The International Residential Code (IRC) allows water heater installation in a crawl space (an unconditioned space under a home, just a few feet high, and over bare dirt), but there are multiple requirements for the installation:

•• Water heater must be approved by manufacturer for crawl space installation (IRC M1302.1). For gas installation, there are no lowboy gas tank water heaters, so forget that; and tankless gas installation will require code-compliant flue to exterior.

•• Access opening and access-way through crawl space to appliance must be minimum of 22-inches wide by 30-inches high, clear of any obstructions, and also large enough to remove the water heater later. Cannot be more than 20-feet from access opening to appliance (IRC M1305.1).

•• Minimum 30-inches by 30-inches level working space in front of the control side to service the water heater (IRC M1305.1).

•• A luminaire (light fixture) near the water is necessary, controlled by a switch at the access opening (IRC M1305.1.3.1).

•• Also need a receptacle outlet near the water heater for service technician to use (IRC M1305.1.3.1).

•• Water heater must be 3-inches above ground if supported from below by concrete slab or other approved material. If water heater suspended above the ground, it must be minimum 6-inches off. (IRC M1305.1.3.1)

•• If the passageway or service space goes more than 12-inches below grade, a concrete or masonry lined passage must be installed for access (IRC 1305.1.4). 

•• The water heater’s TPR (Temperature and Pressure Relief) valve must drain by gravity to a readily visible location outside the crawl space, along with multiple other requirements (IRC P2804). See our article What are the most common installation mistakes with water heater replacement? for more details.

    These standards apply to both tank and tankless electric water heaters. Other concerns when installing a water heater in a crawl crawl space are protection from possible flooding after a rainstorm, accelerated corrosion due to high humidity, and protection of piping from freezing in colder climates.

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Here’s links to a collection of more blog posts about WATER HEATERS:

• Are water heaters required to be raised off the floor? 

• Can a Temperature and Pressure Relief (TPR or T&P) valve be mounted to discharge horizontally?

• Where are gas water heaters not allowed to be installed?  

• Is the minimum size water heater inlet pipe 1/2" or 3/4" according to the building code? 

• Can you use a light switch for a water heater disconnect? 

• How can I tell if a water heater is HUD-approved for mobile/manufactured homes? 

• What is the minimum clearance to doors and windows for an outdoor tankless gas water heater? 

• What is required clearance for access and working space in front of an electric water heater? 

• Why should a tankless water heater have an isolator/service valve kit installed?

• When was a gas water heater first required to be elevated 18 inches above a garage floor?  

• Can the temperature and pressure relief (TPR) valve discharge pipe for a mobile/manufactured home water heater terminate under the home? 

• What is the purpose of a thermostatic mixing valve above a water heater? 

• Does a tankless water heater require a pressure relief valve?

• When is a water heater drain pan required?

• Why is there water in my water heater drain pan?

• What does it mean when a water heater Temperature/Pressure Relief (TPR) discharge pipe is "trapped"? 

• What is a dielectric union?

• What's that powdery crust on the pipe connections at the water heater? 

• Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises? 

• What can I do to make my water heater last longer?

• How can I determine the age of a water heater if the serial number is missing or decoding it is impossible? 

• What does it mean when a gas appliance (water heater, furnace, or range) has been "red tagged"?  

• Why is an older water heater an insurance problem?

   Visit our WATER HEATERS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.