United States
                  Environmental Protection
                  Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
                  Research and Development
EPA/600/SR-98/017
February 1998
&EPA      Project  Summary

                  Emissions from  Outdoor Wood-
                  Burning  Residential  Hot Water
                  Furnaces
                  Joseph C. Valenti and Russell K. Clayton
                    Modern outdoor residential  wood-
                  burning  hot water furnaces  are free-
                  standing units situated outside the en-
                  velope of the structure to be heated.
                  They typically consist of a firebox and
                  water reservoir, assembled  in a hori-
                  zontal configuration.  Hot combustion
                  gases flow from the firebox at one end,
                  through channels or tubes in the water
                  reservoir, to the stack. The gases may
                  pass through the water reservoir once
                  to the stack at the end opposite the
                  firebox (one pass) or an additional set
                  of pipes may bring the gases back to
                  the  stack located above  but isolated
                  from the combustion chamber (double
                  pass). The  heated water is pumped
                  through  radiators in  the dwelling or
                  through a heat exchanger in the heat-
                  ing, ventilation,  and  air-conditioning
                  (HVAC) duct in  response  to the home
                  thermostat. A separate pipe coil in the
                  water reservoir may be used to provide
                  domestic hot water, year-round if de-
                  sired. The furnace draft is controlled
                  by a thermostat monitoring  the tem-
                  perature of the water  in the reservoir.
                  Central  heating furnaces  of  all types
                  are exempt from the EPA wood  heater
                  (wood stove) standard. In this project,
                  emissions  were  measured from  a
                  single-pass and a double-pass furnace
                  at average heat outputs of 15,000 and
                  30,000 Btu/hr (4.4 and 8.8 kW) while
                  burning typical oak cordwood fuel. One
                  furnace was also tested once at each
                  heat output  while fitted with a  proto-
                  type catalytic unit installed in the com-
                  bustion chamber. Emissions measured
                  included: EPA Method 5G participate,
                  semivolatile  and condensible organics,
                  20 target polycyclic aromatic hydrocar-
                  bon  (PAH)  compounds,  and carbon
                  monoxide (CO). Emission results are
 presented  in terms of rate  per hour,
 quantity per unit weight  of  wood
 burned, and  quantity per unit of heat
 delivered. Delivered efficiencies are also
 presented. Compared to  a wide range
 of residential heating options, these fur-
 naces' emissions were of the same or-
 der as other stick wood burning appli-
 ances.
   This Project Summary was developed
 by the National Risk Management Re-
 search Laboratory's Air Pollution Pre-
 vention and Control Division, Research
 Triangle Park, NC, to announce  key
 findings of the research project that is
 fully documented in a separate report
 of the same title (see Project Report
 ordering information at back).

 Introduction
   In the early 1980s, the State of Oregon
 began developing methods for character-
 izing source  emissions from  residential
 wood  combustion units. The  developed
 methods have since blossomed into  test
 methods used to  audit and certify wood-
 burning heaters. From these beginnings,
 the U.S. Environmental Protection Agency
 (EPA)  has established  emission perfor-
 mance standards for residential wood heat-
 ers.
   The federal regulations established by
 the EPA in 1988 limit emissions from resi-
 dential wood heaters,  such  as wood
 stoves, pellet stoves, and factory built fire-
 place inserts. These regulations, however,
 do not include all wood-fired heating ap-
 pliances. For example, central heating fur-
 nace/boilers are not covered  under the
 current regulations.
   In general, emissions from the combus-
 tion of wood in stoves and furnaces con-
 tain significant levels of CO and fine  par-
 ticulate matter (PM)  consisting, in part, of

-------
mutagenic  PAHs.  If atmospheric condi-
tions are  conducive for accumulating
smog-like clouds of emissions, the wood
smoke could pose a health hazard.  With
the potential for such a  condition under
consideration, the EPA established maxi-
mum acceptable emissions levels for the
certification of most residential wood-fired
heaters.
  Typically, the modern outdoor residen-
tial wood-burning hot water furnace is a
freestanding unit situated outside the en-
velope of the structure to be heated. The
unit consists of a closed combustion cham-
ber surrounded by a water tank and vented
through a stack. A wood burning fire  is
contained and controlled in the combus-
tion  chamber or firebox  of the  furnace.
During the combustion  process, heat  is
transferred through the walls of the cham-
ber into the water. The hot water from the
furnace tank can then be circulated through
radiators or air-handling heat  exchangers
to transfer heat into the residence. Some
central heating furnaces are equipped with
additional plumbing to provide  domestic
hot water.
  Most commercial  central  heating  fur-
naces are supplied with an 8-  to 10-ft (2.4
to 3.0 m) tall stack. Typical indoor wood
burning stoves  have chimneys which ex-
tend through the roof of a home to heights
of 20 to 30 ft (6.1 to 9.1 m). The relatively
low chimney  height of the central heating
furnace/boiler, compared to the  conven-
tional wood stove installations, creates a
greater potential for the localization of ob-
jectionable emissions in and  around resi-
dences. Additionally, concerns have been
raised about the manner in which the com-
bustion process is controlled and how the
control affects the emissions.
   The State of Wisconsin has asked the
Control Technology Center of EPA's Air
Pollution Prevention and  Control Division
(APPCD) for assistance  in   determining
whether the need exists to regulate these
furnaces. Therefore,  the EPA has under-
taken the task of evaluating the emissions
from the  central heating furnaces and the
manner in  which the  combustion is  con-
trolled. The objective is to develop baseline
emission factors for comparison with other
residential heating systems.
  In the  full  report,  Section  2 describes
the experimental approach and sampling
and  analytical methods employed. Steps
to ensure project quality are described  in
Section 3.  Data, results, and discussion
are presented in Section  4. The appendi-
ces contain the  detailed data.

Project Description
  Two types of furnaces were selected as
representative of the industry.  The type  of
furnace is defined by the configuration of
the unit. The flue gases exit the combus-
tion chamber by way of a flue that passes
through the water tank. A single-pass fur-
nace allows the flue gases to pass once
through the  flue in the water tank before
exiting through the  chimney.  As the hot
flue gases pass through the flue, heat is
transferred to the water in the tank. In a
double-pass furnace,  flue gases pass
through the  water tank twice before exit-
ing through the chimney. The second pass
of the  stack provides  more surface area
and more contact time  between the hot
flue gases and the water in the tank. Rep-
resentative furnaces of both types were
provided to EPA/APPCD for testing.
  The  outdoor residential wood-burning
hot water furnaces were tested following
EPA Reference Method 28 (M28-40 CFR
Part 60, Appendix  A),  the test method
used to certify and audit wood-fired heat-
ers (stick and pellet  burning woodstoves).
The method  specifies fuel preparation, fur-
nace operation, and the  reporting of the
results. Method 28 requires Method 5G or
5H (CFR Part 60, Appendix A) to deter-
mine the concentrations  of oxygen (O2),
carbon dioxide (CO2),  CO, and PM  in the
emissions.
  For these  tests, some of the fuel prepa-
ration procedures under Method  28 were
modified in favor of preparing the fuel and
operating the  furnace  as recommended
by the  manufacturer. Cordwood was used
instead of the dimensioned lumber speci-
fied for wood heater certification. Method
28A was used to calculate the stack gas
dry molecular weight, as required for flow
measurements. Method 5G was the  pri-
mary sampling method used for the test.
The  sampling  method, Method  5G, was
modified  by  adding  an XAD-2 absorbent
trap to collect organics; this modified sam-
pling method will hereafter be referred to
as Modified Method  5G (MM5G).  The col-
lected  MM5G samples were analyzed for
total PM, total semivolatile organics [some-
times referred to as total chromatographable
organics (TCOs)], condensible  organics as
measured by gravimetric analysis  (GRAV),
and PAHs.  The  efficiencies  of  the units
were measured as a secondary objective
for reporting  emissions relative to the input
heating value of the wood and to their heat
output from the furnace.
  Each furnace was tested at  two heat
output levels,  15,000  and 30,000 Btu/hr
(4.4 and 8.8 kW).  Each  test  was run in
duplicate for a total of four runs per fur-
nace.   In addition, two high heat output
scoping runs were performed on  Furnace
A. Furnace  A was  also tested  once at
each heat output while fitted with a proto-
type catalytic  device  in  the combustion
chamber, giving a total of 12 runs.
Results
  Two basic furnace designs (single- and
double-pass boiler heat exchangers) were
chosen for these tests to see if the design
impacted emissions. Table 1  presents the
particulate and PAH emission factor data
and efficiency aggregated by furnace and
operating mode.  Furnace B showed much
less variability in operation and emissions
data compared  to  Furnace  A. Whether
this is due to (1) furnace design,  (2) the
way the fuel was loaded,  and/or  (3) the
differences in the draft  on/off cycles can-
not be determined  without further tests;
more  than likely, all three variables ex-
erted significant influence.
  Table 2 lists  the emission results for
various  residential  combustion devices.
The  results from this  investigation (see
bottom row in Table 2) were included as
an average from all the tests.  Based on
this very limited  test, it appears that the
total particulate emission factor is compa-
rable to that for conventional wood  stoves.
Note that all particulate values have been
converted to the EPA Method 5H equiva-
lent. The PAH emission factor appears to
be generally the same as that for EPA
certified wood stoves. The data presented
in  Table 2 were originally generated by
different  researchers using  a  variety  of
sampling and analytical methodologies. A
number of assumptions had  to be made
to  "normalize"  the data for  comparison.
Consequently, only order of magnitude dif-
ferences should be considered significant.
Readers are encouraged  to review the
reference  cited in the footnote for  a more
thorough understanding of the data.

Conclusions
  There were  several  data quality prob-
lems with tests of Furnace A, all of which,
though significant, are thought to be small
enough to not bias the results for Furnace
A sufficiently to  cause an order of magni-
tude error. Tests of Furnace  B  had no
reported  data quality problems. All tests
of  Furnace B particulate matter emissions
were  in the range  of  36.5 to 37.6 g/hr
(high heat removal rate - tests B-1  and B-
2)  and 14.3 to 15.5 g/hr (low heat removal
rate - tests B-3 and  B-4). Particulate mat-
ter emissions from Furnace A appear con-
sistently  higher;  but, within the limits  of
these tests, experimental error, and con-
sidering the testing problems  previously
discussed that  may have compromised
the data quality  for Furnace A, a direct
comparison of Furnace A and Furnace B
emissions is without adequate foundation
and, therefore,  is  not  meaningful. How-
ever,  from Table 2,  it  is evident  that all
wood-burning home  heating combustion
equipment, including wood stoves, boil-

-------
ers,  or fireplaces, has  much higher par-
ticulate matter emissions than gas- or oil-
fired home heating furnaces.
Table 1.  Comparison Data Aggregated by Operating Mode and Furnace [Range in ()]

                                   Furnace
Operating
Mode
                                                                             Parameter
                                                          B
High Heat
Low Heat
19.6(14.8-24.5)
 0.347(0.216-0.478)
45.6 (38.8-53.4)

16.6(15.9-17.3)
 0.236 (0.228-0.245)
44.4 (42.4-46.4)
12.0(10.8-13.3)
 0.319(0.315-0.324)
53.8(50.5-57.1)

 9.35 (9.2-9.5)
 0.283 (0.235-0.332)
55.2(55.1-55.4)
M5G Particulates, g/kg
PAH, g/kg
Delivered Efficiency, %

M5G Particulates, g/kg
PAH, g/kg
Delivered Efficiency, %
Table 2.  Overall Comparison of Residential Wood, Oil, and Gas Combustion Emissions3
Combustion Device
                    M5H Particulate
                      mg/MJ input
                PAHs
             mg/MJ input
       Mutagenicityb
       krev/MJ input
Natural gas furnace
         Conventional                       0.44
         High Efficiency                     0.43

Oil furnace
         Retention head                     3.2
         Conventional                      15.1

Conventional wood stove                   786

Certified wood stove
         Non-catalytic                     383
         Catalytic                        425
         Pellet (certified)                   110
         Pellet (exempt)                   176

Fireplace 907 41                           —

Wood furnace
         Cordwood - Swedish lab tests
             Intermittent firing            1862
             Continuous firing             182
             Chips (dry)                   45.3
         US  EPA lab tests
             Furnace AS                 1048
             Furnace B                   681
                                          0.000124
                                          0.000028
                                         40
                                         28
                                         24
                                          0.082
                                          0.014
                                    0.007C
                                 NDc>d
                                                               6
                                                              20

                                                             600
                                                             100
                                         15.3
                                         <0.02

                                         75.6
                                         16.1
                                  148f
                                    0.48f
a All data except that in italics taken from: McCrillis, R.C., "Review and Analysis of Emissions Data for
  Residential Wood-Fired Central Furnaces." In Proceedings of the 88th Annual Meeting of the AWMA.
  Air& Waste Management Association, San Antonio, TX, June 1995, Paper No. 95-RP137.04.
b Microsuspension assay, TA98+S9 unless otherwise noted.
c Ames plate incorporation assay, TA98+S9.
d ND means not detected.
e No data available for this parameter.
f Ames plate incorporation assay, TA100+S9.
9 Only includes comparison data.

-------
   J. Valenti and R. Clayton are with Acurex Environmental Corporation, Research
     Triangle Park, NC 27709.
   Robert C. McCrillis is the EPA Project Officer (see below).
   The complete report, entitled "Emissions from Outdoor Wood-Burning Residential
     Hot Water Furnaces," (Order No. PB98-127087; Cost: $41.00, subject to change)
     will be available only from:
           National Technical Information Service
           5285 Port Royal Road
           Springfield, VA 22161
           Telephone: 703-487-4650
   The EPA Project Officer can be contacted at:
           Air Pollution Prevention and Control Division
           National Risk Management Research Laboratory
           U. S. Environmental Protection Agency
           Research Triangle Park, NC 27711
United States
Environmental Protection Agency
National Risk Management Research (G-72)
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
      BULK RATE
POSTAGE & FEES PAID
         EPA
   PERMIT No. G-35
EPA/600/SR-98/017

-------