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Converted my oil burner to a gas burner and added an electric hot water heater. When i use the shower the hot water turns to luke warm in 12-15 minutes. It was installed by a professional plumber and he seems to be baffled by this problem.

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    how does the oil burner to gas burner conversion relate to the hot water heater? – jsotola Nov 29 '18 at 2:11
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    What size/type/model electric hot water heater? – manassehkatz Nov 29 '18 at 3:38
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    How many gallons is the tank? – Harper Nov 29 '18 at 4:12
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    In the past we purchased a 50 gal tank with 2 elements, even tho it was brand new, one wire on the lower element was never connected, we eventually found it just floating in the insulation near where it was supposed to be connected. Same exact symptoms as yours. Just because it’s brand new a tank don’t assume it’s working correctly, doesn’t have manufacturing defects, or was in some way damaged. – Tyson Nov 29 '18 at 13:24
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    Hello, and welcome to Stack Exchange. Once the shower cools off, is the pipe from the hot water heater still hot? – Daniel Griscom Nov 29 '18 at 17:41
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That's how tanked water heaters work

Before, you had an oil fired water heater. There's no such thing directly, so you probably had an powerful oil fired boiler (hydronic) with enough power to heat the whole house, and as a side-feature, it had a water-water heat exchanger providing hot water. The demands of heating the house are much larger than just hot water, so it had the oomph to provide hot water continuously.

You changed to the cheapest option available, a tanked electric water heater, because the project had to hit a budget number. This is how those work.

Electric tanked water heaters have a tank of water. Typically 30 gallons sometimes larger, and typically 30 amps of electric. It takes 20-60 minutes for the tank to initially warm up. As you use the water, cold water must (law of physics) come in to replace it (the pressure of this water is what provides the flow). The 30A electric heater is not powerful enough to heat water at the rate a shower uses it. So the hot water is eventually used up. The heater needs 20-60 minutes to recover.

Getting 10-15 minutes of hot water would be about right for a low flow 2 GPM showerhead and a common 30 gallon tank.

You can go tankless

What you had before, with your hot water heat exchanger, was effectively a tankless heater because the fuel-fired heat source was so very powerful.

Since you converted the house to gas, you can get a gas tankless heater. Those can be plenty powerful and will do what you want.

Your other option is a tankless electric heater. However fuel is very powerful and it takes a lot of electricity to even compete. Don't be surprised if a "whole house" electric tankless heater large enough that will satisfy your needs will want 100A or more. That's just how much electricity it takes to heat water. It's unfortunately common for people to lowball their tankless electric requirement to either save money or due to electric capacity, and be unhappy with the lukewarm results at high flow. Such people inevitably declare "tankless electrics are junk" and give up, which is a shame.

However with electric, a "whole house" unit isn't necessarily the best plan. With no flues or drains, a tankless electric can go practically anywhere. You can site one right at the shower and have instant hot water. And since it's only serving the shower (and presumably the sink) it can be a smaller unit. Have another one under the kitchen sink to power the faucet, dishwasher etc (with a branch to the washing machine) and you are in good shape. You still need a lot of power.

  • The other other option would be a gas fueled tank. I'm surprised you skipped over it and went straight to tankless. The same capacity gas powered hot water tank can typically provide hot water for considerably longer than electric, because of better recovery rates. The fire is able to transfer quite a bit of heat to the replenishment (cold) water during your shower. Electric tanks try to do this too of course, but they're way slower and can probably only extend your usage by a few minutes, whereas some gas models are rated to provide double their capacity of hot water in the first hour. – CactusCake Jan 9 at 22:36
  • @CactusCake His old water heater was hydronic coming off the oil furnace, that is proven by the fact that he's completely unfamiliar with the concept of hot water running out. The gas furnace guy certainly would've put in a gas water heater if that was feasible, since that's very much in his wheelhouse. I suspect it didn't happen because it is not feasible, likely the barrier issue is no exhaust stack in the water heater location. That was my presumption when I wrote this. – Harper Jan 9 at 22:58
  • Don't you still need an exhaust stack for tankless gas though? – CactusCake Jan 9 at 23:04
  • Oh, forgot I mentioned that! I imagine I was thinking you have a lot more liberty on location with those, since they are lightweight and take little room. They even make ones that go outside. – Harper Jan 9 at 23:10
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Most water heaters are equipped with two elements which help it conserve energy. The upper or lower element only comes on when that area has cooled down, and both come on when the water is drained and new water mixes in. This helps to heat the water faster.

I am guessing one of your elements is not working. If it was installed within one year that's usually covered in the manufacturers warranty and under the installers warranty. I would contact the installer and have them check it out.

Good luck

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Sounds like a bad element. The upper element heats water as it's being used. The lower element helps maintain the temperature within the tank. It's also possible that you have a faulty thermostat.

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It's also possible that your plumber connected the electric circuit incorrectly and your elements are not getting hot enough. That's why he is a plumber, not an electrician...

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