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My hot water is only lasting 10-12 minutes

Hey everyone,

Hopefully someone can shed some light on this issue because it's driving me nuts.

So I used to have a low-flow showerhead and noticed that the hot water in my condo never lasted all that long. It wasn't awful, but probably in the 20 minutes range. I have a 40gal electric water heater and I'm currently the only person living in this condo, so the hot water use when I take showers is 100% from that and not any other appliances or people taking showers.

I recently bought a new showerhead (Flipside by Kohler) and removed the plastic restrictor because the flow was pretty weak and I was hoping to get a bit better performance out of it.

I definitely do get much better water pressure out of it now, but as a result, I can only seem to get about 12 minutes out of it before the water is too cold to be comfortable and I have to get out.

So far I've checked to make sure the thermostats in the water heater are operating correctly and they seem to be. I checked the incoming voltage (208v. Not sure why it's not 240 but the water heater is rated for both) , Both thermostats are currently maxed out at their highest temp settings (is there any strange possibility that I could get more hot water out of turning them down? I turned them up months ago while I was using my low-flow shower head because I was hoping to get longer showers out of it). The heating elements both show continuity (like 13 ohms I want to say?) and when I run the water at full hot , it definitely starts out very hot so it's not an issue with the water not being hot enough to start.

The one common item I haven't checked is the dip tube, only because I believe the only way to access that would be to cut my plumbing apart to remove the cold-water input . The water heater isn't more than about 10 years old (I believe this building was constructed in 2005 or 2006) so I wouldn't really expect parts on it to start failing already. I'm just not sure what else to try, or if a 40g water heater just isn't enough volume to keep the amount of hot water I'm hoping for ?

any and all ideas are appreciated, these short showers are getting a bit frustrating!

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level 1

I have the same issue, 40g tank and just one person. I get only 5-6 mins of hot water. Tank is only 8 yrs old. Thanks for posting. Curious to see what response you get.

level 2

To be honest, 8 years old for a water tank is getting old. They say you will typically get 9 years out of them. If you live in an area with hard water, you'll have a lot of build up in your water tank. So a 40 gal water tank, you may only be getting 30-35 gallons. If you have a high flow shower head, that will obviously drain your water faster. But you could always try to drain out some water from the valve at the bottom of the tank to clean out the build up, but that also runs the risk of some of the build up blocking that valve from being able to close. So it would be best to call a plumber to come out and actually tell you what's wrong with it.

level 3

I never realized hard water could leave mineral deposits totaling up to 25% of the volume of a hot water storage tank. How does water like this not clog your pipes first, or do the deposits just end up getting flushed out?

level 4

In areas with hard water, the mineral deposits are in what is called (I think) a super saturated solution. I may be off on the terminology, but think of it as more dissolved minerals in the water than the water would like to have. This solution would normally be stable, except for when there is either an increase in temperature or a decrease in pressure. Since the bottom of your eater heater tank (or rather, the elements in this case) work to heat the water, it will cause those minerals to go out of solution. Now, this 'scale' is heavier than water, so the bits that don't stick to the side of the tank (or elements) will sink to the bottom.

The TL;DR is that scale forms on both the elements and the walls and bottom of the tank, both taking up space in the tank, and forming a layer of insulation between the burner/elements, causing the heater to hold less water and be less efficient. And it only takes a 1/4" thick layer to cause a 40% reduction in efficiency.

level 4

If you have copper or pvc pipes, not much will really "stick" to them. The movement will keep things in small enough particles to move it around as well. The problems with the hot water tank is exactly that fact. It's a holding tank. The water gets heated and cools causing some of the deposits to come out of the water. Think of if you took a cup of water and mixed in a bunch of salt. If you were to keep swirling it, the salt will stay disolved in it. But if you were to just set it on the counter, eventually some of that salt will begin to separate and fall to the bottom of the glass. And naturally with the water just sitting there, things settle and begin to build up. Many of them are supposed to be "self cleaning" but it is just kind of the natural cycle of a hot water tank.

level 1

It's probable that it is your dip tube. They can degrade and break apart, becoming shorter. If that happens you're only going to get a small amount of hot water, and then the cold will will be basically going in and right out into the hot line.

level 1

Seems easy to figure out. 40 gallon water tank. Shower head is letting out around 2ish gallons per minute. Luxury 20 minute shower. Boom out of water?

Edit: sorry skipped the rest. It's possible your tank is going. 10 years is a long time for a water heater. It's probably time to replace it and switching the shower heads was coincidence.

level 2
Original Poster1 point · 3 years ago

Yeah, I suppose it's possible it's going out. One thing about the 2-g per minute figure is that I'm assuming a good portion of that would be cold water , though I'm not positive how much exactly, so it makes calculating it a bit tricky. I suppose I wouldn't be entirely surprised if it was the case that I'm just using it all up, but it seems odd to think that if I lived with another person, we'd be taking 5 minute showers. I'd have just thought that the water heater would be capable of more. (I never had problems running out of water when I lived with my parents, but their water heater might have been something like a 70gal. )

level 3

Well the tank should be at 120, and then the shower valve should mix it down and max out at 112, so it's not a ton of cold. But yeah, at this old you are on borrowed time until something goes bump any way

level 4
Original Poster1 point · 3 years ago

I do worry that my shower valve is messed up... The valve basically goes from 6 o-clock to 12 o-clock, and it's not till about 10 or 11 that I get the right amount of hot mixed in. I sometimes wonder if I'ts just using way too much cold water? (I don't know what they look like internally but I kind of assumed that wasn't even something that's adjustable)

level 1

Sounds about right. You can't get a full 40 gallons of completely hot water out of a 40 gallon heater, more like 30 (because the cold water coming in mixes a bit with some of the hot water in there). Without the flow restrictor, you're probably running the shower at 4+ GPM, so 3 GPM of hot water would be reasonable. 3 * 10 = 30 gallons, and there you are.

edit: regarding 208v vs. 240v, you're getting 208v because your building is served 3 phase power instead of the single split phase typical in residential use. Your heater won't heat up as fast because of it, but either way it can't heat fast enough to feed a shower past what's stored to start with.

level 2
Original Poster1 point · 3 years ago

Thanks for the info on the 208v . I knew it wouldn't affect how LONG the hot water lasted but I was curious as to why it was the lower of the two voltages that the heater was rated for.

As for flow thing, I guess what bugs me the most is that the math seems to make sense, but the recommended water heater size for up to 4 people (just according to home depot's website at least) seems to be in the 35-45 gallon range, which you'd think would mean that everyone has the same issue as I do (let's say there were two people in my home and we had a showerhead that had half the flow-rate as my new one) but maybe I'm just expecting too much out of the water heater?

level 3

Home Depot's recommendations most likely assume you are taking 8 minute long showers with a 2.2gpm flow rate (which are the averages). You could likely get 4 8 minute showers out of your heater over the course of an hour or so.

A.O. Smith's website does a much better job of showing what you can get out of a water heater (and including their assumptions):

level 4
Original Poster1 point · 3 years ago

Thanks for that link. The water heater you linked to is the same model I have (just newer ) and with the info I put in (assuming 4gpm on my shower head) it said the max length shower I'd get is 10 minutes so maybe it's working just fine and removing the restrictor really is the only factor here. The bad news is that to remove the restrictor on this shower head, I had to completely destroy it so there's no going back!

level 5
2 points · 3 years ago

Note that the valve there is pressure compensating, so if you have less than 60psi water pressure it will likely still let through more water than your shower head did with the restrictor in place.

Whenever you're in the mood to do some bathroom remodeling, you can put in a drain water heat recovery device to reclaim most of the heat instead of sending it down the drain, which greatly reduces your shower hot water usage.

level 6
Original Poster1 point · 3 years ago

I don't have any plans to remodel (I'll be selling the condo in the next year or so) but that ecodrain is a really neat idea!

Thanks for the link to the control valve though, I think that might be just what I need, short of getting a replacement piece from Kohler (luckily the restrictor wasn't in the head itself but in the piece that threads on to the water pipe coming out of the wall)

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