Can the temperature and pressure relief (TPR) valve discharge pipe for a mobile/manufactured home water heater terminate under the home?
Monday, June 25, 2018
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.
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