First Hour Rating For

Storage-type Water Heaters

* Purpose / Goal

* Definition

* Brief History

* Opinions on First Hour Rating

», Maintain present structure

,, Alternative sizing descriptors

* Address specific issues about proposed

methods

EE-RM-94-230 COMMENT 49D

First Hour Rating For 

Storage=type Water Heaters 

e Purpose / Goal 

fa Definition 

e Brief History 

fit Opinions on First Hour Rating 

» Maintain present structure 

» Alternative sizing descriptors 

e Address specific issues about proposed 

methods 
Purpose/ Goal

* Sizing information; a means for

comparing different units

* FTC Labeling: alternative to storage

capacity

* Single descriptor that embodies:

,, storage capacity

,, recovery capability

- heating input rate

- location of heat input

EE-RM-94-230 COMMENT 49D

Purpose / Goal 

e Sizing information; a means for 

comparing different units 

e FTC Labeling: alternative to storage 

capacity 

e Single descriptor that embodies: 

» storage capacity 

» recovery capability 

- heating input rate 

-location of heat input 
Definition

An estimate of the maximum volume

of "hot" water that can be supplied

within an hour that begins with the

water heater fully heated (i.e.., all

thermostats satisfied)

EE-RM-94-230 COMMENT 49D

Definition 

An estimate of the maximum volume 

of "hot" water that can be supplied 

within an hour that begins with the 

water heater fully heated (i.e .. , all 

thermostats satisfied) 
Brief History

* Repeated Test Procedure Revisions

* Reasons Behind Revisions

», minimize impact of mixing and lab tolerances

(thermostat and water inlet) via normalizing

», avoid overstated ratings

», avoid repeatability problem

», avoid understated ratings (test method not

consistent with definition)

EE-RM-94-230 COMMENT 49D

Brief History 

e Repeated Test Procedure Revisions 

e Reasons Behind Revisions 

» minimize impact of mixing and lab tolerances 

(thermostat and water inlet) via normalizing 

» avoid overstated ratings 

» avoid repeatability problem 

» avoid understated ratings (test method not 

consistent with defi n ition) 
Brief History

Fist Hour Rating Is referenced by:

,, FTC: for size ranges in their labeling program

,, HUD: FHA minimum water heater capacity requirement

,, Offered as a guideline in building codes

,, Discussed in the ASHRAE Applications Handbook

,, GAMA Directory shows how to use it

? Is First Hour Rating used within manufacturer

residential sizing guidelines?

EE-RM-94-230 COMMENT 49D

Brief History 

e Fist Hour Rating Is referenced by: 

» FTC: for size ranges in their labeling program 

» HUD: FHA minimum water heater capacity requirement 

» Offered as a guideline in building codes 

» Discussed in the ASHRAE Applications Handbook 

» GAMA Directory shows how to use it 

? Is First Hour Rating used within manufacturer 

residential sizing guidelines? 
Despite the noted references, First Hour Rating's

popularity as a sizing descriptor is questionable

* New Construction

,, purchasing decision: usually builder

,, uses rules of thumb that do not factor in First Hour Rating

* Replacement market

,, purchasing decision: plumber and/or homeowner

,, again, First Hour Rating probably is not considered

,, selection is often driven by the need to restore hot water

service quickly; likely outcome:

- same size/type of unit as presently installed

- closest match from available stock

- one size higher if presently having excessive runouts

EE-RM-94-230 COMMENT 49D

Despite the noted references, First Hour Rating's 

popularity as a sizing descriptor is questionable 

• New Construction 

» purchasing decision: usually builder 

» uses rules of thumb that do not factor in First Hour Rating 

• Replacement market 

» purchasing decision: plumber and/or homeowner 

» again, First Hour Rating probably is not considered 

» selection is often driven by the need to restore hot water 

service quickly; likely outcome: 

- same size/type of unit as presently installed 

- closest match from available stock 

- one size higher if presently having excessive runouts