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"
|Gas and Water Vapor Concentrations Measurements
at Site ID MH23
Are the levels of the pollutants harmful
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
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.