E-5.i

APPENDIX E-5. ADDITIONAL INSTALLATION COSTS DUE TO LARGER

DIAMETER WATER HEATERS

TABLE OF CONTENTS

E-5.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-5.1

E-5.2 DOWNSIZE FOR SPACE CONSTRAINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-5.1

E-5.3 INCREMENTAL DRAIN PAN COSTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-5.8

E-5.4 DOORWAY RESTRICTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-5.10

TABLES

Table E-5.1 First Hour Rating and Related Volumes for Water Heaters . . . . . . . . . . . . . E-5.6

FIGURES

Figure E-5.1 Space Constraints Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-5.3

Figure E-5.2 Schematic of Tempering Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-5.7

Figure E-5.3 Drain Pan Size Increase Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-5.8

Figure E-5.4 Door Jam and Frame Removal Cost Assessment . . . . . . . . . . . . . . . . . . . . E-5.10
E-5.1

APPENDIX E-5. ADDITIONAL INSTALLATION COSTS DUE TO LARGER

DIAMETER WATER HEATERS

The use of thicker insulation is an effective method of achieving improved energy efficiency

in water heaters. The energy factors in the trial standard levels can be achieved with thicker

insulation of 2" to 3" compared to the 1" to 1.5" in common use today. This extra insulation will

increase the diameter of water heaters. In this appendix, we address three issues that would require

additional installation costs due to larger diameter replacement water heaters: installation in tight

spaces when replacing an existing water heater, larger drain pans to fit under the increased diameter

of the water heater, and the access door to the space the water heater is located may not be large

enough to allow the larger water heater to go through.

E-5.1 INTRODUCTION

The large majority of residences will have room to accept water heaters with increased

insulation. About 20% of water heaters are placed in new housing; the rest are replacements in

existing housing. The new housing design and construction process will readily adapt to increased

water heater sizes. For existing housing, most houses will be able to accommodate the increased

water heater dimensions without difficulty. Many homes have water heaters in the open spaces of

garages, basements, or utility rooms. In these cases, there is generally more than sufficient room for

water heaters with slightly increased dimensions. Additionally, water heaters come in a number of

different shapes. If water heaters with increased diameters cannot fit into the existing space, a

different (for example, taller and thinner) water heater may often fit. For manufactured housing,

water heaters are commonly located in a 24" wide by 24" deep space that runs from the floor to the

ceiling. In this situation, a tall water heater should be available that will provide the desired tank

volume and/or first hour rating. 

There will be a small percentage of cases where increases in water heater dimensions will

cause a variety of problems. Some replacement applications may be unable to accommodate the tank

size currently used. To thoroughly categorize problems related to increases in water heater sizes

would take a very extensive national survey of homes, something that has not been done. We believe

that the percentage of installations with space-related problems will be small. We believe these

problems will be more likely to occur in small, high density housing, such as apartments. In some

cases, the door to a closet or attic where the water heater is located may be only large enough to

accommodate the original water heater. A water heater with more insulation—hence larger

dimensions—may need a larger drain pan, require adjustments to the plumbing connections by

adding a tempering valve, or not fit through the door.

We believe that manufacturers and installers can make adjustments to allow water heaters

with thicker insulation to maintain the same overall dimensions of the water heater they will replace

and provide the same utility (i.e., first hour rating). 
E-5.2

E-5.2 DOWNSIZE FOR SPACE CONSTRAINTS

In some locations a water heater is so tight that a replacement water heater with thicker

insulation will not fit. In these cases, we assume it would be replaced with a smaller water heater

and the setpoint temperature increased to offset the reduced tank volume. We make this calculation

only for design options with insulation at least 2.5 inches thick.

Size constraints are addressed by estimating the number of households with smaller closets

and other spaces where water heaters are installed. Costs for adjustments to those installations are

then added. To this end, five assumptions are made:

(1) This condition would only apply in those cases where the water heater is installed in

conditioned space, e.g. not in a garage or an unconditioned basement.

(2) Oil-fired water heaters are located in unconditioned space and no replacement costs due to

space constraints are applied.

(3) This will only apply to small houses or apartments. Houses or apartments with a floor area

of more than 1,000 square feet are excluded. (See Figure E-5.1)

(4) These assumptions are not intended to accurately identify every individual household that

would face space constraints when replacing their water heater. Rather this estimate should

roughly identify the number of households effected.

(5) Those households with space constraints are assumed to use the next smaller standard size

water heater, and increase the water heater setpoint.

The RECS97 sample showed, of homes of less than 1,000 square footage, 32% of households

had electric water heaters and 27% of households had gas water heaters. For the household that has

space constraints, two adjustments were made: (1) adjust the setpoint of the smaller water heaters

upward so that the total energy content in the amount of water that could be delivered is the same

as could have been delivered by the larger, replaced water heater at a lower temperature; and (2) if

the setpoint is > 140°F, the cost of a tempering value is added.

The setpoint is increased so that the heat content of the water in the smaller water heater is

the same as the heat content of the water in the replaced water heater.

The First Hour Rating (FHR) is used as an indicator of the amount of hot water a water is

able to deliver. The heat content of an amount of water equal to the FHR at the household operating

conditions for the replaced water heater is shown in Eq 5.1:

Q F FHR replaced replaced replaced tank inlet =× − HRT T ( ) Eq.E-5.1
E-5.3

recalculate

setpoint

for each RECS house

water heater

in house?

Yes

No

house too

small?

Yes

select next smaller

size water heater

setpoint >

140 oF? Yes

No

Add tempering

valve.

recalculate

hot water use

calculate

energy use

calculate equpment &

installation cost

calculate LCC &

payback

next RECS house

Less than 1000 sq. ft.

See Equation E-5.3

To avoid scalding.

Space

Constraints

No

Figure E-5.1 Space Constraints Flowchart
E-5.4

The heat content of the amount of water in the smaller replacement water heater is calculated

in Eq. E-5.2.

Q FHR T T FHR smaller =×− smaller smaller tank inlet ( ) Eq. E-5.2

Setting the heat content of these water heaters equal and solving for the setpoint temperature

of the smaller tank (Ttank smaller) gives the following equation:

T T FHR

FHR

smaller tank inlet T T replaced

smaller

= ×− + ( ) replaced tank inlet Eq. E-5.3

The next step is to calculate the First Hour Rating for both water heaters - the replaced and

the downsized.

The following is a simplified methodology to calculate the "First Hour Rating" (FHR) for

gas water heaters based on tank volume, the rated input, and a 76% Recovery Efficiency. The

approach is based on an old DOE water heater test procedure. Several manufacturer engineers

confirmed that this approach closely approximates the results of the current First Hour Rating test

procedure. Following the old methodology, the test measured the volume of hot water delivered from

a water heater before the thermostat turned on. This represents the reserve energy stored in the water

heater. The test was conducted as follows:

 1. Set thermostat to maximum (typically 160°F)

 2. Allow water heater to run until it reaches maximum temperature and shuts off.

 3. Allow to set for a couple of minutes

 4. Draw water at a rate of 5 gal/min. until the outlet temperature drops 80°F 

 5. Stop the test

 6. Measure the gallons of water drawn.

 7. Measure the time from the start of the draw to the end of the draw.

The volume measured in this test is the reserve portion of the First Hour Rating.

The recovery portion of the First Hour is calculated by using the RE (Recovery Efficiency)

to compute how much water would be heated to the temperature of the thermostat setting during the

balance of an hour. For example, if the draw from the reserve test above was 7 minutes, then the

recovery would be calculated as if it could run 53 minutes.

It is possible to assume that the First Hour Rating (FHR) has two components, a reserve

component (Reserve FH) and a recovery component (Recovery FH) or :

FHR=(Reserve FH)+(Recovery FH) [gal] Eq. E-5.4

The reserve component is calculated using the following equation:
E-5.5

Reserve FH= (.87)(.95)(Rated Volume) [gal] Eq. E-5.5

where,

0.87 is a correlation coefficient applied in the old test procedure and updated using the

current GAMA directory,

0.95 is a coefficient which accounts for the rated volume, having 5% more volume than the

actual water heater tank.

Rated Volume = the rated volume of the water heater.

The recovery component is calculated using the following equation:

Recovery FH= (Recovery Rate)(60-[Reserve Draw Time]) [gal] Eq. E-5.6

where,

60 is the test hour converted to minutes [min], and

Recovery Rate [gal/hr] is defined in the old test procedure. It is calculated as a function of

the rated input, recovery efficiency and the test temperature difference using the following

equation:

Recovery Rate=(Rated Input)(Recovery Efficiency)/(80)(8.341)(60) [gal/min] Eq. E-5.7

In this equation the constants are defined as follows:

80 is the temperature difference during the reserve portion of the test (160 °F - 80° F = 80°F),

8.341 = coefficient to convert to [gal/min],

60 = coefficient to convert to [min/hr],

Recovery Efficiency is assumed to be 76%, and

Reserve Draw Time is the time to complete the reserve draw by drawing water at a rate of

5 gal/min until the outlet temperature drops by 80°F. It is calculated using the following

equation.

Reserve Draw Time=(Reserve FH)/(5) [minutes] Eq. E-5.8

After completing all the replacements, the equation for the First Hour Rating will be as

follows:

FHR RatedVolume RatedInput RE = × ( . ( . )( ) + − RatedVolume ( )( )

( )( . )( )

087 0 95 [ ( . )( . )( )]

80 8 341 60

60 087 0 95 Eq. E-5.9

It is important to note that this equation can be used for rough estimates only of the First

Hour and does not replace actual testing. Factors such as dip tube length, thermostat height, and tank

diameter are ignored in this calculation, and they effect the actual First Hour Rating.
E-5.6

Based on the above assumptions and equations, the First Hour Ratings for each standard

water heater size is calculated. The rated input varies somewhat from model to model. We used the

following rated input assumptions which match the data used in the engineering models for gas-fired

water heaters: 30 gal - 30,000 Btu/hr, 40 gal - 40,000 Btu/hr, 50 gal - 50,000 Btu/hr, 75 gal - 75,000

Btu/hr; and for electric water heaters: all volumes are rated 15,354 Btu/hr.

Table E-5.1 First Hour Rating and Related Volumes for Water Heaters

Gas-Fired Water Heaters Electric Water Heaters

Size First Hour Rating Size First Hour Rating

30 56 30 53

40 74 40 70

50 90 50 86

75 126 65 109

80 131

The cost of a tempering valve are added to 15% of electric and 9% of gas water heater using

households.

If the temperature of the smaller, replacement tank is above 140 oF, we assume a tempering

valve is used to bring the delivered water temperature back to the setpoint of the replaced water

heater.

A tempering valve mixes hot water from the water heater with cold water. This means less

hot water will be drawn from the water heater. See Figure E-5.2.
E-5.7

Vinlet, Tinlet

tempering

valve

hot water

mixed water

Vsmaller, Tsmaller

cold water

Vwarm, Twarm

Water Heater

(smaller tank) V cold water hot water smaller, Tinlet

Figure E-5.2 Schematic of Tempering Valve

The total amount of water leaving the tempering valve must equal the total amount of water

entering the tempering valve. Also the energy content of the water leaving the tempering valve must

equal the energy content of the water entering. These statements can be written as a system of two

equations and solved for the amount of hot water entering the tempering valve.

V VV warm inlet smaller = + Eq. E-5.10

V T VTV T warm warm inlet inlet smaller smaller × =×+ × Eq. E-5.11

Where the energy content of the water is approximated in Eq. E-5.11 as volume times

temperature.

The amount of water, Vsmaller (at a higher temperature, Tsmaller) drawn from the water heater

can be calculated by solving Eqs. E-5.10 and E-5.11 for Vsmaller.
E-5.8

V V

V T VT

T

smaller warm

warm warm inlet inlet

smaller

= − × −×

Eq. E-5.12

Where Vwarm and Twarm are the average daily draw and the thermostat setpoint for that

household’s original baseline water heater.

The energy calculations for the smaller, replacement water heater are done at the newly

calculated daily average draw and temperature for Vsmaller and Tsmaller.

E-5.3 INCREMENTAL DRAIN PAN COSTS

Some water heaters are installed with drain pans to reduce damage if the water heater should

ever leak. Replacng a drain pan is part of the normal installation cost. Some households may require

a drain pan of a larger size when a wider replacement water heater (due to increased insulation) is

installed under the new standard. We applied an incremental drain pan cost for design options with

2, 2.5, and 3" insulation.

The drain pan size is a function of the water heater diameter. The recommendation by

manufacturers is that the drain pan diameter should be 2 inches larger than the water heater'

diameter. We used RECS 97 to identify the households which would need a larger drain pan. Three

assumptions are made about the application of drain pan size increase costs:

(1) the house has no slab-on-grade floor,

(2) the water heater is not installed in a garage or an unconditioned basement, and

(3) the water heater was not subject to downsizing due to space constraints.

Figure E-5.3 shows the conditions where replacement of a drain pan would apply.

In the engineering analysis we used weighted average cost for each water heater diameter

from the LCC Analysis. The average costs for water heaters with 2-in insulation the drain pan cost

was $0.61 and for 2.5-in and 3-in insulation the drain pan cost was $1.81.
E-5.9

for each RECS house

Yes

slab-on-grade

floor

calculate equpment &

installation cost

calculate LCC &

payback

next RECS house

Drain Pan Size

Increase

Yes

water heater

installed in garage or

unconditioned basement

No

subject to

downsizing due to

space constraints

No

No

Yes

Figure E-5.3 Drain Pan Size Increase Flowchart
E-5.10

E-5.4 DOORWAY RESTRICTIONS

 The cost to enlarge a fraction of door openings has been estimated and accounted for in the

life-cycle cost analysis for water heaters with 3 inch insulation.

Design options that include 3 inch insulation can require an additional cost to account for the

impact on installation cost in replacement applications (e.g., to disassemble and reassemble

doorjambs). We have added a $160 installation cost for removal and replacement of door jambs for

50% of all water heaters located in the conditioned space. From the RECS 1997 data, we determined

that 59% of water heaters are located in a conditioned space. In the Engineering Analysis, we used

the calculated weighted average cost of $43.19 for all design options that include 3-in. insulation.
E-5.11

for each RECS house

Yes

calculate equpment &

installation cost

calculate LCC &

payback

next RECS house

Door Jam and

Frame Removal

Cost

water heater

installed in garage or

unconditioned basement

No

subject to

downsizing due to

space constraints

No

Yes

Figure E-5.4 Door Jam and Frame Removal Cost Assessment