAQ Standard/Guidelines exposure level/time


Vent-free gas product

In the AGAR study, vent-free gas heating products performed well within nationally recognized guidelines for indoor air quality.

Carbon Monoxide (CO)


15 ppm avg/8 hours 25 ppm avg/1 hour

2.5 ppm/8 hours 1.5 ppm/1 hour

Nitrogen Dioxide (NO2)

OSHA and Gas Industry Experts

0.5 ppm avg/1 hour

0.22 ppm/1 hour

Carbon Dioxide (CO2)

Residential IAQ Guidelines/Canada

3500 ppm avg/1 hour

1500 ppm/8 hours

Oxygen (O2)


19.5% minimum/continuous

20.4% continuous

Humidity (H2O)


60% -> 40%* maximum

36.5% maximum with no condensation

Source: AGAResearch Study, GRI Report 96/0093-1996
*Depending on DOE Heating Region

The results

The researchers concluded that vent-free gas heating products performed well within nationally recognized guidelines for indoor air quality.

This research proves that 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 is operated at a lower output level to avoid overheating the living area. However, using an oversized unit is not the most efficient means of operation.

Water vapor levels

When outside temperatures fall, so does relative humidity (water vapor). Many people in cold climates use humidifiers to supplement indoor moisture. Vent-free gas heating products are not intended to replace humidifiers, but they do perform a similar function.

AGAR researchers examined relative humidity at 0°F outdoor temperature and a 0.25 air change rate (ASHRAE’s minimum acceptable air change rate is 0.35/hour). Even under these extreme conditions, the highest relative humidity measured was 49 percent. That’s still well below the recognized comfort level of 60 percent.

If a home is below 0.35 air exchanges per hour (extremely tight construction), additional mechanical ventilation needs to be added before installing a vent-free gas heating appliance.

What is AGAR?

AGAR was the research arm of the International Approval Services (IAS), a nationally recognized independent testing agency. IAS, formerly known as A.G.A. Laboratories, now known as CSA International, has been certifying gas appliances since 1928 to ANSI safety standards. In 1997 AGAR was purchased by Energy International, Inc.

For a copy of the AGAR research project or a video detailing the research, write to the Gas Appliance Manufacturers Association, 2107 Wilson Blvd., Suite 600, Arlington, VA 22201, or call GAMA at 703-525-7060.

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