ASHRAE Journal - April 2013 - 64

iaq applications

New ASHRAE Position Document

Unvented Combustion
By Paul Francisco, Member ASHRAE

U

nvented combustion has been used in the United States for decades.
For example, cooking appliances using natural gas or propane

are very common in homes. Natural gas, propane, and kerosene heaters
also have been used in homes for many years. In the case of cooking, it
has become more common in recent years to install exhaust ventilation,
although recirculating fans are still found in many homes.
In the case of heating, additional
ventilation is rare. The primary changes
over the last few decades for heating appliances have been the requirement for
safety devices such as oxygen depletion
sensors (ODS) and standards that regulate
the heating capacity and allowable emissions from these devices.
In the last several years, unvented
combustion has garnered increasing
attention and controversy. Critics argue
that any release of combustion products
into the occupied space may be harmful. Others argue that these appliances
have a strong safety record and that, of
the hundreds of deaths due to carbon
monoxide poisoning, none have been
shown to be the result of ODS-equipped
unvented appliances.
In response to this issue, ASHRAE
recently published a position document
titled “Unvented Combustion Devices
and Indoor Air Quality.” This document
reviews the current state of knowledge
regarding unvented combustion devices
and provides a number of recommendations. The focus of this position document
is on liquid and gas combustion—specifically natural gas, propane, kerosene,
and denatured alcohol—and on modern
cooking and heating appliances. It does
64

ASHRAE Journal

not address solid fuel combustion or less
technologically advanced appliances.

Combustion Products
Four primary products of combustion
are considered in the document: carbon
monoxide, nitrogen dioxide, moisture,
and particles. (Moisture is not a contaminant on its own, but excessive levels can
promote problematic conditions.) Carbon
dioxide is not discussed in the position
document because the health concerns are
much less clear. Other contaminants, such
as polycyclic aromatic hydrocarbons and
aldehydes are also not discussed.
For each of the four primary products
of combustion, the position document
presents the current understanding of
health concerns. For carbon monoxide
and nitrogen dioxide, current standard and
guideline thresholds are presented (Table
1). The U.S. Environmental Protection
Agency’s National Ambient Air Quality Standards (NAAQS) contains values
that are intended for outdoor air, but in
the absence of values for indoor air they
are often used indoors. In other cases,
such as the World Health Organization
(WHO) and Health Canada, the values are
said to be applicable to indoor air but are
guidelines rather than standards. There are
ashrae.org

no set standards or guidelines for indoor
moisture or particle concentrations.

Appliance Categories and Standards
The position document next describes
the types of appliances of interest, including the intended use of each category
and the requirements of the pertinent
appliance standards. These requirements
include such topics as maximum heating
capacity and maximum emission rates
for combustion products. The allowable
emission rates for different appliance
categories are often very different for the
same combustion product.
The appliance standards are ANSI
Z21.1 for natural gas and propane cooking
appliances, Z21.11.2 for natural gas and
propane space heaters, UL 647 for kerosene heaters, and UL 1370 for denatured
alcohol appliances. The maximum heating capacity for natural gas and propane
heaters is 40,000 Btu/h (10,000 Btu/h [3
kW]) for bedrooms, and 6,000 Btu/h (2
kW) for bathrooms). For kerosene heaters,
the maximum capacity is 30,000 Btu/h (9
kW) for fixed-mounted units and 25,000
Btu/h (7 kW) for portable units. Denatured
alcohol appliances, which are intended to
be decorative rather than for heating, have
a maximum input of 0.25 gallons (0.95 L)
of alcohol per hour.
Regarding emissions, ANSI Z21.11.2
requires that natural gas and propane
heaters have a maximum of 0.02% (200
ppm) carbon monoxide (air-free), and a
maximum of 0.002% (20 ppm) nitrogen
dioxide (air-free). The nitrogen dioxide
limit is based on a recommendation from
the Consumer Product Safety Commission (CPSC) that intended to limit room
concentrations to under 300 ppb. This
limit was incorporated into the standard in
2003 and enforced starting 2005. Note that
the term “air-free” means that this is the
April 2013



ASHRAE Journal - April 2013

Table of Contents for the Digital Edition of ASHRAE Journal - April 2013

ASHRAE Journal - April 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Ground-Coupled Heat Pump and Energy Storage
Fan Efficiency Requirements for Standard 90.1-2013
Technology Award Case Studies:
Geothermal for 5 Ecosystems
Holistic HVAC Design
Standing Columns
Engineer’s Notebook
Data Centers
Emerging Technologies
IAQ Applications
Refrigeration Applications
Special Products
People
International Column
Energy Modeling
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2013 - ASHRAE Journal - April 2013
ASHRAE Journal - April 2013 - Cover2
ASHRAE Journal - April 2013 - 1
ASHRAE Journal - April 2013 - 2
ASHRAE Journal - April 2013 - Contents
ASHRAE Journal - April 2013 - Commentary
ASHRAE Journal - April 2013 - 5
ASHRAE Journal - April 2013 - Industry News
ASHRAE Journal - April 2013 - 7
ASHRAE Journal - April 2013 - 8
ASHRAE Journal - April 2013 - Letters
ASHRAE Journal - April 2013 - Meetings and Shows
ASHRAE Journal - April 2013 - 11
ASHRAE Journal - April 2013 - 12
ASHRAE Journal - April 2013 - 13
ASHRAE Journal - April 2013 - Ground-Coupled Heat Pump and Energy Storage
ASHRAE Journal - April 2013 - 15
ASHRAE Journal - April 2013 - 16
ASHRAE Journal - April 2013 - I1
ASHRAE Journal - April 2013 - I2
ASHRAE Journal - April 2013 - I3
ASHRAE Journal - April 2013 - I4
ASHRAE Journal - April 2013 - 17
ASHRAE Journal - April 2013 - 18
ASHRAE Journal - April 2013 - 19
ASHRAE Journal - April 2013 - 20
ASHRAE Journal - April 2013 - 21
ASHRAE Journal - April 2013 - 22
ASHRAE Journal - April 2013 - 23
ASHRAE Journal - April 2013 - Fan Efficiency Requirements for Standard 90.1-2013
ASHRAE Journal - April 2013 - 25
ASHRAE Journal - April 2013 - 26
ASHRAE Journal - April 2013 - 27
ASHRAE Journal - April 2013 - 28
ASHRAE Journal - April 2013 - 29
ASHRAE Journal - April 2013 - 30
ASHRAE Journal - April 2013 - 31
ASHRAE Journal - April 2013 - Geothermal for 5 Ecosystems
ASHRAE Journal - April 2013 - 33
ASHRAE Journal - April 2013 - 34
ASHRAE Journal - April 2013 - 35
ASHRAE Journal - April 2013 - 36
ASHRAE Journal - April 2013 - 37
ASHRAE Journal - April 2013 - 38
ASHRAE Journal - April 2013 - 39
ASHRAE Journal - April 2013 - Holistic HVAC Design
ASHRAE Journal - April 2013 - 41
ASHRAE Journal - April 2013 - 42
ASHRAE Journal - April 2013 - 43
ASHRAE Journal - April 2013 - 44
ASHRAE Journal - April 2013 - 45
ASHRAE Journal - April 2013 - 46
ASHRAE Journal - April 2013 - 47
ASHRAE Journal - April 2013 - Engineer’s Notebook
ASHRAE Journal - April 2013 - 49
ASHRAE Journal - April 2013 - 50
ASHRAE Journal - April 2013 - 51
ASHRAE Journal - April 2013 - 52
ASHRAE Journal - April 2013 - 53
ASHRAE Journal - April 2013 - Data Centers
ASHRAE Journal - April 2013 - 55
ASHRAE Journal - April 2013 - 56
ASHRAE Journal - April 2013 - 57
ASHRAE Journal - April 2013 - 58
ASHRAE Journal - April 2013 - 59
ASHRAE Journal - April 2013 - Emerging Technologies
ASHRAE Journal - April 2013 - 61
ASHRAE Journal - April 2013 - 62
ASHRAE Journal - April 2013 - 63
ASHRAE Journal - April 2013 - IAQ Applications
ASHRAE Journal - April 2013 - 65
ASHRAE Journal - April 2013 - 66
ASHRAE Journal - April 2013 - Refrigeration Applications
ASHRAE Journal - April 2013 - Special Products
ASHRAE Journal - April 2013 - People
ASHRAE Journal - April 2013 - International Column
ASHRAE Journal - April 2013 - 71
ASHRAE Journal - April 2013 - Energy Modeling
ASHRAE Journal - April 2013 - 73
ASHRAE Journal - April 2013 - Products
ASHRAE Journal - April 2013 - 75
ASHRAE Journal - April 2013 - 76
ASHRAE Journal - April 2013 - 77
ASHRAE Journal - April 2013 - 78
ASHRAE Journal - April 2013 - Classified Advertising
ASHRAE Journal - April 2013 - Advertisers Index
ASHRAE Journal - April 2013 - Cover3
ASHRAE Journal - April 2013 - Cover4
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