GRI-97/0298 

Topical Report 

I Hearth Products Meter Study (1995-1997) 

Prepared by: 

]. Menkedick 

P. Hartford 

S. Collins 

S. Shumaker 

D. Wells 

Battelle 

Gas Research Institute 

Appliances and Water Heating 

September 1997 

GRI-97/0298 

HEARTH PRODUCTS METER STUDY (1995 - 1997) 

TOPICAL REPORT 

Prepared by: 

John Menkedick, Pam Hartford, Shawna Collins, 

Shawn Shumaker, and Darlene Wells 

Battelle 

505 King Avenue 

Columbus, Ohio 43201 

For 

Gas Appliance Technology Center 

Gas Research Institute 

8600 West Bryn Mawr Avenue 

Chicago, Illinois 60631 

Program Team Leader 

Rodney Rinholm 

Appliances and Water Heating 

September 1997 
LEGAL NOTICE 

This report was prepared by Battelle as an account of work sponsored by the Gas 

Research Institute (GR!). Neither GR!, members of GR!, Battelle, officers, trustees, or staff of 

Battelle, nor any person acting on behalf of either: 

a. Makes any warranty or representation, expressed or implied, with respect 

to the accuracy, completeness, or usefulness of the information contained 

in this report, or that the use of any information, apparatus, software, 

method, or process disclosed in this report may not infringe privately 

owned rights; or 

b. Assumes any liability with respect to the use of, or for damages resulting 

from the use of, any information, apparatus, software, method, or process 

disclosed in this report. 

Reference to trade names or specific commercial products, commodities, or services in 

this report does not represent nor constitute an endorsement, recommendation, or favoring by 

GR! or Battelle of the specific commercial product, commodity, or service. 

Topical Report-September, 1997 ii Hearth Products Meter Study 
50272-101 

REPORT DOCUMENTATION 1. REPORT NO. 2. 3. Recipient's Accession No. 

PAGE 

4. Title and Subtitle 5. Report Date 

Hearth Products Meter Study (1995-1997) September 1997 

6. 

7. Author(s) 8. Performing Organization Rept. No. 

Menkedick, J.R., Hartford, P.A., Collins, S.L., Shumaker, S.M., Wells, D.E. 

9. Performing Organization Name and Address 10. Project/Task/Work Unit No. 

Battelle Memorial Institute 

505 King Avenue 11. Contract(C) or Grant(G) No. 

Columbus, Ohio 43201-2693 

(C) 5092-281-2494 

(G) 

12. Sponsoring Organization Name and Address 13. Type of Report & Period Covered 

Gas Research Institute Topical 

8600 West Bryn Mawr Avenue 

Chicago, IL 60631 

14. December 1995 - May 1997 

15. Supplementary Notes 

16. Abstract (Limit 200 words) 

The Hearth Products Meter Study is a multi-year study in which cooperating utilities identify, access, and sub meter 

individual hearth products (and furnaces in most cases) in residences in their service area in order to understand how gas 

hearth products are being used in the field, what factors affect this usage, and the impact on gas load throughout the year 

for different gas hearth products. The report presents data summaries and statistical analysis on final results to predict 

average gas loads and usage patterns as a function of the type of equipment, geographical location, season, household 

type, household demographics, and other parameters deemed important. Statistical models were used to assess the effect 

of multiple factors simultaneously and reduce the possibility of misleading results due to the confounding of effects. The 

results will be used to address a wide range of questions facing utilities including strategic marketing, load forecasting, 

resource planning, and billing estimation. In addition to meeting utilities' needs for load data, the data may also be used to 

ensure that hearth products are treated in a reasonable and fair way by local, state, and federal regulators with regard to 

interests of gas consumers and the gas industry. 

17. Document Analysis 

a. Descriptors 

Gas usage, energy usage, load profiles, hearth products, furnaces, load research 

b. Identifiers, open-ended terms 

Energy, end-use, metering 

c. COSATI Field/Group 

18. Availability Statement 

Availability Unlimited 

(See ANSI-Z39.18) 

Topical Report - September, 1997 

19. Security Class (This Report) 

Unclassified 

20. Security Class (This Page) 

Unclassified 

iii 

21. No. of Pages 

22. Price 

44 

OPTIONAL FORM 272 (4-77) 

(Formerly NTIS-35) 

Department of Commerce 

Hearth Products Meter Study 
This page left intentionally blank 

Topical Report - September, J 997 iv Hearth Products Meter Study 
Title: 

Contractor: 

Principal 

Investigators: 

Report 

Period: 

Objective: 

Technical 

Objective: 

Results: 

RESEARCH SUMMARY 

Hearth Products Meter Study (1995-1997) 

Battelle, 505 King Avenue, Columbus, Ohio 43215 

John Menkedick and Pam Hartford 

Topical Report, Results from December 1995 to May 1997 

To characterize gas usage and factors that influence the usage for a variety of 

gas hearth products in different regions of the United States and Canada. 

Gas hearth products are the fastest growing gas appliance sector with growth 

rates projected to be between 10 and 30 percent per year, depending on the 

type of product. To help the gas industry make strategic decisions concerning 

this tremendous growth, it is necessary to know how gas hearth products are 

being used in the field, what factors affect this usage, and the impact on gas 

load throughout the year for different gas hearth products. Therefore GRI has 

begun the Hearth Products Meter Study, a submetering program for gas hearth 

products coordinated with local distributing companies (LDCs) across the 

U.S. and Canada. The Hearth Products Meter Study is a multi-year study in 

which cooperating utilities identify, access, and submeter individual hearth 

products (and furnaces in most cases) in residences in their service area. 

GRIlBattelle will conduct data summaries and statistical analysis on final 

results to predict average gas loads and usage patterns as a function of the type 

of equipment, geographical location, season, household type, household 

demographics, and any other parameters deemed important. The purpose of 

this topical report is to provide preliminary results based on data available 

through May 31, 1997. 

Demographic, equipment and other questionnaire information collected from 

participating households is summarized in the report. Average heating season. 

hearth product usage ranged from 105 CCF for 34 fireplaces to 171 CCF for 6 

fireplace inserts. Decorative gas logs, with the largest number of samples in 

the study, had an average of 120 CCF for the heating season. Estimated 

hourly pilot usage ranged from 0.35 CF to 2.83 CF. The hearth product load 

profile is flatter than the furnace, but preliminary assessment suggests that 

hearth product usage does increase during peak periods of extremely cold 

weather. The amount of usage, pattern of usage, correlation with degree days, 

and interaction with the furnace all varied significantly across different 

customers. Factors most significantly related to hearth product usage include 

degree day measures, presence of a pilot light, hearth product type, and type of 

Topical Report - September. 1997 v Hearth Products Meter Study 
Technical 

Approach: 

Project 

Implications: 

day. On average, based on the data analyzed to date, 67% of the hearth 

product usage can be characterized as incremental load for the household. 

Data analysis began with validation of the data and handling of missing 

values. This was followed by descriptive statistics and summaries. Statistical 

models were used to assess the effect of multiple factors simultaneously and 

reduce the possibility of misleading results due to the confounding of effects. 

The relationship between hearth product usage and the possible predictors was 

assumed to be linear and have the following form: 

Hearth Product Usage = Po + pj*Predictorj + error, 

where i = 1 to the number of predictors and error is random noise assumed to 

be normally distributed, with mean zero and variance 0 2 independent of the 

predictors. A few variables were considered of primary interest and were 

included in all models, regardless of the usage period (heating season, season, 

month, or day). These included degree day measures, hearth product type, and 

the presence of a pilot light. The steps in the variable selection/reduction 

process for other candidate variables included an assessment of statistical 

correlations, combination of variables, stepwise regression, R2 analysis, and 

professional judgement. A similar modeling approach was used to assess the 

impact of hearth product usage on furnace usage in the winter months. 

The results will be used to address a wide range of questions facing utilities 

including strategic marketing, load forecasting, resource planning, and billing 

estimation. In addition to meeting utilities' needs for load data, the data may 

also be used to ensure that hearth products are treated in a reasonable and fair 

way by local, state, and federal regulators with regard to interests of gas 

consumers and the gas industry. 

GRI Project Manager 

Rodney Rinholm 

Program Team Leader 

Appliances and Water Heating 

Topical Report- September, 1997 vi Hearth Products Meter Study 
TABLE OF CONTENTS 

~ 

EXECUTIVE SUMMARY ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. x 

INTRODUCTION ............................................................. 1 

SECTION 1 STUDY OBJECTNES, DESIGN, AND CURRENT STATUS .............. 2 

1.1 OBJECTIVES ................................................ 2 

1.2 STUDY DESIGN AND CURRENT STATUS ....................... 3 

SECTION 2 DATA BASE DESCRIPTION ....................................... 7 

2.1 WEATHER DATA ............................................ 7 

2.2 DEMOGRAPHIC AND EQUIPMENT INFORMATION .............. 7 

2.3 GAS USAGE DATA .......................................... 7 

SECTION 3 STATISTICAL ANALYSIS ISSUES, DEFINITIONS, AND APPROACH .... 9 

3.1 DATA ISSUES ............................................... 9 

3.2 MISSING DATA ............................................ 10 

3.3 APPROACH TO DATA ANALYSIS ............................ 12 

3.4 BOXPLOTS ................................................ 12 

3.5 HISTOGRAMS ............................................. 13 

3.6 DEFINITION OF SEASONS ................................... 14 

3.7 SIGNIFICANT DIGITS ....................................... 14 

SECTION 4 DESCRIPTIVE STATISTICS AND SUMMARIES ...................... 15 

4.1 QUESTIONNAIRE SUMMARIES .............................. 15 

4.2 HEARTH PRODUCT AND FURNACE GAS USAGE SUMMARIES .. 22 

4.2.1 Heating Season Gas Usage ................................ 22 

4.2.2 Monthly Gas Usage ...................................... 24 

4.2.3 Daily Gas Usage ......................................... 26 

4.2.4 Hourly Gas Usage ....................................... 26 

4.2.5 Pilot Usage ............................................. 29 

4.3 PEAK DAY AND PEAK HOUR USAGE ......................... 30 

SECTION 5 CHARACTERIZATION OF SUBSETS OF CUSTOMERS ............... 35 

SECTION 6 RESULTS - FACTORS RELATED TO HEARTH PRODUCT USAGE ..... 38 

6.1 DESCRIPTION OF AVAILABLE DATA ........................ 38 

6.2 STATISTICAL METHODOLOGY .............................. 39 

6.3 MODELING ANALYSIS RESULTS ............................ 39 

SECTION 7 MODELS TO ASSESS THE HEARTH PRODUCT-FURNACE 

INTERACTION .................................................. 40 

7.1 RESULTS OF MODELING THE INTERACTION .................. 41 

Topical Report - September, 1997 vii Hearth Products Meter Study 
Table 1.1 

Table 4.1 

Table 4.2 

Figure ES.l 

Figure ES.2 

Figure ES.3 

Figure 1.1 

Figure 3.1 

Figure 3.2 

Figure 4.1 

Figure 4.2 

Figure 4.3 

Figure 4.4 

Figure 4.5 

Figure 4.6 

Figure 4.7 

Figure 4.8 

Figure 4.9 

Figure 4.10 

Figure 4.11 

Figure 4.12 

TABLE OF CONTENTS 

(Continued) 

7.2 FACTORS RELATED TO THE INTERACTION BETWEEN 

HEARTH PRODUCT AND FURNACE .......................... 44 

LIST OF TABLES 

Number of Hearth Products Metered Through May 31, 1997. . ................ 6 

Summary of Selected Household and Demographic Characteristics. ........... 17 

Summary of Selected Household and Furnace Equipment Characteristics, 

by Hearth Product. .................................................. 20 

LIST OF FIGURES 

Average Gas Usage (CCF) for the Heating Season (September- May), 

by Hearth Product Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi 

Average Daily Hearth Product and Furnace Gas Usage as a Percent of the 

Maximum Daily Usage ............................................. xii 

Estimated Daily Hearth Product Gas Usage (CCF) for Each Season .......... xiv 

DOE Heating Regions ............................................... 5 

Diagram of a Box Plot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

Diagram of a Histogram ............................................. 13 

Summary of Selected Demographic Characteristics. . ...................... 16 

Distribution of the Age of the Hearth Product, by Type of Hearth Product. ..... 17 

Percentage of Hearth Products Reported to Have a Pilot, by Type of Hearth 

Product. .......................................................... 18 

Type of Temperature Control, Overall and for Each Type of Hearth Product. ... 19 

Reason for Purchasing the Hearth Product (N=80) ......................... 21 

Primary Reason Hearth Product is Typically Used (N=79). . ................ 21 

Heating Season (September, 1996 - May, 1997) Hearth Product Gas Usage, 

by Type of Hearth Product - Histogram. . .............................. 23 

Heating Season (September, 1996 - May, 1997) Hearth Product Gas Usage, 

by Type of Hearth Product - Box Plot. ................................ 24 

Average Monthly Hearth Product Gas Usage, Overall and by Type of Hearth 

Product ............................. '" .......................... 25 

Average Daily Hearth Product and Furnace Gas Usage as a Percent of the 

Maximum Daily Usage by Type of Hearth Product. ....................... 27 

Furnace, Hearth Product, and Total Furnace and Hearth Product Average 

Hourly Gas Usage by Type of Hearth Product for January, 1997 .............. 28 

Distribution of the Estimated Hearth Product Hourly Pilot Gas Usage by 

Type of Hearth Product - Histogram. . ................................ 29 

Topical Report - September, 1997 viii Hearth Products Meter Study 
Figure 4.13 

Figure 4.14 

Figure 4.15 

Figure 4.16 

Figure 5.1 

Figure 5.2 

Figure 5.3 

Figure 5.4 

Figure 7.1 

Figure 7.2 

Figure 7.3 

Figure 7.4 

TABLE OF CONTENTS 

(Continued) 

Distribution of the Estimated Hearth Product Hourly Pilot Gas Usage by 

Type of Hearth Product - Box Plot. .................................. 30 

Ratio of the Peak Weather Day Gas Usage to the Average Daily Gas Usage 

During the Heating Season for the Gas Furnace and Each Hearth Product 

Type ............................................................ 32 

Ratio of the Gas Usage of the Five Coldest Days to the Gas Usage on the 

Top Forty-Five Coldest Days for the Gas Furnace and Each Hearth Product. .... 33 

Comparison of the Average Hourly Furnace and Hearth Product Peak Day 

Gas Usage to the Average Hourly Furnace and Hearth Product Gas Usage 

during January, 1997, by Type of Hearth Product. ......................... 34 

Example of a Customer With Very Heavy Hearth Product Usage that May 

Serve as a Supplemental Heat Source ................................... 35 

Example of a Customer with Moderate Hearth Product Usage Significantly 

Related to Weather ................................................. 36 

Example of a Customer With Regular Hearth Product Usage Independent of 

Weather. . ....................................................... 36 

Example of a Customer With Only Sporadic Hearth Product Usage. . ......... 37 

Usage Data from a Household with Significant Interaction Between Hearth 

Product Gas Usage and Furnace Gas Usage .............................. 42 

Furnace Usage Adjusted for Weather Plotted Against Hearth Product Usage 

Adjusted for Weather for a Household With Significant Interaction ........... 42 

Usage Data from a Household with Little Interaction Between Hearth 

Product Gas Usage and Furnace Gas Usage .............................. 43 

Furnace Usage Adjusted for Weather Plotted Against Hearth Product 

Usage Adjusted for Weather for a Household with Little Interaction ........... 43 

Topical Report - September, 1997 ix Hearth Products Meter Study 
EXECUTIVE SUMMARY 

To help the gas industry develop strategic plans for managing growth, Gas Research 

Institute (GRI) is conducting a multi-year sub-metering study to evaluate gas hearth product use. 

The study is being conducted for GRI by Battelle and cooperating local distribution companies 

(LDC's) throughout the United States and Canada. The overall aim of the study is to 

characterize gas use and the factors affecting that use for a variety of gas hearth products. 

The results will be used to address a wide range of questions facing utilities including 

load forecasting, resource planning, and strategic marketing. In addition, the results will be used 

to ensure that local, state, and federal regulations meet the interests of consumers and the gas 

industry. 

As of May 1997, 118 households from eight LDCs were collecting usage data hourly. 

Usage data is being collected on gas fireplaces, decorative gas logs, vent-free gas logs, fireplace 

inserts, and gas stoves. Geographically, most of the participants are located in DOE heating 

zones IV and V, representing average heating load hours between 2,000 and 3,000 hours. 

It must be emphasized that results in this report are based on only a subset of the data 

already collected. The study has been extended for a third year to run through the 1997-1998 

heating season and additional utilities are expected to join the study for the upcoming heating 

season. As data that were not available for this report is added and the additional data is 

collected during the 1997-1998 heating season, results may change somewhat and comparisons 

and conclusions may become more clear. 

Although the data contains a wealth of information to address study objectives, there are 

three primary cautions that should be kept in mind when interpreting and drawing conclusions 

from the data: 

1. Households entered the study at different times. Therefore different time periods 

contain differing numbers of available households, as well as different households. 

Because of this, some analyses were limited to only those households with data for 

the entire time period of interest (for example, for an entire heating season). 

2. Sample sizes are unequal and in some cases small. For example, while for this 

report there were data available for 49 decorative gas logs, there were only data for 

seven fireplace inserts, and four gas stoves. Therefore sample size should always be 

taken into account when assessing the strength of conclusions that can be drawn 

from the data. 

3. Nineteen households had two hearth products monitored in the home. Unless 

otherwise noted, the summaries presented include the total usage by the two hearth 

products. These homes were not included in the modeling analyses for this report. It 

is anticipated that they will be included in analyses in the final report. 

Topical Report - September, 1997 x Hearth Products Meter Study 
For households included in this report, the majority of homes are two-story or ranch 

suburban homes, 17 years old on average, and averaging 2,378 square feet and 7 rooms. The 

average age of the adults in the home is 43 years, with an average of 1 child per home. Eightytwo percent of the households had an annual income greater than $50,000. 

The majority of the hearth products were less than 5 years old. Twenty percent of the 

decorative logs had pilot lights while more than 50% of the other hearth products types were 

reported to have a pilot. Only six percent of the hearth products were thermostatically controlled 

with the remainder controlled by either an On and Off, or a Low-Medium-High temperature 

control. The most frequent reason for purchasing the hearth product was "Appearance." "Looks 

and Heat" are cited as the primary reason for using the hearth product. 

As illustrated in Figure ES.l, the average heating season hearth product usage for the data 

summarized in this report ranged from 105 CCF for the 34 flreplaces to 171 CCF for the 6 

flreplace inserts. Decorative gas logs, with the largest number of samples in the study, had an 

average of 120 CCF for the heating season. Individual household hearth product heating season 

usage ranged from 0 CCF to 824 CCF with 75% of the population using less than 300 CCF for 

the heating season. Load proflles indicate that overall and within each type of hearth product, the 

hearth product usage is less related to weather than the gas furnace usage with a resulting flatter 

load proflle as illustrated in Figure ES.2. 

180 

G:"160 

0 

0 

-Q) 140 

C) 

ns 

en 

::J 120 

en 

ns 

C) 

g 100 I---

en 

ns 

Q) 80 en -

C) 

c 

:t:J 60 ns - Q) 

l: 

Q) 40 C) -

l! 

Q) 

~ 20 -

0 

Decoratiw Gas Log (0=38) Fireplace (0=34) Fireplace nsert (0= 6) Gas Stow (0= 3) 

Figure ES.l Average Gas Usage (CCF) for the Heating Season (SeptemberMay), by Hearth Product Type. 

Topical Report-September, 1997 xi Hearth Products Meter Study 
Overall 

---------------------r============~ ~ 

1

- Furnace 

e---e---e Hearth Product 

~ 

20 

o 

~~~~~~~~~~~ 09101196 10101196 11101196 12101196 01101197 02101197 03101197 04101197 05101197 06101197 

Date 

8 

Figure ES.2 Average Daily Hearth Product and Furnace Gas Usage as a Percent of 

the Maximum Daily Usage. 

Although the hearth product load profile may be flatter than the furnace, preliminary 

assessment suggests that hearth product usage does increase during peak periods of extremely 

cold weather. On average, hearth product usage is highest from 6:00 p.m. to 11 :00 p.m., and 

higher on weekends, holidays, and peak days. The hearth products' evening peaks add to the 

evening heating load, but do not change the peak hour within a day, though on extremely cold 

days there is an indication the hearth product usage could shift the daily heating load peak from 

the mornings to the evening hours. The estimated hourly pilot usage ranged from 0.35 CF to 

2.83 CF. 

Initial examination of plots of hearth product usage for different customers indicated 

widely varying patterns of usage. The amount of usage, pattern of usage, correlation with degree 

days, and interaction with the furnace all varied significantly across different customers. Subsets 

of customers were identified according to three different usage characteristics: total hearth 

product usage, usage in the shoulder season, and net increase in total household heating load in 

the winter. Classification of customers into a HIGH group for each of the three usage 

characteristics (based on being in the top 20% of usage for the particular characteristic) revealed 

strong correlation between the users in the HIGH group for each usage characteristic, indicating 

that those users who have the highest total hearth product usage also often use the hearth product 

heavily in the shoulder seasons and are also estimated to generate the greatest net increase in total 

household heating load in the winter. 

Topical Report - September. 1997 xii Hearth Products Meter Study 
Statistical modeling analyses indicated that the factors most significantly related to hearth 

product usage include: 

• Degree day measures 

• Presence of a pilot light 

• Hearth product type 

• Type of day 

- weekend or weekday 

- holiday 

- peak day. 

A modeling approach was used to assess the impact of hearth product usage on furnace 

usage in the winter months. The following linear regression model was used: 

Daily Furnace Usage = Po + PI x Daily Degree Days + P2 X Daily Hearth Product Usage 

In this model, the parameter P2 (the slope parameter for Daily Hearth Product Usage) represents 

the decrease or increase in furnace usage (in CCFs) for each CCF of hearth product usage, after 

adjusting both variables for the effect of weather. The average estimated slope for the 72 

households included in the analysis was -0.33, representing a decrease of 0.33 CCF in furnace 

usage for every CCF of hearth product usage. Thus, on average, based on the data analyzed to 

date, 67% of the hearth product usage can be characterized as incremental load for the household. 

Over 70% of the slope estimates were negative indicating that most homes did decrease furnace 

usage as a result of hearth product usage. It is important to note that results based on the current 

data included in this report are heavily influenced by homes with decorative gas logs and 

fireplaces which represent the majority of homes summarized in this report. 

Figure ES-3 presents a characterization of the average daily load throughout the year for a 

service area with the following characteristics: 

• weather that averages, per day, 13 degree days in the shoulder seasons (September, 

October, November, March, April, May), 27 degree days in winter (December, 

January, February), and 49 degree days on the top 5 peak weather days; 

• a distribution of hearth products that includes 46% decorative logs, 44% fireplaces, 

7% fireplace inserts, and 4% gas stoves; and 

• a distribution of hearth products in which 49% of the products had standing pilots. 

Figure ES.3 was estimated using statistical models which related hearth product usage to degree 

day measures, hearth product type, presence of a pilot light, and type of day. In the figure, the 

height of the block for each seasonal period (summer, shoulder, winter, and peak) corresponds to 

the estimated average daily hearth product usage in that period. The height of the shaded portion 

of the block corresponds to the estimated average net increase in total household heating load 

resulting from use of the hearth product (estimated at 67% of average hearth product usage as 

discussed in Section 7.1). 

Topical Report - September, 1997 xiii Hearth Products Meter Study 
u::-

U 

~ 

i 

:::> 

gj 

(!) 

1:) 

::I 

£ 

~ CD 

::J: 

~ 0 

CD 

~ 

! 

1.35 

1.20 

tc15 

0.90 

0.75 

0.60 

0.45 

0.30 

0.15 

Net Increase in Total 

Household Heating Load 

Summer Shoulder 

Days of Use 

Winter 

Figure ES.3 Estimated Daily Hearth Product Gas Usage (CCF) for Each Season. 

Topical Report - September, J 997 xiv Hearth Products Meter Study 
INTRODUCTION 

Gas hearth products are the fastest growing gas appliance sector with growth rates 

projected to be between 10 and 30 percent per year, depending on the type of product. To help 

the gas industry make strategic decisions concerning this tremendous growth, it is necessary to 

know how gas hearth products are being used in the field, what factors affect this usage, and the 

impact on gas load throughout the year for different gas hearth products. Therefore GR! has 

begun the Hearth Products Meter Study, a submetering program for gas hearth products 

coordinated with local distributing companies (LDCs) across the U.S. and Canada. 

The Hearth Products Meter Study is a multi-year study in which cooperating utilities 

identify, access, and submeter individual hearth products (and furnaces in most cases) in 

residences in their service area. GRIlBattelle has designed the study and questionnaires, 

coordinated the activities of all utilities, assisted in gathering the raw data once meters have been 

installed, and performed data reduction analyses within and across service areas. GRIlBattelle 

will conduct data summaries and statistical analysis on final results to predict average gas loads 

and usage patterns as a function of the type of equipment, geographical location, season, 

household type, household demographics, and any other parameters deemed important. 

The purpose of this report is to provide preliminary results based on data available 

through May 31, 1997. 

It must be emphasized that results in this report are based on only a subset of the data 

already collected. The study has been extended for a third year to run through the 1997-1998 

heating season and additional utilities are expected to join the study for the upcoming heating 

season. As data that were not available for this report is added and the additional data is 

collected during the 1997-1998 heating season, results may change somewhat and comparisons 

and conclusions may become more clear. 

Topical Report-September, 1997 1 Hearth Products Meter Study 
SECTION 1 

STUDY OBJECTIVES, DESIGN, AND CURRENT STATUS 

1.1 OBJECTIVES 

The overall objective of the Hearth Products Meter Study is to characterize gas usage and 

factors that influence the usage for a variety of gas hearth products in different regions of the 

United States and Canada. In particular the study has the following specific study objectives: 

OBJECTIVE 1. Estimate annual, monthly, and daily gas usage for different hearth product 

types as it is related to geographic regions, housing types, and other 

explanatory factors. 

OBJECTIVE 2. Identify factors that affect hearth products' gas usage. Construct and 

evaluate statistical models to predict gas usage based on significant 

explanatory factors. These factors may include: 

• weather information such as hourly temperatures, degree days, or 

effective degree days; 

• equipment characteristics such as manufacturer, input btu and 

efficiency rating, type of heat recovery, ignition system and controls, 

thermostat, and vent system; 

• building characteristics such as housing type (multi-family versus 

single family), house size, construction, and age, whether the equipment 

replaces an existing fireplace or is a new installation, and the location 

within the house of the hearth product, as well as the equipment mix of 

gas and electric appliances in the house; 

• demographic information such as age, income, number of residents, 

and lifestyle characteristics. 

OBJECTIVE 3. Characterize the pattern of usage for different gas hearth products. 

Patterns of interest include annual, seasonal, daily, and hourly profiles. 

OBJECTIVE 4. Estimate the effect of hearth product types that serve as a supplemental 

heat source on total household gas usage. In particular, estimate the effect 

of fireplaces, gas stoves, and gas logs on gas furnace, boiler usage, or electric 

heat pump usage. 

OBJECTIVE 5. Characterize the effect of regional differences on gas usage. This includes 

the difference between northern and southern utilities as well as other 

detectable regional differences. 

Topical Report - September, 1997 2 Hearth Products Meter Study 
OBJECTNE 6. Collect data to help characterize usage in units of time (minutes or hours) 

as well as units of gas (BTUs or therms). 

Objectives 1-4 address load forecasting, supply planning and demand side management 

needs. Objectives 2-4 provide information useful for customer service and billing estimation. 

Objectives 3 and 4 provide information that can be used to address the appropriate DOE product 

classification for different hearth product types. Objectives 2,5, and 6 address the need for 

transferability of data between utilities. Finally, all objectives will result in data useful to utilities 

for strategic marketing needs. 

In addition to meeting utilities' needs for load data, the data may also be used to ensure 

that hearth products are treated in a reasonable and fair way by local, state, and federal regulators 

with regard to interests of gas consumers and the gas industry. Participating utilities will have 

access to all of these analyses. Product manufacturers, and ultimately consumers, are also 

expected to benefit from design improvements that are a result of improved information on 

product usage frequency and duration. 

1.2 STUDY DESIGN AND CURRENT STATUS 

The primary intent of the study was to collect sufficient information to characterize the 

relationship between hearth products gas usage and the major factors that affect that usage. 

Therefore, the study was designed to meet data requirements necessary to construct valid 

statistical models that may be used to predict future gas usage. The study did not attempt to 

achieve a probability-based random sampling of hearth products across the United States because 

of 1) the difficulty in identifying the population of households with hearth products, and 2) cost 

constraints associated with the study. However, construction and evaluation of models under a 

wide variety of conditions (weather, region, equipment, housing and occupant characteristics) 

will allow the models to be used, along with population characteristics, to reasonably predict 

usage for any given locality. 

Key factors that were expected to affect gas usage or patterns of usage were included as 

stratification factors in the original study design. These included: 

• Type of hearth product, classified according to the following categories: 

• decorative gas logs, 

• vent-free gas logs, 

• fireplaces, 

• fireplace inserts, and 

• gas stoves. 

• DOE heating region (See Figure 1.1) 

• Age of the hearth product, i.e., whether it is a new appliance (~ 1 year old) or has 

been used for several years (> 1 year old) 

• Type of housing: single family or multi-family housing 

• Location of the hearth product within the house: living/family room or bedroom 

Topical Report - September. 1997 3 Hearth Products Meter Study 
Unfortunately, recruitment difficulties encountered by participating utilities prevented the 

study from meeting original design targets for sample size in all stratification levels. Table 1.1 

below summarizes current information on the number of hearth products metered, through 

May 31, 1997, in the various strata. Additional meters will be installed by LDCs joining the 

study for the 1997-1998 heating season. 

As of May 31, 1997, 118 households from eight LDCs are collecting usage data hourly. 

The current cooperating LDCs are located in British Columbia, Canada; Kentucky; Ontario, 

Canada; Indiana; Utah; New York; Wisconsin; and California. 

Decorative gas logs and fireplaces are the predominant hearth products being monitored. 

In addition, usage data is being collected on fireplace inserts, vent-free gas logs, and gas stoves. 

Geographically, most of the participants are located in DOE heating zones IV and V, 

representing average heating load hours between 2,000 and 3,000. 

Currently, one additional LDC is scheduled to begin collecting usage data during the 

1997-1998 heating seasons. More LDCs from the southeast and southwest as well as LDCs that 

have 

• Households with vent-free fireplaces, 

• Hearth products in multi-family housing, and 

• Hearth products in homes with electric heating 

are actively being recruited to participate in the study during the 1997-1998 heating seasons. 

Topical Report - September, 1997 4 Hearth Products Meter Study 
~ 'G 

2" 

-

~ 

~ 

3000 2500 

0 

::!.. 

I 

~ ~ 

~ 

::i 

"" ~ 

:c 

"'-

'0 

'0 

~ 

VI 

Figure 1.1 DOE Heating Regions 
Table 1.1 Number of Hearth Products Metered Through May 31,1997. 

New 7 0 1 0 Ow 

North (DOE Heating Established 16 0 2 1 0 Region IV or above) Owner 

Unknown 0 0 2 

New 1 0 0 2 Owner 

South (DOE Heating Established 12 0 0 1 

Region III or below) Owner 0 

Unknown 3 0 0 0 Age 

• Other locations include the kitchen or unknown locations. 

Topical Report - September, 1997 6 Hearth Products Meter Study 
SECTION 2 

DATA BASE DESCRIPTION 

The data base consists of daily degree day readings, hourly gas usage (CF) for the hearth 

product and furnace for each participant, and demographic and equipment data collected from 

each participant. 

2.1 WEATHER DATA 

Daily degree day readings were collected on a regular basis from the participating 

utilities. The readings were transferred to Battelle either in electronic format or as hard-copy. 

All weather data were entered into Statistical Analysis Software (SASIII) data sets and validated, 

with discrepancies resolved through communication with participating LDCs. 

2.2 DEMOGRAPHIC AND EQUIPMENT INFORMATION 

The demographic and equipment information were collected and transferred to Battelle 

upon installation of the metering equipment. The information was double entered into Paradox 

data sets. In this manner, any data entry discrepancies were resolved immediately. The data was 

then downloaded into SAS® data sets for validation. The validation identified missing data and 

invalid responses. Any problems found in the demographic and equipment information were 

communicated to the utilities so that a resolution could be made. The final demographic and 

equipment analysis data are maintained in SAS data sets. 

2.3 GAS USAGE DATA 

Two systems are being used to collect hourly gas usage readings from the hearth product 

and the furnace. The first is a Metretek system located at Battelle for which Battelle performs all 

data collection activities. The second is a Metscan system located at certain utilities that have 

their own system and who conduct data collection in-house and transfer the data to Battelle on a 

regular basis. 

Each system collects hourly gas readings and downloads the data to their respective 

central data collection computers daily. This data is downloaded to ASCII files and read into 

SAS data sets for validation. Any problems are communicated with the utility and resolved as 

soon as possible. 

·SASe is a software package used for data management and statistical analysis. 

Topical Report - September, 1997 7 Hearth Products Meter Study 
The Metretek system allows a five day window on the collection of the hourly data. Thus 

if a communications problem arises, there is usually enough time to resolve the problem before 

the data is lost. Very little data has been lost due to communication problems. 

Once the data has been validated, hourly and daily SAS data sets are created for analysis. 

Extensive procedures for backups, archiving, and data security have been put in place and 

documented. Strategies for handling missing data, adjusting for daylight savings time, and 

creating efficient summary data files were developed. 

Topical Report-September, 1997 8 Hearth Products Meter Study 
SECTION 3 

STATISTICAL ANALYSIS ISSUES, 

DEFINITIONS, AND APPROACH 

As discussed in Section 1, the primary intent of this study was to characterize hearth 

product gas usage, the major factors related to that usage, and its effect on total household load. 

Data summaries and statistical analyses for the large amount of data collected in this study were 

chosen in light of these objectives. 

Below is a discussion of the issues related to the data collection, handling of missing data, 

approaches to analyzing the data, and definitions of particular terms and diagrams used 

throughout this report. 

3.1 DATA ISSUES 

Hearth product usage data collection dates summarized in this report ranged from 

November 1995 through May, 1997. Data from households from the eight different LDCs were 

included in the analyses. 

Although the data contains a wealth of information to address study objectives, there are 

three primary cautions that should be kept in mind when interpreting and drawing conclusions 

from the data: 

1. Households entered the study at different times. Therefore different time periods 

contain differing numbers of available households, as well as different households. 

Because of this, some analyses are limited to only those households with data for the 

entire time period of interest (for example, for an entire heating season). However, 

some descriptive summaries include all available data and the increasing number of 

households over time may have an effect on trends observed in these summaries. 

2. Sample sizes are unequal and in some cases small. For example, while there were 

data for 49 decorative gas logs available for this report, there were only data for 

seven fireplace inserts, six vent-free gas logs and four gas stoves. Therefore sample 

size should always be taken into account when assessing the strength of conclusions 

that can be drawn from the data. 

3. Nineteen households had two hearth products monitored in the home. Unless 

otherwise noted, the summaries presented include the total usage by the two hearth 

products. These homes were not included in the modeling analyses for this report. It 

is anticipated that they will be included in analyses in the final report. 

Topical Report - September, 1997 9 Hearth Products Meter Study 
There was one household with extremely high hearth product usage that was determined 

to be a very influential observation and a potential outlier. Since the usage data for this 

household appear valid and accurate, the household was included in all descriptive statistics and 

summaries. However, the household was excluded from some final modeling results because of 

its very uncharacteristic usage and its pronounced effect on model parameter estimates. 

Exclusion of the household is documented throughout the report. 

3.2 MISSING DATA 

Although the data collection equipment was designed to minimize the amount of missing 

data, problems occurred that could not be anticipated (for example, battery failures) and resulted 

in missing data for several homes. In general, the approach to missing values was to use all the 

data whenever possible, while being careful to insure that missing values did not lead to 

inaccurate summary information, or bias estimates such as heating season averages by weighting 

one month or day more heavily than another. Because of the nature of the data, different 

strategies were employed for addressing missing daily hearth product usage as opposed to the 

furnace usage. For the hourly data, the approach for replacing missing hourly usage was the 

same for both the hearth product and furnace. 

In particular, the following strategy was adopted for the furnace and hearth product hourly 

usage data: 

• On days when six or fewer hours of usage data were missing, the missing readings 

were replaced by the average hourly gas usage seen in the hour immediately prior to 

and the hour immediate following the period of missing usage. If more than six 

hours in a day had missing usage no replacement was made and the usage data 

remained missing. 

For the daily usage the following strategy was adopted: 

• Addressing missing usage on a daily level was performed in a two step process. 

First, the hourly data was summed over a 24 hour period from midnight to midnight 

forming a daily total usage. If more than six hours of usage were missing in a day, 

then usage for that day was set to missing. The second step was to consider the 

number of days of missing usage. If there were eight or fewer days with missing 

usage in a month, a daily usage was estimated to replace the missing days. If more 

than eight days in a given month were missing, the daily usage was not estimated and 

remained missing. 

For both the hearth product and the furnace the daily usage estimation process began 

by using a period of 28 days. Ideally, daily meter readings 14 days immediately prior 

to and 14 days immediately following the period of consecutive missing days of 

usage were used to estimate a daily usage. If daily meter readings surrounding the 

period of missing usage were not available then either the daily meter readings from 

Topical Report - September, 1997 10 Hearth Products Meter Study 
the 28 days prior to or the 28 days immediately following the period of missing 

usage were used to estimate a daily usage. 

Since hearth products are not necessarily used every day, the number of days on 

which the hearth product would have been turned on during the missing period was 

estimated. Using the 28 days of usage data discussed above, the probability of 

turning on the hearth product was calculated by counting the number of days the 

hearth product was used and dividing by 28. This "probability" was then multiplied 

by the number of days with missing meter readings and rounded to the nearest whole 

number. This number was always at least one. 

Using the average hearth product usage calculated for the 28 days and the probability 

of the hearth product being turned on, between 1 and 8 days of missing hearth 

product usage was replaced by the estimated usage. The remaining missing daily 

usage was replaced by the estimated pilot usage or zero depending on whether or not 

pilot usage were estimated for the appliance. The estimation of pilot usage is 

discussed in Section 4. 

The method for handling the missing daily furnace usages involved a linear 

regression modeling of the relationship between the daily furnace gas usage and daily 

degree day readings for the 28 days described above. Using the reported degree day 

readings on the days with missing gas usage, the missing usage was replaced by the 

predicted daily furnace gas usage. 

There were ten homes for which data collection problems caused missing data for both 

the hearth product and furnace during much of the 1996-1997 heating season. The problems 

have subsequently been resolved and a full heating season of data should be collected during 

1997-1998. As shown in Table 1.1 there are currently six vent-free gas logs in the study. 

Unfortunately, five of the vent-free gas logs were affected by this data collection problem. Since 

a full heating season of data is only available for one of the vent-free gas logs, the vent-free gas 

logs will not be included in any of the usage summaries or analyses in this report. 

It is also important to note that the sample size available for any particular analysis or 

data summary will vary according to the analysis. For example, while there were 118 households 

on line as of May 31,1997, there were only 81 households with usage data for a complete 

heating season (September-May) due to the staggered start dates and some of the missing data 

problems described above. Similarly, only 72 households met the criteria for modeling the 

interaction between the hearth product and furnace. Due to non-responses, the sample sizes for 

the questionnaire data also vary. For instance, only 66 households provided information on 

annual income. Sample sizes are discussed and listed for the separate analyses and presentations 

throughout the report. 

Topical Report - September, 1997 11 Hearth Products Meter Study 
3.3 APPROACH TO DATA ANALYSIS 

Data analysis began with validation of the data and handling of missing values as 

discussed in Section 2. This was followed by descriptive statistics and summaries which are 

presented in Section 4. However, this type of observational study where a tremendous amount of 

data is collected on many variables leads to unbalanced demographic data (unequal frequencies 

in the different classes and subclasses of variables) and to the confounding of the effect of 

secondary variables when attempting to assess the effect of any given primary variable on gas 

usage. 

For example, simple average monthly hearth product usage for fireplaces with and 

without a thermostat can be calculated. However, while simple averages might show 

(hypothetically) that fireplaces without a thermostat use significantly more gas than those with a 

thermostat, this result might be due to the fact that more fireplaces without a thermostat had pilot 

lights. This hypothetical example illustrates the danger of confounding of effects. 

Statistical models were used to assess the effect of multiple factors simultaneously and 

reduce the possibility of misleading results due to the confounding of effects. All statistical 

models were implemented using Version 6.12 of the SAS® System. 

3.4 BOX PLOTS 

In many cases it is helpful to characterize not just a single statistic (such as the average) 

of a continuous variable, but rather the entire distribution. A common way that this is done in 

this report is through presentation of a box plot. Figure 3-1 illustrates a box plot. 

Maximum 

75th Percentile 

Mean 

50th Percentile (Median) 

25th Percentile 

Minimum 

Figure 3.1 Diagram of a Box Plot. 

Topical Report-September, 1997 12 Hearth Products Meter Study 
To understand how the box plot is read, assume that it represents the distribution of 

annual hearth product usage across all households. The lowest and highest annual usage are 

represented by MINIMUM and MAXIMUM. The 25TH PERCENTILE represents the annual 

usage where 25% of the annual usages are lower and 75% are higher, the 50TH PERCENTILE, 

also called the MEDIAN, represents the annual usage where 50% of the usages are lower and 

50% are higher, and the 75TH PERCENTILE is the annual usage where 75% of the usages are 

lower and only 25% are higher. The length of the box represents the data's interquartile range, or 

the difference between the 25th and 75th percentiles, which is an indicator of data variability. 

The MEAN, represented by the triangle, is the average over all the annual usages. 

3.5 HISTOGRAMS 

Similar to the box plot, a histogram also characterizes the distribution of a continuous 

variable. Figure 3.2 illustrates a histogram. 

To understand how the histogram is read, assume that, similar to the box plot description, 

the histogram in Figure 3.2 represents the distribution of annual hearth product usage across all 

households. 

100 

90 

80 

70 

Ii 60 

'0 

I- 50 '0 

~ 40 0 

30 

20 

10 

0 

~ 

.... 

'" 

~ 

'" .... 

" ~ 

Heating Season Usage (CCF) 

Figure 3.2 Diagram of a Histogram. 

Topical Report - September, 1997 13 Hearth Products Meter Study 
The histogram discretizes continuous data in the following manner. The x-axis represents 

the "bins" in which the heating season usage is categorized. All homes that had less than 100 

CCF of hearth product usage are categorized as "0 - < 100" CCF of heating season usage. All 

homes with 100 to less than 200 CCF of heating season gas usage are categorized into the second 

bin, "100 - < 200". This continues on until all the homes have been put into a bin. The total 

number of homes for which heating season usage is available is determined. Then, for each bin 

the number of homes in the bin are divided by the total number of homes to calculate the percent 

of the total number of homes in the bin. For example, assume there are 50 homes for which 

heating season usage is available and 15 homes with usage in the range of 0 to 99 CCF. The bin, 

"0 - < 100", would have a percent of total (15/50) • 100 = 30 %. 

In the above histogram, 30% of the homes have heating season usage in the range of 0 to 

99 CCF, 40% with usage of 100 CCF to 199 CCF, 20% with usage of200 CCF to 299 CCF, and 

10 % with 500 CCF to 599 CCF. 

3.6 DEFINITION OF SEASONS 

For purposes of this report the four seasons of the year were defined as Fall (September, 

October, November), Winter (December, January, February), Spring (March, April, May), and 

Summer (June, July, August). Reference to the shoulder seasons refers generally to Fall and 

Spring. Instances where the shoulder season is defmed differently from the above definitions for 

Fall and Spring are noted in the text. 

3.7 SIGNIFICANT DIGITS 

Hourly usage data was collected on a daily basis for an individually metered hearth 

product and furnace in each home of the study. The data is downloaded daily to a central 

computer through an automatic reading (AMR) device for validation and processing. The 

resolution of the gas consumption data ranges from Y. cubic foot (CF) to 1 CF. For consistency 

of comparison, all results for metered usage data are presented in units of 1 CF as a minimum. 

Data summaries are presented to three significant digits, or rounded to CF units. 

Topical Report - September, 1997 14 Hearth Products Meter Study 
SECTION 4 

DESCRIPTIVE STATISTICS AND SUMMARIES 

This section contains descriptive summaries of the questionnaire and metered usage data 

collected in this study. As discussed in Chapter 3, sample size and the staggered entry of 

households into the study must be taken into account when interpreting these descriptive 

summaries. In particular, for summaries presented by hearth product type and sampling region, 

sample sizes may strongly influence any conclusions drawn from the simple summary statistics. 

4.1 QUESTIONNAIRE SUMMARIES 

Three questionnaires, Pre-Selection, Site Survey, and Household, were used to gather 

demographic and equipment information from the homeowners participating in the study. 

Generally, responses to the questionnaires were collected prior to or during the installation of the 

monitoring equipment. Due to incomplete responses by some of the households, only 101 

households were available for inclusion in the summaries. Below are selected summaries of the 

questionnaire data. Note that because some questions were not answered for some 

questionnaires, the number of responses for each particular question is provided. 

Figure 4.1 and Table 4.1 characterize the households included in the study to date. 

Generally the homes are suburban two-story or ranch homes, averaging 2,378 square feet with 7 

rooms. The average age of the primary adults in the home is 43 years with 82% of the 

households having an annual income greater than $50,000. The average household size was 3.4 

people, with an average of 1 child in the home. 

Information pertaining to the hearth products and furnaces included in the study are 

summarized in Figures 4.2, 4.3, and 4.4 and Table 4.2. 

The hearth products were fairly new products as shown in Figure 4.2. The majority of the 

products were less than 5 years old when this data was collected in late 1995 and early 1996. 

Note that one decorative gas log was reported to be 32 years old. 

Topical Report - September, 1997 15 Hearth Products Meter Study 
~ 

~ 

So 

~ 

() 

~ r;j 

~ ~ .., 

~ s:: 

~ 

Wood-burning fireplace in the home? (n= 79) 

No 

86% 

Yes 

1"% 

Urban, Suburban, or Rural area? (n= 79) 

Urban 

10% 

Suburban 

77% 

Rural 

13% 

Ranch 

39% 

$40,001-$50,000 

9% 

$30,001-$40,000 

2% 

$20,001-$30,000 

5% 

less than or 

equal to $20,000 

2% 

Style of home (n= 80) 

Spilt level 

6% 

Other Three-Story 

6% 1% 

Two-Story 

48% 

Annual Income (n= 66) 

2"% 

$50,001-$75,000 

29% 

Figure 4.1 Summary of Selected Demographic Characteristics. 
Table 4.1 Summary of Selected Household and Demographic Characteristics. 

.... , -~'i~E··.·.···.·.:.212E8:12lliifdGillF).·· •• ···u····}· ·MeanJ~QL ; .. " .. : ... : ............... • •• -,eX_C· •• N ." '!' 

About how many years old is your home? 17(18.9) 0 95 101 

What is the square footage of your home, excluding 2,378 (776) 1,000 5,000 100 

any basement or garage? 

How many rooms are in your house, excluding 7 (2.0) 3 15 80 bathrooms and basement? 

What are the ages, in years, of the adult occupants 43 (11.4) 25 77 72 living in your household? 

How many people are in your family? 3.4 (1.5) 1 10 101 

How many children live in your household? 1.2 (1.2) 0 6 101 

35 

30 

i 25 

~ 

~ 20 

J 15 

'6 

~ 10 

5 

0 

, 1 ~ 

\ ~ -n 

5& ~ "9.- ~ 

\ ~ ~ W 

'3" ~ 

~ \\ i '3" 

~ ~ \\ 

'S '3" .:;:, 

\\ 

'3" ~ 

\\ 

~ 

Figure 4.2 Distribution of the Age of the Hearth Product, by Type of Hearth Product. 

Topical Report - September, 1997 17 Hearth Products Meter Study 
Figure 4.3 illustrates the difference observed in the study between decorative gas logs and 

other types of hearth products with regard to the prevalence of pilot lights. Only a little over 20% 

of decorative logs had pilot lights while more than 50% of all the other products were reported to 

have a pilot. Note that the percentages are calculated such that homes with two hearth products 

have each hearth product included separately in the analysis. 

100% 100% 

90"10 

80% 76% 

70% .. 

0 

if 

.. 60% 

.c 

J:: 

~ 50% II 

5OOh. 

CI 

.. 

.. 

c 40% II 

u 

.. 

:. 

30% 

22% 

20% 

10% 

0% 

Decoratiw Gas Log (n=49) Fireplace (n=70) Fireplace Insert (n= 7) Gas Stow (n= 4) 

Figure 4.3 Percentage of Hearth Products Reported to Have a Pilot, by Type of Hearth 

Product. 

As illustrated in Figure 4.4, 31 % of the hearth products can only be turned On and Off, 

53% have a Low-Medium-High temperature control, and only 6% of the hearth products are 

thermostatically controlled. Three out of the four hearth products that are thermostatically 

controlled are gas stoves. 

Table 4.2 presents summary statistics on the furnaces in the study. 

Several questions were designed to assess the perception homeowners have about the use 

of their hearth product. Responses to these questions across all hearth product types are 

illustrated in Figures 4.5 and 4.6. 

Topical Report-September, 1997 18 Hearth Products Meter Study 
~ "ti 100% [ 

~ 

~ c 

:t 

I 

~ "ti 80% 

~ 

:! 

0-

l1:I 

,:-, 

.... 

'0 

'0 

'-I 

60% CD 

en 

c:: 

0 

c. 

en 

CD 

a:: 

-c:: 40% 

CD 

.... (,) 

.... '0 CD 

a.. 

20% 

Overall (n=64) Decorative Gas Log Fireplace (n=12) Fireplace Insert (n=6) Gas Stove (n=4) (n=42) 

a2I Low-Medlum-High 53% 67% 8% 67% 25% 

31% 24% 67% 33% 0% 

~ Thermoltat 6% 2% 0% 0% 75% 

2 0% 

Figure 4.4 Type of Temperature Control, Overall and for Each Type of Hearth Product. 
Table 4.2 Summary of Selected Household and Furnace Equipment Characteristics, by Hearth Product. 

Does the fireplace have a fan to 

blow the warm air into the room? 

Was it necessary to build the 

surrounding framework, masonry 

or enclosure for the ? 

Does your furnace have an 

electronic ? 

Does the furnace have a vent 

or flue? 

Question 

What is the input BTU rating for the furnace? 

What is the output BTU rating for the gas furnace? 

How old is the gas furnace (years)? 

What is the heating efficiency rating of the furnace 

in %AFUE? 

73% (n=8) 

27% (n=3) 

89% (n=8) 

11% = 1 

67% (n=12) 

33% (n= 6) 

71% (n= 15) 

29% n= 6) 

76% (n=16) 

24% 

100,351 

(27,965) 

34,000-200,000 

42 

81,216 

(18,674) 

30,600-112,000 

17 

6 (7) 

1-30 

38 

75% (1%) 

74-75 

2 

0% (n=O) 

100% (n=6) 

20% (n=1) 

80% (n=4) 

43% (n=3) 

57% (n=4) 

43% (n=3) 

57% 

25% (n= 1) 

75% (n=3) 

67% (n=2) 

33% =1 

0% (n=O) 

100% (n = 2) 

50% (n=2) 

50% (n=2) 

50% (n=2) 

50% 

Mean (Standard Deviation) 

Minimum - Maximum 

117,857 

(27,212) 

80,000-150,000 

7 

102,300 

(21,382) 

69,000-120,000 

5 

12 (8) 

2-22 

6 

69% (5%) 

63-75 

5 

N 

114,250 

(29,193) 

80,000-140,000 

4 

87,200 

(19,807) 

72,000-109,600 

3 

11 (4) 

7-17 

4 

78% (4%) 

75-80 

2 

23% (n=10) 

77% (n=33) 

11% (n= 1) 

(n=8) 

75% (n=27) 

25% (n= 9) 

80% (n=35) 

20% = 9) 

41% (n= 17) 

59% 

103,182 

(27,154) 

57,000-200,000 

44 

87,177 

(21,511) 

55,000-160,000 

22 

9 (10) 

0-36 

43 

65% (14%) 

52-80 

3 
100% 

60% 54% 

40010 34% 

25% 

20% 

21% 

f---

14% 

I I 11% 

5% 

I I I I 0% 

Figure 4.5 Reason for Purchasing the Hearth Product (N=80). 

100% 

80% 

60% 

48% 

40% 

19% 21% 

20% 

4% 3% 5% 

00,(, r l 0°,(, 1% 

0% 

Figure 4.6 Primary Reason Hearth Product is Typically Used (N=79). 

Topical Report - September. 1997 21 Hearth Products Meter Study 
Figure 4.5 shows that across all the homeowners in the study, the most frequent reason 

for purchasing the hearth product was "Appearance." The primary reason for using the hearth 

product was "Looks and Heat," as shown in Figure 4.6. 

4.2 HEARTH PRODUCT AND FURNACE GAS USAGE SUMMARIES 

This section provides summaries of the heating season, monthly, daily, hourly, and pilot 

usage as well as the patterns of usage by the hearth product owners. Many of the summaries are 

presented over all households and by the type of hearth. Because of the unbalanced nature of the 

data, i.e. varying sample sizes across the type of hearth product, sample sizes will be presented 

with each analysis. 

The data to be included in the metered usage summaries was collected from 

November 29,1995 through May 31, 1997. Only partial heating season usage data is available 

for many of the homes during the 1995-1996 heating season because of the staggered start 

dates - many utilities began installing in late November, 1995 with installations continuing 

through October of 1996. The cut-off date for data in this report was May 31, 1997, to meet 

report deadlines while ensuring that the data was validated and summarized correctly. 

4.2.1 Heating Season Gas Usage 

Figure 4.7 presents a histogram of the distribution of the average heating season gas 

usage by the type of hearth product, while Figure 4.8 illustrates the same information in a box 

plot. For this presentation, only usage in the 1996-1997 heating season is included and is 

referred to as the total heating season usage since the usage was collected between September 1, 

1996 and May 31, 1997. Eighty-one of the 114 homes for which hearth produce usage was 

available had less than 30 days of missing data and are included in the analysis with 44 hearth 

products having a complete heating season of usage with no missing data. 

The histogram in Figure 4.7 shows that more than 35% of the hearth products had an 

average heating season usage between 25 CCFs and 75 CCFs. Nearly 20% of the fireplace 

inserts had heating season usage between 425 and 525 CCFs. 

Topical Report - September, 1997 22 Hearth Products Meter Study 
iii 

0 

.... 

'3 

tt. 

80.-------------------------------------------------------------------, 

60 

40 

6, 

20 

)( 

, . 

. \ ,. 

i ~ , \ , . . \ , \ \ i 

\ \ 

'\ 

\ 

,.\ • 

i \ I . 

/ \ i \ 

,. i 

i \ 

! \ 

i 

~ ~ ~ ~ ¢ ~ ~ # # ~ ~~ ~ ~ ~ ~ ~ ~ ~ 

... rt" ~f)' ~' .vf)' ".rt" ~f)' -.rt" ~f)' f)rt" 

Heating Season Usage (CCF) 

I_Overall -.-Decorative Gas Log --8-- Fireplace · ... h· .. Fireplace Insert -·~- .. Gas Stove I 

Figure 4.7 Heating Season (September, 1996 - May, 1997) Hearth Product Gas Usage, by 

Type of Hearth Product -- Histogram. 

Figure 4.8 shows that the average heating season hearth product gas usage ranged from 

105 CCF for the 34 fireplaces to 171 CCF for the 6 fireplace inserts. Decorative gas logs, with 

the largest sample size, had an average of 120 CCF for the heating season. Both figures illustrate 

the variability in heating season hearth product usage with usage ranging from 0 CCF to 824 

CCF and 75% of the population using less than 300 CCF for the heating season. 

Topical Report - September, 1997 23 Hearth Products Meter Study 
900 

BOO 

700 

CL a BOO 

t 500 :::l 

8 

J400 

g> 

i 300 

200 

100 

~ 0 

\ 

'\ \ 

'5 

~ , 

~ ~ 

1) ~ \ \ \ '5 

, 

'5 $ 

, 

'5 $ , 

~ 

Figure 4.8 Heating Season (September, 1996 - May, 1997) Hearth Product Gas 

Usage, by Type of Hearth Product - Box Plot. 

4.2.2 Monthly Gas Usage 

The average monthly gas usage from February, 1996 through May, 1997 for each type of 

hearth product is presented in Figure 4.9. The summary begins in February since only a few 

hearth products were being monitored in November and December of 1995 and the bulk of the 

monitoring installations did not occur until mid and late January. Because of the staggered start 

dates the number of hearth products being included in the monthly average increases over time 

leveling off in October of 1996. In December, 1996 the number of hearth products included in 

the averages decreased by 10 for one LDC, but nine were added from another LDC. No new 

installations occurred from late December, 1996 through May, 1997. 

Figure 4.9 shows that generally the hearth product usage begins in September. Usage 

increases through the Fall, peaking in December and January for all hearth product types. Usage 

remains nearly constant in February and March and then decreases in April and May. 

Topical Report - September. J 997 24 Hearth Products Meter Study 
"t; ~ 

O· 35 

fa. 

~ 

~ c 

::t 30 

I 

~ "ti 

~ 

::i 

~ 25 

~ 

..... 

~ 'I 20 

15 

10 

5 

o 

Feb-98 Mar-98 Apr-98 May-96 Jun-98 Jul.98 Aug-98 Sep-98 ()Q.98 No¥-98 [)ec..98 Jan-97 Feb-97 Mar-97 Apr-97 May-97 

Feb-98 Mar-98 Apr-98 May-98 Jun-98 JIJI.98 Aug-98 Sep-98 ()Q.98 No¥-98 [)ec..98 Jan-97 Feb-97 Mar-97 Apr-97 May-97 

OOwral 20.2 21.9 13.8 7.8 4.2 3.5 3.2 3.7 9.8 18.2 21.2 23 15.8 18.2 10.1 5.4 

C Oecoratw Gas Log 17.5 23.8 10.5 8.1 2 0.9 0.7 2.8 8 17.8 25.7 24.3 13.4 13.2 8.8 3.8 

ORrepIace 20.8 22 17.4 10.2 7 8.8 8.4 5.2 11.2 13.8 15.1 21.2 17.2 18.4 12.1 8 

• Fireplace IIIB1 29.7 17.1 9.8 3.8 0.4 0.2 0.2 3.8 18.7 23.8 28.5 28.8 19.8 19.1 14.8 7.8 

GlGasSWt 15.8 11.1 8.2 3.8 2.8 0.7 0.7 2.3 5.4 12.7 18.1 20.8 15.2 13.7 13.5 4.7 

Figure 4.9 Average Monthly Hearth Product Gas Usage, Overall and by Type of Hearth Product. 
4.2.3 Daily Gas Usage 

All available data collected in the 1996-1997 heating season was included in the summary 

of the daily gas usage. Figure 4.10 presents a load profile of the ratio of the average daily usage 

to the maximum daily usage during the heating season for the hearth product and gas furnace 

separately. Included in the graphs are the average daily degree readings associated with each day 

of usage from September 1, 1996 through May 31, 1997. 

The load profiles in Figure 4.10 indicate that overall and within each type of hearth 

product, the hearth product usage is less related to weather than the gas furnace usage with a 

resulting flatter load profile. On average there is an increase in hearth product usage as the 

weather gets colder, but the increase appears to level off during the heart of the heating season 

except for a few spikes on colder days. The usage decreases slowly as the weather gets warmer. 

Generally, the usage levels are similar across all hearth product types. 

4.2.4 Hourly Gas Usage 

Similar to the daily gas usage summaries, the hourly summaries are presented as load 

profiles. For January, 1997, the hearth product, furnace, and total hearth product and furnace 

average hourly gas usages are compared across a 24 hour period by the type of hearth product are 

presented in Figure 4.11. 

Across all the hearth products, the hourly use pattern throughout the day appears to be 

very similar. Generally, the furnace is the major contributor to the total heating load assuming 

the total heating load is only the furnace and the hearth product usage throughout the day. The 

peak usage for the furnace occurs in the morning hours while the peak usage for the hearth 

product occurs in the evening hours. A peak also occurs in the morning hours for the decorative 

gas logs though this peak is much lower than the evening peak. On average, the hearth products' 

evening peaks add to the evening heating load, but do not change the peak usage hour within a 

day. For the decorative gas logs, fireplaces, and fireplace inserts, when the hearth product is used 

in the evening, the furnace gas usage appears to decrease. An assessment of the effect of hearth 

product usage on the gas furnace usage accounting for weather is provided in Section 6. 

Topical Report - September, 1997 26 Hearth Products Meter Study 
CNeralI 

~~~~--~--~--~--~--~--~--~--T 

---------- -

---------- -

Gas SIcMI 

~~~~~--~--~--~~--~~~~ 

---------- -

8 

8 

DecoraIiYe Gas Log 

8 

~~~~~~~~ 

---------- - Ftreplace Insert 

.. I 

.. 

~~~~--~--~--~--~--~--~--T_~~ 

---------- -

8 

Figure 4.10 Average Daily Hearth Product and Furnace Gas Usage as a Percent of the 

Maximum Daily Usage by Type of Hearth Product. 

Topical Report - September, J 997 27 Hearth Products Meter Study 
Overall Decorative Gas Log 

0,5.r------~ 

Rreplace Rreplace Insert 

o~'------------------r=-~~------~--~~ 

I ::: ::.,. I'ImIoe rd HIaIh -

~ .......... HIaIh_ 

Gas Stove 

~'------------------r==================~l 

I 

::: ;:.,., I'ImIoe rd HIaIh -

........... HeII1h_ 

Figure 4.11 Furnace, Hearth Product, and Total Furnace and Hearth Product Average 

Hourly Gas Usage by Type of Hearth Product for January, 1997. 

Topical Report - September, 1997 28 Hearth Products Meter Study 
4.2.5 Pilot Usage 

Using the hourly data, the hourly pilot usage was estimated for each hearth product. The 

estimated hearth product pilot hourly gas usage for each type of hearth product is provided in 

Figures 4.12 and 4.13. For the 59 homes that indicated they have a pilot on at least one hearth 

product, the fireplace pilot usage had the most variability ranging from 0.5 CF to 2.83 CF per 

hour, with most of the fireplace pilots estimated to use 1.3 CF per hour. More than 60% of the 

decorative gas log pilot usage ranged between 0.75 CF to 1.25 CF. Seventy-five percent of the 

fireplace insert pilots and 50% of the gas stove pilots had an average hourly pilot usage of 

1.25 CF or less. 

70 

60 4 iii 

1\ 

1\ , , '\ 

I \ I \ 

50 :'~ I \ I \ ~ I \ i·, " 

r \ '. 

I \ : 

I \ 

40 I \ J I \ I \ r \ 

'& I \ 

tt- I \ : 

30 \ ,. \ : i 

~. ;' \ 

" \ 

:' \ 

20 :;' \ 

\ '. \ '; 

\ 

I 

0-<.25 .25-<,50.50-<.75.75-<1.01.0-<1.25 1.25-< 1.5-<1.751.75-<2.0 2.0+ 

1.50 

Eltlmltad Hourly Pilot U .. ga (CF) 

• Overall --<>--Oecorative Gil Log - -8 - - Fireplace .•• . .t. .... Fireplace Insert .. _--)11[--. Gal Stove I 

Figure 4.12 Distribution of the Estimated Hearth Product Hourly Pilot Gas Usage 

by Type of Hearth Product - Histogram. 

Topical Report - September, 1997 29 Hearth Products Meter Study 
3.0 

2.5 

~ 

~ 2.0 

::::> 

~ 1.5 f 

I to 

~ 

0.5 

0.0 

\ ~ ':!\ ~ \ \ ~ 

'S \ ~ 

~ II 'S 

~ \I 

S 'S ~ 

II 

'S £) 

\I 

:9 

Figure 4.13 Distribution of the Estimated Hearth Product Hourly Pilot Gas Usage by 

Type of Hearth Product - Box Plot. 

4.3 PEAK DAY AND PEAK HOUR USAGE 

Peak day and peak hour gas usage is of interest to utilities for many reasons including 

supply planning and load forecasting. 

As described in Section 2 utilities reported daily degree readings beginning with the first 

installation of monitoring equipment in their service area. For this section, the coldest days in the 

1996-1997 heating season were calculated. Note that the gas usage for many of the hearth 

products in the study were not being monitored when the actual peak weather day occurred in the 

1995-1996 heating season, therefore data from this heating season was not included in this 

analysis. 

For the 1996-1997 heating season, Figure 4.10 presented earlier shows a load profile of 

the ratio of the average daily usage to the maximum daily usage during the heating season for the 

hearth product and gas furnace separately. The figure shows that, on average, peak hearth 

product usage or very near the peak is attained mUltiple times throughout the heating season. In 

addition, the hearth product peak usage is not as highly correlated with weather as the furnace 

usage. Note that 100% was not achieved for either the furnace or the hearth product since the 

Topical Report - September. 1997 30 Hearth Products Meter Study 
peak day gas usage was different for many of the homes and the graphs present the average of the 

percent of usage to the maximum usage taken across households. 

An examination of the load profiles presented in Figure 4.10 indicate a flatter load profile 

for hearth products than for furnaces. The load factor for furnaces is often calculated as the 

average daily furnace usage divided by the usage on the peak weather day (or system peak). An 

identical statistic cannot be calculated for hearth products because of the occurrence of zero 

hearth product usage on the peak weather day for some households. However, the inverse of this 

statistic, usage on peak day divided by average usage, can be calculated. As an indicator of how 

much the hearth product contributes during periods of peak cold weather conditions, the average 

ratios for hearth products are presented in Figure 4.14. To provide additional information on this 

question Figure 4.15 presents the average, across households, of the ratio of the average usage on 

the top five peak weather days to the average usage on the top 45 weather days for both the 

hearth product and the furnace. This statistic provides a better measure of whether hearth 

product usage is increased during periods of extremely cold weather over its normal usage during 

cold winter weather. Figure 4.15 indicates that average hearth product usage on the top five 

coldest days averaged over 1.5 times as much as average hearth product usage on the top 45 

coldest days. In fact, for all appliances except the fireplace, the increase in peak usage, on a 

percentage basis, exceeded the increase in peak usage exhibited by the furnace. Preliminary 

statistical modeling results discussed in Section 6.3 also indicated a statistically significant 

increase in hearth product usage, after adjusting for weather, on the peak weather days (five 

coldest days). This preliminary assessment suggests that while the hearth product load profile 

may be flatter than the furnace, the hearth products may likely be used during peak periods of 

extremely cold weather. This also indicates further efforts to characterize this effect may be 

worthwhile. 

Topical Report-September, 1997 31 Hearth Products Meter Study 
CD 

CI 

a:l 

1/1 

:l 

>-

a:l 

c 

CD 

CI 

e 

CD 

~ 0 

... 

CD 

CI 

a:l 

1/1 

:l 

>- a:l 

C 

~ 

a:l 

CD 

g,. 

-0 

.2 

.. 

a:l 

Ill: 

8 

7 

6 

5 

4 

3 

2 

1 

0 

Overall (n-SO ) Decorative Gas Log Fireplace (n=32 ) 

(n-39 ) 

Fireplace Insert 

(n-6 ) 

10 Hearth Product. Gas Furnace 1 

Gas Stove (n-3 ) 

Figure 4.14 Ratio of the Peak Weather Day Gas Usage to the Average Daily Gas Usage 

During the Heating Season for the Gas Furnace and Each Hearth Product 

Type. 

Topical Report-September, 1997 32 Hearth Products Meter Study 
Ic 

... 

'" GI 

a. 

~ 

gle 

0 

GI 

i 

:J 

S 

~ 

c '" 

11 

GI 

a. 

II) 

gIg 

:J • " 

'8 

i 

II: 

2 

1.8 

1.6 

1.4 

1.2 

1 

0.8 

0.6 

0.4 

0.2 

0 

Overall (n-81 ) Decorative Oa. Log Fireplace (n-35 ) 

(n-37) 

Fireplace In.ert 

(n-. ) 

10 Hearth Product. Oa. Furnace I 

Oa. Stove (n-3 ) 

Figure 4.15 Ratio of the Gas Usage of the Five Coldest Days to the Gas Usage on the Top 

Forty-Five Coldest Days for the Gas Furnace and Each Hearth Product. 

Figure 4.16 provides a comparison of the average hourly gas usage during January, 1997 

for the hearth products, furnace, and total hearth product and furnace to the hearth product, 

furnace, and total hearth product and furnace gas usage on the peak weather day that occurred 

during January, 1997 for the respective utility. This figure provides an indication that on this 

peak weather day the hearth product may be a supplemental heat source and the gas usage from 

the hearth product may shift the daily peak from the morning to evening hours. 

Topical Report - September, 1997 33 Hearth Products Meter Study 
Overall 

1.0-r;========;--------------, 

&-+--<> ~_"""PIocIJcI _ Funooo 

e--&-e bill _ FunocoH' 

+ -~ ~ t-IeII1h ProducI 

CL .8 .Q -(lo- -E'J fufWIce 

~ 0 1L-.~_~_bIII~~Rm_ .. ~IP_~ 

1M 

~ f ~4 

f~ 

Rreplace 

Gas Stove 

1.0-r;===========;--------------, 

o.o~- -

1 23' 5 6 7 8 • ~ n ~ ~ u ~ ~ D • S m ~ ~ ~ ~ 

Decorative Gas Log 

1.0-r;=========,------------, 

Hour 

Rreplace Insert 

In-r;=~==_==....,,==PIocIJcI====,--------­

+ 

&-&-e ~-- --..... 1:UI 

I'8wIh 

~ 

ProcU:t 

~ 

[L 0 B <9'- ~ Ft.mIc8 ~ . IL"--<>-" _bIII_FunocoH' _______ -' 

I o. 

~ i 0.4 

« t~ 

Figure 4.16 Comparison of the Average Hourly Furnace and Hearth Product Peak Day 

Gas Usage to the Average Hourly Furnace and Hearth Product Gas Usage 

during January, 1997, by Type of Hearth Product. 

Topical Report - September, 1997 34 Hearth Products Meter Study 
SECTIONS 

CHARACTERIZATION OF SUBSETS OF CUSTOMERS 

Initial examination of plots of hearth product usage for different customers indicated 

widely varying patterns of usage. Some customers are very heavy users; some are very light 

users. Some display a heavy interaction with the furnace; others display little or no interaction. 

Some use the hearth product extensively early in the season; others delay use of the hearth 

product until later in the heating season. For example, Figures 5.1 through 5.4 present both 

furnace and hearth product usage plotted versus degree day reading for four households with 

markedly different usage patterns. Figure 5.1 illustrates a household where the hearth product 

appears to be used as a significant supplemental heat source. Figure 5.2 presents a household 

with less hearth product usage but where the hearth product still has an obvious relationship with 

weather. Figure 5.3 presents a household with hearth product usage that appears independent of 

weather. Finally, Figure 5.4 presents an example of a hearth product with only sporadic usage. 

14 

13 

12 0 

11 

10 0 

9 0 0 0 

0 

8 0 

o 5 10 15 20 25 30 35 40 45 50 55 60 65 70 

Daily Degree Day Reading 

Legend: .~- - Hearth Product <> -<J -., Furnace 

Figure 5.1 Example of a Customer With Very Heavy Hearth Product Usage that May 

Serve as a Supplemental Heat Source. 

Topical Report - September, 1997 35 Hearth Products Meter Study 
14 

13 o 

12 o 

a 0 9-' 

11 , 0 

10 o 0 0' 

9 o , 0 o 

rL 

() 8 Q. 

Q) 7 

~ 6 :::> 5 

4 

3 

2 

1 

0 

0 5 ID ffi ro ~ ~ ~ ~ ~ ro ~ 00 ~ m 

Daily Degree Day Reading 

Legend: ~- - Hearth Product 0- -<) -" Furnace 

Figure 5.2 Example of a Customer with Moderate Hearth Product Usage Significantly 

Related to Weather. 

14 

13 

12 

11 

10 

9 o o 0 

rL 

a 8 

~ 7 

6 :::> 5 

4 

3 

2 

0 

o 5 10 15 ro 25 ~ ~ ~ ~ ro ~ 00 ~ 70 

Daily Degree Day Reading 

Legend: ~--- Hearth Product 0--<)-" Fumaoe 

Figure 5.3 Example of a Customer With Regular Hearth Product Usage Independent of 

Weather. 

Topical Report - September, 1997 36 Hearth Products Meter Study 
14 

13 

12 

11 

10 

9 

~ 8 

g 

Q) 7 

i' 6 

::> 

5 

4 

3 

2 

o o 0 ,;9 

o 

o 

----------------------------

o 5 ro ~ ~ ~ ~ ~ ~ ~ ~ ~ 00 ffi ro 

Daily Degree Day Reading 

Legend: ~-- ~ Hearth Product ()- -0 -" Rmace 

Figure 5.4 Example of a Customer With Only Sporadic Hearth Product Usage. 

Subsets of customers were identified according to three different usage characteristics: 

total hearth product usage, usage in the shoulder season, and net increase in total household 

heating load in the winter. Classification of customers into a HIGH group for each of the three 

usage characteristics (based on being in the top 20% of usage for the particular characteristic) 

revealed strong correlation between the users in the HIGH group for each usage characteristic, 

indicating that those users who have the highest total hearth product usage also often use the 

hearth product heavily in the shoulder seasons and are also estimated to generate the greatest net 

increase in total household heating load in the winter. 

Topical Report - September, 1997 37 Hearth Products Meter Study 
SECTION 6 

RESULTS-FACTORS RELATED TO 

HEARTH PRODUCT USAGE 

Statistical methods were used to assess the relationship between hearth product gas usage 

and major factors that may affect that usage. Identifying factors related to hearth product usage 

presents a special challenge because of the wide range of factors influencing the use of hearth 

products. Unlike furnace usage, which is highly dependent on weather, house size, and 

efficiency rating, hearth product usage mayor may not be explained by weather and equipment or 

household characteristics. 

Identification of factors related to hearth product usage was accomplished through a 

series of statistical analyses used to construct models to predict hearth product usage that were 

included in a proprietary report for participants in the study. The intent was to develop models 

that use equipment, building, demographic, region, weather, and type of day information to 

characterize hearth product usage and patterns of usage. Preliminary information regarding 

which predictor variables were associated with hearth product usage was obtained from crosstabulation tables and simple correlation statistics that indicate changes in gas consumption 

related to changes in the predictor variable. The advantage of statistical modeling was the ability 

to assess multiple factors simultaneously. 

6.1 DESCRIPTION OF AVAILABLE DATA 

Hearth product usage data collection dates summarized in this report ranged from 

September, 1995 through May, 1997. There were limits on the amount of information that could 

be extracted from the data. This was primarily due to the staggered dates of entry into the study 

for households from the various LDCs (local distribution companies). It is expected that the 

models may change somewhat and comparisons and conclusions become more clear as more data 

can be included in the analyses. Another limitation of the data was the unequal numbers of each 

hearth product type. For example, data from 107 households were used in the analyses in the 

following sections. Of these, 49 have Decorative Gas Logs, while only four have gas stoves. 

The unbalanced nature of the data makes it difficult to discern differences among the groups. 

One household with extremely high hearth product usage was determined to be an 

influential observation and a potential outlier. The usage from this household was very 

influential on modeling results and was excluded from the final analyses on which conclusions 

presented in this report are based. 

Also note that the homes with two hearth products in the home were not included in the 

following analyses. It is expected that analyses will be performed in the future on these homes. 

Topical Report - September, J 997 38 Hearth Products Meter Study 
6.2 STATISTICAL METHODOLOGY 

The relationship between hearth product usage and the possible predictors was assumed 

to be linear and have the following form: 

Hearth Product Usage = Po + pj*Predictorj + error, 

where i = 1 to the number of predictors and error is random noise assumed to be normally 

distributed, with mean zero and variance 0 2 independent of the predictors. Numerous variables 

exist that could be important predictors of hearth product usage. Thus, prior to the assessment of 

the statistical models, it was necessary to reduce the number of variables considered to be 

possible predictors. 

A few variables were considered of primary interest and were included in all models, 

regardless of the usage period (heating season, season, month, or day). These included degree 

day measures, hearth product type, and the presence of a pilot light. These three variables were 

included in all of the models based on their assumed predictive power. In addition, usage period 

indicators (heating season, season, and month), demographic and equipment variables correlated 

with hearth product usage, and classification variables such as DOE heating region and LDC 

service area were assessed to determine the best predictive model for hearth product usage. The 

steps in the variable selection/reduction process included an assessment of statistical correlations, 

combination of variables, stepwise regression, R 2 analysis, and professional judgement. 

6.3 MODELING ANALYSIS RESULTS 

The statistical modeling analyses indicated that factors most significantly related to hearth 

product usage include: 

• Degree day measures 

• Presence of a pilot light 

• Hearth product type 

• Type of day 

- weekend/weekday 

holiday 

- peak day. 

LDC service area and DOE heating region were also assessed as candidate variables for 

each model. However, in general, after including the effect of weather in the model, no 

additional effect of service area or region was detectable. Likewise, after including the effect of 

weather in the models, the additional effect of season or month was usually not statistically 

significant, although there were indications of higher usage in December and January. 

Topical Report - September, 1997 39 Hearth Products Meter Study 
SECTION 7 

MODELS TO ASSESS THE HEARTH 

PRODUCT-FURNACE INTERACTION 

A question of primary interest is how does hearth product gas usage interact with furnace 

gas .usage, and what is the resulting net impact on total household heating load. There are many 

possible scenarios. The use of the hearth product may be supplemental to furnace usage or 

hearth product usage may replace furnace usage. Hearth products may be used as a means of 

localized heating which would reduce the total household heating gas consumption, or they may 

heat a previously unheated or poorly heated space, thereby increasing total consumption. Some 

hearth product types may affect the central heating system gas usage more than others due to 

equipment and venting characteristics. This section presents models and analyses that address 

these issues. 

The effect of a hearth product on total household usage may be broken into two separate 

effects. First is the effect of the actual installation of the hearth product. This may be the result 

of closing (or opening) a previous fireplace vent (such as replacement of a previous woodburning fireplace). Since the Hearth Product Meter Study does not include any homes that were 

metered both before and after installation of the hearth product, the first effect was not able to be 

assessed directly from the data currently available to this study. 

The second effect of a hearth product on total household usage concerns how actual ~ 

of the hearth product affects the central heating system usage. For example, for each therm of 

fireplace usage, how much is the furnace usage increased or decreased. During periods of regular 

furnace usage (i.e., the winter months), the effect of hearth product usage on furnace usage can 

be estimated by statistical models. It should be recognized that if the hearth product is used in 

the shoulder periods to replace furnace usage altogether, that effect will not be captured in these 

models. 

To illustrate how households can differ in the observed interaction between hearth 

product and furnace, Figures 7.1 and 7.2 present data from households with markedly different 

interactions with the furnace. Figure 7.1 presents data from a household in the study that 

illustrates a likely interaction between use of the hearth product and furnace. Days with heavy 

hearth product usage have lower furnace usage. Figure 7.2 illustrates this interaction for the 

same household by plotting furnace usage adjusted for weather versus hearth product usage 

adjusted for weather, showing a clear relationship between the two. Figure 7.3 presents data 

from a different household in the study that suggests little or no interaction between hearth 

product and furnace usage. Furnace usage appears independent of the hearth product usage. In 

Figure 7.4, the plot of furnace usage adjusted for weather versus hearth product usage adjusted 

for weather also shows no relationship, only a random scatter of points for this household. 

Topical Report - September, 1997 40 Hearth Products Meter Study 
7.1 RESULTS OF MODELING THE INTERACTION 

A modeling approach was used to assess the impact of hearth product usage on furnace 

usage in the winter months. The following linear regression model was used: 

Daily Furnace Usage = Po + PI x Daily Degree Days + P2 X Daily Hearth Product Usage 

In this model, the parameter P2 (the slope parameter for Daily Hearth Product Usage) represents 

the decrease or increase in furnace usage (in CCFs) for each CCF of hearth product usage, after 

adjusting both variables for the effect of weather. This model was fit to each household using 

data from December, January, and February. The households included were limited to those that 

had at least 10 days of hearth product usage and 10 days of furnace usage during the relevant 

period. A total of 98 households were used in this modeling effort. 

The average estimated slope for the 72 households was -0.33, representing a decrease of 

0.33 CCF in furnace usage for every CCF of hearth product usage. Over 70% of the slope 

estimates were negative indicating that most homes did decrease furnace usage as a result of 

hearth product usage. Assuming that the slope parameters for these households represent a 

random sample from a normal distribution of all such estimates, the average slope estimate 

(-0.33) can be interpreted as the average decrease in furnace usage due to hearth product usage, 

after adjusting for weather. Thus, on average, 1 CCF of hearth product usage leads to a 0.33 

CCF decrease in furnace usage, implying that the remaining 0.67 CCF represents a net increase 

to the total household load. Therefore, on average, based on the data analyzed to date, 67% of 

the hearth product usage can be characterized as incremental load. It is important to note that 

results based on the current data included in this report are heavily influenced by homes with 

decorative gas logs and fireplaces which represent the majority of homes summarized in this 

report. 

Topical Report - September. 1997 41 Hearth Products Meter Study 
14 

13 

12 

11 

10 

9 

CL 

a 8 

~ 7 

6 

:::> 

5 

4 

3 

2 

° 'be ° 

o 5 ro ffi ~ ~ ~ ~ ~ ~ ro ~ 00 ~ m 

Daily Degree Day Reading 

Lagend: ._-- Hearth Product 0- -<l - 8 Furnace 

Figure 7.1 Usage Data from a Household with Significant Interaction Between Hearth 

Product Gas Usage and Furnace Gas Usage. 

2 

'. 

. -.. 

. ,.. . .. --, -, . '''''.' ". fi- _ • • 

-'' J, ~ .' • -, • 

o 

. 

~~~ . .- ... \-', . " . -', , • a. " .. 41:,.- .' • 

. ",: . :. .--;~----: .: ..... : ... :-'-....... I~. , • 0 ' 

o. -,0 

0, 

-2~~~~~~~~~~~~~~~~~~ __ ~~~~ 

-2 -1 o 2 

Hearth Product Dally Gas Usage (CCF) Adjusted for Weather 

Figure 7.2 Furnace Usage Adjusted for Weather Plotted Against Hearth Product Usage 

Adjusted for Weather for a Household With Significant Interaction. 

Topical Report - September, 1997 42 Hearth Products Meter Study 
14 

13 

12 

11 

10 

9 

8 

7 

6 

5 

o 

o 

.. . . .' : .. •• I 

o 

o 

. . . . 

o 5 10 15 20 25 30 35 40 45 50 55 60 65 70 

Daily Degree Day Reading 

Legend: .--~ Hearth Product 

Figure 7.3 Usage Data from a Household with Little Interaction Between Hearth Product 

Gas Usage and Furnace Gas Usage. 

6 

i 5 

4 

~ 

! 3 

~ 2 

~ 1 

J 0 

~ -1 

~ 

j -2 

-3 

......... 

. . . 

. -. . . .. ... .... .-

.-. ~ .... .. - . ... ~.. . . :( 1-t. : , .. :- • . ..,. \ ... .,.. --- -.-; - -:~.'~ ;-(-:_ - _._ - _. ___ ._ ... e __ ; __ .! ...... _____ ). ________ . _______________ . __________ _ 

.: .\~ .. :: .. ... . 

-2 

•• ~ 111,- ,;:.,.: • 

. .. ," .- .. - -.. .",. .. . . ... : .. . -. ... . .. -.. . -. . . .. 

-1 0 1 2 3 4 5 6 

Hearth Product Dally Gas Usage (CCF) Adjusted for Weather 

7 

Figure 7.4 Furnace Usage Adjusted for Weather Plotted Against Hearth Product Usage 

Adjusted for Weather for a Household with Little Interaction. 

Topical Report-September, 1997 43 Hearth Products Meter Study 
7.2 FACTORS RELATED TO THE INTERACTION BETWEEN 

HEARTH PRODUCT AND FURNACE 

Additional analyses were conducted to identify variables that could be used to predict the 

estimated effect of hearth product usage on furnace usage. Four different variables were tested 

individually for their effect on the interaction. None of the four variables (hearth product type, 

DOE heating region, LDC service area, and location of the hearth product) had a statistically 

significant relationship with the hearth product-furnace interaction using data available for this 

report. 

Topical Report - September, 1997 44 Hearth Products Meter Study 



Headquarters 

Gas Research Institute 

8600 West Bryn Mawr Avenue 

Chicago, Illinois 60631-3562 

3121399-8100 

Washington Operations Division 

Gas Research Institute 

1600 Wilson Boulevard 

Suite 900 

Arlington, Virginia 22209 

7031526- 7800 

I