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I recently had a new water heater installed and since then, the hot water has taken a very long time to reach the faucets. For reference: I was able to fill 1.5 gallons (nearly 6 litre) with the cold water that came out before the hot water arrived. Before the new installation, the hot water arrived almost immediately. I'm wondering what might be causing the delay, and how I might be able to resolve it, as I feel awful wasting so much water!

I'm attaching some images of:

The original setup: 50 gallon water heater, I don't know how old but the hot water arrived fast and the water pressure was strong. Despite that, it leaked and had to be replaced.

enter image description here

The new set up: 40 gallon (150 litre) Rheem Perf Plus 40 Gal. 4500-Watt Elements Medium Electric Water Heater WA OR Version with 9-Year Tank Warranty and 240-Volts.

enter image description here

Note: I didn't want a Rheem, but it's all I could afford that was readily available where I live. I tried to order a few other brands, but they got cancelled due to backorders. So if there's a possible resolution that doesn't require finding a new water heater, that would be ideal.

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    Water heater brand should only affect how much hot water you get. Smaller tank and your ten minute hot showers might only last 8 or 9 minutes. Replacement tank should not affect how fast hot water gets to a point if everything else is the same.
    – crip659
    Feb 13 at 22:01
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    The valve on the pipe on the right appears to be closed. Maybe it's just the angle the picture was taken at, but the handle should be parallel (open) with the pipes. To me it looks like it's perpendicular to them, therefore closed. I'm surprised you're getting any hot water at all. Maybe it's cracked open just a tiny bit and you're getting a very slow flow so it takes a while...
    – FreeMan
    Feb 13 at 22:55
  • @FreeMan good catch, I suspect that's a confounding factor in this setup.
    – KMJ
    Feb 13 at 23:13
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    do you have recirculating pump in your system, is it on and working
    – Traveler
    Feb 14 at 0:37
  • You're sure that valve is at WOT?
    – Huesmann
    Feb 14 at 17:18

4 Answers 4

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Looking at your setup, I strongly suspect that your current setup added something which your old setup did not have: a heat trap. On the top of your new water heater, you can see the two short pieces of steel pipe between the heater outlets and the plumbing. These are ball or flap heat traps. They prevent hot water from leaving the heater when there is no demand for hot flow. Your old water heater doesn't appear to have heat traps.

What this means is that your old water heater was probably continually heating the hot water pipes that go to the rest of your house. When you turned on a tap, there was already water in the pipes that is at least warm. The new heater doesn't start putting hot water in the hot plumbing until you turn on the tap, so you have to flush out the cold water and heat the plumbing up before you get hot water at the tap.

If this is what was happening, you should notice it as a small reduction on your electric bill next month. I wouldn't worry about wasting a gallon or two of water when you need hot water, personally. The energy savings could well be worth it.

If this turns out to be correct and you would like the old behavior replicated, you can do it by having the output heat trap removed or a circulation pump installed. The circulation pump will do a better job of getting the hot water to taps, but might require additional plumbing in order to work.

Also, you might want to insulate those pipes. That will make your hot water quicker regardless of how the rest of this system is configured.

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    I don't understand. You're saying that in the old system, there was hot water leaving the water heater even when there is no demand for hot flow, i.e. when no taps were open? Then where was that hot water going? It would have to go somewhere, right? I don't see how you can heat a pipe without flowing hot water through it, which means it must necessarily come out at the other end. Unless it was being recirculated, but OP says they didn't have a recirculating pump. Feb 14 at 7:17
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    @NateEldredge it sounds like depending on pipe geometry, you can get some circulation via convection. There’s some decent graphics on wikipedia. No need for full circulation to have the pipes warmer than ambient Feb 14 at 9:53
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    Heat traps are a thing because convection happens inside the pipes of hot water systems. Some older central heating systems are actually 'one pipe' systems with no return.
    – KMJ
    Feb 14 at 16:06
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    A popular science presenter released a video on this topic (solutal convection) youtube.com/watch?v=kuLX76g7Fec
    – sleblanc
    Feb 26 at 5:16
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Is the setpoint the same as it was on your old water heater? My guess is that the temperature has been set lower. It is a trend in the effort of lowering energy costs and prevent scalding injuries to have a lower setpoint at the factory, and the person who installed the water heater might have purposely set it lower, or might have omitted to adjust the setpoint.

Cooler water feels like it takes a longer time before it reaches the desired temperature.

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  • Ohhh,,., Excellent point!
    – FreeMan
    Feb 15 at 15:35
  • I wonder where this is a trend. I've seen residential water heaters set to 120 or 125F around here ever since I started paying attention to such things.
    – KMJ
    Feb 15 at 19:53
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Try to measure or guess the length of pipe from the water heater to the faucet. Then, using the internal diameter, compute the volume.

I'm French, so I'll use metric:

Suppose your pipes have 20mm inner diameter, or 0.020m, that's pi.r²=3.14mm²=0.000314m² cross section, so 1 meter of pipe contains 0.000314m3 of water, or 0.314 liters. So 10 meters contain 4.9 liters, which is not far from a gallon.

The result you find should be coherent with how much water you have to pull from the tap to get it hot. If it is, there's nothing wrong with your installation.

In order to have instant hot water, you can keep the pipes hot with circulation, but this will cost you a lot in electricity, because long pipes lose a lot of heat to ambient air.

A better solution is to put a small water heater (called "point of use water heater"), maybe 10-15 liters (3-4 gallons) right under the sink. You can feed it from your main water heater so it does not run out, or feed it from cold water if the volume is enough to wash your dishes, which will be more efficient due to less heat lost in the pipes. The drawback is that it uses about 70% of the cupboard under the sink, but you get instant hot water (as in: really instant).

One meter of uninsulated pipe at 60°C dissipates about 50W, which translates to 438 kWh/year, so if you use a circulator the electricity cost can be so high that the small water heater under the sink pays for itself in a year or two.

Now about your washing machine, if it is closer to the water heater then hot water will get to it quickly. Even if it is not, if it's a model that can work with hot and cold water, you should check if it has a heating element. If it does have one, then no worries, it will heat the water. Energy cost will be the same whether the heating is done by the electric water heater or the washer's electric heating element. It would be different if you got your hot water from cheaper energy like gas.

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    While calculating flow rate will give the OP an idea of how much time he should expect it to take to get hot water, based on the pics provided there isn't a significant difference in the plumbing distance between the old & new setups, therefore there shouldn't be a significant difference in the amount of time it takes to get hot water. The question is "why the difference", not "how long should it take".
    – FreeMan
    Feb 14 at 13:31
  • Also, what does the last paragraph have to do with anything in the OP's post?
    – FreeMan
    Feb 14 at 13:32
  • Last paragraph because he was worrying about his washer in the comments. For the rest, calculating pipe internal volume and comparing to how much water has to come out before it gets hot is a way to know if there's something fishy going on. It's not possible to know which situation was weird (before or after) without knowing the length of the pipe!
    – bobflux
    Feb 14 at 15:05
  • Regarding washing machines with heating elements, it’s my understanding that these are a relatively rare novelty in the US just like dishwashers with heating elements. Feb 15 at 21:40
  • Do the dishwashers and clothes washers with internal water heaters specify that the water supply can be the cold only or do they suggest that the hot should be used if it is available? That is, do the instructions state that cold supply alone can be used but that hot (in addition to cold for the clothes washer) gives improved performance? Feb 18 at 1:34
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The inside diameter of the dip tube(cold water inlet) smaller like 3/8” of a inch diameter. There should have been another blue dip tube that came with the tank in which would have a larger diameter inside. Is the flow at hot water tap fast or good flow coming out. If flow is good then I would say the problem is at the tank at the settings like someone else suggested, you should start there. The Rheem tank is a good tank.

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    Hi Mr Plumber, this site does not work like a discussion forum. We expect answer to add something new, not reiterate what's already been said. Feb 20 at 10:05

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