ASHRAE Journal - May 2022 - 34

TECHNICAL FEATURE
positions. All of them are reasonable and supportable,
but we want to highlight and paraphrase four of them
here as being relevant to the appliances in question and
the development of this article:
* Standards need to be updated based on the field
evidence that occupants are being exposed to unacceptable
levels of carbon monoxide.
* Occupants should not use unvented appliances if
they have concerns about the risks of products of combustion.
*
Ventilation rates should be reassessed when considering
these appliances in buildings with air tightness
control.
* Appliance sizing and installation should be revisited
in modern homes.
Position Document on Indoor Air Quality
ASHRAE revised its Position Document on Indoor Air
Quality6 in 2020. It does not directly address unvented
combustion, but does provide the context of how the
Society should think about the issue. A part of the
document stresses how source control is a key aspect
of providing acceptable indoor air quality, and this
includes both low-emission materials, consumer products
and appliances, as well as low-emission occupant
activities.
ASHRAE Position
This IAQ position document has five Society positions,
which are concise enough to quote:
* " IAQ impacts people's health, comfort, well-being,
learning outcomes and work performance. Improved
IAQ brings substantial health and economic benefits
from a broad public health perspective, as well as to
individual building owners and occupants.
* " The provision of acceptable IAQ is an essential
building service and central to ASHRAE's purpose.
* " Achieving and maintaining good IAQ should be included
in all decisions that affect the design and operation
of buildings and HVAC systems, including efforts to
improve building energy efficiency, sustainability and
resiliency.
* " The importance of IAQ and the fundamentals of
achieving good IAQ through building design and operation
should be included in educational programs.
* " ASHRAE's IAQ standards should be adopted by
building codes and regulations. "
34
ASHRAE JOURNAL ashrae.o rg M AY 2022
The implication of these positions is that ASHRAE has
an obligation to examine the health and acceptability
impacts of unvented combustion devices and determine
if any requirements are needed. Significant jurisdictions,
standards and voluntary programs have banned
or severely constrained the use of unvented combustion
equipment outside of kitchen equipment (e.g.,
Canada, Energy Star, California, Building America, EPA,
U.S. Department of Housing and Urban Development,
Standard 189.1). In the following section we will examine
what, if any, justification there is for limiting the use
of such unvented combustion equipment in homes.
Contaminant Focus
Standards such as ASHRAE's Standard 62 series are
often considered ventilation standards, but that can be
an oversimplification. The purpose of these standards
is to provide acceptable indoor air quality (AIAQ); AIAQ
requires that contaminants of concern be held to acceptable
levels. Ventilation is the primary mechanism for
removing contaminants and has generally been set
in standards to provide AIAQ for typical contaminant
sources, but the overall objective is focused on IAQ not
ventilation.
When unusual or high-polluting events occur, the
nominal ventilation rates may not be sufficient to provide
AIAQ, and either additional ventilation or source
control may be necessary. To do this, we must focus
on the appropriate contaminants of concern and do a
mass balance. Given the minimum ventilation rates
of Standard 62.2, we can determine acceptable source
levels if we first can determine acceptable contaminant
levels.
Acceptable Levels of Contaminants of Concern
To determine acceptable levels, the literature and
standards and guidelines for each contaminant are
consulted. These acceptability levels are established in
terms of the increment that the appliance is allowed to
create. Possible synergies between contaminants are
ignored.
In setting acceptability levels, it is important to
remember that the appliance is not the only source of
these particular contaminants; some contaminants
have other significant indoor or outdoor sources. To the
extent that such levels are known or can be reasonably
estimated, they are included in our analysis. Homes that
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