Under a contract with Manufactured Housing Research Alliance, ADM Associates, Inc. conducted a field study to measure indoor air pollution and moisture levels in fuel switching manufactured homes. The project consultant was Mr. Greg Traynor, a nationally recognized expert on indoor air pollution effects resulting from combustion equipment. Fuel switching is defined as any use of non-electric heaters to supplement electric space heating in manufactured homes.

A sample of 21 manufactured homes was recruited for field-testing. To qualify for the testing, a manufactured home had to have been built in 1993 or later, have electric heat, and have an alternative fuel heater. Special recruitment procedures were used to identify manufactured homes meeting these criteria. The final sample included homes using three types of fuel; twelve (12) of the test homes used kerosene for alternative heating, seven (7) used liquid propane gas (LPG), and two (2) used wood. This study focused on determining the concentration levels at the test homes for three gases that are major contributors to poor indoor air quality: carbon monoxide (CO), carbon dioxide (CO2), and nitrogen dioxide (NO2).

Analysis of the field data provided responses to the general research questions that motivated the study.

Do fuel switching heaters increase indoor air pollutants or moisture levels in manufactured homes?

The results of this study showed that operation of an alternative fuel heater (i.e., an unvented or partially-vented combustion appliance) does increase indoor pollutant concentrations of CO, CO2, NO2, and water vapor. However, relative humidity levels do not always increase due to a simultaneous increase in indoor temperature. The amount of pollutant increase depends on many factors, including the degree of venting, the type of appliance, the burning conditions of the appliance, the fuel type, the building volume, the building air infiltration rate, and the appliance usage pattern.

What are typical and extreme levels of pollutants produced by fuel switching heaters?

The test results yielded the following regarding typical and extreme levels of pollutants produced by fuel switching heaters.

Typical indoor CO levels ranged from 2-21 parts per million (ppm) for homes with kerosene heaters and 2-40 ppm for homes with propane heaters. Projected (assumed, qualitative) worst-case scenarios yielded indoor CO concentration ranges of 3-57 ppm for homes with kerosene heaters and 1-80 ppm for homes with propane heaters.

Typical indoor CO2 levels ranged from 1900-6760 ppm for homes with kerosene heaters and 1990-6000 ppm for homes with propane heaters. Projected (assumed, qualitative) worst-case scenarios yielded indoor CO2 concentration ranges of 2270-13800 ppm for homes with kerosene heaters and 2080-11900 ppm for homes with propane heaters. Typical indoor NO2 levels ranged from 0.012-0.098 ppm for homes with kerosene heaters and 0.022-0.277 ppm for homes with propane heaters. Worst-case scenarios yielded values at or below those measured under "typical" conditions.

Gas and Water Vapor Concentrations Measurements at Site ID MH23

Are the levels of the pollutants harmful to occupants?

Do they deteriorate building materials? Homeowners who regularly use alternative fuel heaters are exposed to ongoing low to high levels of CO, CO2 and NO2. Users of backup heaters can be exposed to accumulating levels of gases over several days during power outages.

Based on comparison with published air quality guidelines, many of the homes in this study had CO and/or CO2 levels that could be harmful to selected populations. Using actual peak measurements assumed to be typical, indoor CO levels reached concentrations in some homes that could increase the onset of angina and cause low birth weights for pregnant women. Many elevated CO2 concentrations were above the US Occupational Safety and Health Administration's (OSHA's) guideline for a healthy workforce. Sensitive populations could experience a lightheaded sensation and increased breathing rates at the levels observed.

Indoor NO2 levels observed did not appear to pose a health threat to the occupants based on comparison to appropriate guidelines. This finding needs to be confirmed with additional studies especially to confirm the high reactivity rates found in these manufactured homes.

Indoor relative humidity levels were uniformly low during all tests. Unless condensation actually occurs on a regular basis, the growth of biological contaminants will be minimal as will the deterioration of building materials. There was no evidence in this study that would imply that alternative fuel heaters cause the deterioration of building materials.

Are there particular types of heaters that are more prone to cause problems?

The indoor pollutant levels caused by unvented kerosene and propane space heaters were remarkably similar in the homes studied. Two homes with vented fireplaces, when operated in the proper vented mode, showed much lower CO, CO2 and NO2 concentrations than the homes with unvented kerosene and propane heaters and only showed trace amounts of CO. Assuming the indoor particle emissions (not measured) from the fireplaces were minimal, vented fireplaces appear to result in lower overall indoor pollutant levels than unvented kerosene and propane heaters.