Tankless coil installation location sketch (C) Daniel Friedman How to install a Tankless Coil for Hot Water Heating
Tankless coil installation procedure

  • TANKLESS COIL INSTALLATION PROCEDURE - CONTENTS: typical steps in the installation or replacement of a tankless heater coil or "tankless coil" installed on a hot water or steam boiler to produce domestic hot water for washing & bathing: how is a tankless coil installed, warnings about leaks, breaking off bolts, and proper gasket handling.
  • POST a QUESTION or READ FAQs about installing or replacing a tankless coil for hot water supply
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Tankless heater coil installation on a boiler: this article describes the steps in installing or replacing a tankless coil on a hot water (hydronic) or steam boiler.

Tankless coils are used to provide domestic hot water by heating building water as it passes through a heat-exchanging coil immersed in the heating boiler's hot water contents.

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Tankless Heater Coil Installation Procedures

Tankless coil operation, adapted from (C) Daniel FriedmanAt page top we include a sketch showing the typical installation of a tankless coil on a residential heating boiler. Notice in the page top sketch that a mixing valve or anti-scald valve has been installed between the cold inlet to the tankless coil and the hot outlet pipe from that device.

[Click to enlarge any image]

At left we've adapted a U.S. sketch from a confusing article that mixes up TANKLESS COILS (boiler-mounted devices that we discuss in this article),

INDIRECT FIRED WATER HEATERS (a tank of hot water heated by a heat exchanger inside the tank that itself is heated by water from the heating boiler),
and TANKLESS WATER HEATERS (stand-alone, instant, tankless water heaters). - U.S.DOE (2014)

As you can see, a tankless coil used for making hot water is a heat exchanger that is inserted into the heating boiler's very hot water. As cold water flows through the inside of the tankless coil it is heated up, leaving the coil hot.

On some heating boiler designs the tankless mounting plate is round (photo below). When I find a pile of tankless coils like this I know the building occupants have not been having a good time in the shower. On other tankless heater coil designs the coil mounting plate may be round as we illustrate in M.C.'s photo later in this article. And tankless coils may mount on any of the boiler sides or even on its top, depending on the boiler's design.

Photograph of a multi function combination control on a heating boiler

On steam boilers a tankless coil may also be mounted but will always be below the boiler's water level.

Step by Step Tankless Coil Installation Procedure

Watch out: when installing a tankless coil to follow the manufacturer's instructions about handling and sealing the boiler-to-coil gasket (some may specify no sealant is used), and about uniform torquing of the coil faceplate mounting bolts.

Tankless coil installation schematic, adapted from Crown BDS-Series boiler installation instructions - InspectAPedia Crown Boiler Co.

Sketch at left adapted from Crown Boiler's BDS boiler installation instructions. Contact information for the Crown Boiler Company is given below.

Tankless coil piping schematic example for a Crown heating boiler

At above left we illustrate the typical piping arrangement into and out of a tankless coil water heating system. Cold water is piped to an inlet marked "COLD" and building hot water supply piping is connected to the tankless coil outlet marked "HOT".

[Click to enlarge any image]

This tankless coil piping example from Crown Boilers indicates the use of a mixing valve or anti-scald valve right at the heating boiler. The company includes an interesting warning reading as follows [Quoting - Crown BDS Installation Manual]

Photo of an anti-scald tempering valveWARNING: Thermostatic mixing valves are intended to increase the supply of hot water available from the coil. They are not intended to prevent a scald hazard.

Really? I speculate that the company's lawyers got a hold of this one - nobody wants to be named in a scald lawsuit. Some manufacturers may hold the view that anti-scald devices should be installed at each fixture, at the point of use.

Our photo shows a typical mixing valve produced by Watts Regulator Co. The mixing valve manufacturer's installation instructions for these devices include similar warnings.

Also be sure to follow the mixing valve manufacturer's installation instructions. For example Watts recommends:

To prolong the life of the Model LF1170-M2 or LFL1170-M2 valve [not shown here], it is recommended that it be trapped as shown ...: i.e. the hot water inlet to the LF1170-M2 valve should be 8" – 12" (200 – 305mm) below the hot water supply feed. - "Instructions Series LF1170 and LFL1170 Hot Water Temperature Control Valves", Watts Regulator Co. (2013)

See details about the piping, intallation specifications and warnings for tempering or mixing valve installations

Reader Question: do I leave-on or remove tie wires found on the tankless coil before I install it on my heating boiler?

Tankless coil ready for installation on a Crown heating boiler (C) InspectApediaI am installing two DHW coils on a Crown Series 24 steam boiler (sectional, 6-sections). The coils came tied with bailing wire. The bailing wire is not copper, it does however seem to be in logical areas to keep the coils together and ridged. Is this done just for shipping? Should I remove the bailing wire, or does it stay on the coils helping hold them together?

This ... is of the DHW cools for my Crown boiler. This is just one of them, and shows the bailing wire in question. My gut says remove it, but ? - M.C. 2/24/2014


Before we saw the photo we were not sure of the right answer. But from the photo I'd certainly expect that was junk wire intended to be removed. These are "tie wires" intended to prevent the coil sections from damage due to flopping around during shipping. I'm also a little worried about tankless coils showing up exposed - it's the fins and tubing that transfer heat from boiler water to water in the coil - I wouldn't want the coils to be bent, dinged, or crushed. Is this new equipment?

Don't leave these wires t in place - you would risk unwanted corrosion on the coil itself once it's installed, as well as risking dropping junk into the boiler interior as the wire rusts and falls off.

But if on removal the coils seem to flop too loosely, I'd look carefully at how they'll be suspended in the boiler interior - and let me know if that looks odd and we'll pursue it with Crown.

Dual-coil heating boiler with two tankless coils (C) Danil FriedmanFor example if the coil tubing were so flexible that it fell inside the boiler ending in contact with a hot spot that'd not be very attractive.

Also take a look at MIXING / ANTI-SCALD VALVES - you may want to install a mixing valve if one is not already provided, both to avoid a scalding risk and to permit more efficient use of the coil.

Our photo (left) illustrates a heating boiler with two rectangular tankless coils installed. [Click to enlarge any image]

I would not leave a wire of a different metal wrapped around a coil to be inserted into the boiler - without first checking with the manufacturer. I can imagine two very different situations:

A different metal wire wrapped for stability during shipping might actually cause corrosion by galvanic action when the coil is inserted into the boiler - so should be removed

On the other hand

A manufacturer *might* have wrapped a different metal wire around the coil tubing as a sacrificial anode much as we see inserted into a domestic water heater tank.

So what we need is to know the manufacturer of the coil, or if there is none, we'd contact the boiler manufacturer - Crown - to find out what's up.

Are there any installation instructions with boiler? If not I'd download those as they may address this question. Here is contact information for your boiler manufacturer:

Crown Boiler Co.
P.O. Box 14818
3633 I Street
Philadelphia, PA 19134
(215) 535-8900


Reader follow-up:

You are correct this boiler has two coils. they are not wired to each other, they came shipped separately and with adequate protection. The inlet is standard pipe thread, and in the mounting plate the inlet spits off to three separate finned copper tubes that each go into the boiler and make a few passes then come back to a fitting that runs them all back to one tube.

On the three tubes that zigzag back and forth on their several passes they are tied together with bailing wire. Would the bailing wire just rust away eventually, meaning that it is there just for shipping, and should be removed?

I confirmed with [the boiler manufacturer] Crown that they should be removed.


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