A:-!DII _I Alr·condltlonlng, Heating, ... _II and Refrigeration Institute 

November 19,2012 

Dr. David Danielson 

Assistant Secretary for Energy Efficiency and Renewable Energy 

United States Department of Energy 

1000 Independence Avenue SW 

Washington, D.C. 20585 

Re: Revision of AFUE Measurements Calculated under Cunent U.S. Department of 

Energy Test Procedures for Two Stage or Modulating Condensing Boilers 

Deal' Assistant Secretary Danielson: 

An internal audit by AHRI of the test results of products tested as part of AHRI' s celiification 

programs revealed an aspect ofthe current DOE efficiency test procedures for residential 

furnaces and boilers that may result in an inaccurate AFUE measurement for a subcategory of 

residential gas boilers. The subcategory is models that are designed to condense and to operate 

at more than a single input rate, (i.e., two-stage or modulating condensing boilers). The flaw in 

the test procedures is in the calculations used to determine the AFUE when the option to skip the 

heat-up and cool-down tests is selected. 

It must be noted that these ratings were based on the current DOE efficiency test procedures, and 

the enor is due to a flaw in those procedures rather than a failure to properly conduct the DOE 

test procedure. We want to assure you that all these models employ condensing technology to 

achieve the highest efficiencies possible today, so they have AFUEs that exceed the CutTent 

federal minimum AFUE for these models. 

The following summarizes the flaw in the test procedure: 

Section 9.10 allows the person conducting the test to omit the heat-up and cool-down 

tests for condensing furnaces or boilers which have no measurable air flow through the 

model during the off cycle. 

The test procedure has separate sections specifying the AFUE calculation for condensing 

furnaces or boilers that have a single input rate (Section 11.3) and condensing furnaces or 

boilers that modulate the input rate (Section 11.5). 

Only Section 11.3 includes alternative calculations to be used when the option allowed by 

9.10 is selected (i.e., no heat-up and cool-down tests are conducted). In this case, a 

2111 Wilson Boulevard I Suite 500 I Arlington I Virginia I 22201-3001 USA 

PHONE 703 5248800 I FAX 703562 1942 I www.ahrinet.org 
AHRI Letter to DOE Re: AFUE for Two Step and Modulating Residential Boilers 

November 19,2012 

default draft factor of 0.05 is used, and the AFUE is calculated using steady state 

efficiency values. 

Section 9.10 is an option available to all condensing models that qualify. However, there 

are no specific calculations in Section 11.5 to detennine the AFUE for a condensing 

fumace or boiler that modulates the input rate when the option allowed by 9.10 is 

selected (i.e. no heat-up and cool-down tests are conducted). 

In 2001, GAMA developed a Windows TM based AFUE program, which converted the Fortran 

AFUE program developed by the National Institute of Standards and Technology (NIST). At 

that time, we were advised by NIST of an error in its program and were provided with a 

correction for condensing, single input models. Included in the correction was the direction to 

use "0" for the heat-up and cool-down temperatures in the Windows TM AFUE program when the 

option allowed by Section 9.1 0 was selected. 

We have discovered that inserting "0" for heat-up and cool-down temperatures for modulating 

condensing boilers overestimates the AFUE of the model. We are CU1l'ently reviewing the 

listings for all two-stage and modulating condensing boilers in our residential boiler efficiency 

certification program to determine the full extent of this issue. (This may be an issue for 

residential furnaces as well but our present information is that the heat--up and cool--down tests 

are always conducted on condensing furnace models.) 

Recognizing the significance of this matter, we are taking the following actions: 

• Developing appropriate calculations to determine AFUE for two-stage and modulating 

condensing boilers that parallel the corresponding calculation for single input rate, 

condensing boilers when the option of 9.1 0 is selected. 

• Requiring all new model celtifications and AHRI certification tests of all currently listed 

models for this subcategory of boilers to include heat-up and cool-down tests, even if the 

model's AFUE is based on the option allowed by Section 9.10. 

• Requiring the manufacturers of all existing models in this subcategory of boilers that are 

listed in our Directory of Certified Product Performance to do one of the following: (1) 

drop the rating to 90%; (2) discontinue the model; or (3) provide tests results which 

include the heat-up and cool-down tests that support a higher rating. We are 

implementing this immediately. 

By mid-December 2012, we will provide to DOE a suggested AFUE calculation for two-stage 

and modulating condensing boilers when the option of 9.10 is used, and will request its 

expedited review and adoption. We are available to meet with DOE staff to explain the 

derivation of this calculation. Once this altemative calculation is accepted and the manufacturer 

provides new test data using the altemative calculation, the ratings for those models where 

option 1 was selected will be revised, and discontinued models will be restored with revised 

ratings. 

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ARRI Letter to DOE Re: AFUE for Two Step and Modulating Residential Boilers 

November 19, 2012 

We also recommend that DOE immediately notify other manufacturers of modulating 

condensing boilers that are not part of the ARRI certification program (Allied Engineering 

Company Div. ofE·Z·Rect Manufacturing Ltd; Baxi Spa; Conematic Heating Systems Inc.; 

Hamilton Engineering; Navien America Inc.; Quietside; and Quincy Hydronic Technologies) of 

this en'Qf in the DOE test procedure, and require them to take immediate actions to ensure the 

accurate rating of their equipment. 

AHRI is committed to working with DOE to resolve this issue as expeditiously as possible. 

Sincerely, 

Stephen R. Yur 

President and CEO 

Air·Conditioning, Heating, and Refrigeration Institute (ARRI) 

cc: Timothy G. Lynch 

John Cymbalsky 

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Residential High-Efficiency Boiler AFUE Ratings 

Meeting with DOE and AHRI 

November 19, 2012 

DOE Test Procedure (ASH RAE 103) - Equipment Classification 

Section 9.10 applies 

11/19/2012 

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DOE Test Procedure (ASH RAE 103) - Summary of tests 

I> For all equipment 

- Steadv-state efficiencv test 

- Part-load efficiency test 

• Cool-down test Section 9.10 

- Tracer gas test (optional) Required P'LAHRI to apply Section 9.10 

I>- For condensing equipment 

- Condensate collection test at steady-state and during heat-up cooldown tests 

I> For modulating equipment 

- Repeat all applicable tests for maximum fire and minimum fire 

DOE Test Procedure (ASHRAE 103) 

Section 9.10 applies 

11/19/2012 

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NIST AFUE Program and GAMA AFUE Calculator 

,.. Program Developed by NIST 

- A graphical user interface was developed by GAMA 

17 When option 9.10 was selected for condensing equipment 

- Instructed to enter zeroes for heat-up and cool-down tests 

.. Calculated Results: 

- Accurate for condensing/non-modulating equipment 

- Not-accurate for condensing/modulating equipment 

• Causes AFUE to be over stated by 1 to 4 percent 

AHRI Actions - Effective Immediately 

l>- Requiring heat~up and cool-down testing for condensing, modulating 

equipment for qualification and verification testing, even if the model's AFUE 

is based on the option allowed by Section 9.10 . 

.,. Requiring the manufacturers of all existing models In this subcategory of 

boilers listed in AHRi Oirectory of Certified Product Performance to do one of 

the following: 

- Drop the rating to 90%; 

- Discontinue the model; or 

- Provide test results including the heat-up and cool-down tests, which 

support a higher rating. 

P- Developing appropriate calculations to determine AFUE for two-stage and 

modulating condensing boilers that parallel the corresponding calculation for 

single input rate, condensing boilers when the option of 9.10 is selected. 

11/19/2012 

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