Document ID: EPA-HQ-OAR-2009-0734-1760
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2015-02-04T05:00Z

MEMORANDUM

DATE: 	January 30, 2015

SUBJECT:	Estimated Emissions from Residential Wood Heaters

FROM:	Jill Mozier, EC/R Inc.
      Beth Friedman, EC/R Inc.

TO:		David Cole, EPA/OAQPS 
      Gil Wood, EPA/OAQPS		
		Amanda Aldridge, EPA/OAQPS

	The purpose of this memorandum is to present an estimate of the fine particulate matter (PM2.5), volatile organic compound (VOC) and carbon monoxide (CO) emissions from wood heater appliances based on projected sales of new units and based on emissions under the final NSPS.

   I. PM Methodology

      A. 	Estimating Average Emissions per Appliance	
	We used the EPA Residential Wood Combustion (RWC) emission estimation tool, which is an Access(TM) database that compiles nationwide RWC emissions using county level, process specific data and calculations. We summed the nationwide number of appliances and total tons of wood burned for each of the relevant emission inventory categories (Table 1) in the inventory.  

               Table 1.  RWC Emission Inventory Categories Used
                                       
Woodstove: fireplace inserts; EPA certified; non-catalytic
Woodstove: fireplace inserts; EPA certified; catalytic
Woodstove: freestanding, EPA certified, non-catalytic
Woodstove: freestanding, EPA certified, catalytic
Woodstove: pellet-fired, general
Woodstove: freestanding, non-EPA certified
Hydronic heater: outdoor
Furnaces:  indoor, cordwood

	We then made some adjustments/assumptions to the baseline RWC inventory. First, we deleted data in the RWC database for non-certified stoves and inserts, as these cannot be sold. With the exception of wood stoves, we applied the PM2.5 emission factors for each class to the total tons of wood burned and calculated an average emission rate/appliance/category. 

      In the case of wood stoves, the RWC database uses an average of all PM10 AP-42 emission factors. The RWC database assumes that PM10 and PM2.5 factors are identical. At a minimum, we estimate that all new wood stoves meet the AP-42 PM10 emission factors for "Phase II" stoves (the current NSPS promulgated in 1988) and therefore started with the lower AP-42 Phase II emission factors for catalytic and non-catalytic stoves at baseline, rather than the higher average of all AP-42 emission factors used in the RWC database. Furthermore, to avoid any potential for overstating baseline emissions, we went a step further and assumed that all new shipments will meet the current Washington State limits, which are approximately 40 percent less than the 1988 NSPS Phase II limits. We therefore used baseline emission factors which are 60 percent of the AP-42 Phase II emission factors  -  less than half the value used in the RWC to represent the average of all AP-42 emission factors  -  in order to ensure a forward-looking and understated baseline.

	Second, we estimated that outdoor hydronic heaters and indoor hydronic heaters have the same emission profile. 

	Single burn rate stoves are not included in the RWC database as separate identifiable units. We estimated that they would have the same baseline emission factor as freestanding non-certified wood stoves, i.e., 30.6 lb/ton of wood burned. We used the average tons burned per appliance factor as representative of these stoves as well. 
 
	We used this subset of the RWC database to calculate a baseline average emission rate/appliance (or "emission inventory category"), including an adjustment of the RWC emission factor to the current Washington State limits for currently certified wood stoves, as discussed above. We multiplied the total tons of wood burned for the appliance by the RWC emission factor (adjusted as appropriate) to calculate the total tons of PM2.5 emissions. We divided this value by the number of appliances in the category to calculate the baseline average PM2.5 emissions per individual appliance (Table 2).
            Table 2.  PM2.5 Tons per Appliance Estimate (Baseline)

*Non-EPA certified wood stove emission factor and tons/appliance were used to represent single burn rate stoves.	
      
      The next step was to develop emission factors representing the final NSPS. The NSPS limits used in this analysis are based on phased-in compliance dates, or "steps", for subcategories of appliances. Subpart AAA will regulate "room heaters" and includes adjustable burn rate stoves, single burn rate stoves, and pellet stoves. Subpart QQQQ will regulate "central heaters" and includes outdoor and indoor hydronic heaters and forced-air furnaces. Following is a summary of the current NSPS implementation assumptions for appliances within the regulated subcategories. The final NSPS is a phased standard with compliance dates of 2015 and 2020 for all appliances. In addition, forced-air furnaces will have a Step 1 PM emission limit for small forced-air furnaces in 2016 and for large forced-air furnaces in 2017, as discussed below. The Step 2 PM emission limit compliance date is 2020 for all appliances.  
       
Subpart AAA ("room heaters"):  

         Adjustable burn rate, single burn rate, and pellet stoves:  Step 1 PM emission limit of 4.5 g/hr upon promulgation in 2015; and Step 2 PM emission limit of 2.0 g/hr five years after promulgation in 2020. Note: The Step 1 limit is the 1995 Washington State standard for non-catalytic stoves; and the Step 2 limit is already met by the top performing catalytic, non-catalytic and pellet stove models. Specifically, this industry data from 2010 indicate that approximately 90% (130 out of 145 catalytic, non-catalytic and pellet stoves combined) already meet the Step 1 limit. We expect that manufacturers will focus on existing models that meet the Washington State limits in order to comply with the Step 1 standard. Furthermore, certification data indicate that 26% of non-catalytic and catalytic stoves combined and 70% of pellet stoves already meet the Step 2 standard. Although previously unregulated and a less developed technology than adjustable burn rate stoves, single burn rate stove designs have been undergoing R&D in anticipation of the proposed NSPS and cleaner designs are nearly market-ready.

Subpart QQQQ ("central heaters"):

      * Hydronic heaters (both outdoor and indoor):  Step 1 PM emission limit of 0.32 lb/mm BTU heat output (weighted average and an 18 g/hr cap for each individual test run) upon promulgation in 2015; and Step 2 PM emission limit of 0.10 lb/mm BTU heat output (at each burn rate) five years after promulgation in 2020. Note: The Step 1 limit is identical to the EPA "Phase 2" voluntary program limit and is therefore already met by all 50 of the 50 currently Phase 2 qualified hydronic heater models built by U.S. manufacturers participating in the voluntary program. In addition, there are 19 qualification tests that have been recently submitted to EPA and, if valid, are all expected to be added to the Phase 2 qualification list very soon. The Step 2 limit is already met by 9 of the 50 (18%) hydronic heater models built by U.S. manufacturers participating in the voluntary program, as well as over 100 European manufacturers per test method EN 303-05. It should be noted that to-date cleaner models continue to become Phase 2 qualified and additional manufacturers not participating in the voluntary program may also have models meeting Step 1 and Step 2. We assume that 18% of existing hydronic heaters can meet the Step 2 limit without intensive R&D efforts.

      * Forced-Air Furnaces:  Work practice/operational standards will be required of all forced-air furnaces upon the rule's 2015 effective date. A Step 1 PM emission limit of 0.93 lb/mm BTU heat output will be required by 2016 (1 year after the 2015 effective date) for small forced-air furnaces (<65,000 BTU/hr models, representing approximately 25% of current sales) and this same limit of 0.93 lb/mm BTU will be required by 2017 (2 years after the 2015 effective date) for large forced-air furnaces (>=65,000 BTU/hr models, representing approximately 75% of current sales). A Step 2 PM emission limit of 0.15 lb/mm BTU heat output will be required for all forced-air furnace models five years after promulgation in 2020. Note: The phased timelines are based on the technological and economic limitations of testing and certifying approximately 50 previously untested forced - air furnaces in the 60 days between signature and the effective date and also on industry comments on the proposed rule, explaining the design challenges for small and large forced-air furnaces, respectively. The Step 1 PM emission limits and the Step 2 PM emission limits are based on test data from development of the Canadian standard B415.1-10, conversations with industry regarding cleaner forced-air furnace models currently being tested in R&D and comments on the proposed rule. Forced-air furnace designs able to meet the Step 2 PM emission limit are expected to be based on technology transferred from hydronic heater designs and/or wood stove designs. 	
      We developed adjusted emission factors to reflect the limits discussed above, which were then used to calculate new average tons of emissions per appliance for each RWC appliance type in Tables 1 and 2. Adjustments were assumed for NSPS emission factors (as noted below) in order to not over state emission reductions. Actual emission reductions may be greater than reductions resulting from our emission factor adjustments for the purpose of this analysis. Following is a description of how the RWC factors were adjusted for each appliance type.
      
      * Woodstove: all EPA certified.  As noted above, we determined the ratio of emissions between the existing 1988 NSPS limits compared to the Washington State standards. For both catalytic and non-catalytic devices, the Washington standard is 60% of the 1988 NSPS. We assumed this same ratio would apply to the emission factors and multiplied the RWC emission factor (for Phase II certified models) by 60%. We used these adjusted RWC emission factors (shown in Table 2) as both baseline and Step 1 PM emission factors for catalytic and non-catalytic stoves. It should be noted that the assumption that at baseline all wood stoves already meet the Washington State standards may slightly underestimate baseline emissions, as not 100% of wood stoves currently sold do meet the Washington State standards. We made this simplifying assumption in order to avoid any potential for overstating baseline emissions. 
         Furthermore, we estimated that the Step 1 PM emission factor was the same as the baseline emission factor, because, as noted above, approximately 90% of current wood stove models already meet the Step 1 PM limit according to industry data. For the Step 2 PM emission factor for non-catalytic models, we scaled the Step 1 PM emission factor by the ratio of the Step 2 PM limit to the Step 1 PM limit (or 2.0/4.5 = 0.44). Again, in order to not overstate emission reductions, for catalytic models, we scaled the Step 1 PM emission factor by the ratio of the Step 2 PM limit to the Washington State PM standard for catalytic stoves (or 2.0/2.5 = 0.8). For consistency with our shipment data (described in section B) and because the RWC database provides four separate emission factors for catalytic and non-catalytic, freestanding models and fireplace inserts, we used the weighted average value for all four wood stove types to represent the total population of adjustable burn rate wood stoves. Finally, we multiplied the resulting PM emission factors by the total tons burned for the appliance type (provided by the RWC database) and then divided that by the appliance population (also provided by the RWC database) to derive the tons/appliance of PM2.5 emissions. The emission factors and tons/appliance are shown in the green rows in Table 3. 
      * Woodstove:  pellet fired, general. We used the RWC emission factor shown in Table 2 as both the baseline and Step 1 PM emission factor for pellet stoves because nearly all current pellet stove models already meet the Step 1 PM standard according to industry data.[1][0] For the Step 2 PM emission factor, we scaled the Step 1 PM emission factor by the ratio of the Step 2 PM limit to the Step 1 PM limit (or 2.0/4.5 = 0.44). We multiplied the resulting emission factors by the total tons burned for pellet stoves and then divided that by the pellet stove appliance population to derive the tons/appliance of PM2.5 emissions. The emission factors and tons/appliance are shown in the orange row in Table 3. 
      * Woodstove: freestanding, non-EPA certified (single burn rate stoves). As described above, we assumed that the freestanding non-EPA certified wood stove emission inventory category includes the population of single burn rate stoves. We therefore used the RWC emission factor for freestanding non-EPA certified wood stoves (30.6 lb/ton) as the baseline emission factor for single burn rate stoves. For the Step 1 PM emission factor, we used the same emission factor as a certified non-catalytic stove meeting the Washington State PM standards (i.e., 8.76 lb/ton) because the same standard is being proposed for single burn rate stoves as for adjustable burn rate stoves. Likewise, we used the same emission factor used for non-catalytic stoves for the Step 2 PM emission factor. We multiplied the resulting emission factors by the total tons burned for this appliance category and then divided that by the appliance population to derive the tons/appliance of PM2.5 emissions. The emission factors and tons/appliance are shown in the grey row in Table 3. 
      * Hydronic heater: outdoor/indoor. As noted above, we estimated that indoor hydronic heaters (a minority of the hydronic heater population) have the same emission profile as the outdoor hydronic heater appliance category provided in the RWC. According to the EPA voluntary hydronic heater program, the "Phase 2" heaters that are presumed to represent the Step 1 limit are 90% cleaner than older unqualified units, as determined in laboratory tests on crib wood. We estimate that the majority of the existing inventory is represented by these unqualified units, and applied a 90% reduction to the RWC baseline emission factor shown in Table 2 (64 lb/ton) in order to derive the Step 1 PM emission factor (of 6.4 lb/ton). For the Step 2 PM emission factor, we scaled the Step 1 PM emission factor by the ratio of the Step 2 PM limit to the Step 1 PM limit (or 0.10/0.32 = 0.31). We multiplied the resulting emission factors by the total tons burned for the hydronic heater RWC appliance category and then divided that by the hydronic heater appliance population to derive the tons/appliance of PM2.5 emissions.  The emission factors and tons/appliance are shown in the blue row in Table 3. 
      * Furnace: indoor, cordwood. At baseline, we estimated that forced-air furnaces have the same updated emission factor as hydronic heaters (64 lb/ton), consistent with the fact that hydronic heaters and forced-air furnaces have the same emission factor in version 4.1 of EPA's RWC tool. For the Step 1 PM emission factor, we scaled the baseline emission factor by 75% (to 16 lb/ton) because background material provided in the Canadian standards review process stated that that the emission limit associated with this method would result in an approximately 75% reduction in emissions compared to a non-qualifying furnace. We estimate that the Step 2 PM emission limit of 0.15 lb/mm BTU (based on cord wood, consistent with the test method) is roughly equivalent to the hydronic heater crib wood-based limit of 0.10 lb/mm BTU. We also estimate that the baseline emission factor for each appliance category is the same; therefore we used the same Step 2 PM emission factor for forced-air furnaces as used for hydronic heaters (2.00 lb/ton). We multiplied the emission factors by the total tons burned for the cordwood furnace RWC appliance category and then divided that by the furnace appliance population to derive the tons/appliance of PM2.5 emissions. The emission factors and tons/appliance are shown in the lavender row in Table 3.  
      
      Table 3 shows the baseline, Step 1 PM emission factor and Step 2 PM emission factor for each appliance type resulting from our assumptions and adjustments described above. We used the appropriate tons/appliance with annual shipment data (Section B) to estimate annual PM2.5 emissions (Section C), based on the phased emission reduction dates. 

                                       
Table 3.  NSPS Adjusted Emission Factors for PM2.5  -  Baseline, Step 1 PM Emission Limits and Step 2 PM Emission Limits 

*For forced-air furnaces, the compliance dates are 2015 for work practice/operational standards, 2016 for the Step 1 PM emission limit for small furnaces and 2017 for the Step 1 PM emission limits for large furnaces.

      B. 
      C. 	Shipment Data, Model Design Lifespan and Emitting Lifespan	
	We used data in the Frost & Sullivan Market (F&S) report on 2008 shipments by product category, and F&S revenue forecasts which incorporated the weak economy in years 2009 and 2010, to calculate the reduced number of shipments in years 2009 and 2010. Forced air furnaces were outside the scope of the F&S report. Instead, we used manufacturer estimates of total industry sales in 2008 and applied the F&S market factors to estimate shipments through 2010. The F&S wood stove numbers included both certified and non-certified stoves, so we estimated numbers of non-certified stove shipments out of the total reported wood stove category (i.e., 40,000 single burn rate stoves shipped in 2008).[1][5] These shipments were deleted from the total wood stove category shipments. We expanded the 2008 single burn rate estimate using the F&S factors.  
      
      For years 2011 through 2029 estimated shipments are generally based on a forecasted revenue growth rate of 2.0%, in keeping with the average annual growth in real GDP predicted by the US Bureau of Economic Analysis. There is not a perfect correlation between shipments and revenue (for example, because of their higher unit cost, pellet stoves generate more absolute revenue than wood stoves), but we think the overall trend in the projection is reasonable in the absence of specific shipment projections. The only exceptions to the use of a 2.0% GDP-based growth rate are for years 2012 and 2018, in which we used industry estimates for hydronic heater and wood stove shipments, respectively. For year 2012, an HPBA consultant estimated there were 13,100 baseline hydronic heater sales. For year 2018, the same HPBA consultant projected there to be 100,000 wood stove sales. We adjusted our estimated shipment data accordingly. (It should be noted that these two industry estimates are slightly higher than the estimates for those years would be based on the 2.0% GDP-based growth rate; but over the entire analysis period, using the predicted GDP growth rate as a basis is appropriate.) Table 4 on the next page shows a truncated summary of the shipment data through year 2023. 
      
      Our cost effectiveness analysis (CE) assumes a 10-year model design lifespan as well as a 20-year use/emitting appliance lifespan. These assumptions were made to best characterize the actual model design and use lifespans. For proposal, we used a 20-year model design lifespan, reasoning that many models developed for the 1988 NSPS are still being sold (after 25 years), with many "new" models retaining the same internal working parts with merely exterior cosmetic changes. Respectful of comments on the proposed rule, however, in which some industry representatives commented that a shorter model lifespan is more accurate, we reduced our assumed model design lifespan to 10 years for this analysis. Regarding the emitting lifespan of the appliance, most wood heaters in consumer homes emit for at least 20 years and often much longer. Therefore our CE analysis tracks shipments through year 2029 (assuming a 10-year design life for a model meeting the Step 2 limit in year 2020) and emissions through year 2048 (assuming a 20-year emitting life for an appliance shipped in year 2029). Table 4 is a truncated summary of our actual shipment data which extended through years 2029. See the CE analysis spreadsheets for the complete shipment data.

      D. 	Estimated PM2.5 Emissions from Shipments of New Appliances	
	As described above, we calculated the average emissions per appliance type using the emission factor for each category multiplied by the inventory value of total tons of wood burned divided by the number of appliances in the inventory population. This tons/appliance value was then multiplied by the number of shipments to calculate total emissions from each appliance category per year under baseline conditions, i.e., in the absence of an NSPS. In order to not overstate potential emission reductions, baseline emissions were discounted by the percentage of appliances already meeting the Step 2 PM emission limits (i.e., the 26% of wood stoves, 70% of pellet stoves, and 18% of hydronic heaters estimated to already meet Step 2 PM emission limits, as noted in subsection A). 
	
	Table 5 on the next page shows a truncated summary of the estimated PM2.5 emissions (in tons) under baseline conditions through year 2023. We then estimated emissions under the NSPS (Table 6) based on the phased-in timeline for each appliance. The emission estimates assume that the total number of shipped units meet the PM emission limit in the year the PM emission limit is required. As noted above, we discounted NSPS emissions by the percentage of appliances already meeting the Step 2 PM emission limit. Tables 5 and 6 show emission estimates out to year 2023 under baseline and NSPS scenarios. Like Table 4, these are truncated summaries. 

      Our CE analysis tracks emission reductions out through 2048, assuming a 10-year design life for a model meeting each phased-in (stepped) limit, and assuming that stoves shipped in the 10[th] year of design life will be emitting in homes for another 20 years. The CE analysis incorporates "trailing emissions" as part of our 20-year emitting lifespan assumption. For example, our analysis estimates that a stove shipped in 2015 will emit in homes for 20 years  -  or until 2034 (inclusive of both 2015 and 2034). We therefore drop emissions from this stove in our analysis in year 2035. Likewise, we drop emissions for a stove shipped in 2016 in year 2036, and so on. The CE analysis spreadsheets show all years of emission data, under both baseline and NSPS scenarios, as well as cumulative PM2.5 emission reductions through year 2048. Spreadsheets are provided for appliances regulated under Subpart AAA "Room Heaters" (i.e., wood stoves, pellet stoves, and single burn rate stoves), as well as for appliances under Subpart QQQQ "Central Heaters" (i.e., forced air furnaces and hydronic heaters). The CE analysis[2][2] also includes a spreadsheet showing cumulative emissions and emission reductions for Subparts AAA and QQQQ combined. 

                                       
Table 4.  Estimated Annual Shipped Units
                                       
                                       
                                       
                                       
                                       
                                       
Table 5. Estimated PM2.5 Emissions (Tons)  -  Baseline Scenario*
                                       

      *Estimates are reduced for the percentage of appliances assumed to already meet the Step 2 PM emission limit (26% of wood stoves, 70% of pellet stoves and 18% of hydronic heaters), in order to not overstate emission reductions attributable to this NSPS.

                                       
                                       
                                       
                                       
Table 6. Estimated PM2.5 Emissions (Tons)  -  NSPS Scenario*

                                       
                                       
                                       
*Step 1 PM emission limit in 2015 and Step 2 PM emission limit in 2020 for all appliances, except forced-air furnaces have work practice/operational standards in 2015, Step 1 PM emission limits for small furnaces in 2016, Step 1 PM emission limits for large furnaces in 2017 and Step 2 PM emission limits for all furnaces in 2020. In order to not overstate emission reductions attributable to this NSPS, estimates are reduced for the percentage of appliances estimated to already meet the Step 2 PM emission limits (26% of wood stoves, 70% of pellet stoves and 18% of hydronic heaters). In this analysis, emission reductions for forced-air furnaces are not quantified for the work practice/operational standard required in 2015, although stakeholders agree that work practice/operational standards will reduce emissions.

                                       

                                          
                                          
                                       
   II. Volatile Organic Compound Methodology
      We used the same methodology described in Section I to develop emission estimates for VOC emissions. Using the RWC database, we developed an estimate of VOC emissions per appliance using baseline emission factors. Then, using the same NSPS phase-in assumptions and anticipated emission reductions (i.e., that VOC reductions are comparable to PM2.5 reductions), we developed emission factors, as shown in Table 7.
      
	Next, using the same assumptions as we used for PM2.5, we calculated VOC emissions at baseline and under the NSPS scenario for each stepped limit, as shown in Tables 8 and 9.

	Finally, cumulative VOC emissions and emission reductions under the NSPS were calculated based on a 10-year model design lifespan for shipments and a 20-year appliance use lifespan for emissions, as explained in Sections I-B and I-C. Although VOC emissions are not being regulated under this NSPS, estimated VOC emissions and emission reductions are provided separately in our CE analysis spreadsheets. 
   
   III. Carbon Monoxide Methodology
      We used the same methodology described in Section I to develop emission estimates for CO emissions. Using the RWC database, we developed an estimate of CO emissions per appliance using baseline emission factors. Then, using the same NSPS phase-in assumptions and anticipated emission reductions (i.e., that CO reductions are comparable to PM2.5 reductions), we developed emission factors, as shown in Table 10.
      
	Next, using the same assumptions as we used for PM2.5, we calculated CO emissions at baseline and under the NSPS scenario for each stepped limit, as shown in Tables 11 and 12.

	Finally, cumulative CO emissions and emission reductions under the NSPS were calculated based on a 10-year model design lifespan for shipments and a 20-year appliance use lifespan for emissions, as explained in Sections I-B and I-C. Although CO emissions are not being regulated under this NSPS, estimated CO emissions and emission reductions are provided separately in our CE analysis spreadsheets.
                                       
                                       
      Table 7.  NSPS Adjusted Emission Factors for Volatile Organic Compounds  -  Baseline, Step 1 and Step 2

                                       
                                       

                                       
                                       

* For forced-air furnaces, the compliance dates are 2015 for work practice/operational standards, 2016 for the Step 1 PM emission limit for small furnaces and 2017 for the Step 1 PM emission limits for large furnaces.

                                          
                                          
                                          
                                          
                                          
                                          
                                          
      Table 8. Estimated Volatile Organic Compound Emissions (Tons)  -  Baseline Scenario* 

                                       
                                       
                                       
Table 9. Estimated Volatile Organic Compound Emissions (Tons)  -  NSPS Scenario*

*Step 1 PM emission limit in 2015 and Step 2 PM emission limit in 2020 for all appliances, except forced-air furnaces have work practice/operational standards in 2015, Step 1 PM emission limits for small furnaces in 2016, Step 1 PM emission limits for large furnaces in 2017 and Step 2 PM emission limits for all furnaces in 2020. In order to not overstate emission reductions attributable to this NSPS, estimates are reduced for the percentage of appliances estimated to already meet the Step 2 PM emission limits (26% of wood stoves, 70% of pellet stoves and 18% of hydronic heaters). In this analysis, emission reductions for forced-air furnaces are not quantified for the work practice/operational standard required in 2015, although stakeholders agree that work practice/operational standards will reduce emissions.
      
      Table 10. NSPS Adjusted Emission Factors for Carbon Monoxide  -  Baseline, Step 1 and Step 2 

                                          

* For forced-air furnaces, the compliance dates are 2015 for work practice/operational standards, 2016 for the Step 1 PM emission limit for small furnaces and 2017 for the Step 1 PM emission limits for large furnaces.

Table 11. Estimated Carbon Monoxide Emissions (Tons)  -  Baseline Scenario*

Table 12. Estimated Carbon Monoxide Emissions (Tons)  -  NSPS Scenario*

*Step 1 PM emission limit in 2015 and Step 2 PM emission limit in 2020 for all appliances, except forced-air furnaces have work practice/operational standards in 2015, Step 1 PM emission limits for small furnaces in 2016, Step 1 PM emission limits for large furnaces in 2017 and Step 2 PM emission limits for all furnaces in 2020. In order to not overstate emission reductions attributable to this NSPS, estimates are reduced for the percentage of appliances estimated to already meet the Step 2 PM emission limits (26% of wood stoves, 70% of pellet stoves and 18% of hydronic heaters). In this analysis, emission reductions for forced-air furnaces are not quantified for the work practice/operational standard required in 2015, although stakeholders agree that work practice/operational standards will reduce emissions.