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. 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