ASHRAE Journal - May 2022 - 32

TECHNICAL FEATURE
Impacts of Unvented
Space Heaters
BY MAX SHERMAN, PH.D., FELLOW/LIFE MEMBER ASHRAE; PHILIP FAIREY, LIFE MEMBER ASHRAE; ROY CRAWFORD, PH.D., LIFE MEMBER ASHRAE
Combustion of fossil fuels produces a variety of contaminants, many of which can be
hazardous to health. Most combustion equipment in buildings vents these contaminants
directly to outdoors, but products exist that release the contaminants directly
to the indoor air. These contaminants are a potential hazard that could make the
indoor air unacceptable. This article reviews the relevant combustion process, the
contaminants and their acceptable levels in the context of ASHRAE standards and
position documents, with particular emphasis on unvented residential space heaters.
The authors find that nitrogen dioxide (NO2) and carbon dioxide (CO2) are the
critical contaminants of concern and that operation of unvented space heaters above
a volume-normalized capacity of 0.4 Btu/h · ft3 (4 W/m3) constitutes a high-polluting
event that should be avoided.
Unvented combustion is common in homes. That
includes kitchen appliances, decorative appliances,
open fireplaces, indoor barbeques, smoking, candles
and space heaters. All unvented combustion produces
contaminants that must be accounted for when considering
indoor air quality (IAQ) and health impacts.
ASHRAE has several position documents and standards
related to unvented combustion. Combustion processes
produce carbon dioxide and water vapor as by-products,
and some combustion sources produce additional
contaminants such as nitrogen dioxide, particles and
carbon monoxide.
For the smallest activities or shortest operating times,
especially for the most low-polluting combustion, contaminant
emission can be considered insignificant and
thus be ignored. At the opposite end of the capacity
spectrum, unvented combustion could be life threatening,
which motivates and informs various appliance and
building standards. Regardless of the size of the appliance,
however, a point exists at which products of combustion
are produced in excess of the levels amenable to
acceptable IAQ.
This article will narrow its focus to unvented space
heaters and related products intended for residential
use that are operated long enough to approach steady
state.
ASHRAE Residential Ventilation and IAQ Context
Historically, when energy costs were not a factor,
homes were generally quite leaky, and this led to large
Max Sherman, Ph.D., is principal, EPB Consulting Group and a professor at University of Nottingham. Philip Fairey is deputy director, FSEC Energy Research Center, University of
Central Florida, Cocoa, Fla. Roy Crawford, Ph.D., is director of advanced technology, Johnson Controls, Inc., Norman, Okla.
32
ASHRAE JOURNAL ashrae.o rg M AY 2022

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ASHRAE Journal - May 2022

Table of Contents for the Digital Edition of ASHRAE Journal - May 2022

Contents
ASHRAE Journal - May 2022 - Intro
ASHRAE Journal - May 2022 - Cover1
ASHRAE Journal - May 2022 - Cover2
ASHRAE Journal - May 2022 - 1
ASHRAE Journal - May 2022 - Contents
ASHRAE Journal - May 2022 - 3
ASHRAE Journal - May 2022 - 4
ASHRAE Journal - May 2022 - 5
ASHRAE Journal - May 2022 - 6
ASHRAE Journal - May 2022 - 7
ASHRAE Journal - May 2022 - 8
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ASHRAE Journal - May 2022 - Cover3
ASHRAE Journal - May 2022 - Cover4
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