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Hot Water Heater Size Charts
Water Heater Sizing Guidelines
- POST a QUESTION or COMMENT about how to improve hot water quantity and flow rate from a residential hot water heating system.
How to determine the size or capacity of hot water heating equipment needed at a building.
The peak hot water demand rate and number of hot water users as well as a number of other factors determine the necessary water heating capacity or hot water storage for buildings.
This article includes tables of typical hot water daily usage volume and hot water peak use rates by building type for residential and commercial buildings, drawing on several expert sources and a range of hot water use research articles.
This article series explains how to improve the total quantity of hot water available from your water heating system. Here we discuss How much hot water do we get out of a hot water heater tank? How to improve hot water water quantity from any water heater.
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Water Heater Size / Capacity Requirements
How to determine the size of water heating equipment needed for a residential or commercial building.
Quantity of hot water means the total volume of hot water available. Flow rate of hot water, is the gallons per minute of hot water delivered somewhere (out of the heater or at a plumbing fixture).
Hot water pressure, as most folks mean it, refers to the flow rate at the fixture.
Question: what is the number of water heaters required in 3 story commercial building
2017/09/14 anil said:
Can anyone give comments on number of water heaters required in 3 story commercial building?
This question was posted originally at HOT WATER CIRCULATOR PUMP SPEEDS DELIVERY
Reply:
Anil
Interesting question but not one that I could answer in a useful way as I have not a shred of information about your specific building, its intended use, number of occupants, number of bathrooms. You would work in a different sequence of than just an arbitrary number. Below we provide two tables that will help you out:
The National Renewable Energy Laboratory cited below has provided the following table showing the estimated gallons of hot water usage per person per day for U.S. buildings. Hot water usage requirements for your building could be very different as you'll see by the hot water requirements questions I pose below.
Hot Water Usage by Building Type1 |
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| Building Type | Estimated Hot Water Use Per Person Per Day | Comments | ||
| US Gallons |
Imperial Gallons |
Liters | ||
| Hospital | 52 | 43 | 197 | |
| Hotel / Motel | 20 | 16.7 | 76 | |
| House | 15.8 | 13.1 | 60 | Typical one-family residence |
| Office | 1.1 | 0.9 | 4.1 | |
| Restaurant | 2.4 | 2.0 | 9 | |
| School | 0.5 | 0.4 | 2 | |
| School with Showers | 1.9 | 1.6 | 7.2 | |
Notes: adapted from the NREL source given below. Source: DOMESTIC HOT WATER ASSESSMENT GUILDELINES [PDF] National Renewable Energy Lab (NREL), 1617 Cole Blvd., Golden CO 80401 USA Tel: 303-275-3000 Website: www.nrel.gov, retrieved 2017/09/15, original source: https://www.nrel.gov/docs/fy11osti/50118.pdf |
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Watch out: the data above describes estimates of total hot water consumption per person per day but it does not reflect the peak hot water demand rate. In hospitals, hotels, motels, restaurants, schools and other buildings, or special areas within those buildings (such as a kitchen or laundry), satisfying the peak hot water demand usage rate can require greater water heating capacity.
See the next table below to find examples of peak hot water demand rates in gallons or litres per hour.
Table of Peak Hot Water Service Demand in Buildings1 |
|||||
| Space Type | Hot Water Usage Rate per Hour |
Temperature at Point of Use2 |
Data Sources | ||
| Gal/H | L/H | °F | °C | ||
| Guest room, small hotel | 1.75 | 6.6 | 110 | 43 | Jiang et al. 2008, ASHRAE 2007 |
| Guest room, large hotel | 1.25 | 4.7 | Jiang et al. 2008, ASHRAE 2007 | ||
| Laundry, small hotel | 67.5 | 255.5 | 140 | 60 | Jiang et al. 2008, ASHRAE 2007 |
| Laundry, large hotel | 156.6 | 592.8 | Jiang et al. 2008, ASHRAE 2007 | ||
| Restrooms (primary school) | 56.5 | 214.0 | 110 | 43 | ASHRAE 2007 |
| Restrooms (secondary school) | 104.4 | 395.0 | ASHRAE 2007 | ||
| Gym (secondary school) | 189.5 | 717.2 | ASHRAE 2007 | ||
| Small office | 3.0 | 11.4 | Jarnagin et al. 2006, ASHRAE 2007 | ||
| Medium office (per floor) | 9.9 | 37.5 | Jarnagin et al. 2006, ASHRAE 2007 | ||
| Large office (per floor) | 21.3 | 80.6 | Jarnagin et al. 2006, ASHRAE 2007 | ||
| Apartment | 3.5 | 13.2 | Gowri et al. 2007 | ||
| Outpatient healthcare | 30.0 | 113.5 | Doebber et al. 2009 | ||
| Hospital Hot Water Requirements | |||||
| ER waiting room | 1.0 | 3.8 | 120 | 49 | Engineering judgment1 |
| Operating / surgical cytoscopic | 2.0 | 7.6 | Engineering judgment1 | ||
| Laboratory | 2.0 | 7.6 | Engineering judgment1 | ||
| Patient room | 1.0 | 3.8 | Engineering judgment1 | ||
Notes: 1. This InspectApedia table was excerpted / adapted from: Deru, Michael, Kristin Field, Daniel Studer, Kyle Benne, Brent Griffith, Paul Torcellini, Bing Liu, Mark Halverson, Dave Winiarski, Michael Rosenberg, Mehry Yazdanian, Joe Huang, Drury Crawley COMMERCIAL REFERENCE BUILDING MODELS OF THE NATIONAL BUILDING STOCK [PDF], Technical Report NREL/TP-5500-46861 February 2011, (Page 17), 2. See also ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES |
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Hot Water Requirements Basic Design Questions
Questions that need to be addressed when estimating the total hot water capacity usage and then how that hot water is produced, stored, and distributed in a building include at the very least the following:
- How many occupants are there in the building? What is the peak occupancy? At what times are the peak occupancy and the peak hot water use?
- How many bathrooms and bathroom fixtures are required?
- What types of hot water uses are there in the building: residential bathing, worker day-bathing, cooking, industrial processes that use hot water, industrial cleaning applications?
- What is the peak simultaneous (multi-user) washroom and other hot water use?
- What is the required temperature of the hot water at the point of delivery.
Watch out: while scalding proection is necesssary to avoid burning hot water users, some applications such as restaurant and hospital cleaning facilities may require higher temperatures as may some industrial processes. See also ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES - What is the water heating fuel source
- What are the building type, layout, footprint, height, incoming water pressure?
- What sized water tanks need to be located where in the building to serve its population economically and effectively
- What is the climate where the building is located. Climate is a factor in typical daily hot water usage for reasons discussed in several of the sources I cite below.
You need to find both the total hot water volume required over a given period of time and how it needs to be distributed: to how many locations?
Then you'd decide between a single large central water heater or multiple individual water heaters and their locations.
In the United States the US DOE offers some advice on "sizing a water heater" that might help you out. Below we provide several references and guides for choosing the water heating size or capacity or flow rate for both commercial and residential buildings.
Water Heater Sizing Guides & Tables for Water Heating Equipment, Calorifiers, Hot Water Cylinders, Geysers
- DETAILS OF COMMERCIAL WATER USE AND POTENTIAL SAVINGS, BY SECTOR, OFFICE BUILDINGS, Appendix E [PDF] (SIC codes 60–64, 67, 73, 81, 87, and 90), New York City, USA, retrieved 2017/09/15, original source: http://www.nyc.gov/html/dep/html/residents/wateruse.shtml
Except: Offices buildings house a wide variety of companies ranging from insurance brokers to law offices. Although the types of offices differ, their employees are usually engaged in similar activities and can therefore be aggregated under one category.
We did not, however, include SIC code 65 (real estate) or SIC code 86 (membership organizations) in our analysis, because the GEDs estimated were unreasonably high; indicating problems with either the data or the categorization.
For example, we suspect that SIC code 65 includes multi-family housing in addition to real estate offices because it includes in its description “apartment building operators,” and rental offices are often located within apartment complexes, where water is used for residential purposes. - DOMESTIC HOT WATER ASSESSMENT GUILDELINES [PDF] National Renewable Energy Lab (NREL), 1617 Cole Blvd., Golden CO 80401 USA Tel: 303-275-3000 Website: www.nrel.gov, retrieved 2017/09/15, original source: https://www.nrel.gov/docs/fy11osti/50118.pdf
- Deru, Michael, Kristin Field, Daniel Studer, Kyle Benne, Brent Griffith, Paul Torcellini, Bing Liu, Mark Halverson, Dave Winiarski, Michael Rosenberg, Mehry Yazdanian, Joe Huang, Drury Crawley COMMERCIAL REFERENCE BUILDING MODELS OF THE NATIONAL BUILDING STOCK [PDF], Technical Report NREL/TP-5500-46861 February 2011, National Renewable Energy Lab (NREL), 1617 Cole Blvd., Golden CO 80401 USA Tel: 303-275-3000 Website: www.nrel.gov, retrieved 2017/09/15, original source: https://www.nrel.gov/docs/fy11osti/46861.pdf
- Danny S. Parker, Danny S., Philip W. Fairey, James D. Lutz, ESTIMATING DAILY DOMESTIC HOT WATER USE IN NORTH AMERICAN HOMES FSEC-PF-464-15 [PDF]
Florida Solar Energy Center (FSEC), 1679 Clearlake Road, Cocoa FL 32922 USA, Tel: 321-638-1000, Website: www.floridaenergycenter.org, Presented at ASHRAE Conference, June 30, 2015, 1791 Tullie Circle NE, Atlanta Georgia, 30329, Tel: 404-636-8400, Website: www.ashrae.org, retrieved 2017/09/15, original source: http://www.fsec.ucf.edu/en/publications/pdf/FSEC-PF-464-15.pdf
Abstract:
Water heating in the U.S. is a major component of total energy consumption in buildings, accounting for approximately 18% of total consumption in the residential sector (EIA 2010).
While there are many factors influencing hot-water energy use (location, fuel, combustion and heating efficiency, and standby losses), the actual volume of daily water to be heated is a fundamental quantity for any reasonable estimate of hot-water energy use.
This study uses measured annual hot-water use in various North American climates to evaluate hot-water use in homes.The findings show that the quantity of hot-water use is correlated most closely to the mains water temperatures and the occupant demographics of the homes with 70% of the available measurement dataexplainedwhenoccupantdemographicsarewellknown.
The study proposes a new methodology for estimating the quantities of hot-water use in homes as a function of climate location and occupancy demographics, segregating machine hot-water use, fixture hot-water use, and distribution system hot-water waste. - RESIDENTIAL WATER USE TABLE [PDF], New York City Department of Environmental Protection, retrieved 2017/09/15, original source: http://www.nyc.gov/html/dep/html/residents/wateruse.shtml
- SIZING a NEW TANKLESS or DEMAND-TYPE WATER HEATER, [PDF] U.S.DOE, Office of Energy Efficiency & Renewable Energy, Forrestal Building, 10-00 Independence Ave., SW, WShington DC 20686, retrieved 2017/09/14, original source: https://energy.gov/energysaver/sizing-new-water-heater
Excerpt:
A properly sized water heater will meet your household's hot water needs while operating more efficiently.
Therefore, before purchasing a water heater, make sure it's the correct size.
Here you'll find information about how to size these systems:
Tankless or demand-type water heaters, Solar water heating system, Storage and heat pump (with tank) water heaters. - WATER HEATING ENERGY-EFFICIENT STRATEGIES FOR SUPPLYING HOT WATER IN THE HOME, [PDF] U.S. DOE/GO-102001-0785 (2001) retrieved 2017/09/15, original source: https://www1.eere.energy.gov/buildings/publications/pdfs/building_america/26465.pdf
...
Continue reading at HOT WATER QUANTITY IMPROVEMENT - how to get more hot water, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
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Citations & References
In addition to any citations in the article above, a full list is available on request.
- Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
- AO Smith produces AO Smith water heaters in addition to Reliance, State, Maytag and others.
www.aosmith.com/prod/wpc.htm AOS's gas water heater manuals offering advice and safety warnings about adding water heater insulation are available at
www.statewaterheaters.com/lit/im/res-Elec/184671-000.pdf and at
www.hotwater.com/lit/im/res_gas/184123-000.pdf - Rheem who also makes electric water heaters provides a manual for electric water heaters at
waterheating.rheem.com/content/resources/documents/use_care/ResElecProfessional.pdf. - Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates'Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.HOT WATER HEATERS - a detailed guide to all types of hot water sources, problems, inspection, repair - In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
CONTINUE READING or RECOMMENDED ARTICLES.
- Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The HOME REFERENCE BOOK - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.
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