Guide to Indirect-Fired Hot Water Heaters
InspectAPedia^® -

Description of Indirect-Fired or "remote" Hot Water Heaters - water tanks heated by a connection to a heating boiler or other heat source.
How to obtain more hot water quantity, pressure, flow, at less cost
Options for replacement of tankless coils as domestic hot water source
Questions & answers about indirect-fired hot water heaters

Indirect water heater properties: here we define and explain indirect-fired hot water heaters, describing the characteristics & advantages of this method for making domestic hot water where a gas or oil fired heating boiler is installed.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

Installing an indirect-fired water heater

Thanks to Carson Dunlop, a Toronto Home Inspection Firm and Home Inspection Educator, for permission to use sketches shown in this article.

Below we describe some alternative ways to make hot water, either to replace or to supplement an existing hot water supply system. After knowing what the hot water problem really is, there are steps we can take to get more hot water or to increase hot water pressure.

As we explain at TANKLESS COILS, a conventional tankless coil system imbeds a finned copper tube coil inside of the hot heating boiler water, running domestic cold water through the tankless coil where physically separated boiler water heats the coil and thus heats water passing through the coil.

An indirect-fired water heater also uses a finned-copper tube coil in a different approach to providing more domestic hot water.

In our photo at left, the white Super Stor™ tank is an indirect-fired water heater. Water in this tank is heated by a plumbing loop circulating hot boiler water through a heating coil in the bottom of the Super Stor™ water heater tank.

Indirect fired water heaters: In some other buildings domestic hot water is produced by cycling hot water from a hydronic or steam boiler through a loop inside of a steel tank. The water in the tank is heated by the water in the coil.

Modern systems using this approach use the term indirect-fired water heater and such systems are sold by various companies such as the SuperStor^TM unit shown here as the white tank to the right of the heating boiler.

You may also notice the WellXTrol^TM blue water tank off to the left of the boiler as well as in the left foreground covered partly by a cardboard box we have a white-yellow fiberglass close to the thin blue vertical water softener - water treatment equipment in the same photo. And just to be complete, the little tank over the boiler next to our service technician is the expansion tank for this heating boiler.

Indirect fired water heater tanks for domestic hot water, such as the SuperStor^TM are usually located close to the heating boiler and will have both cold and hot water lines leaving the tank to supply the building with domestic hot water and a loop of piping that runs between the [usually the] bottom of the tank and a nearby heating boiler. Follow the pipes to see which pipes are performing which function.

The difference between Range Boiler Water Heaters and Indirect-fired Water Heaters is in the details. The heat exchanger that heats water in the range boiler is in or at the heating boiler. The water in an indirect fired water heater such as the SuperStor^TM unit is heated by a finned copper coil located inside the hot water tank. The internal coil is in turn heated by circulating water inside the coil to and from the heating boiler. The range boiler is an old concept in use for about 100 years. Indirect fired water heaters are a modern system and are in current sales and use.

Plumbing Connections for an Indirect Fired Water Heater

Where an indirect-fired water heater is installed, the coil is inserted not in the heating boiler, but rather in the bottom of a hot water tank. You can see this design in our photo at left (the blue tank is the indirect fired water heater) and also in our sketch at page top, provided courtesy of Carson Dunlop.

Water from the heating boiler (not domestic cold water) is circulated from the boiler, through the coil, and back to the heating boiler. The coil, in turn, heats water stored in the separate hot water tank.

This installation is a bit fancy: the blue indirect fired water heater is heated by the gray Weil McLain™ oil fired heating boiler.

The blue water heater tank is in turn being used in this case to provide a big reservoir of hot water to a water-to-air heating coil installed in the light gray/tan air handler at far left in the photo. This home uses that air handler for both central air conditioning and also for heat. Other pipes connected to the Weil McLain boiler may indicate that that boiler also provides hot water heat to some building areas. (Click on the photo for details).

But the principle is the same. Hot water from the blue indirect-fired water heater tank could have just as well been used to provide domestic hot water for washing and bathing as well as for heating the water-to-air heating system, as well as serving both purposes.

Controls on Indirect Fired Water Heaters

Extrol water heater, indirect fired (C) Daniel Friedman An indirect fired water heater such as the Super Stor™ or Extrol™ water heater (shown at left) unit will include a temperature control that is usually mounted on the water tank itself.

When the hot water temperature drops below the control set point, the control will turn on a circulator pump that will cycle hot boiler water through the heating coil inside of the Super Stor™ tank.

The indirect-fired water heater does not itself turn on the heating boiler. Rather, when temperatures inside the separate heating boiler drop below a low limit (or hot water maintenance level) set on the heating boiler's own control, that system will turn on its burner to re-heat the boiler water directly.

Efficiency of Indirect Fired Water Heaters

An indirect-fired water heater is a more efficient way to use a home heating boiler to make domestic hot water. Why? Because the heating boiler will run less often, and when it does run, it will have a longer "on" cycle (as it has to heat up the tank of hot water). Both of these conditions are a more efficient way to burn home heating oil than using a tankless coil.

In sum, during the heating season, when a heating boiler is likely to be "hot" most of the time anyway because it is heating the home, a tankless coil installed on a heating boiler is a reasonable way to obtain some domestic hot water from the system, though in most installations a tankless coil will not be able to produce as much hot water for as long a time period as what we can obtain from a separate water heater.

But an indirect-fired water heater always makes more efficient use of the home heating boiler, year round. And since the consumer can decide how big a hot water tank she wants, 50 or even 100 gallons of hot water can be kept in reserve. More than we can normally obtain from a conventional domestic tankless coil on a heating boiler.

Readers should also read Range Boiler Water Heaters where we describe an older type of indirect-fired water heating system installed at many older homes.

The characteristics of various water heaters such as life expectancy, cost, safety, and capacity are discussed at WATER HEATER PROBLEM DIAGNOSIS
WATER HEATER PROPERTIES

Ways to improve hot water quantity, pressure, and flow are discussed beginning at HOT WATER IMPROVEMENTS and continuing at HOT WATER QUANTITY IMPROVEMENT.

Frequently Asked Questions (FAQs) about indirect-fired hot water heaters

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

HTML Comment Box is loading comments...

Recommend / Share this Article

...

Technical Reviewers & References

InspectAPedia.com^® - Daniel Friedman - Publisher & Editor.
InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

ALTERNATIVE HOT WATER SOURCES
  Electric Shower Heaters
  High Efficiency Water Heaters
  Indirect-fired Water Heaters
  Instantaneous Water Heaters
  Multiple water heaters in parallel
  Multiple water heaters in series
  Range Boiler Water Heaters
  Side Arm Coil Water Heaters
  Solar Water Heaters
  Tankless Coil for Hot Water
  Tankless Water Heaters

Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Carbon Dioxide Gas Toxicity
Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
...

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
...

Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair

Ask a Question or Search InspectAPedia

Installing an indirect-fired water heater

Plumbing Connections for an Indirect Fired Water Heater

Controls on Indirect Fired Water Heaters

Efficiency of Indirect Fired Water Heaters

Frequently Asked Questions (FAQs) about indirect-fired hot water heaters

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair