# Hot Water Calculations

Posted by Raymond VinZant Plm Prof on January 8th, 2003 08:00 PM
In reply to Domestic Hot Water Sizing by Marcel on January 8th, 2003 01:51 PM [Go to top of thread]

For each fixture unit you calculate it is equal to 7.5 gpm of flow. In addition, you need 10 gallons of hot water per day per person. You can either provide the storage capacity to equal those measurements (42 units x 2 people x 20 gallons){substitute appropriate people and gallons} or you can provide a certain percent storage and the equal number of btu's to meet that demand. Since every btu of water heats 1 pound of water (8.33 pounds per gallon) 1 degree f., figure out how many degrees of rise (temp differential from inlet temp to required temp of 130 degrees) you will need. Typically a building like yours will have at least 3 commercial 100 gallon water heaters with aproximately 299,000 btu of heating.
As John says though, check with Rheem water heaters, or AO Smith and they will size it for you, just to try and get your business.
Good Luck