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Mobile home furnace (C) Daniel FriedmanUnvented Gas Heater Safety Warnings

CO, CO2, NO2 & Moisture Hazards in Manufactured & Mobile Homes

Use of un-vented gas heaters in homes:

This article explains possible hazards when using an LP gas or natural gas fueled un-vented heater inside a building and cites safety standards, codes, and research on the dangers of un-vented gas heaters used indoors.

This article series explains how to recognize and fix combustion air defects on heating appliances such as boilers, furnaces, and water heaters. These articles answer most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs.

Our photo at page top shows a mobile home oil fired furnace installed in a closet with an airtight door; there was no outside combustion air supply. The heating system could not work properly nor safely in this home.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Safety Concerns with Un-Vented Gas-Fired Heaters in Mobile Homes & Manufactured Homes

Mobile home furnace (C) Daniel Friedman Watch out: inadequate combustion air supply to a gas burner (and less often to an oil burner) is very dangerous and can produce potentially fatal carbon monoxide.

If you suspect unsafe heating system operation or a carbon monoxide problem be sure everyone leaves the building immediately and then call your local fire department for assistance.

Our photos show an un-vented gas heater used as the primary heat source in a mobile home.

Is it safe to use an un-vented heater in a mobile home?

Our InspectApedia reader asked:

Can I install a 36000 non vented heater in a Mobil home? 2017/06/05 John

Reply: not without safety concerns and IAQ questions

John,

You don't specify the kind of heater, its fuel, nor its manufacturer and brand, nor where the heater is to be installed, so it's tough for me to offer exact advice. You also didn't tell me where you live. Your state, province, city or other local code probably regulates your use of an un-vented heater in your home and may or may not outright prohibit them.

Even where standards such as ANSI Z21 designed to improve the safe use of gas heaters apply, you could not use a 36,000 non-vented heater in a mobile home bedroom, so just where the heater is to be installed and how it's to be used are key considerations.

Do Not use an Un-Vented Gas Heater as a Primary Heat Source

Quoting a U.S. ASHRAE position paper:

Unvented combustion appliances should never be used as the primary/sole source of heating. - ASHRAE position paper cited below

There is a risk of lack of oxygen or of fatal carbon monoxide poisoning (CO) when un-vented heaters are used in homes, particularly when the total space is small.

The risks are particularly great with older un-vented heating equipment that lacks a built-in oxygen sensor designed to turn off the appliance if the oxygen level drops to an unsafe level. There are also indoor air quality concerns with carbon dioxide (CO2), Nitrous oxide (NO2) and high levels of indoor moisture or water vapor produced by un-vented gas heaters.

See CARBON MONOXIDE - CO

and CARBON MONOXIDE WARNINGS: HOME HEATERS

and COMBUSTION AIR SAFETY in MOBILE HOMES

Vent-Free Heater Industry Position on Safety of Un-Vented Gas Heaters

The vent-free heating industry defends the use of un-vented gas fired heating appliances made since 1980 and asserts a less frightening position:

Every vent-free gas product marketed in the U.S. today, regardless of the size, shape, appearance, heat output, or price, has been approved by a recognized listing agency. This involves testing to a rigorous safety standard, in this case ANSI Z21.11.2. But what does that mean to the average consumer?

The American National Standards Institute (ANSI) oversees a process for the development and constant upgrades of safety standards for virtually every class of home appliance available in the marketplace. Every manufacturer must submit their designs for testing to the applicable standard by an independent laboratory.
...
In 1980, the ANSI standard for these products was revised to require each unit to be equipped with an oxygen detection safety sensor (ODS). The ODS is remarkably equivalent in function/reliability to what a circuit breaker is to electrical current.

The ODS automatically shuts off the unit in the unlikely situation that carbon monoxide is elevating and there is oxygen depleting in the vicinity of the unit (regardless of the CO source). - source: Vent-Free Gas Products Alliance [an industry association] c/o AHRI 2111 Wilson Boulevard, Suite 500 Arlington, VA 22201-3001 www.ventfree.org original source: Ventfree, www.ventfree.org/content/view/42/18/

You will see in that industry-article that the vent-free heaters described are not intended for use as a primary heat source for a mobile home or any other home. Quoting further:

Vent-free gas products provide warmth to a chilly area of the home, enable the family to focus heat in gathering areas while reducing the central heating cost, can convert a wood burning fireplace to a convenient attractive heating site, or can update a home by adding a fully dressed out space heating fireplace.

In the event of power outage, there will always be heat available from the non-electrically dependent vent-free gas appliance. - Ventfree op.cit.

Experts Warn about Oxygen Depletion Sensor Reliability for Un-Vented Gas Heaters

Really? Experts do not completely agree that oxygen depletion sensors provide adequate safety for un-vented gas fired heaters.

What about carbon monoxide risks? CO, a colorless, odorless, tasteless, non-irritating poison, is highly toxic and can cause death or permanent brain and organ damage. CO poisons more people than all other poisons combined. When properly maintained and adjusted, gas heaters produce low amounts of carbon monoxide.

One cause of carbon monoxide poisoning from unvented heaters– incomplete combustion caused by lack of air–has been virtually eliminated in newer heaters by use of Oxygen Depletion Sensors (ODS).

Unfortunately, the ODS does not respond to incomplete combustion caused by improper gas pressure; dust, dirt, or rust on the burner; incorrect placement of artificial logs in a gas fireplace; or disruption of the burner by air currents. CO poisoning from unvented heaters remains a concern.
…
Can the health hazards of an unvented heater be reduced? The most effective method to reduce the hazards is to discontinue use of the unvented heater by switching to vented gas or electric appliances. - (Greiner T.H. 1998)

The article continues to make suggestions for reducing the risk if you are nevertheless going to use an un-vented gas heater. The article also cites risks from CO2, nitrogen dioxide (NO2), and water vapor.

Field Experience Found Unsafe CO2 Emissions from Heaters that Include an Oxygen Depletion Sensor

Perfect combustion of propane or natural gas would produce just CO2 and water vapor. Is combustion reliably perfect? No.

I have tested four LP gas fueled fireplace heaters in a home in Mexico over the last ten years. All of these heaters carried a U.S. certification label. These were all appliances not designed for use as a primary home heating source. All of them included an oxygen sensor, and all of them, left operating long enough in a closed room or set of rooms, ultimately turned "off" automatically.

However in every instance, hours before the Oxygen sensor turned off the heater, in 100% of the cases, a properly located, installed, and tested carbon monoxide detector (CO) alarm, sounded to indicate unsafe levels of carbon monoxide in the home. A response of home occupants to the CO alarm sound can include simply turning off or removing the battery from the CO alarm, in my OPINION, then risking death of the building's occupants.

Building Code Limitations on Vent Free Gas Heater Use

Here is an example of an LP-gas room heater installation code from a U.S. state (Alabama) discussing use of vent-free gas heaters in a mobile home:

§ 9-17-122. Installation of heaters—used manufactured homes.

The following LP-Gas room heaters may be installed in a used manufactured home as follows:

LP-Gas listed vented room heaters equipped with a 100 percent safety pilot and a vent spill switch or LP-Gas listed unvented room heaters equipped with factory equipped oxygen depletion safety shut-off systems may be installed in a used stationary manufactured home (mobile home) but not in sleeping quarters or bathrooms in the manufactured home (mobile home) when the installation of the heater is not prohibited by the appliance manufacturer and when the input rating of the room heater does not exceed 20 BTU per hour per cubic foot of space and combustion and ventilation air is provided as specified in Section 5.3 of the National Fuel Gas Code, NFPA 54.

All room 27 heaters installed pursuant to this section shall be securely anchored to the wall or floor. (Acts 1994, No. 94-706, p. 1369, § 3.) - Alabama Room Heating Law, ret. 2017/06/05

The hazards of un-vented heaters, particularly in mobile homes, has been known for a long time. In addition to the risk of fatal carbon monoxide (CO) poisoning there are indoor air quality issues including excess moisture and carbon dioxide CO2 and other combustion products.

Manufactured Home Warning on Use of Unvented Heaters

Here is a quote from the Manufactured Housing Research Alliance

Do not use unvented propane, kerosene, or other unvented combustion heaters. About a gallon of water vapor is released into the air for every gallon of fuel consumed. This is a significant source of water vapor that can quickly cause damage.

Some unvented heaters can also increase pollutant levels and contribute to health problems. - "MOISTURE PROBLEMS in MANUFACTURED HOMES", Manufactured Housing Research Alliance

Supporting research on safety of un-vented gas heaters

...


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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Soot problems after oil burner puffback

We had a furnace blow back a while ago, still noticing soot/black build up coming out of the heating vents on the walls.. this is a rental property. is this dangerous to our health? landlord does not seem concerned (Jan 6, 2015) mahgy

Reply:

Mahgy

No one can assess exposure levels of soot nor health risks accurately from a simple e-text, but in general, breathing soot is not healthy. If the heating system is no longer producing soot (which is itself unsafe) then the duct system may need cleaning.

 

What if I don't see any source of combustion air for my gas heater?

What if there is no visible combustion AIR? (June 25, 2015) Anonymous

Reply: visible clues of adequate combustion air

Anon you'd need to be more specific. Most building codes and standards discussing combustion air supply include a square-foot area size specification.

For example if a heater of input BTUh amount X is in an open space of Z square feet then the area is deemed capable of providing adequate combustion air.

Those guidelines presume a standard minimum rate of building air leakage or air exchange rate.

In the article above you can read details at the paragraph titled

Cubic Feet of Room Space as a Measure of Adequacy of Combustion Air: Total Input BTUH / 1000 x 50

 

OK if combustion air source for water heater is from under the mobile home / trailer?

Does combustion air for mobile home water heaters enter from under the trailer? (Mar 19, 2016) Anonymous

Reply:

Anon:

In some installations it might;

Watch Out: if your water heater is gas or oil fired and lacks adequate combustion air the unit is unsafe and could kill the home's occupants.

We need to find the brand and model of your mobile home water heater and then look at its installation instructions.

Review MOBILE HOME WATER HEATERS 

and find your water heater manual in our library of free downloads

at WATER HEATER AGE & MANUALS

...

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Citations & References

In addition to any citations in the article above, a full list is available on request.

  • American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbook - Fundamentals, 1993, Chapter 15, page 15.9 Air For Combustion.
  • ASME CSD-1- Controls and Safety Devices for Automatically Fired Boilers, 1992 with addendum 1a 1993. section CG-260 Combustion Air.
  • BOCA - National Mechanical Code, 1990, article 10, Combustion Air.
  • NFPA 31 - Installation of Oil Burning Equipment, 1992, section 1-5 Air for Combustion and Ventilation.
  • NFPA 54: National Fuel Gas Code (2015), addresses heating appliance combstion air ventilation specifications. NFPA 54, ANSI Z223.1 provides minimum safety requirements for the design and installation of fuel gas piping systems in homes and other buildings.
  • NFPA 85: Boiler and Combustion Systems Hazards Code: NFPA 85 contributes to operating safety and prevents explosions and implosions in boilers with greater than 12.5 MMBTUH, pulverized fuel systems, and heat recovery steam generators.
  • NFPA 87: Recommended Practice for Fluid Heaters, This recommended practice provides safety guidance for fluid heaters and related equipment to minimize fire and explosion hazards that can endanger the fluid heater, the building, or personnel
  • SBCCI- Standard Mechanical Code, 1991, section 305 Combustion and Ventilation Air.
  • Axtman, William H., "Combustion Air Requirements: The Forgotten Element in Boiler Rooms", Grayh Gull Associates, retired executive director of the American Boiler Manufacturers Association, National Board Technical Series, Winter 1995 National Board Bulletin. Retrieved 26 January 2015, original source: http://www.nationalboard.org/index.aspx?pageID=164&ID=191
    Excerpt:

    Several safety codes such as the National Fire Protection Association's standards, NFPA 54 - National Fuel Gas code, NFPA 31 - Installation of Oil Burning Equipment, and the American Society of Mechanical Engineers (ASME) CSD-l Controls and Safety Devices for Automatically Fired Boilers have sections covering the requirements for combustion air intakes.

    In addition, building codes such as the Building Officials and Code Administrators International (BOCA) National Mechanical Code and the Standard Mechanical Code published by the Southern Building Code Congress International (SBCCI) have air requirements for combustion.

    Editor's note: Some ASME Boiler and Pressure Vessel Code requirements may have changed because of advances in material technology and/or actual experience. The reader is cautioned to refer to the latest edition and addenda of the ASME Boiler and Pressure Vessel Code for current requirements.
  • Nussbaumer, Thomas. "Combustion and co-combustion of biomass: fundamentals, technologies, and primary measures for emission reduction." Energy & fuels 17, no. 6 (2003): 1510-1521.
  • Utiskul, Yunyong P., Wu, Neil P., Biteau, Hubert, "Combstion Air Requirements for Power Burner Appliances, Final Report", The Fire Protection Research Foundation, The Fire Protection Research Foundation
    One Batterymarch Park
    Quincy, MA, USA 02169-7471
    Email: foundation@nfpa.org
    http://www.nfpa.org/foundation, retrieved 25 Jan 2015, original source: http://www.nfpa.org/~/media/files/research/research%20foundation/rfcombustionairrequirements.ashx, Executive Summary:

    Gas-fired appliances require combustion air to properly function. Adequate air is necessary for
    supporting combustion of the appliance burner, dilution of flue gas, and proper ventilation of the
    space where the appliance is installed.

    Current standards and model codes outline requirements
    and methods to supply the combustion air. One method is to provide outdoor combustion air
    through openings or air ducts communicating with the outdoors through natural ventilation.

    Most standards require the outdoor opening(s) be prescriptively sized based on the total energy
    input rating of the appliance.

    However, in the United States, the current standards contain no
    separate provisions to address the opening size supplying the combustion air for
    commercial/industrial sized appliances, which typically have a high energy input rating of
    greater than 300 kBtu/hr and are equipped with a power burner unit.

    As a result, the opening(s) can be excessively sized when determined based on the current standards.

    This research project establishes minimum outdoor combustion air requirements specific to gasfired
    appliances utilizing power burners with input ratings no greater than 12.5 MBtu/hr.

    A review of the available literature, engineering guidelines, and current standards and model codes
    related to combustion air requirements was performed.

    This report provides an understanding of the technical basis for the existing provisions for combustion air and their applicability to
    power burner appliances.

    This report also identifies the range of energy input ratings for gasfired
    appliances equipped with power burners, and compares the combustion air requirements
    specified by a range of appliance manufacturers.

    A theoretical model for air flow through openings was developed and the modeling results, together with the data gathered through the
    literature review, were used to provide a baseline to establish the theorized combustion air

    requirements suitable for power burner appliances.
    ...
  • [1] Jeff Wilcox, "Evaluating Duct Work, How to Evaluate Furnace Duct Work & Cure Short Cycling or Inadequate Ductwork Problems" Vermont Department for Children and Families, Office of Economic Opportunity, - dcf.vermont.gov/sites/dcf/files/pdf/oeo/WAPManual/AppendixI.pdf‎ retrieved 12/5/2013. Geoff Wilcox Vermont Office of Economic Opportunity Weatherization Assistance Program Waterbury, VT (802) 769-8376 Geoff.wilcox@state.vt.us Reference Material for the original article came from: 1. Saturn Mechanical Systems Field Guide 2. Bacharach (Rudy Leatherman)
  • Field Controls provides instructions for the installation of LP and Natural Gas spill sensor switches, for example for their Gas Spillage Sensing Kit Model GSK-3, GSK-4, GSK-250M switches. Contact your heating service technician directly, or contact Field controls at fieldcontrols.com for more information. These switch models include a manual reset switch. Field Controls, Kingston NC 28504 - Tel 252-522-3031.
  • Tjernlund Products provides instructions for the installation and use of their controls, including the WHKE Millivolt Interlock Kit for use with their UC1 Universal Control, MAC1E or MAC4E auxiliary controls for gas fired equipment. This document also describes Tjernlund's recommended combustion air safety check which we recommended in this article. Contact Tjernlund Products at tjernlund.com or at 800-255-4208.
  • Bacarach Fyrite Combustion Analyzer equipment [Website] contact: MSAsafety.com or MSA Bacarach Solutions: HVAC/R Solutions, Tel: 1-800-672-4678, Email: customer.service@msasafety.com or Tel: 1-800-672-2222 Email: US.CS@MSASAFETY.COM or in Canada, CANADA.CS@MSASAFETY.COM - more details are at OIL BURNER CO2 TEST
  • R.E. Prescott Company, a producer of other REPCO™ residential and industrial products as well as a provider of design-build engineering services is at 10 Railroad Avenue, Exeter, NH 03833. Tel: 603-722-04321 or 888-786-7482.

    Trish O'Keefe from Prescott informed us (10/7/2009) that their company had nothing to do with the failed Repco heating boilers discussed at InspectAPedia.com.
  • In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested

    CONTINUE READING or RECOMMENDED ARTICLES.

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