The requirements for the TPR valve discharge piping are virtually identical for both site-built and mobile homes, with one big exception: the International Residential Code (IRC) and residential edition of the Florida Building Code (FBC) specify that the piping “discharge to a termination point readily observable by the building occupants,” but the HUD-code [3280.609 (c) (1) (iii)] specifies that it “shall be directed downward and discharge beneath the manufactured home.”

    We wish it wasn’t that way, but it is. Termination of TPR discharge piping under a mobile home means that if the valve opens and releases hot water, the homeowner will not be aware of it unless there is more water released than can be absorbed by the ground under the home and it spills out beyond the skirting, or someone hears the faint sound of running water under the home.

    The TPR valve can open for either of two reasons: 1) the temperature or pressure inside the tank rises to a dangerous level and the valve automatically opens to avoid a tank explosion, or 2) as TPR valves age, some of them fail by slowly, but steadily, leaking a small stream of hot water 24-hours a day. The water heater in the photo above was an example of the second situation. It was original to the construction of the mobile home, 17-years old, and dripping hot water continuously under the home—but not enough to be noticed unless you were crawling around under it. Here’s a photo below of what it looked like under the home.

    Obviously, this kind of defect is an expensive waste of energy and avoidable. We always suggest to homebuyers that they extend the TPR discharge piping to a location just outside the skirting and pointed downward, as a safety upgrade. 

    Water heaters in older mobile homes that we inspect are often in poor condition, and part of the reason is that they are concealed in a compartment with a cover panel secured with 8 or 10 screws. A water heater in a site-built home gets seen occasionally by the homeowner in the garage, behind a door in a hall closet, or a corner of the laundry room, so any corrosion or minor leakage problems can be caught before they cause a flood in the home. Water heaters in mobile homes usually fail by leaking, and the first indication is soggy carpet or wallboard in an adjacent room. The floor under the water heater often has to be replaced along with the water heater. Because of this second concealment issue, we urge buyers of older mobile homes to unscrew the cover panel and check their water heater at least annually.

    Also, see our blog post What is the difference between a manufactured/mobile home water heater and a regular water heater? 

• • • • • • • • • • • • • • • • • • • • • • • • • • • • 

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?  

• What does ECO INSTALLED mean on a water heater data sticker?

• 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?

• Can you wire a 240-volt water heater with 120 volts? 

• Is it alright to have a shut-off valve on both the hot and cold water pipes at a water heater?  

• 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 is the water heater older than the house? 

• Does a water heater need a shut-off valve? 

• 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 gas water heater still work with no electricity during a power outage?  

•  Why do water heaters have a sacrificial anode? 

• Does a tankless water heater in an attic require a drain pan? 

• Does an electric water heater require a disconnect? 

• Is a catch pan and drain piping required for a replacement water heater?

• What is the difference between a single element and dual element electric water heater? 

• What is an FVIR water heater?

• What is a heat pump water heater?

• What is a dielectric union?

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

• What are the most common installation mistakes with water heater replacement?

• 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? 

• How does a hydronic heating system work?

• What is the difference between a regular water heater and a direct vent water heater? 

• What is the difference between a regular water heater and a power vent water heater?

• What is backdrafting at a gas water heater? 

• How do I determine if a water heater is gas or electric?

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

• What's the valve with the flip-up handle on the water heater for?

• Why is an older water heater an insurance problem?

    Visit our WATER HEATERS and MOBILE/MANUFACTURED HOMES pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.