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Thread: Electric vs. Gas tankless water heater

  1. #1
    DIY Junior Member dnwake's Avatar
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    Default Electric vs. Gas tankless water heater

    I live in California, and I currently have a (too small) tank gas water heater in the house I've just bought. Gas heating is supposed to be be cheaper than electric heating in California. However, all the tankless gas heaters I've looked at seem to have low user satisfaction, while the Stiebel Eltron Tempra electric has high reviews. Can anyone give advice on whether to go for a gas or electric tankless water heater? Thanks.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Personally, I wouldn't use a tankless in the current state of affairs! But, if I did, I would not want an electric one unless the rates were REALLY low...NG pricing in most places is much better bang for the buck. In either case, you may need to upgrade your service, either gas or (almost certainly) electric. A tankless system can work and depending on where in CA you live, you may have a better chance than some living where it's colder. You need to read the fine print on the available volume with various inlet temperatures. It's all about how much temperature rise it can provide. In some cases, to get a decent volume, you may need to run several of the tankless systems in series. If you have a large soaking tub, or expect to use multiple showers at the same time, you will need a substantial unit, or more than one. The costs to install and annual maintenance make payback questionable compared to a properly sized, decent gas WH. If you have the ability to install a waste heat recovery system (you'd need to have more than one story...they need a vertical drop to be efficient), you can make either system 'appear' bigger when showering. It does not help when doing something like filling the tub or the WM, or doing dishes since you aren't draining the hot waste water down the drain WHILE it's in use...you need it all up front, which is where a tank works best.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    In the Trades mtcummins's Avatar
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    If you want to spend money on an efficient heater, I'd get a very well insulated condensing tank. They reach efficiencies well into the 90s.

    And make sure you maintain the anode rods and flush the tank out a bit at least yearly. You'll spend far less money on the system, it will perform under most normal conditions at about the same efficiency, last as long or longer with proper maintenance, etc.

    check out www.waterheaterrescue.com for a lot more info (and they sell some products as well) about how to make your tank heater last a LONG time and run efficiently.

  4. #4
    DIY Junior Member Amish Electrician's Avatar
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    Speaking as a Master Electrician, and a licensed Electrical Contractor ...

    Forget about an electric tank-less water heater. Adding electrical power to a tank-less heater is a BIG deal. Things tend to snowball.

    First, you'll need three 2-pole, large capacity circuits to the heater. Your existing panel probably does not have six full-size breaker spaces available, and the electrical service to the house might `not have the extra capacity. Walls will have to be opened, etc. The bill for the electrical alone can easily reach $5000- and that does not include patching the walls, or any plumbing work.

    Gas appears to be much better at creating a lot of heat in a hurry, and the nicer units can adjust the flame- meaning they can handle a wide range of flow situations.

    Dollar-wise, you probably won't see much difference in the energy cost between the two. I say this because California utilities price both gas and electric by the 'therm' energy equivalent. That means that the gas needed to heat your water ought to cost the same as the electric needed to heat the same water.

    Now ... speaking as a DIY ... it appears to me that the real advantages of a tank-less heater become clear only when the hot water is distributed through a manifold to multiple small PEX lines. The two technologies seem to be a match made in heaven. If your house is plumbed in the traditional manner - a large main line branching off to branches as it runs the length of the house - I really don't see much economic benefit to a tank-less system. I'm sure the pros here will correct me / educate me if I missed something.

  5. #5
    In the Trades mtcummins's Avatar
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    yes, I forgot the gas/electric thing in my post. I would also definitely recommend gas, no matter which type heater you go with.

    the advantage a tankless has is that if your house sits empty for 9 hours/day while you're at work, and 7-8 hrs you're not using any water while you sleep, there's no standby losses. Older, and newer cheaper tanks often have very little insulation, so you burn a lot of energy just keeping water hot standing there.

    if you don't have that situation, and certainly on weekends etc even if you do, then you lose all the benefit right away. this is b/c tankless heaters are extremely INefficient at heating water. They use way more energy to do so than a tank. So you need a LOT of standby losses from a tank to start to make up for this inefficiency.

    I imagine that in california, you can't even buy the cheap tanks with minimal insulation, but i'm not sure about that. i would guess that the benefit would be very minimal at best as far as energy use, and the cost of the unit can easily become 4x that of a tank, if all is ideal. throw in the need for larger service lines, different venting requirements than you have now, etc, and that can jump to 10x.

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    In the Trades Gary Swart's Avatar
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    Gas is always cheaper than electricity, but just like the electric heaters require a major upgrade in electrical service, gas requires a much larger service than is normally provided.

  7. #7
    DIY Senior Member lifespeed's Avatar
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    First let me start by saying I have a tankless water heater and love it. I will address some comments:

    Energy efficiency. I pay $12 - $14/month for gas in the summer, compared to $30 with my old tank. It was not that old, either. I am definitely saving money with tankless.

    Scale build-up in the heat exchanger. This can definitely be an issue. I chose to address it by installing a water softener, which has also ensured my other plumbing fixtures have a long life. I actually had a toilet valve fail due to hard water. Regardless of softener or not, you should install flush valves from the manufacturer. And if you have hard water, you will need to flush it annually to ensure long life. These are low maintenance only if you soften the water.

    Gas vs. electric. Gas, of course! And you may need to upgrade your gas pipe size to provide 200K BTU, depending on the specifics of your situation. It is even possible you will need the gas company to install a larger meter, but they should do this at no charge.

    GPM at temperature rise, and pressure drop at high flow. Both of these issues are trade-offs against tankless burner capacity and heat exchanger size. I got the largest unit simply because there is no down side to a large heater, and the large heat exchanger reduces pressure drop. I used Noritz NRC1111.

    I absolutely love our tankless heater. The water temperature never fluctuates, never runs out, and is very efficient. I did go through extra effort and expense to install it because of the gas pipe upgrade, but I don't regret it for a minute. Gas tankless is an option worth considering.
    Lifespeed

  8. #8
    DIY Senior Member lifespeed's Avatar
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    Quote Originally Posted by jadnashua View Post
    A tankless system can work and depending on where in CA you live, you may have a better chance than some living where it's colder. You need to read the fine print on the available volume with various inlet temperatures. It's all about how much temperature rise it can provide. In some cases, to get a decent volume, you may need to run several of the tankless systems in series. If you have a large soaking tub, or expect to use multiple showers at the same time, you will need a substantial unit, or more than one.
    The larger tankless units are more than adequate for all but the most extreme situations, eg. inlet water temperatures near freezing feeding multiple fixtures simultaneously.
    Lifespeed

  9. #9

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    If you have the gas supply for it, go gas. Google Tankless 101 for a ton of info on these things and please consider purchasing from a Local dealer familiar with these machines and have them do the installation. I see a lot of bad DIY installations and also bad jobs from other contractors who have not done them before, screw it up thinking they know everything and then run around telling people that tankless don't work. THey work great, but only if you get a good one and have installed by someone who knows what they are doing. My opinion, get a Rinnai or Noritz! go to their wesites and use their dealer locate and choose one of the best on their list. You'll end up getting a great job at a fair price.

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