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Selecting the Right Ventless (Vent-Free) Gas Heating Appliance for Your Home

Vent Free gas heating may be the answer to your zone heating needs, but check with your local code official before buying.

ULMost states in the U.S. now allow for the sale and installation of vent-free gas products. However, there are 45,000 different code officials in the country, and some areas have not changed their codes to the new International "I" codes and may be in the process of doing so. 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 inadequate ventilation (moisture on the insides of windows, mildew, and the shower or bath humidity lingers), more 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. Homeowners in these areas should check with their local codes officials.
  • State of Massachusetts - if you buy a unit in Massachusetts, be sure to get a copy of the Massachuetts Regulations from your retail store prior to installation. This is the 49th state to allow for vent-free products and special permits are required.


Who sets the standards?

The American National Standards Institute - known as ANSI - maintains a strict standard for vent-free gas heating appliances. The standard, called ANSI Z21.11.2, is updated constantly to provide for product safety and performance, based on the latest technology.


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 certified as complying with the ANSI Z21.11.2 standard by a nationally recognized laboratory.


NATIONAL MODEL CODES/CODE GROUPS

The following seven model codes/code groups 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) 
  • International Residential Code (IRC)


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.


Ventless Gas Product Sizing Chart

  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:
    • a - 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.
    • b - Select the house construction: loose, average or tight.
    • c - Select the type of heater control system desired: thermostatic or manual operation.
    • d - Determine the region of the country where the house is located.
  2. INFORMATION THAT THE CONSUMER MUST PROVIDE:
    • a - Find the heater input rate (in Btuh/ft3) from Table A according to the above information from 1b, 1c and 1d.
    • b - 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.



Research Shows What Customers Already Know

All homeowners want to be certain that their home appliances meet nationally recognized guidelines for indoor air quality (IAQ) and do not emit excessive humidity. That's why the Vent-Free Gas Products Alliance - a coalition of members of the Vent-Free Gas Products Division of GAMA, an association of appliance and equipment manufacturers - commissioned independent testing of vent-free gas products by two of the nation's leading testing firms. The research findings are as follows.


INDEPENDENT RESEARCH ON VENT-FREE GAS PRODUCTS AND INDOOR AIR QUALITY

To document how vent-free gas products affect indoor air quality, the American Gas Association Research (AGAR) Laboratories performed an extensive, independent scientific study. They ran trials with real vent-free products in a real home - the AGAR research and demonstration house.

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 indoor air quality guidelines and recommendations.


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

The table below shows how vent-free gas products per-form compared to national indoor air quality guidelines and standards.


AGAR Study

Source: AGAResearch Study, GRI Report 96/0093 - 1996
* Recommended maximum levels of Carbon Monoxide (CO) are set by the Consumer Product Safety Commission, with sensitive populations - such as children, pregnant women and the elderly - as the benchmark.
** Depending on DOE Heating Region † The American Gas Association's Research Division (AGAR) is the research arm of the International Approval Services (IAS), 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. IAS is now CSA America and is located in Cleveland, OH.


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.

Independent Research On Vent-Free Gas Products And Humidity

Most people are aware that sustained high humidity can encourage mold growth. But what causes sustained high humidity in a home? To answer this question regarding ventfree supplemental gas heating products, the Vent-Free Gas Products Alliance decided to find out once and for all.

The Alliance commissioned an independent research study to get the answer. The study, titled Impacts Of Vent-Free Gas Heating Products On Indoor Relative Humidity, was designed to address the following question: "Do vent-free gas heating products generate enough water vapor to raise indoor relative humidity levels high enough to foster mold growth?"

The rigorous and comprehensive study was completed in December 2002 by risksciences, LLC, an independent scientific consulting firm nationally recognized for its expertise in human exposure modeling in residential environments. The research study concluded:

For the vast majority of homes in the U.S., ventfree gas heating products DO NOT generate enough water vapor to raise indoor humidity levels high enough to foster mold growth.

Furthermore, the findings indicated that greater emphasis should be placed on other factors that can cause humidity levels to exceed mold formation thresholds, such as aging homes, outdated construction, poorly sealed or leaky windows, wall insulation, insufficient ventilation, and maintenance of air conditioning systems.

See the table below for the results of the research study on vent-free gas products and humidity - and breathe easy. 

Risksciences Study

Source: risksciences, LLC, research study, December, 2002
1 Based on 200,000 iterations - 20,000 iterations per region, with and without a vent-free gas appliance.
2 Based on 1,000-hour heating temperature.
3 Rounded range that encompasses the average monthly minimum to the average monthly maximum
outdoor relative humidity for the period November through February for all five DOE regions
(i.e., DOE Regions I, II, III, IV, and V), based on 30-year climatological data (NOAA 2001).

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