water heater pressure relief draining?
hello all….
In my area, the pressure relief valves on water heaters just drain onto the floor in they’re installed in a basement. I’m getting ready to finish most of my basement, so I want to know what my options are. I’m pretty handy at most aspects of home construction and maintenance, but I don’t do it for a living, so I leave these technical/code questions to the experts.
Can I:
1. Plumb in into my my regular plumbing? I have a full bath plumbed in right next to it, so that would be easy. But I didn’t know if the velocity of the PRV cutting loose might shoot water backwards out of the tub or sink drains. If that velocity is a problem, could I put a large (maybe 6″ diameter) section of pipe between the water heater and the bath plumbing to give it room to dissipate the pressure and volume?
2. Drill a hole through the basement floor and let it drain with the groundwater? My basement is a level walkout on a gentle slope, so I think groundwater coming up through a hole just isn’t going to happen. My concern would be whether the gravel under the floor would allow the water to come out as fast/hard as it needs to.
or am I stuck with:
3. Running a line all the way to and through the back wall of the basement?
thanks in advance to everyone!
Replies
There might be some variations in this, but I think that codes want two main concerns.
1) is FREE DISCHARGE AT MAXINUM PRESSURE AND TEMPATURE. That bascially elimates any discharge that is confined. IE not into a hole in the floor or even into a trapped drain.
2) I am not as sure about this, but I believe that they want it to be observable so you know if it has is discharging.
Now some, warm weather locations, REQUIRE and external discharge of the PTV. But in cold weather locations a leaking valve can allow an external pipe to freeze up. And that ain't good.
But how often does one go off? Very, very, rarely.
Unless you re in a warm area I would just keep the floor drain. You might want to do some minor work to control any damage the water might do such as caulking the bottom plates to keep surface water in that area.
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Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
In addition to Bill Hartmans answers I think that the codes also are concerned about injury if the release is plumbed to a sink or fixture someone might be using when the valve opened.
His answer is correct as far as my knowledge of the codes go .
To summarize, there are four concerns (not all clearly spelled out in the code, but implied):
1) The flow must not be restricted in any way, or arranged such that the outlet might become plugged. (This includes the requirement that any attached discharge pipe be at least as large as the valve's outlet size.)
2) The outlet must not be arranged such that it might siphon water back into the water heater should the sewers back up. (Yeah, unlikely, but they're really retentive about this point.)
3) The outlet must be arranged such that large-quantity discharge (vs minor dripping) is reasonably obvious.
4) The outlet must not be arranged such that someone standing nearby might be seriously splashed with (very!!) hot water, should the valve discharge either intentionally (someone toggling it) or due to over temp/pressure conditions. Also, common-sense precautions should be taken against flooding, water splashing electrical equipment, etc.
In areas where outside discharge is not required, the best approach is probably to discharge into a standpipe (like for a washing machine) with the bottom end of the discharge pipe standing an inch or two above the top end of the standpipe (ie, so you can see "daylight" between them). The open end of the standpipe should be significantly larger than the discharge pipe (though it's OK for it to get smaller before entering the trap, so long as the pipe is large enough to handle full flow).
Several schools of though on this subject. I don't like to see a hole drilled in the floor with a pipe running through it, be it concrete or wood sub floor. The reason is most times if the tpr valve starts seeping you are unable to detect it. Seeping is what these valves do best, this slow leak is a sign the valve needs replaced. Under the right conditions this can go on for years, waste lots of water and energy. Codes say the drain pipe should end no less than six inches from the floor for safety reasons. My recomemended setup would be a cake pan under the drain pipe. Cast an eye on it occasionally as you pass by. The odds of this ever opening full blast are similiar to winning the lottery.
Options #1 and #2 are out of the question period. Plumbing code only allows T&P discharge lines to drain by indirect means. Meaning they must drain through an air gap of approximately 1-1/2" to the floor in the room installed or drain with the same 1-1/2" air gap into a water heater pan.
The pan is a metal or plastic device approximately 28" in diameter by 1-1/2" high. The water heater sits in this pan to protect surrounding flooring or in most cases when heaters are installed in attics the surrounding ceiling and insulation. These pan drains then must terminate indirectly over a floor drain or to within 6"-24" of the exterior grade.
Depending on the State and local jurisdiction where you are located there maybe more applicable codes/ordinances, just call your local inspection department.
Your PRV, like many, was probably installed without the code-required drainpipe, of the same diameter as the PRV's outlet (usually a 3/4" copper pipe soldered onto a 3/4" sweat to MIP fitting, then threaded into the PRV outlet). Pvc or pex is not ok for this.
Run this drainpipe directly down to near the floor, usually no higher than 6" off the floor (check local code), for the reasons mentioned by others.
These PRVs do end up seeping over time. In some cases, the hot water attacks the heat sensor tube's protective coating, exposing raw metal to the full heat. The worn sensor reacts to what is still a normal temperature by expanding more than it would if it had undamaged coating, so it compresses the spring and pushes the valve slightly open = seepage.
PRVs work on the same principle as a car's cooling system thermostat. A copper pellet expands with heat, pushes against a spring, opens a gate, allowing full system flow.
504.6.1 Discharge.
The relief valve shall discharge full size to a safe place of disposal such as the floor, outside the building, or an indirect waste receptor. The discharge pipe shall not have any trapped sections and shall have a visible air gap or air gap fitting located in the same room as the water heater. The discharge shall be installed in a manner that does not cause personal injury to occupants in the immediate area or structural damage to the building.
Plumbing Code - 2002 Edition
504.6.2 Materials.
Relief valve discharge piping shall be of those materials listed in Section 605.5 or shall be tested, rated and approved for such use in accordance with ASME A112.4.1. Piping from safety pan drains shall be of those materials listed in Table 605.5.
TABLE 605.5WATER DISTRIBUTION PIPE
MATERIAL
STANDARD
Brass pipe
ASTM B 43
Chlorinated polyvinyl chloride (CPVC) plastic pipe and tubing
ASTM D 2846; ASTM F 441; ASTM F 442; CSA B137.6
Copper or copper–alloy pipe
ASTM B 42; ASTM B 302
Copper or copper–alloy tubing (Type K, WK, L, WL, M or WM)a
ASTM B 75; ASTM B 88; ASTM B 251; ASTM B 447
Cross–linked polyethylene (PEX) plastic tubing
ASTM F 877; CSA CAN/CSA–B137.5
Cross–linked polyethylene/ aluminum/ cross–linked polyethylene (PEX–AL–PEX) pipe
ASTM F 1281; CSA CAN/CSA–B137.10
Galvanized steel pipe
ASTM A 53
Polybutylene (PB) plastic pipe and tubing
ASTM D 3309; CSA CAN3–B137.8
Above is the current North Carolina, USA code. Here PEX is legal, PVC not.
Start with a fresh relief valve and have the vertical discharge pipe end in a JC bucket.