Intertek Testing Services Page 1 of 13 9/28/2010 

North American and European Wood-Fired Boiler Testing 

Comparison 

Rick Curkeet, PE Chief Engineer – Hearth Products 

INTRODUCTION 

The following is a comparison of EN 303-5 to EPA Method 28 WHH, ASTM 

E2618 and CSA B415.1-2010. These are the currently active standard test 

methods for evaluation of emissions and heating performance of hydronic central 

heating appliances that use wood or other bio-mass (primarily wood based 

pellets) as fuel. 

EN 303-5 is roughly equivalent to the combined requirements of the ASME 

Pressure Vessel Code for heating boilers, UL or CSA appliance safety standards 

and EPA , ASTM or CSA Emissions and Efficiency test procedures. This paper 

will focus only on the emissions and efficiency related testing procedures in these 

standards. 

I am not too concerned about issues related to pellet burning appliances. These 

products are relatively easy to engineer for clean combustion and control of 

output rate. Control over the fuel feed rate and combustion air have led to very 

few problems in meeting emissions requirements. I am therefore confining my 

comments to manually fueled cordwood appliances. 

EN 303-5 provides only very general guidance and virtually no detailed 

procedures or calculations for emissions and efficiency measurements. I think 

I understand the basics that are being specified, but it's a very different test than 

we do under EPA, ASTM or CSA methods. Perhaps there are detailed test 

methods for emissions measurement procedures in other documents, but I found 

no references to such procedures in EN 303-5. 

It has already been well documented that the test methods currently published 

have several substantial technical and philosophical differences. The primary 

philosophical difference is that in NA we tend to try to envision typical or worstcase behavior of the user and design tests to make sure performance is 

acceptable even when the user does not follow the manufacturer’s 

recommended operating procedures. The EU standards appear to assume that 

users do follow manufacturer’s recommendations closely. 

The following is a summary of those technical differences that I believe need to 

be addressed. I do not think that it is reasonable to expect that tests run under 

the EN 303-5 procedure to be comparable or correlate to those obtained from the 

North American standards currently in use. I, therefore, believe that the most 

expeditious route to international compatibility in emissions and efficiency testing 

of these appliances is the development of a harmonized international standard. 
Intertek Testing Services Page 2 of 13 9/28/2010 

Before discussing differences and similarities between EN 303-5 and North 

American standards, the differences between the three NA standards should be 

understood. 

NORTH AMERICAN TEST METHODS 

First, EPA Method 28 OWHH was issued while the ASTM E2618 standard was in 

its early development stage. In fact, M28 OWHH was essentially “draft 4” of what 

ultimately became ASTM E2618. The first published edition of ASTM E2618 was 

“draft 12” which went through the rigorous ASTM consensus balloting process. 

There are, therefore, many differences between the EPA version and the ASTM 

Standard. Many are minor, but a few are quite significant. These include the use 

of oak cordwood, measurement of direct heat output on the load side of the 

system and an appendix for testing thermal mass storage units in the ASTM 

standard. The EPA M28 OWHH requires the use of oak 4 x 4 cribs, heat output 

measurement on the supply side1

 of the system and has no thermal mass 

storage procedure. 

CSA B415.1-2010 specifies the use of ASTM E2618 for hydronic unit testing, but 

modifies the heat output categories and weighting of the results to be less 

focused on the lower heat output rates than the ASTM and EPA methods. Table 

1 is a compilation of some of the more significant differences 

 

1

 At high output rates load vs. supply side measurements tend to agree well, but at low output 

rates the temperature difference (delta-T) between supply outlet and return become very small 

while the load side delta-T gets larger. Since accurate delta-T measurement is critical, the larger 

the delta-T, the more accurate the heat output determination for any specific measurement 

accuracy. In addition, the load side water flow rate and temperature used to remove heat through 

a water-to-water heat exchanger tend to be very constant. Supply side water temperature 

fluctuates and calibration of the water flow meter at elevated temperatures adds uncertainty. 

Thus, load side measurements are significantly more accurate for lower output rates. The loss in 

the piping between the unit and the heat exchanger should be the only difference between load 

and supply side outputs and this has be shown to be relatively insignificant due to small surface 

areas and use of insulated piping. 
Intertek Testing Services Page 3 of 13 9/28/2010 

Table 1 

Parameter M 28 OWHH ASTM E2618 CSA B415.1 

Fuel Oak 4 x 4 crib – 10 

lb/ft3

Oak Cordwood – *10 

or more lb/ft3

Cordwood w/ sp. g. of 

0.6-0.73 – *10 or more 

lb/ft3

Output Rates <15%, 16-24%, 25-

50% and 100% 

<15%, 16-24%, 25-

50% and 100% 

<35%, 35-53%,53-76%, 

100% 

Emissions/ 

Efficiency Average 

Weightings 

**Low- 43.7% 

Med Low – 23.8% 

Med High – 27.5% 

High – 5% 

**Low- 43.7% 

Med Low – 23.8% 

Med High – 27.5% 

High – 5% 

***Low – 25% 

Med Low – 25% 

Med High – 25% 

High – 25% 

Output 

Measurement 

Delivered at supply 

side. 

Delivered at load 

side. 

Delivered at load side 

and Overall by Stack 

Loss. 

Particulate Limits 0.32 lb/MMBtu Del. 

Output (0.138 g/MJ) 

Not Specified. 0.137 g/MJ Del. Output. 

Thermal Storage Not Addressed Covered for units 

with sufficient 

storage for 100% of 

fuel load output. 

Not Addressed directly, 

but covered by reference 

to ASTM E2618. 

Fuel M.C. (dry 

basis) 

19-25% 18-28% 18-28% 

Coal Bed Weight 10-20% of test load 10-20% of test load 10- 25% of test load 

Emissions 

Measurement 

Method 

ASTM E2515 ASTM E2515 ASTM E2515 

Efficiency Input 

Basis 

HHV & LHV HHV & LHV HHV 

Draft Natural w/15’ Height Natural w/15’ Height Natural w/15’ Height 

* 10 lb/ft3

 is the default, larger loads are used if specified by the manufacturer. 

** Year Round operation weightings as currently required by EPA Voluntary 

Program (Phase 2). Heat Season Only Weightings are: Low- 17.5%, Med. Low – 

27.5%, Med. High – 45%, High – 10%. 

*** Weightings per B415/EPA NSPS Probability Distribution if maximum burn rate 

is less than 5.3 kg/hr. 

The ASTM E06.54 subcommittee currently has a task group working on revisions 

to E2618 which will likely include harmonization with CSA B415.1 and the 

addition of test procedures for appliances linked to remote or partial heat storage 

systems. 

There has been a substantial amount of work done through both ASTM and CSA 

in the development of consensus standards for evaluation of emissions and 

efficiency performance of wood fire hydronic heaters. This work included several 
Intertek Testing Services Page 4 of 13 9/28/2010 

significant research programs to validate the procedures. Thus, EPA Method 28 

WHH should, in my view, be considered obsolete and not be used as a basis for 

further research testing. 

EN 303-5 vs. EPA M28 OWHH, ASTM E2618-09 & CSA B415.1-10 

There are many important differences between the method of measuring 

emissions between EN 303-5 and the EPA/ASTM/CSA Standards. These 

include what is measured, how it’s measured and how the appliance is operated. 

I will not address the sections of EN 303-5 that deal with safety testing or 

pressure vessel construction as these have been well documented elsewhere. 

(See “Biomass Boiler &Furnace Emissions and Safety Regulations In the Northeast States 

Evaluation and Options for Regional Consistency”, CONEG Policy Research Center, Inc., June 

2009.)

WHAT IS MEASURED? 

The most obvious difference is that EN 303-5 measures particulate (dust) as only 

material that is solid at the flue gas temperature or on a filter at a temperature 

that is about the same as the flue gas temperature ~ 180 oC (356 oF). In the NA 

methods, particulate is measured by the dilution tunnel method (ASTM E2515) 

and includes both solid material and organic compounds which condense to 

liquid or solid form at temperatures of 20 to 32 oC (68 to 90 oF). Thus, in terms of 

solid particulate, NA standards collect significantly more material than is reported 

as “dust” per EN 303-5. EN 303-5 does, however, also require measurement 

and reporting of Organically Bound Carbon (OGC) which would exclude the 

“dust” but presumably include all organic material that passes through the heated 

filter. This would therefore include material that remains in gas form at lower 

temperatures which would not be collected in the NA measurements.

In theory, the relationship between what is measured by ASTM E2515 and what 

is measured by EN 303-5 should look like: 

ASTM E2515 = EN 303-5 Dust + EN 303-5 OGC – Non-Condensable Gases, 

or, 

ASTM E2515 + Non-Condensable Gases = EN 303-5 Dust + EN 303-5 OGC 

Unfortunately, there is considerable evidence that the production of relative 

amounts of solid, condensable and gaseous organics from wood combustion is 

highly variable relative to combustion conditions. Poor combustion tends to 

produce higher levels of gaseous and condensable hydrocarbons and lower 

proportions of solids. As combustion improves, light hydrocarbons (gases) tend 

to be reduced the most and the proportions of solids and condensables 

increases while the total amount decreases. Very clean combustion produces 
Intertek Testing Services Page 5 of 13 9/28/2010 

almost no hydrocarbons and only small amounts of soot – mostly carbon 

particles. Under some conditions fine ash particles may be entrained in the flue 

gas stream and contribute to the solid particulate catch. However, ash particles 

typically are larger that the PM 2.5 or PM 10 material of most interest in air 

quality regulation and do not remain suspended in the air shed for a significant 

time. None of the methods I know of provide a method of segregating organic 

from inorganic (i.e. ash) particles. 

I would not expect that it will be feasible to relate the EN 303-5 and ASTM E2515 

emissions measurements unless the procedure includes a means of 

measurement the “non-condensable gas” proportion of the overall emissions. I 

am not aware of any data that would indicate what the relative proportions of this 

component of emissions might be or whether the relationship would be 

consistent. 

I believe that it is well understood that the term “particulate” as used in air quality 

management is defined by the measurement method applied. That is, 

“particulate” is essentially what the specified measurement process captures. 

METHOD PRECISION 

We should not be “getting the cart before the horse” in this process. For any test 

method that produces quantitative results it is critically important to have some 

idea of the variability or “precision” in results that the method produces. This is 

statistically referred to as Repeatability (within lab) and Reproducibility (between 

labs). Perhaps this has been evaluated for EN 303-5 and our Swedish 

colleagues can enlighten us as to the magnitude of expected variation within and 

between laboratories. 

Precision is typically evaluated through an Interlaboratory Study (ILS) where 

multiple labs run replicate tests on identical artifacts. A bare-bones ILS requires 

a minimum of 6 labs, 6 materials or products representative of the anticipated 

range of expected results and at least 3 replicate tests of each. This would result 

in a minimum of 108 data points where each data point would represent one 

complete test series of each product. It seems clear that funding for a project of 

this magnitude is unlikely to materialize anytime soon. 

Intertek has done some work in several research programs, in support of the 

ASTM and CSA standards development, on repeatability (within lab) and the 

results indicate that variation in results can be quite significant. It will be very 

difficult to attempt to quantify a relationship between test methods if the variability 

in test results is close to magnitude of the differences in results between the 

methods. In statistical terms, one must be able to distinguish between “random” 

and “systematic” differences. If random variability is large, it becomes impossible 

to determine the magnitude of systematic differences. My best estimate based 
Intertek Testing Services Page 6 of 13 9/28/2010 

on data available is that repeatability in particulate emissions measurements is at 

best ± 20% and more typically ± 60-80% of the value reported. 

APPLIANCE OPERATION DIFFERENCES 

Setting aside the differences in what is measured, the most obvious differences 

between EN 303-5 and the NA procedures are the differences in appliance 

operation. Key differences are summarized in table 4. 

Table 4 

Parameter EN 303-5 M28 OWHH/E2618/B415.1 

Emissions Test Output Rate – 

Dust/Particulate 

100% Four rates from <30% to 100% 

(Weighted Ave.) 

Emissions – OGC 

Appliance Output Rate for Tests

100% and Mfgr. Specified 

minimum no less than 30% 

(Average or Individual Run 

compliance not specified) 

Not measured. 

Emissions – CO 

Appliance Output Rate for Tests

100% Mfgr. Specified 

minimum no less than 30% 

(Average or Individual Run 

compliance not specified) 

Measured in B415.1 at 4 

output rates but no limit 

specified. 

Efficiency Tests 

Appliance Output Rate for Tests

100% and Mfgr. Specified 

minimum no less than 30% 

All 4 output rates. 

Sampling Time Four 30 minute periods (2 

hrs) w/ 2 fuel loads. 

Full duration of each test. 

Sampling location In Stack or D.T. Dilution Tunnel 

Fuel Load Size Per Manufacturer Specified by Standard 

Fuel Moisture 13.6 – 25% 18-25% 

Efficiency Input Basis Lower Heating Value Higher Heating Value 

Emissions reporting units mg/M3 (@10% O2) g/MJ (lb/MMBtu Output) 

Flue Draught Regulated to specified 

maximum. 

Natural from specified 

chimney. 

Coal bed size. Visual judgment 10-20% of test load weight 

Test Duration Unclear as a scale is not 

required. 

Scale used to determine when 

100% of test load is consumed. 

Heat Storage (Accumulator) Recommended if minimum 

heat output is > 30% of max. 

Size calculated, but not 

used in tests. 

If specified, requires test with 

heat storage. (No current 

coverage for partial heat 

storage) 

Emissions Regulated CO, OGC, Dust Particulate 
Intertek Testing Services Page 7 of 13 9/28/2010 

FLUE DRAUGHT 

Draught regulators (barometric dampers) are rarely used on wood burning 

equipment in North America. A draught limiter can have a significant impact on 

the burn rate profile of the appliances which could in turn affect performance. 

The requirement to use a draught limiter as specified draft in EN 303-5 therefore 

has the potential to alter the burn characteristics and performance when 

compared to the NA test procedures. 

SAMPLING LOCATION 

In-stack emissions sampling for small scale wood heating equipment cannot, in 

my experience, be done accurately. EPA Method 5, from which EPA Method 5H 

was derived, was developed for industrial and commercial scale systems 

characterized by relatively constant and high velocity stack flow conditions. This 

allows for the use of a pitot tube to measure flow rate and provides the basis for 

a reasonably accurate means of setting a known proportional sampling rate. 

In smaller scale residential appliances, stack flow velocities are typically much 

smaller and quite variable. Flow rates are often too low to be measured by a 

pitot tube. Many attempts have been made to use other methods to determine 

stack flow rates. These include injection of tracer gases and measurement of 

dilution ratio in the stack, carbon mass balance calculation based on stack CO 

and CO2 concentrations and fuel carbon content and CO2 dilution ratio from stack 

concentration to dilution tunnel concentration. 

When compared to each other, these techniques virtually always give 

substantially different results. None has been demonstrated to be accurate. If 

we cannot accurately measure stack flow rates in real time, we cannot know 

accurately what proportion of that flow is being collected by the sampling system. 

And if we do not know what proportion of the flow has been sampled we do not 

know what the actual emissions rate really is. 

This is the problem that led to the use of a dilution tunnel for emissions 

measurement which is now embodied in ASTM E2515 and is used in all recent 

North American solid fuel appliance emissions test methods. Any comparison 

between EN 303-5 and North American methods should, therefore, be limited to 

the dilution tunnel option within EN 303-5. 

SAMPLING TIME 

EN 303-5 (5.9.1.1) specifies emissions collection for Dust for 4 thirty minute 

periods over the course of two fuel burning down cycles with the unit operating at 
Intertek Testing Services Page 8 of 13 9/28/2010 

nominal output. If, for example, one fueling results in 3 hours of burning down 

time, the sampling would occur from when the fuel is loaded to 30 minutes, form 

90 to 120 minutes, from 180 to 210 minutes (beginning of second fuel load) and 

from 270 to 300 minutes. This would result in sampling for 2 hours out of the 6 

the unit operates. It would also result in no sampling during the second 1⁄2 hour 

after fuel is loaded. In my experience this part of a burning cycle is frequently 

where the most particulate emissions are produced. Thus, EN 303-5 would 

seem to have the potential to miss a potentially very significant proportion of the 

emissions production. In the NA standards sampling is conducted through the 

entire burning process and therefore accurately measures the total emissions 

produced. 

HEAT STORAGE SYSTEMS 

By far the most significant operational difference is the measurement of 

particulate emissions only at full output load under EN 303-5 (5.7.3). Virtually all 

wood fired boilers with reasonably well design combustion chambers and 

properly proportion combustion air will produce their lowest emissions and 

highest efficiency when run at full output load. However, all appliances I have 

seen must incorporate temperature limiting controls that substantially reduce 

combustion air supplies to prevent overheating when the heating load is small 

and firebox is full. EN 303-5 does recommend the use of a heat accumulator 

(a.k.a. “thermal storage”) to reduce the potential for the appliance to cycle 

between high and low combustion rates, but does not specify testing with the 

recommended heat accumulator included. 

In the colder regions of the US, the rule of thumb is that central heating 

equipment in single family homes will typically be called on to provide less than 

60% of their nominal output for more than 80% of the heating season. Output of 

more than 80% of the nominal output is typically required less than 3% of the 

heating season. (See Figure 1 for ASHRAE Bin Data for Chicago, IL.) This reality 

leads to some complexity in the proper sizing and use of heat accumulators. A 

unit that can sustain its nominal heat output for several hours on a full load of 

wood will need to store a substantial portion of its heat output if refueled when 

the building heat demand happens to be low. To avoid over heating and still 

burn most of the load on high leads to requirements for much larger heat storage 

capacity that is commonly specified or the use of a heat dissipation system to 

dump excess heat and prevent over heating. If the user happens to reload the 

appliance while the heat storage is already near its upper temperature limit, the 

appliance will quickly go into a cycling mode which may include extended periods 

of operation at its reduced rate. (See Appendix 1 for an example.) 
Intertek Testing Services Page 9 of 13 9/28/2010 

Figure 1 

Assuming that the heat storage provided is adequate, it will certainly be true that 

at normally lower heat demand levels, the storage will supply the required heat 

demand for many hours after a fuel load has been consumed. This means that 

most fires will require a “cold-start”. That is, the user will need to start a new fire 

as there will not be a coal bed left from the previous fire. This will certainly have 

an impact on potential emissions which is not a factor in “hot-to-hot” test cycles. 

As indicated by typical heat demand data, appliances with large heat storage 

capacity will rarely be operated on a hot-to-hot fueling cycle with full wood loads. 

For a heat accumulator type system, it would seem to be imperative to provide 

the user with direction on when to fire the appliance. This would typically require 

a temperature indication of the heat storage media and instructions to fire the unit 

only when the storage temperature approaches the lower recommended 

operating level. E.g. “Fire unit only when the heat storage temperature is below 

60 oC.” In reality, it would, of course, be acceptable to provide direction that 

might include fueling with heat storage at higher temperatures using less fuel. 

Perhaps recommending a half load if the temperature is 65 to 70 oC. 

In general, I do not think standards should be design restrictive. They should be 

performance based and provide only an appropriate and accurate measurement 

process and reasonable performance requirements. We have already seen 

ASHRAE BIN DATA -Chicago

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

% of Heating Season

% of Nominal Load
Intertek Testing Services Page 10 of 13 9/28/2010 

wood fired boilers that achieve remarkably low emissions results over a broad 

range of heat outputs that do not require heat accumulators. These units are 

able to modulate heat outputs to match applied demand and still burn very 

cleanly. There may well be many design strategies that could prove to be as 

good or better that we do not currently know of. If a regulatory standard requires 

a specific type of technology, the effect is to stifle innovation and development of 

potentially even more effective designs. I have no doubt that heat storage 

systems are effective, but they have an associated added cost and space burden 

that might be avoided with other solutions. 

EMISSIONS RATING UNITS 

I believe emissions should be reported in terms of mass per unit of useful heat 

output – g/MJ or lbs/MMBtu. The mg/m3 @ 10% O2 used in EN 303-5 does not 

provide a readily understood measurement. It also does not give direct credit to 

higher efficiency designs. That is, the value would not change if the heat 

exchange efficiency of an appliance were significantly increased. Emissions in 

terms of mass per heat output also provides a basis for fair comparison between 

wood heating appliances of different types – e.g. room heaters, furnaces, boilers 

etc. can be compared directly in terms of their impact on air quality versus the 

useful heat they supply. 

EFFICIENCY REPORTING 

I am fundamentally opposed to the use of Lower Heating Value (LHV) as the 

basis for efficiency determinations. In North America virtually all fuel burning 

heating appliances are rated for heating efficiency expressed as a percentage of 

the fuel’s Higher Heating Value. Propane, natural gas and fuel oil all have some 

hydrogen content and thus also have a difference between higher and lower 

heating values. 

The use of LHV as a basis for efficiency reporting is predicated on the argument 

that latent heat of water produced in the combustion process is unrecoverable 

and thus all that can be transferred is sensible heat. The issue becomes quite 

clear if we look at the theoretical process that would result in 100% efficiency. 

Using the Higher Heating Value we could achieve 100% efficiency with complete 

combustion (e.g. 100% of fuel converted to water and CO2) and simply venting 

the product into the heated space. All the available heat would be released and 

none would be lost to areas outside the heated space (unvented gas-fired 

heaters approach this condition). Thus, all the fuel’s Higher Heating Value would 

be captured. This condition could also be approached with a vented appliance 

with sufficient heat exchange capacity to cool the flue gas to close to the ambient 

room temperature. But water would condense in the system in this process. 
Intertek Testing Services Page 11 of 13 9/28/2010 

For a LHV based 100% efficiency we would also need to achieve complete 

combustion and then capture 100% of the sensible heat, but none of the latent 

heat. This would mean cooling the flue products back to ambient temperature, 

but not allowing water to condense. Since the dew point of the flue gases would 

typically be well over 60 oC, this would be a physical impossibility. A unit that 

was capable of nearly full recovery of both sensible and latent heat could, thus, 

result in an LHV efficiency of more than 100%. This, of course, appears to defy 

the first law of thermal dynamics — you cannot get more energy out of a system 

than goes into it (conservation of energy). While an expert in the subject would 

understand that more than 100% efficiency ratings are possible due to the use of 

LHV, it would seem to be an issue that would result in some challenges to the 

credibility of such ratings. 

There is certainly no scientific or physical barrier to designing a “condensing” 

wood fired appliance. There are many condensing gas and oil appliances on the 

market with HHV efficiencies that are well into the 90% -98% range. It is 

probably only a matter of time before we see wood-fired appliances that would be 

rated at over 100% based on LHV if this remains the basis for efficiency 

reporting. 

See: Well-to-Wheel Studies, Heating Values, and the Energy Conservation Principle, Ulf 

Bossel, European Fuel Cell Forum, Morgenacherstrasse 2F 

CH-5452 Oberrohrdorf / Switzerland, forum@efcf.com, www.efcf.com 

29 October 2003 for a discussion of this issue. 

OVERALL HEAT OUTPUT 

CSA B415.1-2010 includes an effective “Stack-Loss” efficiency method that is 

capable of determining the total heat output from the appliance – both through 

the heated water delivery and through radiation and convection directly to the 

space around the appliance. This is important in that the direct heating of the 

space around the appliance constitutes useful heating in many applications, but 

wasted heat when the appliance is installed outdoors or in an unheated space. 

Emissions requirements based on mass per useful heat output should include 

provisions to determine which heat output should be the basis for the emissions 

requirement. i.e. “Total Heat Output” for indoor units vs. “Delivered Heat Output” 

for outdoor units. 

SUMMARY 

It is my view that the EN 303-5 procedures and those currently used by EPA are 

seriously flawed as well as being incompatible. The differences are both 

philosophical and technical. We do not currently have a completely sufficient test 

method that is capable of properly measuring and rating emissions performance 

for all product types either in the EU or North America. However, between ASTM 

E2618, E2515 and CSA B415.1-2010, we do have most of what we need in 

terms of well developed and carefully defined test procedures. These are 
Intertek Testing Services Page 12 of 13 9/28/2010 

international consensus standards and can be revised and improved to deal with 

technical challenges on an on-going basis. I urge consideration of using these 

forums as a readily available platform for development of international standards. 

We currently lack a good understanding of variability in emissions and efficiency 

test results related to all forms of wood heating equipment. It is clear that the 

process can be highly variable, but we do not yet have sufficient information to 

determine how much variability might be controlled or reduced by various 

technological advances in product design or improvements to test methods. 

Research into this area has not been substantial to date and significant funding 

will surely be needed if we are going to quantify variability and explore methods 

of reducing it. However, it appears likely that a substantial variability is simply 

inherent in the wood combustion process and results from interactions between 

numerous variables that we neither understand nor can readily control. 

It has always been challenging to harmonize product standards used in 

government regulations on an international basis. It is clear to me that there is 

virtually zero chance of establishing a simple relationship between EN 303-5 

emissions ratings and compliance with regulations that EPA would likely impose 

under the forthcoming revised NSPS. That is, if an appliance achieves an 

emissions rating of “X” under EN 303-5 it would meet a rating of “Y” under the 

EPA specified procedure or vice versa. 

GOING FORWARD 

In my view, the way forward must involve development of new or revised 

consensus test methods that fully address the needs of all stakeholders. I think it 

will require considerable work to create internationally acceptable standards and 

test methods. 

There are a few basic principles of performance test method development that I 

think must be kept in mind. These are: 

 Measure performance that is meaningful. 

 Test methods must adequately simulate actual product use. 

 Test results must be sufficiently repeatable and reproducible (i.e. 

“precise”) to assure that compliance issues can be fairly resolved. 

(“Validated”). 

 Results provided to the end user must be clear and easily understood. 

 Procedures must be clearly defined and unambiguous. 

 Keep the process as simple as possible while allowing as much flexibility 

as possible. 

 The costs of the process must not be so high that they are unaffordable or 

result in increasing the price of the end products sufficiently to make them 

non-competitive in the market. 
Intertek Testing Services Page 13 of 13 9/28/2010 

Respectfully Submitted: 

Rick Curkeet, PE 

INTERTEK – Chief Engineer 

Appendix 1 

EN 303-5 Heat Accumulator 

Example: 

Unit output (QN): 30 kW (102 000 Btu/h) 

Burn duration at full load (TB): 3 hours. 

Total output: 90 kWh (306 000 Btu) 

Low output rate (Qmin): 10 kW (34 120 Btu/hr) 

Heat Load (QH): = 7.5 kW (25 590 Btu/hr) 

EN 303-5 Heat accumulator size: Vsp = 15 x TB x QN (1-0.3(QH/Qmin)) 

Vsp = 15 x 3 x 30 (1-0.3(7.5/10)) = 1046.25 l (277 gal., 2306 lbs H2O) 

Storage Capacity: 

Lower Temp. limit: 60 oC (140 oF) 

Upper Temp. Limit: 90 oC (194 oF) 

Heat Storage Capacity: 1046 l x 1 kg/l x (90-60) x 1.1622 Wh/kg-cal / 1000 W/kW 

= 36.478 kWh 

 (1046 l x 2.204 lb/l x (194-140) = 124 491 Btu) 

At nominal output: 7.5 kW (25 590 Btu/hr) to load, 22.5 kW (76 770 Btu/hr) to 

storage. 

36.478/22.5 = 1.62 hours to upper storage temperature limit. 

After 1.62 hours – Output drops to 10 kW. 2.5 kW higher than load. Unit 

operates in this mode for additional 4.14 hours. 2.5 x 4.14 = 10.25 kWh (34 973 

Btu), or 11.4% of the appliance output must be diverted to heat dissipater 

(wasted). 

After fuel is consumed, heat stored will satisfy 7.5 kW load for 4.86 hours before 

returning to starting temperature. Total heating time: 10.63 hours.