Inspecting Unvented Gas Space Heaters
By Gregg Harwood, Professional Home Inspection Service
Most states allow the use of unvented gas heaters in residences. In August of this year New York State approved the installation of ventless gas space heaters by amending the Uniform Fire Prevention and Building Code. The Code change specifies the following:
1) Unvented heaters shall conform to ASNI Z21.11.2
2) Unvented heaters shall not be used as a primary heat source
3) Unvented heaters shall comply with section 7.2.2 of NFPA 54 (National Fuel Gas Code)
4) Unvented heaters shall comply with regulations promulgated by the Health Department. These regulations include package labeling requirements and a requirement that heater-sizing guidelines be posted at the point of sale. It is interesting to note that the labeling suggests that the consumer chose the appropriate sized unit, but there is nothing in the law that requires it.
Unvented heaters are 99.9% efficient, relatively inexpensive and easy to install. This makes them very attractive to consumers and it won't be long before they will start showing up in houses that we inspect. These units are available in three different burner types; blue flame, which as a relatively short, crisp uniform pattern; yellow flame, which is used in some fireplace log sets and is a taller pattern; and radiant, which uses ceramic bricks to radiate heat. There are also three different styles of heater; wall mount; fireplace and log sets.
All unvented heaters come with an Oxygen Depletion Sensor (ODS) which will shut the unit down if the room oxygen level falls below 18%. The ODS is simply the pilot light and thermocouple combination. These components are configured so that when the oxygen level drops the pilot goes out or wanders "looking" for oxygen. In either case the thermocouple cools and the unit is shut down. The burners on unvented equipment is not adjustable. The fuel and air mix is preset at the factory. These units are available in natural gas and LP versions and are not convertible.
Concerns over unvented heaters center on air quality issues. The Vent-Free Gas Products Alliance sites an AGAResearch study which shows emissions of carbon monoxide (CO), nitrogen dioxide (NO}, and humidity to be within national guidelines unless the house is of extremely tight construction or the heater is oversized for the space. The NYS legislature has addressed these issues by requiring that the unvented appliances not be installed as the primary heat source and by suggesting that consumers follow the sizing guidelines. However, the fact that these appliances are sold directly to the homeowner and are easy to install as a weekend project ensures that we will see improper installations in homes that we inspect. The following is a checklist of things to consider when inspecting unvented appliances.
- Is the unit that you are looking at a standard vented or an unvented type?
- Does the unit have adequate clearance to combustibles? For example, DESA (Comfort Glow products) requires 6" clearance from the sides of their wall mount units, 36" from the top and 3" from the bottom. These clearances may vary by manufacturer. The clearances from the opening of a fireplace to a combustible mantle may need to be greater than we are used to due to the fact that the unvented appliance is operating with the damper closed.
- Is there a gas line shut off valve with in 6 feet of the heater? (NFPA 54, 5.5.4)
- Is the ODS in place and operable?
- Are there problems with the flame pattern? The pilot should burn steadily with no lifting. Blue flame burners should not have yellow tips. There should be no soot deposits. Yellow flame tips and soot are indications of incomplete combustion and CO production. Yellow flame burners on unvented logs and fireplaces create this effect by introducing excess air into the burner, not by burning too rich.
- Is the heater properly sized? To figure the sizing one needs to calculate the room size, or combined rooms if no doors are present which could be closed, and then refer to the manufacturer's NYS sizing guidelines. The guidelines are divided up into loose, average and tight houses. They are also divided for manual control heaters versus thermostatic as well as isolated space versus freely-communicating space. An isolated space is a room with closeable doors where as a freely-communicating space can readily draw air from other parts of the building. Performing these calculations is beyond what is called for in a general home inspection. However, by looking at a 10,000 BTU unit in an average home we can get a feel for the space required. This heater, in a freely-communicating, space needs 2941 cubic feet or 368 square feet of floor space with 8-foot ceilings. That is about 1\\3 of the space on one floor of a 1200 square foot ranch house. Now if this same unit is in a room with closeable doors, the space requirements increase to 490 square feet, or a large 20 X 24 room. The burning of LP and natural gas gives off water vapor as a by-product. Look for signs of excess moisture in the house when trying to determine if the heater is appropriately sized for the space. Refer your client to the owner's manual, which should be on-site, for further information. (NFPA 54, 5.1.21 requires that installation, operation and maintenance instructions be left for the owner. Much of the information that a homeowner needs in order to operate this equipment safely is well beyond the level of detail, which is required in a general home inspection.)