Service Water Heating Systems
ASHRAE Technical Committee 6.6

Scope of TC 6.6

TC 6.6 is concerned with two general areas: (1) service water requirements, and (2) design of the system for heating and distributing service hot water. The heating system design requires knowledge of storage capacities, heat recovery systems, etc.


The ASHRAE Handbook is published in a series of four volumes, one of which is revised each year, ensuring that no volume is older than four years.  The Handbook can be purchased at the ASHRAE Bookstore by clicking on this link.

The TC is responsible for the following chapter in the HVAC Applications Volume.

Service Water Heating
Water heating energy use is second only to space conditioning in most residential buildings, and is also significant in many commercial and industrial settings. In some climates and applications, water heating is the largest energy use in a building. Moreover, quick availability of adequate amounts of hot water is an important factor in user satisfaction. Both water and energy waste can be significant in poorly designed service water-heating systems: from over- or undersizing pipes and equipment, from poor building layout, and from poor system design and operating strategies. Good service water-heating system design and operating practices will reduce operating costs and can often reduce first costs. The information in this chapter is thus critical for the sustainable design and operation of many buildings.

The ASHRAE HVAC APPLICATIONS HANDBOOK may be purchased from the on-line bookstore by clicking on the highlighted text.

Comment on the Handbook: ASHRAE welcomes your comments on the Handbook or a specific Handbook chapter.  To submit a comment about any aspect or part of the Handbook series, you can use the Handbook Comment Form.

Review a Handbook Chapter: To provide your feedback about a specific Handbook chapter, you can answer the brief survey questions on the Handbook Chapter Review Form.


Technical committees develop and sponsor technical sessions at the winter and annual conferences. Information about their future technical program is discussed at each TC meeting and at the TC’s Program Subcommittee meeting

ASHRAE publishes papers and transactions from presentations at its conference events. In addition, ASHRAE records most of the seminar sessions from its conferences on DVD. These DVDs are ideal for use at chapter meetings, in university courses, or company lunch and learns. Products available from the most recent conference may be found here.


Technical Committees are responsible for identifying research topics, proposing research projects, selecting bidders, and monitoring research projects funded by ASHRAE. Information about their specific research program is discussed at each TC meeting and at the TC’s Research Subcommittee meeting.


ASHRAE writes standards for the purpose of establishing consensus for: 1) methods of test for use in commerce and 2) performance criteria for use as facilitators with which to guide the industry. ASHRAE publishes the following three types of voluntary consensus standards: Method of Measurement or Test (MOT), Standard Design and Standard Practice. ASHRAE does not write rating standards unless a suitable rating standard will not otherwise be available. ASHRAE is accredited by the American National Standards Institute (ANSI) and follows ANSI's requirements for due process and standards development. Standards may be purchased at the ASHRAE Bookstore.

TC 6.6 is involved with the following standards as a cognizant or co-cognizant TC:

Guideline 12: Minimizing the Risk of Legionellosis Associated With Building Water Systems (co-cognizant with TC6.7)
ASHRAE 95: Methods of Testing to Determine the Thermal Performance of Solar Domestic Water Heating Systems
ANSI/ASHRAE Standard 118.1: Method of Testing for Rating Commercial Gas, Electric, and Oil Service Water Heating Equipment
ANSI/ASHRAE Standard 118.2: Method of Testing for Rating Residential Water Heaters
ANSI/ASHRAE Standard 124: Methods of Testing for Rating Combination Space-Heating and Water-Heating Appliances
ANSI/ASHRAE Standard 137: Methods of Testing for Efficiency of Space-Conditioning/Water-Heating Appliances that Include a Desuperheater Water Heater
ANSI/ASHRAE Standard 146: Method of Testing and Rating Pool Heaters
ANSI/ASHRAE Standard 188: Legionellosis: Risk Management for Building Water Systems
(co-cognizant with Environmental Health Committee - lead and TC3.6)
Proposed Standard: SPC 191P: Standard for the Efficient Use of Water in Building, Site and Mechanical Systems
(co-cognizant with TC2.8 - lead)

Other Activities

TIP: If MTG involvement add here otherwise leave blank.

TC 6.6 is involved with MTG OBB: Occupant Behavior in Buildings


ASHRAE Technical FAQs are provided as a service to ASHRAE members, users of ASHRAE publications, and the general public. While every effort has been made to ensure their accuracy and reliability, they are advisory and provided for informational purposes only, and in many cases represent only one person’s view. They are not intended and should not be relied on as an official statement of ASHRAE. Technical questions not addressed may be submitted to the ASHRAE Technical Services department at