Tankless Water Heater


Install an Electric Tankless Water Heater

Tankless water heaters are great, and for cabins they’re really great. Of all the upgrades I have made at the cabin, replacing the aging tranditional water heater with the wall-mounted miracle that is the tankless water heater is one of my all time favorites.

We initially upgraded to a tankless water heater to make room in our mechanical room for a new and relocated furnace.

The small size and space savings is really amazing, but, after years of use I now realize the biggest benefit may be the ready-in-an-instant, on-demand hot water. This is huge for an occasional use cabin.

On arrival to the cabin we have hot water. I can’t imagine what its like with a standard storage hot water heater at a cabin.

Let see… find a flash light, get some matches, lite the pilot, fire up 80 gallons of 40 degree water and then wait.  How long does that take?  You get the point. Read on for an overview of tankless water heaters and a step by step walk through of an electric tankless water heater install.

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 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
  • Electric units require substantial power ( 1 – 3 40 – 60 amp circuits!)
  • 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 period of non-use – turn on and wait to heat entire tank
  • Pay for heating (and reheating) entire tank
  • Unit life 10 – 15 years
  • Cost less to purchase / install
  • 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. 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: stiebel-eltron-usa.com)

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.

Tankless Water Heater Install – Preparation

Preparation and Materials

Project Overview

  • Level: Advanced
  • Time: Hours – Days
  • Cost: $600 – $1000 +

Project Big Picture

  1. Plan placement.
  2. Mount unit.
  3. Plumb unit.
  4. Wire unit.
  5. Test and use.
Materials – Water Heater and Plumbing

Materials – Electrical Circuit

ItemWhat I usedCost
Tankless Electric Water Heater$800
Stainless Steel Flexible Water Supply Line$15 / ea
Nibco 3/4″ copper union$12
Solder Torch$90
Solder / Flux$20
Teflon Pipe Tape$7
ItemWhat I usedCost
Circuit Breakers$25 / ea
6 AWG Copper Wirevaries w/ length
Steel EMT Conduitvaries
Conduit Elbows$3 / ea
Conduit Fittings$5 / ea
Conduit Fittings$15 / 25
Conduit Clamps$7 / 20pc
  • Hand tools for unit mounting
  • Hand tools for plumbing
  • Hand tools for electrical work
  • Screws to mount unit and conduit

Tankless Water Heater Install – Step by Step

  1. Plan water heater placement.

    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.

  2. Assemble water heater, supplies and tools.

    Gather water heater, plumbing supplies, electrical supplies and tools.

    Basic electrical supplies for wiring tankless water heater.

    Hand tools for water heater electrical work.

  3. Mount water heater.

    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.

  4. 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.

  5. Plan and Connect the Electrical Circuits.
     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 60 amp circuits. My unit calls for two 60 amp 240 volt circuits and for these circuits I needed 2 double pole 60 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 60 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 60amp 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.

  6. Close Unit Cover, Turn On Electricity and Power Up Unit.

    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.


As a followup, we have used the Stiebel Eltron Tempra 24 plus in our central Minnesota cabin for almost 2 years and could not be more happy with the performance. Our cabin has only one bathroom, but the plumbing to the shower is 3/4″ and the shower head set up for high flow, so the demands for a shower can be high.

We find setting the unit to around 130° in the winter and around 120° in the summer provides perfectly hot showers and gives us all the hot water we need. One aspect of using the unit with a well reservoir tank that we have noticed is the effect of changing water temperature related to refilling of the reservoir tank. Our reservoir tank is located in our warm mechanical room, and water in the tank eventually warms to the temperature of this room.

Once we start to draw down the water in the tank, it is replaced with cold well water and the supply water temperature quickly drops. The end effect is changing hot water temperature at the tap. This is usually not a big problem, but we will plan our showers accordingly and know the second shower will need adjustment of the shower mixer.


Tankless Water Heater Install Image Gallery


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