I'm looking for a cheap and easy way to extend the amount of hot water available for showers in my house.

I've got a 40 gallon water heater, installed about 1 year ago, and I wish I'd purchased the 50 gallon. In the colder months, it will run out of hot water in about 10 minutes of showering. I have measured the inlet water temperature using a thermocouple pressed against the copper pipe and found that it can range from as low as 8C during the depths of winter to 22C during the warmer months.

I'd like to counter the effect of the super-cold winter water by pre-heating the water before it gets into the tank. I'd prefer a solution that doesn't require any plumbing, but will consider that if I have to. I've heard that there is something called tempering tanks that could be used to store room-temperature water.

I'm considering using a wrap-on copper pipe heating wire or tape on the incoming water line to pre-heat. Something like this or this. I could wire it to only turn on when the burner is activated. I have about 15 feet of exposed copper pipe that I could easily access and put the wrap on.

I'm also considering if I use this method if I should wrap the cold water pipe in an insulating pipe-wrap to avoid losing half the heat to the room. But I worry about overheating the heating wire itself or the pipe wrap.

Would this method work? Is there another method I should consider instead?

EDIT: All of the accessible hot water piping (about 15 feet worth) is already pipe-wrapped. The rest is in the walls, can't get to it.

  • 1
    15 feet of water pipe will only hold a little water, might get lucky and warm up a couple cups before you get cold water again.
    – crip659
    Nov 15, 2022 at 0:35
  • Is your current water heater gas or electric? If it's gas, then replacing it with a tankless may be a viable option.
    – maples
    Nov 15, 2022 at 1:18
  • @crip659 I was thinking it would raise the temperature of the water slightly as it runs by, so that the water heater doesn't have to heat it up quite as much. I wasn't expecting the pipe to act as a reservoir.
    – rothloup
    Nov 15, 2022 at 2:23
  • @maples it's gas, but I literally just bought it less than a year ago and I was quoted 6k for tankless at that time. that's not in the bank for me.
    – rothloup
    Nov 15, 2022 at 2:24
  • 1
    Get a water saving shower head. I have a 30 gallon electric and I have no problem getting more than 10 minutes of hot water. If you already have a water saving head then there's something wrong with the install or the thermostat is set too low. Nov 15, 2022 at 3:39

4 Answers 4


You can install a water tank booster which typically is sold as a kit that includes a thermostatic mixing valve, temperature gauge and braided hose with fittings. What it does is allow you to set the water heater at a higher than normal temperature (say 160F) and then the mixing valve mixes cold water with the hot water and outputs a normal temperature water (say 120F). This provides 2 advantages. One is that the higher temperature of the water in the water heater prevents the occurrence of contamination such as the virus that causes Legionnaire's Disease. The second is that the mixing valve keeps the water temperature at a safe level preventing any possibility of scalding. Since the hot water is mixed with the cold water, the volume of hot water supplied by the hot water heater is less than without the mixing process thus effectively increasing the capacity of the hot water heater. These kits are sold by Amazon, Home Depot and others. An example is the Cash Acme 3/4 Inch Tank Booster Water Heater Thermostatic Valve sold by Amazon.

  • Interesting. I'll have to hire a plumber to install it, but thanks for mentioning it. I've never known these devices exist. Is it code compliant in most places?
    – rothloup
    Nov 15, 2022 at 2:29
  • 1
    My valve was installed by a licensed plumber in Long Island, New York. I don't see how it would violate any code.
    – Barry
    Nov 15, 2022 at 2:37

A few options:

  • install a continuous water heater before the tank.
  • bump up the tank thermostat setting, if not already maximum. You'll dial the temp lower at the tap and use less tank water for a shower
  • in addition to bumping the tank temperature, add a mixing valve or tempering valve at the tank to avoid scalding
  • recover heat from the drain using "drain water heat recovery"
  • insulate all hot water piping from tank to shower
  • Thanks. The only one of those that is viable is the continuous heater before the tank. #2 risks scalding, #3 requires access to the drain, which I don't have, and I've already done #4 as much as I can.
    – rothloup
    Nov 15, 2022 at 2:26
  • 1
    @rothloup ok, edited to include a "tempering valve" it mixes hot down, without causing a cross over (an issue with simple cross over valves if the down-stream is pressured e.g. when installed before bath/kitchen fixture rather than part of it with just a spout to follow)
    – P2000
    Nov 15, 2022 at 2:38

A typical keep-from-freezing pipe wrap that plugs into a 15A 120V receptacle can't be more than 1500W. I actually suspect they're a lot less than that. But even at 1500W, that's not nearly enough to make a substantive difference. If the water is just sitting there, it will heat up the water in the pipe. But that isn't very much - even a 1" pipe would have less than a gallon in 15 feet of pipe. So the only way this can work is if it heats the water as it passes through. Use enough electricity and you have created a tankless electric water heater!

But there's a catch. A typical tankless water heater heating up 2.5 gallons per minute uses 13,000W - that's almost 9 times as much power! Which means that to do this effectively you will need a lot of electricity running around that 15' pipe, requiring a big circuit installed to do it. Or to do it safely and effectively, get an actual tankless water heater, install the big circuit, get it plumbed into your system and you have limitless hot water. But at a cost - many people don't have 40A or more of capacity in their electric service to add tankless electric hot water.

Bottom line: Little fixes won't do it. Big fixes will - but they either mean a much bigger tank, a second tank or a lot of power and tankless.

  • True, but I'm not trying to replace a tankless water heater - I'm just trying to raise the temp a few degrees so the gas tank heater doesn't have to work quite as hard and doesn't get cooled down as fast. I have no idea if it can be done in 15 feet of pipe. I was hoping someone could enlighten me about it. I don't quite have the background to calculate that for water moving through a pipe.
    – rothloup
    Nov 15, 2022 at 2:34
  • It isn't a matter of pipe length so much as input electricity. If 13kw gives you 2.5gpm, 1.5 kw (all you will get without some upgrades) will get 0.3 gpm. Not enough to make a big difference. Nov 15, 2022 at 2:47
  • 1
    of course, I understand the comparison you are making. But there is also a difference in temperature rise. that 13 kw heater is trying to go for maybe 100 F rise? I only need about 10 C - 15 C (18-27F). That's about 1/3 of the heat. But your comparative approach makes sense to me - maybe I can use it to estimate how much rise I can expect.
    – rothloup
    Nov 15, 2022 at 5:14

Using a tempering valve and setting the tank temperature higher is the simplest method I know of. Also deals with the potential of legionella bacteria by killing them off with high temperatures.

The tempering valve connects to the tank output and a cold water line, such as the tank inlet. The water in the tank is heated to temperatures that would be unsafe for direct use due to scalding concerns, and them mixed to a safe temperature by the tempering valve on the way out to your fixtures. The mixing of cold into hotter water to make safely hot water means you get a larger volume of safely hot water than you have in your tank.

Technically the tempering valve can go anywhere along the path, but I find having one at the tank itself simpler than multiples around the house. It also costs less.

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