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How to Install an Electric Tankless Water Heater

A great upgrade for the cabin, an electric tankless water heater is virtually maintenance-free and instant on.

Tankless water heaters are great, and for cabins, they’re really great. They do, however, come with some downside, but tankless water heaters offer compelling benefits for the occasional-use cabin or vacation home. Of all the upgrades I’ve made at the cabin, replacing the traditional water heater with this tankless units is one of my all time favorites.

Tankless water heater install - a step by step how to.
How to install a tankless water heater.

Tankless Water Heaters - Perfect for Cabins and Vacation Homes

Tankless water heaters are great for cabins. They are very popular outside of the United States for many of the same reasons that they are perfect for vacation homes and cabins – they are significantly more size and energy efficient compared to traditional tank water heaters.

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Here is a summary of some of the benefits of a tankless waters:

  • small size/wall mountable
  • unlimited hot water
  • instant hot water (no waiting to heat the tank of water)
  • more efficient water heating/lower energy use.

The limitations of a tankless water heater include:

  • large instantaneous energy requirements (electric or gas)
  • high initial cost of the unit/installation
  • heating limitations based on flow and inlet water temperature (can be significant)

For us, we were interested in saving space. We needed to move a furnace into our smallish utility room and getting rid of the old, floor standing tank water heater freed up the space we needed to install a new furnace. The small size and space savings of a wall mounted tankless water heater is pretty amazing – they literally take up the space of a briefcase.

And while the space savings is great, the biggest benefit we have found after converting to tankless is the instant-on, ready-when-we-get-there hot water. Not needing to get hot water for an occasional-use property like our cabin is huge.

Tankless water heaters + cabins = match made in heaven!

Tankless Water Heaters vs. Traditional Tank Water Heaters:

A tankless water heater offers space savings, endless hot water, lower cost of operation and no tank heating delays with the trade-off of higher initial cost and hot water flow limitations.

Tankless Water Heater (On Demand)

  • small size / space requirement
  • Instant hot water after a period of non-use – turn on and use
  • Pay for what you use (+ pilot if gas) and only when you use it
  • Unit life 20 + years
  • Cost more to purchase/install
  • Substantial energy demand when in use (40 – 180 amps for electric units and high-flows for gas units)
  • Flow (use) limitations based on supply water temperature

Traditional Tank Water Heater (Storage)

  • large size / space requirement
  • Entire tank heated before hot water available after a period of non-use – turn on and wait to heat an entire tank
  • Pay for heating (and reheating) entire tank
  • Unit life 10 – 15 years
  • Cost less to purchase/install
  • Lower energy requirements vs tankless when operating
  • Stable temperature for entire tank volume no matter supply temperature

Electric vs. Gas Tankless Water Heater Comparison

On demand tankless water heaters are typically offered with one of two fuel sources, gas (natural gas or propane) or electric. Selecting between gas and electric balances costs, performance, installation and maintenance requirements of each.

Electric Tankless Water Heater

  • Requires one to three 240v 40-60 amp circuits
  • Does not require combustion air ducts, exhaust venting, gas supply
  • Install anywhere 240v supply circuit wiring can go
  • Install less complex and expensive (install electrical circuit, plumbing)
  • More efficient typically ~ 95%
  • Electricity typically more expensive vs. gas
  • May have narrower range of heating capacity (100° – 140°) adjustment
  • Nearly maintenance free (replace inlet screen)

Gas Tankless Water Heater

  • Requires gas supply, combustion air, exhaust venting, 120v circuit
  • Does not require 240v high amperage circuits
  • Install where combustion air, exhaust venting, 120v circuit can go
  • Install more complex and expensive (install gas line, combustion/exhaust venting, plumbing)
  • Less efficient typically ~ 85%
  • Gas typically less expensive vs. electricity
  • May have wider range of heating capacity (100° – 180°) adjustment
  • Some mainenance required (burner, pilot, venting)

Selecting the Correct Size Tankless Water Heater

Picking the proper size water heater is important.  This is especially true with tankless water heaters as they have no reserve (tank) and are required to heat the water flow in “real time”. Tankless water heaters heat the cold water supply as it passes through the unit and therefore are limited by the flow rate of the water and temperature of the cold water supplied to the unit.

Larger flow needs (large homes, multiple bathrooms (showers), high flow showers, etc) and colder supply water (cold climates, winter use) require larger units

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Sizing is particularly important with electrical units which generally have a smaller range of heating capacity (max setting typically = 140°) compared to gas units (max settings up to 180°) and offer less flexibility once installed. Most manufactures have charts to help you select the proper size unit. Here is an example of the selection chart on the Stiebel Eltron site:

Stiebel Eltron electric tankless water heater selection guide.
Tankless water heater selection guide (source:

Get Your Own Tankless Water Heater Once you decide on a tankless water heater, you will need it installed. Installation for these units can be expensive, especially for gas units. For many DIYers, installation of a tankless water heater is a fairly straightforward project. Read on for a step by step of the installation of my electric tankless water heater. I rate this an advanced level project simply because of the high voltage, high amperage electrical work. Due to the potential danger of working with high voltage, high amperage circuits, do not attempt the electrical portion of this project unless you are qualified to do so. You could certainly mount and plumb the unit and hire out the wiring. Safety first.


Prior to any electrical work ensure that the main breaker panel is off. Consult federal, state and local codes. Call a qualified Electrician if you have any questions or not comfortable with this type of electrical work.

OVERVIEW | How we installed an electric tankless water heater in our cabin utility room - costs, logistics and gas vs. electric comparison.

Difficulty: Intermediate
Time: 1 Day
  • 4 Hours plumbing
  • 4 Hours electrical
Cost: $500 - 1000
  • 100 plumbing parts
  • 100 electrical
  • 700 water heater
Steps Summary | How we installed an electric tankless water heater in our cabin utility room - costs, logistics and gas vs. electric comparison.:
  1. Plan placement of on demand water heater
  2. Assemble water heater, supplies and tools
  3. Mount water heater
  4. Plan and Attach Water Connections
  5. Plan and Connect the electric
  6. Close unit and power up

SUPPLIES LIST | How we installed an electric tankless water heater in our cabin utility room - costs, logistics and gas vs. electric comparison.

TOOLS LIST | How we installed an electric tankless water heater in our cabin utility room - costs, logistics and gas vs. electric comparison.

STEPS | How we installed an electric tankless water heater in our cabin utility room - costs, logistics and gas vs. electric comparison.

  1. Plan placement of on demand water heater
  2. Consider proximity to electrical supply, plumbing connections and accessibility for temperature adjustment and service. Also consider plumbing distance from heater to end use fixtures. Long plumbing runs will result in longer lag time between faucet opening and heated water arrival.

    Plumbing diagram showing plumbing and electrical connections to tankless water heater.
    Plan placement of tankless water heater — consider access to unit, ease of plumbing, distance to end use (longer = more lag time for hot water) and ease of wiring.

  3. Assemble water heater, supplies and tools
  4. Gather water heater, plumbing supplies, electrical supplies and tools.

    Basic electrical supplies for wiring tankless water heater.
    Hand tools for water heater electrical work.

  5. Mount water heater
  6. Position heater on wall in intended mounting position and mark mounting hole positions on wall. Using supplied or suitable fasteners, connect the heater to the wall. Unit must be mounted in upright position, unless otherwise noted by manufacturer. Leave at least 6″ around water heater cabinet for service and clearance for cabinet door opening when choosing a mounting location. Mount the unit upright, in a dry area and one protected from freezing temperatures.

    Mounting tankless water heater.
    Mount the unit upright in a secure, dry position on an accessible wall.

  7. Plan and Attach Water Connections
    • Plan and Attach Water Connections.Check local, state and national codes prior to proceeding. Most units require periodic water supply line disconnection for service (inlet filter screen cleaning) and therefore should be plumbed with an easy to disconnect and reconnect attachment. Many use flexible stainless steel connections for this. These are the same connectors used to attach to water softeners and other water heaters. I used a 3/4 inch Falcon Stainless Mega-Flow Super Water-Flex line. Using these flexible connectors also simplifies the plumbing process for this arm of the water connection.
      Tankless water heater plumbing supply connection with flexible stainless steel connection.
      Flexible stainless supply water connection and outlet plumbing with disconnect coupling.

      The oulet (hot) water connection should also incorporate a disconnect connection to allow for service or replacement. I used a brass coupling with rigid copper tubing. All NPT (normal pipe thread) connections will require Teflon thread tape or paste. Coupling connections do not and should not recieve thread treatment as this can limit the compression of the device and inhibit proper seating of the brass interface resulting in leaks. When using sweat (solder) connections, complete as many of the connections (especially those close to the unit connection) prior to assembly of the plumbing in order to limit potential heat damage to the water heater.

      Closeup of plumbing connections at the base of the Stiebel Eltron tankless water heater.
      Secure unit fittings with second wrench when making connections

      When making the connections to the inlet and outlet fittings of the unit, use care to avoid rotational damage to the unit plumbing by using two wrenches for connections. Once all connections are complete open water supply and check for leaks. Repair any leaks prior to proceeding with electrical connections.

  8. Plan and Connect the Electrical Circuits
  9. Prior to any electrical work make sure that the main breaker panel is off!

    Consult state and local codes. Call a qualified Electrician to perform this work if you have any questions. Depending on the make and model of your water heater, you will require one to three double pole (240 volt) 40 or 50 amp circuits. My unit calls for two 50 amp 240 volt circuits and for these circuits I needed 2 double pole 50 amp breakers (check codes to determine if GFIC protection is required), and AWG #6 copper wire. I needed enough wire to to run two wires for each circuit and a shared ground. Check wire requirements for the specific circuit requirements for your unit.

    Electrical breaker panel in mechical room showing two 60 amp breakers for electric tankless water heater.
    Power requirements for this unit = 2 x 50 amp circiuts!

    Using the appropriate size conduit (3/4″ in my case), measure, cut and connect the conduit circuits from your unit to the breaker panel. I used rigid galvanized conduit with pre-bent turns and compression fittings. Depending on the distance and complexity of the conduit run, you may find it much easier to run the conductors (wires) through the conduit sequentially, as you connect the conduit. Pulling #6 copper through long or complicated runs of conduit is no fun and can be much easier if the wire is passed as you construct the conduit.

    Stiebel Eltron Tempra 24 Plus electric tankless water heater connecting input and output plumbing.
    Electrical circuits for the Stiebel Eltron unit. Dual 240v 50amp circuits – closeup of conductor connections inside unit.

    Attach the conductors to the appropriate connectors in the unit. Consult the product manual for your unit. The connections should be marked by “L1” “L2” (Live 1, Live 2) or similar and the ground connection indicated by a ground symbol (⏚). Remember these are double pole wiring and each live conductor is “hot”. The ground for this unit is a single conductor connected to the ground connection.

  10. Close Unit Cover, Turn On Electricity and Power Up Unit
  11. Close water heater cover and fasten cabinet screw. Turn on power breakers. Check unit display to varify power and operation. Open hot water faucet to purge system of air. Adjust temperature setting of unit control to desired level. Confirm unit function and hot water at tap. Adjust temperature as needed.

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  1. Hello, please help, I live 60 miles from the closest professional that could do this.
    I’m just replacing my seisco 28 with a tempra 24. I’m confused because I have 2 60 Amp double poled circuits each with its own ground. I’m not sure what to do with extra ground.
    Ignore it. Or put both in ground same ground spot

  2. I am looking to install one in a small second home. The home is on a crawl space. My plan was to install it in a kitchen floor cabinet (30″ wide x 34″ tall) where the current regular tank plumbing comes up from crawl space.

    Any issue putting in the cabinet? I also have well water, have you used scale inhibition filter or other filters?

    • Hi Paul,

      Each manufacturer will have clearance requirements for service and safe operation. Aside from these, I am not aware of any code issues with enclosing your water heater. This may not apply to gas units. Obviously the safest route would be to ask your local inspector.

      I do use a whole house in-line sediment filter for our well water system, which is upstream from the water heater.

      Thanks for using the site.


  3. How do I winterize the unit for a Buffalo winter? Will it handle 15 below wind chill in a cottage on Lake Ontario with no heat? We have to drain a 40 gallon heater each year – want to get away from that

  4. Great information, thanks for taking the time to document this DIY install.
    I have everything basically set to install a 24Plus in a 2 bath, 2 BR SC beach home. I have a question regarding the electrical. I was going to run both ground wires and connect them to the unit, but I see you only have one. Did you twist the other ground to the attached one further back in your wiring? Also, I was planning on running both circuits wiring through a single conduit. What do you think?

    • Hi Rae,

      Thanks for using our site and thanks for the kind words.

      The Stiebel Eltron units do not require more than a single (appropriately sized) ground. Here is a wiring diagram for the 24 plus tankless heater. The wiring block will be labeled from left to right as follows: ⏚, L1, L2, L1, L2. The ground symbol (⏚) is the connection block for your single ground wire and the L1 and L2 are connection blocks for the hot leads from the double pole (240v) breakers. So for this unit from left to right you should connect the following: ground,hot,hot,hot,hot.

      As far as the conduit and number of wires you can run in a single conduit will depend on the size of the conduit and the size of the wires. Active conductors (wires) product heat which limits the number and size of wires within a conduit. You may also use a sheathed cable of the appropriate size that does not require conduit. If you do use a combined sheathed product (Romex type), you probably should not run it in conduit as it is not allowed to dissipate heat correctly.

      For the Tempra 24 Plus requiring 50A circuits you should use AWG 6 wire, therefore if you use 1″ conduit you can run up to 6 wires. If you use 3/4″ conduit (as I did) you can only run up to 4 wires and will require two runs of conduit.

      To determine the number of single wires you can run in a single conduit, use a guide like this one from Alan Wire: Conduit Wire Fill Chart

      Here is a link to the Stiebel Eltron Tempra tankless water heater pdf install guide:

      Stiebel Eltron Tempra 24 Plus tankless electric water heater installation guide


      • Thanks for the information, and the chart. I have 3/4″ non-metallic liquidtight conduit which I planned on running the 4 hots and a single ground wire though. Am I correct that you just cut and tied off the second ground wire since the Stiebel only requires one ground? I’m using sheathed 6/2 AWG, but I will take the outer sheath off before running it through the conduit. One last question. I already purchased some flexible 3/4 inch hose from Lowes for the hot and cold. How much better with the flow rate be using the brand you linked to? If negligible I’d rather not spend any more $.

        • Rae,

          Concerning the wire, I would not recommend removing the sheathing of the wire you have. The sheathed wire is only rated for the load you plan to use if left intact. Using the individual wires after manually stripping them is a bad idea – doing this with a 240v 50 amp circuit is a really bad idea.

          I would recommend using the sheathed wire as is or within a conduit approved for the wire. You may need to contact the wire manufacture for more info regarding running sheathed wire within conduit.

          Alternatively, you could return the sheathed wire and use AWG 6 THHN individual wires (you can easily get them from most building supply stores like Home Depot or Lowes). Stiebel Eltron recommends stranded wire too.

          Regarding the flexible stainless connectors, it really depends on what they carry at your local Lowes. I have found that some of the local Ace Hardware stores carry Falcon stainless water connectors. You can look through the connector to get an idea if there will be a significant reduction in flow – lower flow connectors will have narrower internal diameters or areas of narrowing.

          Good luck. I would do a bit of checking before you wire this thing to be sure you are doing it in a safe, code compliant way. These units use a lot of electricity – be safe!


          • Thanks for the advice. I think maybe I wasn’t clear about the wire I’m using. It looks like I’m using the same wire you are – It is stranded 6 AWG. Comes with 2 individually sheathed hots and a ground bundled together in thick rubbery Romex. The Romex sheath is what I was going to remove to run the last couple feet to the Stiebel, until I just realized that the ground is bare The way I have it connected in the panel is with both grounds, and I was planning initially on just plugging them both into the ‘ground block’. I suppose this would work fine as well

          • I just installed this same unit but was confused about the ground wire as well. Should I not have both ground wires together? I turned on the unit and it triggered both circuits. Could it have been that I have both ground running together? This unit won’t turn on now.

            • Enrique,
              You only need one ground back to the electrical panel. The ground needs to connect to the ground buss if a subpanel or the ground/neutral buss if connected to your main panel.

              Each of the other two (or four if your unit requires two circuits) are hot line wires (L1, L2) coming from your double-pole 240v breaker and should not be connected to the ground. Go back and make sure the wires are connected properly according to the wiring diagram for your unit. The single ground will connect to the unit lug marked with a ground symbol. The other wires (all of which are hot) connect to the L1, L2 line (hot) lugs in the unit.

              If the unit does not operate, try re-setting the thermal high-limit switch demonstrated here:

              Good luck and be safe – if you have any questions about the electrical connections call an electrician!


  5. Hi,
    Great write up on this. It gives me inspiration to attempt this myself as I feel I am an advanced diy and have worked on numerous plumbing projects. I would hire an electrician though. I am curious why you went with the soldering route for the hot out rather than the flex easy connect line. If I installed one similar to this probably the 20 model I live in Florida would I need to solder the hot line or could I use an easier connect line?
    Thanks again.

    • Hi John,

      Thanks for the comments and question.

      You can use flexible stainless connectors for both the hot and cold side. I can’t exactly recall why I didn’t use one on the hot side – it would have advantages (easy disconnect, flexible if any movement, etc). The connectors I used (Falcon Stainless) are rating for working temps of -40 – 220 degrees Fahrenheit and are intended for hot water too.

      If you use the flexible connectors, I would highly recommend using the best quality products. Those from Falcon Stainless are very good and offer better flow and much higher quality compared to the cheaper braided connectors.


      • Beautiful. Yes, I agree quality is better. I plan to use the same Falcon connectors along with the same brand tankless. It appears it might be the one tankless that is getting rave reviews. Some that I read about only have problems. Hopefully the electrician will say our junction box can handle the tankless and everything will go smooth for install. Thanks again.

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