Hot Water at Home - sometimes Hot, sometimes Not So Hot - why?

Factual Questions
1

When hot water has recently been run, like after someone has a hot shower, there is always plenty of hot water for the next person.

But if no-one’s run any hot water for a while, it seems like there is much less hot water.

For example, last night I decided to have a bath. There wasn’t enough hot water, not even CLOSE!

Why is that? Does our hot water tank need to be insulated (wrapped in one of those shiny ‘blankets’)? Our is it hooped, and do we need a new one?

I’m wondering if the tank just isn’t keeping the water hot enough, and it’s gradually cooling off after it gets heated …

My boyfriend says no, that the tank is supposed to keep the water at a certain temperature all the time.

Any ideas?

Thanks,
S.

2

I have this same problem, even after buying a new water heater. The thermostat has to perform 2 functions. Turn the heat on when the water drops below a certain point, and turn the heat off when the temperature goes above a certain point. If the sensors for these 2 events are not close enough together, you may wind up with less hot water than you would like.

There are a couple of ways you could work around this. One would be to turn up the thermostat on the water heater. This would mean that your undiluted hot water will be hotter than you are used to, and may not be safe if you have young children around the house, but it would also raise the threshold for turning the heat on.

Another workaround is to turn on a hot water tap 15-30 minutes before you plan to take a bath, and let it run for a minute or so. This will bring fresh cold water into the tank and will lower the temperature enough so that the heater will kick on.

If you find something that works better, let me know.

3

Before your shower, you run a lot of hot water through the pipes to clear out the standing (cold) water ; during the shower, the water heater is refilling and heating more cold water; after the shower, the water heater catches up and holds hot water, ready to flow through hot pipes full of more hot water.

The efficiency of your water heater can be increased with an insulating blanket, which may speed up the heating of cold water. If your water heater has sediment, that will reduce the volume of hot water available.

4

This happens in my house, and I think I know why. Whether it’s the same in your case I don’t know…

My hot water tank heats up overnight, to take advantage of the cheaper off-peak power. It is well insulated so it is still nice and hot by the following evening.

After I use some hot water, the tank obviously refills slowly, so immediately after using some hot water, the cold water coming in hasn’t had a chance to dilute the remaining hot water and cool it down. An hour later, it is noticeably colder.

5

(I should add that the heater only comes on overnight, unless I manually flip the override “booster” switch. I’m not too sure of the mechanics of how it refills, etc, but I generally have plenty of hot water throughout the day. It’s only if I do loads of laundry and/or we both want a deep baths that I need to put the booster on for half an hour or so. I don’t know how common this set-up is - here in the UK it’s called “Economy Seven” I believe.)

6

Obviously, this can’t really be happening. Functioning or malfunctioning heaters can’t predict whether there will be one or two baths.

What I think is happening is your boyfriend is running the water a while before starting to bath when he’s first and you aren’t. If you have a long run between the heater and the outlet, it takes a while.

You can insulate the pipes if accessible, there’s stuff for that and you should do it if the pipes run thru unheated areas like a basement or crawl space.

As far as the heat, touch the side. If it’s usually warm, you need to insulate. But in that case, it’s more cost effective to buy a new heater. Heaters generally been built insulated for a long time. If the sides are hot, you probably have an old uninsulated one and they lose efficency over time because the non-H20 particles drop from gravity to the heating element and stick.

7

aahala - I’m not saying the heater can predict our water usage.

Colophon, I’ve never heard of such a system - I don’t think that would work for us. But it makes sense! :slight_smile:

To the others - we’ve turned the thermostat up, and it didn’t really help or make much of a difference.

FBG &** Nametag** - your answers pretty much jibe (sp?) with my thoughts too - you just explained it better.

I will see if an insulating blanket makes a difference, as long as I can convince McDeath that it’s worth a try … :slight_smile:

But let me tell you, NOTHING is more frustrating than running a bubble bath, lighting the candles, getting all psyched up for a nice, relaxing, hot soak … and getting in to find the water tepid, at best. GRRRRRRR. :mad:

8

The system Colophon describes is applicable only to electric water heaters. If yours is gas, ignore the info. In the states, most power companies call it ‘off-peak’ meaning that it is separately metered, and you pay less per kWh than you do for ordinary electrical usage. The downside is that your hours of usage are restricted, so if you run out of hot water, you’re out of luck and hot water. Flush the tank, particularly if you’re in an area with hard water. Buildup in the bottom of the tank can act like an insulator.

9

the answer is a tankless water heater, providing you have about $700 to part with.

Try google. These on-demand systems are impressive–and tiny.

10

So … how does one flush a water tank? :confused:

11

Down near the bottom is what looks like male garden hose threads. They may be on a knob, or there may be a valve right there. Connect a garden hose to that fitting and run the hose out into the driveway, or into the sump hole. If you’re in a basement with no sump hole or pump, you’ll have to rig up a temporary deal using a drywall bucket and a small sump pump.

Anyway, once that is set up, you want to shut off the water going in to the heater (cold valve), open the drain at the bottom, and also open a hot tap in the house. Drain out a 5 gallons or so, and don’t be surprised if the water is rusty or looks foul. Then close the valve on the bottom of the heater, close the hot tap in the house, and open the cold water inlet. This will help to stir up crud in the bottom of the heater. Repeat this procedure several times until you get a basically clean discharge from the bottom of the heater.

12

One other point-if the heater is electric, shut off power during the flushing. Were you to drain enough water out that the upper element became exposed, it could burn out.

13

I’ve seen this behavior with my water heater which is an oil-fired device, and the following discussion, such as it is, is based on that heater.

My impression is that hot water heaters are fairly unsophisticated devices.
They draw the water from up high on the tank, whereas the thermostat (at least on mine) is somewhere near the center of the tank. And hot water rises. So when the heater has been running for a while (e.g. you’re using hot water), you’re immediately siphoning off all the hot water that just came off the heating element before it has a chance to mix with the cooler water. This means that you’re getting water that’s significantly hotter than the thermostat is set for. Of course, if you draw the water too fast, then the heater can’t keep up, and the water becomes tepid instead.

However, if you let the thing sit over night, for example, you achieve an average temperature in the tank that’s whatever your thermostat’s lower limit is set for, including the area of the tank near the hot water output line. And that may be an unsatisfyingly chilly temperature.

14 
 You can buy switches like that in the US if your electric company has off-peak rates and you want to economize.     It's basically nothing more than a heavy duty version of those switches that turn your lights on at a set time every night; e.g. a motorized wheel with a couple of contacts on it that flip a relay.       If your utility company doesn't charge differential rates, you can still use the switch to keep the water heater from cycling excessively, but then you get into one of those "is it cheaper to keep the air conditioner on all day or turn it on when you get home" math problems.
15

You’re correct except for one item Finagle which is the dip tube. The cold water inlet is connected to a long plastic pipe that forces the incoming water to go to the bottom of the tank. Oil and gas fired heaters work on the water at the very bottom, which then mixes with the ‘previously heated’ water as it makes its way upward towards the hot outlet.

There is some degree of stratification when the heater is not in use, but absent other issues, a properly functioning heater should be capable of fairly quick recovery.

16

Stainz, please accept my apologies for misunderstanding your OP. I THOUGHT you were reporting the first of two baths were usually warmer than a single one, which was why I was perplexed.

For what it’s worth, I asked about this draining question when I put in a new NG heater a year or two ago. The dude said he thought it a waste of time, but if I wanted to do it, do it often and start right at the beginning of a new unit. The major issue was what was permanently attached to the coil not the “fluffy” stuff and fluffy stuff is about all you get when you drain it.

17

aahala - sorry if I sounded snippy …! But thanks for clarifying what you meant. Friends? :slight_smile:

Hmmm maybe this draining thing is something worth trying …

This problem does seem worse in the winter, I guess obviously, because the cold water is “colder” …

Thanks Dopers for helping me/us out! I’ll run some hot water for a little while before my next attempt at a bath, to “prime” the whole system …

Stainz

18

Hehehe. I will give you one method, but I don’t recommend it normally. When I was 14 or so, I was working on a science fair project at my best friend’s house, in the basement. We needed to use some electric tool, a drill or a saw or something, and the nearest outlet was the old outlet that was screwed to a two foot piece of 2x4 (which was attached to nothing else. It was just a length of Romex coming out of the breaker box, to a loose outlet that was screwed to a board. Brilliant!). It was sitting on top of the water heater, and when I went to grab it, I hit it, and it fell to the ground, breaking off the flush valve. The water started coming out pretty quickly.

We both knew enough farmer plumbing and electrical to know to turn off the power at the breaker box, and to start looking for the main water shutoff into the house…and looking, and looking, and looking. For 20 some minutes we looked, all the while water poured into the basement. It was getting pretty deep, so my friend broke down and started calling around, to different family members. He couldn’t get either of his parents, but got an uncle who headed over. Meanwhile, his younger brother remembered that thier water was piped from next door (a country church), and was sort of a late addition (my friend’s family lived in what used to be the township schoolhouse, 1 or two rooms, and the original construction predated indoor plumbing, so everything was a bit oddly set up. Well, we went over to the church and found the valve, and finally were able to shut off water to the house.

There was, by this time, about 3-5 inches of water covering the whole basement floor, and just then, his parents came home from work. Well, they were very pleasant about it, all things considered (started laughing, actually). Gave us a scoop shovel, a shop vac, and a pail, and had us get out what we could. Luckily, it was an unfinished basement, so damage was minimal. The next year, they finished the basement, since the flooding had helped clean the floor.

Oh, and just as we were finishing up the cleanup, my friend’s dad came down to install the new drain valve on the hot water heater. He showed us the cold-water intake, and valve that would shut off the flow, which would have been helpful a few hours before. Good times.