E

C

/R Incorporated Providing Environmental Technical Support Since 1989

501 Eastowne Dr., Suite 250  Chapel Hill, North Carolina 27514

Telephone: (919) 484-0222  Fax: (919) 484-0122

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 tool1, which is an 

AccessTM 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

 

1 Emission factors are based on EPA's Residential Wood Combustion Tool version 4.1 with updates from the 2012 EPA 

report (Gullett et al. Environmental, Energy Market, and Health Characterization of Wood-Fired Hydronic Heater, Final 

Report, June 2012).
2

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.2The 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).

 

2 AP-42, Chapter 1.10, Residential Wood Stoves, Table 1.10-1. See: 

http://www.epa.gov/ttnchie1/ap42/ch01/final/c01s10.pdf.
3

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 forcedair 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 noncatalytic stoves; and the Step 2 limit is already met by the top performing catalytic, noncatalytic 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.3 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.

4 Although previously

unregulated and a less developed technology than adjustable burn rate stoves, single burn rate 

 

3

Final HPBA Heater Database version 2/25/10, EC/R received from Bob Ferguson for HPBA on 4/26/10

4 Memorandum to USEPA from EC/R, Inc. Derivation of wood heater model percentages meeting Step 2 standards. 

November 2014.

Emission Inventory Category Pollutant

Baseline 

Emission 

factor 

(lb/ton)

Baseline 

Emissions 

(tons)

Baseline 

Tons/appl

Woodstove: fireplace inserts; EPA certified; noncatalytic Primary PM2.5 8.76 5,371 0.0041

Woodstove: fireplace inserts; EPA certified; catalytic Primary PM2.5 9.72 2,023 0.0047

Woodstove: freestanding, EPA certified, non-catalytic Primary PM2.5 8.76 6,745 0.0077

Woodstove: freestanding, EPA certified, catalytic Primary PM2.5 9.72 3,769 0.0101

Woodstove: pellet-fired, general Primary PM2.5 3.06 1,798 0.0021

Single Burn Rate Stoves* Primary PM2.5 30.6 71,424 0.0324

Hydronic heater: outdoor Primary PM2.5 64 116,933 0.3208

Furnace: indoor, cordwood Primary PM2.5 64 83,972 0.2392
4

stove designs have been undergoing R&D in anticipation of the proposed NSPS and cleaner 

designs are nearly market-ready.

5

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 program6, as well as over 100 European 

manufacturers per test method EN 303-05.7It 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 B415.1-108, conversations with industry regarding 

cleaner forced-air furnace models currently being tested in R&D9and 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. 

 

5

2/8/13 telephone discussion between Gil Wood, USEPA, and a manufacturer of single burn rate stoves.

6

See list of cleaner hydronic heaters participating in EPA’s Phase 2 voluntary Hydronic Heater Program at 

http://www.epa.gov/burnwise/owhhlist.html.

7 European Wood-Heating Technology Survey: An Overview of Combustion Principles and the Energy and Emissions 

Performance Characteristics of Commercially Available Systems in Austria, Germany, Denmark, Norway, and Sweden; 

Final Report; Prepared for the New York State Energy Research and Development Authority; NYSERDA Report 10–01; 

April 2010.

8 CSA B415.1-10, Performance Testing of Solid-Fuel-Burning Heating Appliances. Appendix D. March 2010.

9

2/8/13 telephone discussion between Gil Wood, USEPA, and a manufacturer of forced-air furnaces.
5

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.10 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.10For 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. 

 

10 Final HPBA Heater Database version 2/25/10, EC/R received from Bob Ferguson for HPBA on 4/26/10
6

 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 noncatalytic 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.

11 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.12 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.13 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 

 

11 See the EPA Burn Wise Website regarding the Hydronic Heater Voluntary Program: 

http://www.epa.gov/burnwise/participation.html.

12 Emission factors are based on EPA's Residential Wood Combustion Tool version 4.1 with updates from the 2012 EPA 

report (Gullett et al. Environmental, Energy Market, and Health Characterization of Wood-Fired Hydronic Heater, Final 

Report, June 2012).

13 CSA B415.1-10, Performance Testing of Solid-Fuel-Burning Heating Appliances. Appendix D. March 2010.
7

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. 
8

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.

Emission Inventory Category Pollutant

Baseline 

Emission 

factor 

(lb/ton)

Baseline 

Emissions 

(tons)

Baseline 

Tons/appl

2015* 

Step 1

Emission 

Factor

2015* 

Step 1 

Emissions 

(tons)

2015* 

Step 1 

Tons/appl

2020 

Step 2 

Emission 

Factor 

2020 

Step 2

Emissions 

(tons)

2020 

Step 2 

Tons/appl

Woodstove: fireplace inserts; EPA 

certified; non-catalytic Primary PM2.5 8.76 5,371 0.0041 8.76 5,371 0.0041 3.89 2,387 0.0018

Woodstove: fireplace inserts; EPA 

certified; catalytic Primary PM2.5 9.72 2,023 0.0047 9.72 2,023 0.0047 7.78 1,618 0.0038

Woodstove: freestanding, EPA 

certified, non-catalytic Primary PM2.5 8.76 6,745 0.0077 8.76 6,745 0.0077 3.89 2,998 0.0034

Woodstove: freestanding, EPA 

certified, catalytic Primary PM2.5 9.72 3,769 0.0101 9.72 3,769 0.0101 7.78 3,016 0.0081

Woodstove: pellet-fired, general Primary PM2.5 3.06 1,798 0.0021 3.06 1,798 0.0021 1.36 799 0.0009

Single Burn Rate Stoves Primary PM2.5 30.6 71,424 0.0324 8.76 20,447 0.0093 3.89 9,088 0.0041

Hydronic heater: outdoor Primary PM2.5 64 116,933 0.3208 6.4 11,693 0.0321 2.00 3,654 0.0100

Furnace: indoor, cordwood* Primary PM2.5 64 83,972 0.2392 16 20,993 0.0598 2.00 2,624 0.0075

0.0060 Baseline woodstove weighted average (Tons/appl)

0.0060 2015 Step 1 woodstove weighted average (Tons/appl)

0.0034 2020 Step 2 woodstove weighted average (Tons/appl)
9

B. Shipment Data, Model Design Lifespan and Emitting Lifespan

We used data in the Frost & Sullivan Market (F&S) report14 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 200815 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).15These 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.

16 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.17 For year 2018, the same HPBA consultant 

projected there to be 100,000 wood stove sales.18 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)19 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 rule20, however, in which some 

 

14 Market Research and Report on North American Residential Wood Heaters, Fireplaces, and Hearth Heating 

Products Market. Prepared by Frost & Sullivan. April 26, 2010. P. 31 -32.

15 NSPS Review and Comments. Confidential Business Information submitted by manufacturer. September 2010.

16 Global Economic Outlook 2014, projections prepared by the Conference Board, May 2014 update; 

http://www.conference-board.org/data/globaloutlook.cfm

17 Cost-Effectiveness Analysis of Alternative Hydronic Heater New Source Performance Standards, prepared for the 

Hearth, Patio, and Barbecue Association by NERA Economic Consulting, May 2014. (Attachment 3 of HPBA’s 

comment to the Docket EPA-HQ-OAR-2009-0734)

18 Cost-Effectiveness Analysis of Alternative Woodstove New Source Performance Standards, prepared for the 

Hearth, Patio, and Barbecue Association by NERA Economic Consulting, May 2014. (Attachment 2 of HPBA’s 

comment to Docket EPA-HQ-OAR-2009-0734)

19 Memorandum to USEPA from EC/R, Inc. Residential Wood Heater Cost Effectiveness Analysis. January, 2015.

20 Comments on the proposed NSPS are available electronically through http://www.regulations.gov by searching 

Docket IDs EPA-HQ-OAR-2009-0734.
10

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 

spreadsheets21 for the complete shipment data.

C. 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 analysis22

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 analysis22also 

includes a spreadsheet showing cumulative emissions and emission reductions for Subparts AAA 

and QQQQ combined. 

 

21 See January 2015 cost effectiveness (CE) spreadsheets including for PM2.5 the Revised Final Wood Heater NSPS 

PM CE 7% for the CE analysis supporting the NSPS. All of these spreadsheets are found in the public docket for 

this rulemaking.

22 Memorandum to USEPA from EC/R, Inc. Residential Wood Heater Cost Effectiveness Analysis. January, 2015.
11

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.

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023

Wood Stoves 126,527 80,851 77,617 79,169 80,752 82,367 84,015 85,695 87,409 89,157 100,000 102,000 104,040 106,121 108,243 110,408

Single Burn Rate 

Stoves 40,000 25,560 24,538 25,028 25,529 26,039 26,560 27,091 27,633 28,186 28,750 29,325 29,911 30,509 31,120 31,742

Pellet Stoves 130,381 83,313 79,981 81,581 83,212 84,876 86,574 88,305 90,072 91,873 93,710 95,585 97,496 99,446 101,435 103,464

Furnace: indoor,

cordwood 41,000 26,199 25,151 25,654 26,167 26,690 27,224 27,769 28,324 28,891 29,468 30,058 30,659 31,272 31,898 32,536

Hydronic Heating 

Systems 13,385 8,553 8,211 8,375 13,100 13,362 13,629 13,902 14,180 14,463 14,753 15,048 15,349 15,656 15,969 16,288

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023

Wood Stoves 563 360 345 352 359 367 374 381 389 397 445 454 463 472 482 491

Single Burn Rate 

Stoves 1,295 827 794 810 826 843 860 877 895 912 931 949 968 988 1,007 1,027

Pellet Stoves 83 53 51 52 53 54 55 56 57 59 60 61 62 63 65 66

Furnace: indoor,

cordwood 9,808 6,267 6,017 6,137 6,260 6,385 6,513 6,643 6,776 6,911 7,049 7,190 7,334 7,481 7,631 7,783

Hydronic Heating 

Systems 3,520 2,250 2,160 2,203 3,446 3,514 3,585 3,656 3,730 3,804 3,880 3,958 4,037 4,118 4,200 4,284

Total 15,269 9,757 9,367 9,554 10,944 11,163 11,386 11,614 11,846 12,083 12,365 12,612 12,865 13,122 13,384 13,652
12

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.

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023

Wood Stoves 563 360 345 352 359 367 374 381 389 397 445 454 259 264 269 275

Single Burn Rate 

Stoves 1,295 827 794 810 826 843 860 251 256 261 266 272 123 126 128 131

Pellet Stoves 83 53 51 52 53 54 55 56 57 59 60 61 28 28 29 29

Furnace: indoor,

cordwood 9,808 6,267 6,017 6,137 6,260 6,385 6,513 6,643 5,505 1,728 1,762 1,798 229 234 238 243

Hydronic Heating 

Systems 3,520 2,250 2,160 2,203 3,446 3,514 3,585 366 373 380 388 396 126 129 131 134

Total 15,269 9,757 9,367 9,554 10,944 11,163 11,386 7,697 6,581 2,825 2,922 2,980 765 780 796 812
13

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.23

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.

24

 

23 See January 2015 cost effectiveness (CE) spreadsheets for VOC entitled Revised Final Wood Heater NSPS VOC 

CE 7%, available in the public docket for this rulemaking.

24 See January 2015 cost effectiveness (CE) spreadsheets for CO entitled Revised Final Wood Heater NSPS CO CE 

7%, available in the public docket for this rulemaking. 
14

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.

Emission Inventory Category Pollutant

Baseline 

Emission 

factor 

(lb/ton)

Baseline 

Emissions 

(tons)

Baseline 

Tons/appl

2015 

Step 1 

Emission 

Factor

2015 

Step 1

Emissions 

(tons)

2015 

Step 1 

Tons/appl

2020 

Step 2

Emission 

Factor 

2020 

Step 2

Emissions 

(tons)

2020 

Step 2 

Tons/appl

Woodstove: fireplace inserts; EPA certified; non-catalytic Volatile Organic Compounds 12 7,357 0.0056 12 7,357 0.0056 5.33 3,270 0.0025

Woodstove: fireplace inserts; EPA certified; catalytic Volatile Organic Compounds 15 3,121 0.0073 15 3,121 0.0073 12.00 2,497 0.0058

Woodstove: freestanding, EPA certified, non-catalytic Volatile Organic Compounds 12 9,240 0.0106 12 9,240 0.0106 5.33 4,107 0.0047

Woodstove: freestanding, EPA certified, catalytic Volatile Organic Compounds 15 5,817 0.0155 15 5,817 0.0155 12.00 4,654 0.0124

Woodstove: pellet-fired, general Volatile Organic Compounds 0.041 24 0.0000 0.041 24 0.0000 0.02 11 0.0000

Single Burn Rate Stoves Volatile Organic Compounds 53 123,709 0.0561 12 28,010 0.0127 5.33 12,449 0.0056

Hydronic heater: outdoor Volatile Organic Compounds 67.4 123,145 0.3378 6.74 12,314 0.0338 2.11 3,848 0.0106

Furnace: indoor, cordwood Volatile Organic Compounds 67.4 88,433 0.2519 16.85 22,108 0.0630 2.11 2,764 0.0079

0.0086 Baseline woodstove weighted average (Tons/appl)

0.0086 2015 Step 1 woodstove weighted average (Tons/appl)

0.0049 2020 Step 2 woodstove weighted average (Tons/appl)
15

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.

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023

Wood Stoves 803 513 493 502 512 523 533 544 555 566 635 647 660 673 687 701

Single Burn Rate 

Stoves 2,243 1,433 1,376 1,403 1,431 1,460 1,489 1,519 1,549 1,580 1,612 1,644 1,677 1,711 1,745 1,780

Pellet Stoves 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Furnace: indoor,

cordwood 10,329 6,600 6,336 6,463 6,592 6,724 6,859 6,996 7,136 7,278 7,424 7,572 7,724 7,878 8,036 8,197

Hydronic Heating 

Systems 3,707 2,369 2,274 2,320 3,629 3,701 3,775 3,851 3,928 4,006 4,086 4,168 4,251 4,336 4,423 4,512

Total 17,083 10,916 10,480 10,689 12,165 12,409 12,657 12,910 13,168 13,431 13,758 14,033 14,313 14,600 14,892 15,189

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023

Wood Stoves 803 513 493 502 512 523 533 544 555 566 635 647 376 383 391 399

Single Burn Rate 

Stoves 2,243 1,433 1,376 1,403 1,431 1,460 1,489 344 351 358 365 372 169 172 176 179

Pellet Stoves 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0

Furnace: indoor,

cordwood 10,329 6,600 6,336 6,463 6,592 6,724 6,859 6,996 5,798 1,820 1,856 1,893 241 246 251 256

Hydronic Heating 

Systems 3,707 2,369 2,274 2,320 3,629 3,701 3,775 385 393 401 409 417 133 136 138 141

Total 17,083 10,916 10,480 10,689 12,165 12,409 12,657 8,269 7,097 3,145 3,265 3,330 919 937 956 975
16

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.

Emission Inventory Category Pollutant

Baseline 

Emission 

factor 

(lb/ton)

Baseline 

Emissions 

(tons)

Baseline 

Tons/appl

2015 

Step 1 

Emission 

Factor

2015 

Step 1

Emissions 

(tons)

2015 

Step 1

Tons/appl

2020 

Step 2

Emission 

Factor 

2020 

Step 2

Emissions 

(tons)

2020 

Step 2

Tons/appl

Woodstove: fireplace inserts; EPA certified; non-catalyticCarbon Monoxide 140.8 86,323 0.0662 140.8 86,323 0.0662 62.6 38,366 0.0294

Woodstove: fireplace inserts; EPA certified; catalytic Carbon Monoxide 104.4 21,725 0.0509 104.4 21,725 0.0509 83.5 17,380 0.0407

Woodstove: freestanding, EPA certified, non-catalytic Carbon Monoxide 140.8 108,418 0.1241 140.8 108,418 0.1241 62.6 48,186 0.0552

Woodstove: freestanding, EPA certified, catalytic Carbon Monoxide 104.4 40,486 0.1082 104.4 40,486 0.1082 83.5 32,389 0.0866

Woodstove: pellet-fired, general Carbon Monoxide 15.9 9,344 0.0110 15.9 9,344 0.0110 7.1 4,153 0.0049

Single Burn Rate Stoves Carbon Monoxide 230.8 538,716 0.2442 140.8 328,645 0.1489 62.6 146,064 0.0662

Hydronic heater: outdoor Carbon Monoxide 360 657,748 1.8042 36 65,775 0.1804 11.3 20,555 0.0564

Furnace: indoor, cordwood Carbon Monoxide 360 472,341 1.3456 90 118,085 0.3364 11.3 14,761 0.0421

0.0863 Baseline woodstove weighted average (Tons/appl)

0.0863 2015 Step 1 woodstove weighted average (Tons/appl)

0.0458 2020 Step 2 woodstove weighted average (Tons/appl)
17

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.

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023

Wood Stoves 8,079 5,163 4,956 5,055 5,156 5,259 5,365 5,472 5,581 5,693 6,385 6,513 6,643 6,776 6,912 7,050

Single Burn Rate 

Stoves 9,766 6,241 5,991 6,111 6,233 6,358 6,485 6,614 6,747 6,882 7,019 7,160 7,303 7,449 7,598 7,750

Pellet Stoves 432 276 265 270 275 281 287 292 298 304 310 316 323 329 336 342

Furnace: indoor,

cordwood 55,170 35,254 33,844 34,520 35,211 35,915 36,633 37,366 38,113 38,876 39,653 40,446 41,255 42,080 42,922 43,780

Hydronic Heating 

Systems 19,803 12,654 12,148 12,391 19,381 19,769 20,164 20,567 20,979 21,398 21,826 22,263 22,708 23,162 23,625 24,098

Total 93,249 59,586 57,203 58,347 66,256 67,582 68,933 70,312 71,718 73,152 75,194 76,698 78,232 79,796 81,392 83,020