Hot water heater questions

Okay, first let’s get this out of the way: I know that it doesn’t heat hot water, which is already hot; it heats cold water. I don’t know why it’s not called a cold water heater. But that’s not my question.

We moved into our house about 3 1/2 years ago, and the house itself was five or six years old at the time. So the age of the house (and the water heater) is aproaching ten years. This is a standard natural gas fueled heater located in our garage.

Over the past few months we’ve noticed that we cannot run the shower for more than about 15 minutes without completely running out of hot water. In fact, even when I take a shorter (10 min) shower, I have to keep turning the faucet to hotter and hotter settings to keep the water temp the same. Once the hot water is gone, it takes a much longer time than it should for it to be replenished (I’m told gas heaters should heat the water very quickly).

I don’t think any maintenance has ever been done on the heater. About two months ago I attached a garden hose to the valve at the bottom and drained it, thinking that maybe there would be a lot of sediment collected in the bottom, but all the drained water looked clear to me.

So, what’s the normal lifespan of a gas water heater? Do I need a new one? Is that something that I could install myself? I’ve done a bit of home carpentry and electic wiring but my plumbing experience is limited to replacing faucets, and I’m nervous about working with the gas line.

Thanks for your input…

Opinion: pay a professional, get a new water heater.
Personally (more opinion) I’d go for a new heater/tank. Cons Reports actually just did a good review (not crazy about all their reviews, but this was good) of water heaters.

Those with longer warranties used beefier materials. They were made better. They recommend paying a little extra to get a lot more life from the tank.

It’s possible the dip tube rotted and fell off. When you use hot water it is immediatly replaced by cold water. There is a tube inside the tank that carries the incomming cold water to the bottom of the tank (the hot water you use comes out the top). If this tube rots and falls off incomming cold water will immediatly mix with the hot water at the top of the tank so you do not get very much hot water. Unfourtunatly these are built into the tank and cannot be easily replaced.

It sounds like you have a bad dip tube. Replace the unit.

The water in a water heater enters from the top but goes through a tube to the bottom. Hot water is pulled from the top of the tank. In a lot of the cheaper water heaters, the dip tube is also the sacrificial anode (which corrodes first so that the other parts of the heater won’t.

Regardless, the dip tube eventually corrodes and falls away. The tank volume is effectivly reduced since the water in the bottom of the tank is never circulated, and your showers get shorter.

Note to self: type faster.

Is there a reason that cold water is supplied at the top of a hot water tank, and then piped to the bottom? The only one I could think of was to prevent water from flowing backwards, out of a cold water feed, if the cold water entered at the bottm.

But it would seem that a check valve and a plumbing setup that ran the cold water inlet pipe from the top of the tank level to an inlet at the bottom would prevent this. All without dip tubes that rot away.

Is there a reason that cold water is supplied at the top of a hot water tank, and then piped to the bottom? The only one I could think of was to prevent water from flowing backwards, out of a cold water feed, if the cold water entered at the bottm.

But it would seem that a check valve and a plumbing setup that ran the cold water inlet pipe from the top of the tank level to an inlet at the bottom would prevent this. All without dip tubes that rot away.

My guess is that it’s easier to plumb, since the cold water supplies the heater and both pipes head off into the house. Also, you don’t have to drain the heater if you need to disconnect it.

This also has some rings of what happend at the Butler household. This was ultimately solved by the BIL by replacing the mixing valve on boiler. We have Oil heat .

Our next heater (ours is now 20 years old), will be propane fueled, as the BIL likes to work on these more than he likes oil.

I go with whatever our HVAC guy says, especially as his prices are great for his favorite sister. (ok, the only, but…) :slight_smile:


And to answer the question you didn’t ask, in the industry it is neither a hot water heater nor a cold water heater. It is called either a water heater or a domestic water heater, domestic meaning home. Even if your plumber calls it a hot water heater, he is most likely just saying that out of habit.
A hot water heater would be something that takes already warm water and makes it hotter, usually for a boiler (if the water going in is already hot, the more expensive to install and maintain boiler can be smaller) or other industrial-type applications. But these things wouldn’t be called hot water heaters, either, usually they are called something like pre-heat units or some-such.

I am not a plumber, just a lowly mechancial designer in an engineering firm.

Thanks everyone, for your answers.

Is there anyway to confirm it is the dip tube before I get the thing replaced? In any case, that sounds like the most likely scenario. I guess it’s time to start shopping around.

What about tankless water heaters? I know these are common in Europe (and Asia?). Why are they not used in the US?

They are, and they’re becoming more common. But, at least for the present, they’re very much more expensive initially than a conventional water heater.

Some tank failures result in water running continuously onto the floor under the unit. I once lived on first floor in an building with 2 apt. units over 2 others, and the water heater in the upstairs unit over my first-floor neighbor failed and totally flooded the neighbor’s apt. The heater was about 10 years old. I moved out before the one over me failed. Later I lived in a ground floor unit under another unit but we all had floor drains (later building code, I guess, or more compassionate/liability-conscious landlords).

The only way I can think of is to disconnect the cold inlet and probably drain the tank so you can see into the inlet. You’ll also need a good but small flashlight to illuminate the opening. An alternative would be to also remove the T&P valve on the side of the vessel. Then you could look in the top while illuminating from the side or vice-versa. FWIW, all of the heaters that I can remember selling over the last 20 years have had nonmetallic dip tubes to avoid the anodic issue mentioned, but there was one manufacturer a number of years back that had problems with the plastic becoming brittle and breaking.

I’m gonna guess that they are not as popular in the US because space in US houses is not at quite the premium it is in Europe. The small efficiency benefit of not having a tank to radiate heat is just not worth the added cost of the tankless unit, especially considering that in half the country for half the year, the heat loss from a water heater is not loss at all but just another source of heat.

And many early US tankless models had control problems, which may have kept some plumbers leery of them.

One word of warning, professional installation on a gas water heater will probably end up being at least as expensive as the water heater itself. Especially if you live in a city that requires a freaken building permit to replace a water heater, and they’ve changed their code to require an expansion tank installed as well.

No, I’m not bitter.


Yes you can change your “cold water heater” if code permits, often you need a licensed plumber to tap into a city water supply; well water negates that problem but it depends upon where you live. There are now flexible gas and water lines that again if legal where you live that make changing a water heater quite simple.
A dip tube delivers cold water to the bottom of the tank where most of the heat is generated from the fire; and using the principle that heat rises, the hottest water should be at the top. Cold water enters then bottom gets heated and rises to the top ready to head to your shower.
You can disconnect the water heater and remove the cold water nipple screwed into the water heater tank which should be attached to or give you access to the dip tube (more often than not plastic) which is replaceable.
Also in draining your water heater you should have shut off the water supply and drained the tank completely, it seems the muck comes out last. Just running water out of it doesn’t do the trick. Sediment problems are often diagnosed by a lot of popping and hissing sounds while the tank is heating up.
And finally at tens years old change it, it is not worth the effort to do all that and not spend a few extra bucks to get a new one. All that fixing and it is liable to spring a leak the next day not to mention the economics of running an old out of date water heater.

Not to hijack but I once worked in house where the guys water heater was dated to the 40’s it was kind of neat to see it still in operation but hell the pilot light alone seemed like it could have heated my house today, anyone have a really old water heater in their house?

The principle of hot things rising applies especially to gases - how true is it of water? You’ve got an enclosed space where water is coming in, and and equal amount is going out somewhere else. There will be a lot of turbulence just from this flow. I’m skeptical that the seemingly tiny density difference would actually have a significant effect in making the relatively warmer water rise up.

I think the reason that you have a dip tube is that you want the incoming cold water and the outgoing hot water to be at opposite ends. My educated gut feel tells me that this would work equally well if the hot water came off the bottom via a dip tube and the cold came in at the top. If I’m wrong about this, I’m sure that the helpful folks here will supply the appropriate physics cites to educate me, and I always appreciate being educated.

Hot water rises in the same way that hot air does. Water expands with increasing temperature (above the point of maximum density at ~4deg C IIRC), so hot water is less dense than cold water. There is some mixing, but not too much. If the cold water was introduced at the top of the tank and the hot water drawn off the bottom, it would not work as well.

For the OP, I would concur that your dip tube is likely gone, or at least leaking badly. If it were the tank filling with sediment, your HW capacity would not have dropped so dramatically. Replacement is not TOO difficult, but legally would require pulling a permit. A professional plumber is recommended. It should run about 2-3 hours of labor, at most.

LordVor, I am not aware of a plumbing code that requires an expansion tank on a domestic water heater, but I am not aware of every jurisdiction’s amendments.