It takes 3-4 minutes of the shower running before the hot water reaches my upstairs bathroom. I'd like to not have to waste all that water and time. My initial though was to install an inline water heater to supply my bathroom. Is this feasible? Or are there other solutions?


I was thinking something like this:

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  • To supply the volume of water required for a tub and shower would require lots of current for an electric heater. It's possible that your current breaker box would not have the capacity for that extra demand. – Les Jan 11 '13 at 17:14
  • I added a small on-demand water heater under my sink. It required 8 or 10 gauge wire. The heater worked well with one major drawback. After closing the faucet, the heater would shut off, but the heater element was still hot. Wait several seconds, turn the water on and it is VERY hot for a few seconds. – Les Jan 11 '13 at 17:17
  • @Les, when you say volume of water required for a tub and shower, do you mean at the same time? I'm okay living with the knowledge that I can't draw a bath while the shower is running. (They are next to each other in the bathroom.) As far as concurrency goes, I'd at most be using the shower and a sink at the same time. – Matt Jan 11 '13 at 20:57
  • @all, also, if you'd like to provide an answer, please do so below. I'd like to avoid answers in the comments section here. (I'll want to mark the best answer as right, when I'm ready.) – Matt Jan 11 '13 at 20:59
  • @Matt, you would have to size the heater for the volume you require (gallons per minute @ a certain temperature rise). The output water temperature at my sink varies seasonally. In winter, the water coming into the heater is colder than summer. The heater raises the temperature by X degrees (it does not heat it to X degrees). – Les Jan 14 '13 at 17:17

If you lag the hot water pipes you can help reduce the time it takes for the water to heat up as the water in the pipes will stay warmer for longer. Obviously this won't help first thing in the morning when the water's cold.

Installing a heater is certainly an option as it will reduce the 3-4 minute "lead time" - especially if you site it as near to the shower as possible. However you have to consider the following:

  1. Is the cost of installing and running the heater less than the cost of heating the water that remains in the pipes and left to go cold.
  2. If you pay for the amount of water you use then will the reduction in your water bill pay for the heater?
  3. Can your shower be connected to an instant hot water feed? If you have a pumped shower then you probably can't do this.
  • 1. I'm not sure how much it would cost to install, but I would weight it against the cost, you mentioned, of the wasted heated water left in the pipes, and also the cost of all the extra water I'm dumping right down the drain (75 gallons per day wasted?). There is also harder to measure value of convenience and sense of environmentalism. – Matt Jan 9 '13 at 20:03
  • 2. I'm not sure what you mean by an instant hot water feed. How is that different than an inline heater in the bathroom? What is a pumped shower? I'm living in your standard, run of the mill, suburban home. – Matt Jan 9 '13 at 20:04
  • @Matt - Instant hot water is a system that doesn't involve a tank to store the hot water. As you run the hot tap the system heats the water almost instantly. A pumped shower uses a water pump to increase the flow of water to the shower. They can only be used were you have a intermediate tanks of hot and cold water to act as a buffer. – ChrisF Jan 9 '13 at 22:56
  • I guess instant water heater is what I meant by inline water heater. I envisioned a small, electric, tankless heater installed in my bathroom, that could supply both sinks, the shower, and the bath. – Matt Jan 10 '13 at 14:15
  • FWIW I have a Noritz on demand water heater in my home, when our contractor was installing it he recommended going with gas rather than electric for a whole-home model. Not sure about whether electric would be suitable for just heating bathroom water. – Darth Continent Jan 10 '13 at 14:43

Combine convenience with reducing water usage would be worth the added expense of in-line heater, if you can afford purchase. From a conservation standpoint it would be best to have the in-line heater fed by a cold water line. I have not done this myself, but I am considering. I haven't determined if gas or electric is preferable. I think both are available.

  • The cold water line makes sense to me. You don't want the hot pipes to drag water out of the tank downstairs, just to cool off in-pipe after you shut off the water. – Matt Jan 11 '13 at 16:11
  • I supposed I envisioned capping off the hot water pipe in my bathroom, and then redirecting cold water, through the inline heater, and into the hot pipes supplying the sinks, shower and tub. – Matt Jan 11 '13 at 16:13
  • I've added a drawing of my concept. I just want to find out if this "cap and reroute" method would work. – Matt Jan 11 '13 at 16:28
  • From what reading I've done on the subject, electric tankless water heaters are more efficient than gas (generally I've seen 98% vs 85%). Which is more preferable really depends on: the total cost of installation; the ready availability of a source of natural gas/propane/electrical supply; the difference in cost between the two (electric and gas)in the size of water heater you need; desired location to install the water heater; the difference between the cost of gas versus electricity in your area; anticipated needs and anticipated water usage; personal preference. – ND Geek Jan 29 '13 at 20:19
  • 1
    Also, depending on how cold your cold line is, you may not get enough heat from an in-line heater. Gas, while less efficient in converting gas directly to heat, is more efficient in generating overall heat (in-line heaters are rated in how much they raise the temperature, and gas is generally more efficient per up front dollar, I believe). – ND Geek Jan 29 '13 at 20:22

With your cap method you have reduced the volume of water available to just what can be delivered by the single cold water pipe. With current hot/cold piping you have the volume of the hot + the cold pipe - obviously greater than the cold alone. With just the cold will not as strong of flow (volume or pressure). To determine if the cold flow alone will be adequate, just run each fixture with the cold alone on high and see if you are satisfied with the flow. If you are satisfied, the cap method should be fine.

  • Can you explain my error in logic? The output of a shower head is always the same, regardless of your heat setting. This is because the heat setting adjusts the output of each pipe inversely. So, max hot = 100% hot pipe + 0% cold pipe. Max cold = 0% hot pipe + 100% cold pipe. Nice temp = (maybe) 70% hot pipe + 30% cold pipe. So, if I use my cap method, I would get the same pressure I would get elsewhere in the house. I'd get 100% of the cold pipe pressure, it's just a matter of what percentage of that water I heat up. – Matt Jan 18 '13 at 16:25
  • The pressure will drop with increased flow, due to friction losses in the pipe. At some point, your small cold water pipe won't be able to supply enough pressure. Your shower used to be served by two parallel feeds, one hot, one cold. now it's all served by the cold feed. Imagine if your whole neighborhood were trying to draw their water through your cold water pipe--it wouldn't work. – mac Jan 18 '13 at 17:37

Another option to provide quicker hot water is a recirculating pump. These are usually installed on a timer to start up before you need them. They do not waste water but do use a bit more energy via your hot water heater.

Often these are installed with a return loop on the hot water from the furthest fixture, but there are so models which can use the cold water supply as a return loop, avoiding the need for the extra plumbing.

  • I'd like to not have to schedule the hot water. And I'd wonder if the cost of a circulation pump would exceed the cost of an inline heater with it's savings in engery. – Matt Jan 18 '13 at 16:17

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