Draining water heater TPR valve

[DirtyBrad]

I just purchased a new 50 gallon natural gas water heater and have been doing my research on installing it, but I'm not clear on how the TPR valve should drain. The old unit had a vertical pipe that just terminated about 18" from the floor, so any water would just dump out next to the water heater.

I've read that I should have the valve draining to a floor drain, but I don't have one. The water heater is located in a small room in the basement with a bare concrete floor and the rest of the basement is finished with tile. Obviously, I'm left with the possibility of this thing just draining endlessly into my basement and I'd like to prevent that.

I do have a standpipe drain whose opening is slightly higher than the TPR valve. My AC drains into that by way of an electric pump mounted about two feet up from the floor and 20' or so of plastic tubing. That pump has multiple openings, so my thought was to just run a pipe from the new TPR to it and let it do its thing. I also considered getting a second pump, so there would be one dedicated to each appliance.

I have a few reservations about this. First, I'm not sure if those pumps can handle the kind of output the TPR valve might be putting out. Second, I wouldn't know if the valve was tripping. I saw an emergency sump pump that had battery backup and would sound an alarm if activated, but I don't have a sump pit. I guess I could put it in a bucket or something and run a hose into that, but it feels pretty hacky.

Just looking for general thoughts and suggestions on this, thanks for your time.

 

[Terry]

The TPR needs to gravity drain.
Most of them terminate 6" above the ground or floor.

You can also run them to a floor drain, or to a pump basin.
At the most, these things only put out a little water. The spring is pretty strong.
But even that little bit will be enough to let off dangerous pressure.
The pipe draining the T&P needs to be full size 3/4"
The tubing from the pump basin can be smaller, it's not going to keep up with it if it's running full stream anyway.

 

[Sponsor]

 

[DirtyBrad]

That's interesting, thank you. When we bought the house six months ago, the inspector warned us that the water heater was at the end of its service life (12 years, I think?). What prompted replacing it with the new one was coming home to that thing leaking water onto the floor in a very steady stream.

In trying to bridge the gap to the new one being installed, I've been turning the supply to it and the heat on only briefly when I need a shower and it very often runs steadily then. Last night, I heated the water, turned off the heat and the supply. This morning, my girlfriend got up, turned on the supply (but not the heat), took her shower (water was still hot enough from last night), then turned off the supply. When I got up an hour later, the water had overflowed a 5-gallon bucket and was still flowing steadily.

Seems like any way you slice it, the old valve is shot, right?

If I'm only going to get a small amount of water pushed out of that thing when it's working, I should be okay running a hose down into my condensation pump then, right?

 

[Nukeman]

I can tell you when things go wrong, the TPR can make a real mess (found that out the hard way). Our WH was in the closet under the basement stairs (finished basement, no drain for the TPR). Came in from working outside (was going to leave for lunch), but decided to go down to the basement to put some tools away. I then hear water rushing and everything is soaked. The TPR was wide open (probably stuck) putting out as much as the city line could supply. Caused lots of damage. I'm not sure what happened in my case, but I believe that it must have been a failed t-stat causing the heaters to stay on. I know it wasn't just the case of the TPR opening when it shouldn't because I also found that the seam on the tank split as well (so I know the pressure got up there).

Anyway, to be safe, I would try real hard to gravity drain it and not rely on buckets/pumps. How far away is this standpipe? In the same room? Perhaps you can lower it to be able to drain by gravity.

If yours is opening, it could be a bad TPR (you can replace without replacing the WH) or your pressure may be getting too high. This can be especially true if there is a check valve between the city and your water supply and have no expansion tank (or a bad one). The expanding water causes the pressure to build and the TPR to open.

 

[DirtyBrad]

nukeman, I thought about cutting the standpipe down for this. It was in there before for a W/D which has since been moved, so no reason it has to be up as high as it is. The only issue is that it's on the opposite wall from the water heater, such that I'd have to run the drain line all the way around the room. Not the end of the world, but I was hoping to get away with just up and over with a pump.

Actually, now that I think of it, if I moved that drain pipe over, it would be closer to the water heater and my condensation pump, so maybe that's the best way to go. That just leaves the question of me not knowing about the valve going off since there will be no evidence. Is worrying about that just being paranoid?

I figured it was just the valve, but like I said, the water heater is old so I figured this was my cue to replace it rather than having to worry about the next thing. Plus, it'll be nice when we move to be able to say that the furnace, AC, and water heater are all 2010.

I was reading about the check valves. Our house is old, 1950, and I'm not aware of any. There's no expansion tank, but I bought one to be on the safe side because there doesn't seem to be any negative with having one.

 

[Jimbo]

There has to be a reason for the TP to be discharging, and it is rarely anything to do with the water heater.

Could be the TP itself is just bad, and that can be replaced. It is often related to a pressure issue in the house. If your pressure regulator has failed, you could be seeing high pressure, and the tp is doing its job. Check your pressure.

 

[Nukeman]

When you pipe the T&P to the drain, you usually have to have an air gap (and usually in the same room as the WH). So you might run the T&P in copper over to a wall, have it point down into a larger pipe (PVC for instance) and then run that pipe to your drain point. You'd leave a gap (1.5" or so) between the copper and the PVC so you could see if the T&P is dripping.

I agree with jimbo that you should 1st see what your pressure is actually doing. If it is a bad T&P, they are pretty cheap and simple to replace. Might as well keep the extra cash on hand for other expenses that might pop up. You never know what is going to happen after moving into a new place. The old WH might keep on going for years to come. You just never know.

 

[DirtyBrad]

I got a pressure gauge and will be checking that out tonight.

I already have the new water heater, so that bridge is crossed.

With an air gap, is that actually above the pipe or just putting the pipe inside a larger one similar to a washer outlet house hooked over a standpipe?

 

[Shacko]

>>>With an air gap, is that actually above the pipe or just putting the pipe inside a larger one similar to a washer outlet house hooked over a standpipe?<<<

What you need is a air gap which is above the drain, you have to be able to see it when it's draining; down inside of the drain pipe is called an air break.

 

[Jadnashua]

The T&P valve is a safety device that under normal circumstances, should never release water. It will release water if the temperature gets too high (normally something like 180-190 degrees - i.e., before it could boil and really ruin your day), OR, if the pressure gets too high (typically around 150 pounds).

If it does leak, and neither of those are causing it, it is defective and should be replaced. Doesn't matter if it is new, or old, if it is leaking with no good reason, it is defective and must be replaced.

A common reason the water pressure may be high is either the supply is too high, the prv is bad, or you either don't have an expansion tank when you need one, or the one you have is defective. When the cold water goes into the tank, then gets heated, it expands. If your system needs an expansion tank and doesn't have one, the pressure can easily get high enough to cause a discharge. May not be a lot, but it will happen each time after you stop using water, and that cold (if there was enough) gets reheated and expands.

 

[hj]

quote; First, I'm not sure if those pumps can handle the kind of output the TPR valve might be putting out

You can be ABSOLUTELY certain the pump will not keep up with a discharging T&P valve. When it opens due to high temperature it operates at FULL volume, hopefully just until the tank is cooled down. Releasing due to pressure, it will run until the pressure is below its set point, which may, or may not, ever happen depending on why the pressure is too high. You cannot run the discharge to a point higher than the valve, because water standing in the pipe can rust the spring in the valve, and then it may NEVER operate even when it is supposed to.

 

[DirtyBrad]

I got the heater installed last night. I bought an expansion tank, but did not end up installing it yet.

When I got home, I tested the pressure on my outside faucet. It was 90psi. The expansion tank I bought, a Watts DET 12, said that it shouldn't be installed where the pressure was above 80psi. Which seems a little strange, since the little chart on the box has a slot for a 50-gallon water heater and 90psi.

I read up on pressure reducing valves and the Watts' diagram showed the tank installed just downstream of one such that only the water to the water heater was reduced. That made sense to me, but I'm not sure I have room to do it. My cold water pipe comes into the utility room horizontally along the ceiling then hits a T, going straight down to the water heater and up to my shower. I could put the PRV in before the T, but then I'm reducing my shower water pressure. There's only about two feet between that T and the water heater cold water inlet. Last night, I cut about 6" down from the T and installed a Sharkbite valve and hose.

I put a pressure gauge on the drain valve and kept an eye on it after filling the tank for the first time. It maxed out at 100psi and was still there this morning. There's an unused washer hookup in the same room and that's at 90psi, same as my outside faucet last night.

I might be able to squeeze a pressure reducing valve, cutoff valve, and then the expansion tank, but it would be tight and the tank would be horizontal right over the water heater. As there was no expansion tank in the system before, it seemed like the smart bet to get it going without it, use the Sharkbites, which I can easily remove later, and ask you guys what you thought.

As far as the draining, I'm going to take your suggestion and run my standpipe around the room over near the water heater. That'll let me run a hose from the relief valve over the drain and also leave a much shorter run for my existing condensation pump.

 

[Jadnashua]

An expansion tank only MAINTAINS the existing pressure by allowing the water that expands from being heated a place to go (otherwise, the pressure just goes up until the water is heated, or something leaks, to relieve it). It has nothing to do with lowering your static system supply pressure. In most locales, anything in excess of 80# should have a PRV installed, so with a static of 90, and it is often more at night, you should have one.

The expansion tank should go after the prv and the shutoff to the WH on the cold, or inlet side to the WH. To lower the pressure to the whole house, the PRV is often installed immediately after the water meter, before stuff branches off. SOme people prefer to put it after the tap off for the outside faucets. The PRV should protect all of the normal fixtures in the house, not just the hot line.

Because when an expansion tank fails (they all do eventually), it will become full of water and quite heavy, it should be supported. A suitable strap or platform is fine. You don't want it to put a large load on your pipes and fittings.

 

[DirtyBrad]

Is there plumbing code that pertains to max pressure? I can't find anything but minimum.

If it's not a code question, how big is the extra 10psi practically? All the PRVs I've seen have had a max of 75psi. I have nice water pressure in the house and I hate to think about losing more than 15% of it to something that might not actually be an issue.

I was planning on strapping the tank if I went horizontal, but that's good advice about it getting full of water. If I wind up with either a PRV near the meter or not using one at all, I can mount the tank vertically a bit farther up from the water heater, but I'll be sure to secure it.

 

[Gary Swart]

90 psi is way too much for your toilets, washing machine,and dishwasher valves. It is totally unwise to have that much pressure against them. You don't need that much pressure anyway. 60-65 psi is plenty and even less good. I have mine set at 50 psi and it is just fine. Don't confuse pressure with flow. They are related, but not the same. The expansion tank goes in the supply live after the pressure regulator and before the line branches to the water heater and other fixtures in the house. The pressure regulator's pressure and the air pressure in the expansion tank should be balanced. I actually installed a gauge in the supply line between the PRV and expansion tank to make checking it quick and easy. That way I can tell at a glance if the PRV is still functioning correctly. Pressure in the expansion tank is checked with a ordinary tire pressure gauge.

 

[DirtyBrad]

Gary, thank you very much for the information. I will look to put in a PRV after my outside faucet line but before everything else.

Can you expand on pressure vs. flow? I can see where different systems could have different pressures, but the same flow. But if the only variable is the pressure, I can't picture how I can have just as strong a shower with less water pressure.

 

[Nukeman]

With something like a shower head, there is usually a restrictor and almost all of the pressure drop will occur there. Basically, increasing the pressure might get a tiny bit more flow, but you won't notice.

Also, flow is related to square root of the pressure difference.

So, going from 25 psi to 50 psi will get you 1.41x the flow.

Going from 25 psi to 100 psi will get you 2x the flow.

So the point is that even if you lose a bit of flow going from 90 psi to 75 psi, you won't be losing much: sqrt(75/90) = 0.913 (91.3% of previous flow). At 80 psi, you'll see 94.3% of previous flow.

 

[Gsalet]

The other solution is a watts model 210 This valve replaces the t&p valve so when the temperature or pressure gets too high it turns off the gas to the heater.
Thats right you have to pipe the gas to and from the watts 210 valve

 

[Redwood]

The other solution is a watts model 210 This valve replaces the t&p valve so when the temperature or pressure gets too high it turns off the gas to the heater.
Thats right you have to pipe the gas to and from the watts 210 valve

However with this a separate pressure relief valve is used.