ASHRAE Journal - October 2022 - 7

LETTERS
The common unit for heat is
Btu. It takes only 0.018 Btu to
raise one cubic foot of air 1 degree
Fahrenheit. So, it should not be
surprising that 1,000 Btu will raise
55,556 ft3 of air 1 degree.
Taking a sample home with a calculated
heat load,1 at an adjusted
ventilation rate of 0.35 ACH2 and
installing a properly sized heater3
we can estimate the temperature
rise using an ASHRAE Standard
62.2 Committee endorsed model.4
This example uses a space volume
of 6,400 ft3, is located in DOE
Climate Zone 3 and the unvented
heater input rate is 20,000 Btu/h.
Setting the infi ltration air to the
coldest average outdoor air temperature
in winter at 33°F, and the
starting indoor air temperature at
68°F, we can observe the temperature
rise over time.
We fi nd it takes approximately 35
minutes to reach a set temperature
of 75°F, and 55 minutes to reach
78°F. Both are reasonable human
comfort levels for most people
according to ASHRAE Standard 55.
Simply using available sources to
model temperature rise in a space
clearly reveals a shortened operating
cycle time of the heater. This
is far shorter than the 4- to 6-plus
hours of operation to reach steadystate
emission levels assumed by the
article. This is just one example of
many that demonstrate that the vast
majority of installations will likely
never reach steady-state condition
when operating at full input rate.
In effect, the article incorrectly
combines and distorts assumptions
that rarely exist in typical
installations and then applies the
same extreme assumptions to all
situations. This is a risky approach
to standards development that
seek to prohibit the use of targeted
products.
References
1. 2021 ASHRAE Handbook-Fundamentals,
Chap. 17, Residential Cooling and Heating
Load Calculations.
2. ANSI/ASHRAE Standard 62.2-2019,
Ventilation and Acceptable Indoor Air Quality in
Residential Buildings.
3. DeWerth, D.W., et al. 1996.
" Development of Sizing Guidelines for
Vent-Free Supplemental Heating Products. "
American Gas Association Research
Division.
4. Francisco, P.W., et al., 2008.
" Combustion Product Concentrations of
Unvented Gas Fireplaces. " HUD Grant
Number ILLHH0125-04.
David Delaquila, Member ASHRAE, Warren, Ohio
The May 2022 ASHRAE Journal
article, " Impacts of Unvented Space
Heaters, " requires a reasoned
response based upon sound engineering
and product experience.
Here are some simple facts for your
readers to receive a balanced look
at this important topic.
* As the most scrutinized
product in the gas market, peerreviewed
and published research
performed by AGAResearch, Risksciences,
Infoscientifi c, TechTrans,
and toXcel, performed by modelers,
engineers and toxicologists,
produced consistent indoor air
quality (IAQ) fi ndings that match
the industry's stellar safety record
of 25 million units installed over
the past four decades in the U.S.
* AGAResearch developed a
mathematical model for predicting
unvented heater operating performance
and IAQ impact. Verifi cation
testing in two separate controlled
structures confi rmed its accuracy
by matching theoretical and
real-world results. The untested
model cited in the article bears no
resemblance to the verifi ed AGAR
model, thereby arriving at erroneous
results.
* Numerous research projects,
peer reviewed and published,
utilized mass balance mathematical
models that included many variables
affecting unvented heater IAQ
impact, much like those used in
numerous ASHRAE research projects.
The simplistic algebraic model
developed by the article's authors
distilled down to hardly anything,
and unbelievably, it excluded
temperature. The steady-state IAQ
levels determined by the authors
would occur only at extraordinarily
high room temperatures unfi t for
human occupation.
* Industry product liability
information was provided to SSPC
62.2, which included the article's
three authors. One would think
that if these products are as problematic
as the article's authors
suggest, lawsuits would be common.
However, the litigation proof
simply doesn't exist, and both the
United States Consumer Product
Safety Commission and CSA Group
(ANSI Secretariat for many products)
have publicly commended the
industry for its safety record.
In summary, the simple question
is what makes so many credible
researchers with IAQ fi ndings
backed by exhaustive product use
history, proven mass balance models
that include many more variables
affecting the operation of an
unvented heater confi rming its
minute impact on IAQ, along with a
stellar product liability record,
wrong and the article's authors
right? The simple answer is that it
doesn't.
Don Denton
O CTO B E R 2 0 2 2 ashrae.o rg ASHRAE JOURNAL
7
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ASHRAE Journal - October 2022

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