Pulaski

Well off the top of my head, for an 80gal water heater there would be about 665lb of water, and probably about 100lb for the tank, for a total of about just about 350 Kommigrams.

ETA. Apparently an 80gal water heater from AO Smith weighs 175lb, so that would make a total of 840lb or 385 Kommigrams.

scrubbedexpat142

350 kommigrams, wow, that's about 200 freedomgrams, scary!

ddsrph

I installed only a 30 gallon in the house I built 5 years ago. Electric tank type and plenty for two people. Does posters have an expansion tank in their hot water heaters? I put one on mine as I discovered their existence doing research on plumbing when doing my house. The theory is during the heating of the water it expands and with almost all water systems there is a back flow preventer valve at the meter and the this pressure has no where to go. Can lead to premature tank failure especially if the anode is not looked after. Here is my expansion tank as I installed.

sid nv

Installation looks fine to me, but does it have the cat's approval?

ddsrph

My wife has three cats in the house and feeds several strays on the porch.

Mic1

Temperature/pressure relief valve discharge should terminate outside or into a sealed internal drain. If that TPRV blows, it could vent almost boiling water at 10 bar......be too much for that drip tray to handle. Be careful.

ddsrph

That’s a good point. I could probably run a hose to the drip tray drain line with a one way valve to prevent the flow from going into tray. I will look into that.

Pulaski

You should look into what the TN code allows. In NC the pipe from the relief valve cannot, for some reason be pex (my guess is that pex is usually slightly curved so can't be positioned to reliably drain into the pan), it has to be either copper or PVC, so I suspect that a flexible hose might not be acceptable.

It is usual in my experience to just have the pipe from the relief run down to the drip tray, as a working relief valve should never do more than dribble a bit. The whole purpose of the valve is to stop pressure build up, not allow it to build up to a dangerous degree, then let go dramatically! If the valve "fails" by seizing and not allowing excess pressure to be released then all bets are off and where the water would have drained if the valve had worked properly will be the least of your problems, but if you watched Mythbusters you already know that.
Just a couple of weeks before the original Mythbusters water heater episode aired (I think there were at least three of them), a house a few miles away from Pulaski Manor had a water heater failure. The water heater left the home through the roof, and was found a couple of hundred feet away!

So the main takeaway from this discussion is to test the valve regularly - I think the usual recommendation is every six months.

ddsrph

I had some time this morning and have bought the items needed to run a pipe down to the drip pan drain. I remember now that at my other house I did similar. My drip pan is connected not to the house drain but to a 3 inch pvc pipe that runs to attic for a radon pump. Below this three inch pipe connects to a inside foundation complete perimeter French drain that is under the slab gravel backfill that varies from 2 to 5 feet of gravel.

SpoogleDrummer

Not with mine, there are all water sensors at the bottom of my heater that shut the heater and water off in the event it detects water so I have to have the pipe go directly to the drainage pipe for the washing machine or at least that's the plan once I get around to getting the bits I need. It's a PITA drying it out once it detects water but still better than having to dry out 2 rooms that got flooded when the first heater I replaced pissed water everywhere.

Pulaski

Isn't that what you would want to happen if the pressure release valve starts releasing water?
That sounds like, er .... several projects I have in progress.

ddsrph

Is it some special model that has those extra safety features? Did the old heater leak due to hole in tank or was it coming from the pressure relief valve?

SpoogleDrummer

Is it? I thought the valve releasing the water would be enough without having to shut the heater off. I got the sensor wet whilst installing it and it was a pain drying it out with the tank empty having to lift it up to dry underneath and I still had to bypass the sensor for the day whilst it finished drying, I really don't want to try whilst it's full of water.

It's a Rheem Smart water heater: https://www.homedepot.com/p/Rheem-Gl...55U1/309627116 I wouldn't say it's too special but it's what was in stock and once I decide something needs fixing I need to fix it now as waiting for a delivery will usually mean I lose interest/motivation and it won't get done until Noah turns up with his ark to rescue the pets.

The original heater seemed to leak out the bottom, no idea how old it was as it came with the house and and probably failed about a year or two in to owning the house. The one I just replaced I only bought because it looked exactly the same as the original despite being a different brand (Whirlpool), I had zero plumbing or DIY experience and didn't fancy switching pipes so switching out like for like was the best solution (well paying someone to do it might have been the best solution but I'd just bought a house and had 2 babies so to say I was broke would be an understatement). I managed to smash up the drip pan in the process of installing it so I was always keeping an eye out of any possibly leak from that one yet still treated it like crap and never flushed it as I wasn't aware that was something you needed to do until it was about 8 years old by which time the damage was done. It started to leak from behind the panel where the temperature gauge is and that was enough for me to replace it as it was probably 12 years old by then.

ddsrph

Since my drain pan has a good drain connection and like Pulaski mentioned the safety valve only lets out pressure and not a lot of water I am
just running a 3/4 inch clear line down to the pan. This way I can let it drain into a bucket during valve checks.

Mic1

As Pulaski says, he is exactly right about not being able to run the PRV in PEX. In most states that i know and definitely in the UK, and discharge from a PRV or TPRV has to be in copper and the longer the run, the bigger the bore to prevent any possible back pressure,

The valve actually incorporates 2 safety features, it opens if the pressure is too high (hot or cold) or opens if the temperature of the water exceeds (from memory) 95 degrees C. Basically, the rule book says that you can install the tank in an X,Y,Z manner when it comes to the inlet and outlet pipework but one thing that you MUST do in accordance with codes or water board byelaws is the PRV/TPRV and associated discharge pipework.

On the pressure side, again as Pulaski says, it will trickle and not cause a major issue. However, if it opens due to excessive temperature, it can go from 0-100 in seconds. Keep in mind that under that pressure and that tempertaure, the water will almost exit as super heated steam. It's a very rare failure as gas fuelled units should have thermostats galore to prevent the water getting anywhere near this temperature. However, when they heated using electric immersions, it has been known for the thermostat inside the element to fuse together in the contact 'closed' position. In effect, there is nothing to interrupt the flow of electricity to the element, it will just get hotter and hotter until something gives. The UK plumbing industry changed the regulation overnight when it came to immersions, virtually all were pulled off the shelves and new ones were introduced with a secondary, overheat thermostat with a manual reset. The reason for the sudden change, two little children were killed when an immersion thermostat jammed closed on a cylinder, the cylinder temp rose to boiling point, hot water gravitated up to the plastic cold tank, heated the stored water to boiling resulting in the tank sides splitting and covered the littluns whilst asleep in their cots with boiling water killing them instantly, apparently. It's beyond comprehension that they should lose their lives in this way.

I know it's not quite the same as the systems in the US, but what i'm trying to say is that safety back up features on anything containing stored hot water should be taken very seriously indeed.

My advice, find out what your particular code requires and get it done properly. Do not guess it.