Older furnace subjected to flooding (C) Daniel Friedman How to Determine the Age & Life Expectancy of Heating Boilers & Furnaces

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Age of heating equipment & Systems:

How to determine the age of your heating system and components. Here we provide several excellent sources for de-coding the data tag information on heating equipment.

This article provides documents that explain and translate all of the data found on information tags and stickers used on heating & heat pump equipment, including equipment age, heating capacity, electrical requirements, and operating characteristics.

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Heating System Equipment Age - 3 Guides for Reading HVAC & Water Heater Equipment Data Tags & Serial Numbers

Article Contents:

Steam convector heater (C) Daniel Friedman


HVAC data tag decoding guides: For help in decoding air conditioner, boiler, furnace, heat pump, water heater data tags and determining the age, model, or specifications of that equipment, see



AGE of WATER HEATERS There we provide documents with extensive equipment data tag decoding information. This article series answers most questions about all types of heating systems and gives important inspection, safety, and repair advice.

Free Online HVAC Equipment Data Tag Decoder

We provide links to individual manufacturer's data tag decoding guides (Lennox, below), and to two excellent equipment data tag decoding books, by Scott LeMarr (online at this website) and the Carson Dunlop & Associates Ltd. Technical reference - the most extensive such document we've found.

For many heating or cooling equipment manufacturers, especially after 2000, decoding the equipment tag to obtain the age of the device is pretty easy.

Here is an example of data tag age decoding for Peerless Heating Boilers: If the boiler was manufactured from 1984 to 1999, the serial number ends in a four digit date code. “123456-1284” would be manufactured in December, 1984. If the boiler was manufactured from 2000 to present, the serial number ends in a six digit date code. “123456-200505” would be manufactured in May, 2005.

Lennox pulse furnace data tag (C) Daniel FriedmanBut equipment age, capacity, specifications are not always so easy to recognize on the data tag. Here we explain how to dig out that information.

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1. Lennox HVAC products Age: see our Lennox Heater & Air Conditioner Model & Serial Number Decoding Guide at this website. Also see

2. FURNACE AGE DECODING CHART provided by home inspector Scott LeMarr has generously shared his FURNACE AGE DECODING CHART document that decodes both furnace age for many brands of water heater, including hot water systems produced by the following manufacturers. [PDF linked to return here. You can also use the "BACK" button on your browser to return to this page at InspectAPedia.com.]

LeMarr's document provides decoding data for the following manufacturers: Ambassador water heaters, American water heaters [3], ACE water heaters, A.O.Smith water heaters, Apollo, Aqua Temp, Aqua Therm, Best water heaters, Bosch water heaters, Bradford White, Cafos, Champion, Crosley, Energy Saver, Envirotemp water heaters, GE water heaters, Glascote water heaters, Golden Knight water heaters, GSW, Hotpoint water heaters, JC Penny, Jetglas, JW or John Wood, Kenmore water heaters (Sears Brand), Lochinvar, Lowes, Mainstream, Maytag water heaters, Montgomery Wards, Knight, PermGlas, Reliance water heaters, Revere, Rheem water heaters, Rheem/Rudd/Richmond water heaters, Rinnai, Security, Shamrock water heaters, Standard water heaters, State/Reliance/Sears brand water heaters, Thermo-King, Vanguard water heaters, US Craftsmaster, US Water Heaters, and Whirlpool water heaters.

Mr. LeMarr has also shared his free WATER HEATER AGE DETERMINATION CHART with InspectApedia readers.

3. Carson Dunlop Associates' Technical Reference Guide decodes equipment data tags

HVAC Technical Reference Guide (C) Carson Dunlop AssociatesCarson Dunlop Associates' Technical Reference Guide (below) provides the most extensive HVAC equipment data tag decoder & other information to determine the age of boilers, furnaces, water heaters, air conditioners, and heat pumps by decoding the product serial number.

For the most complete and very detailed HVAC equipment data tag and age decoding information anywhere (about 128 manufacturers & brands)

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment

Special Offer
: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.

The Carson Dunlop Technical Reference Guide provides both equipment data tag decoding data and also manufacturer contact information as well as historical dates for many brands of heating and cooling equipment. Included in the manufacturers listed are also makers of ancillary equipment such as controls, circulator pumps, etc., not just boilers, furnaces, and heat pumps themselves.

Here at InspectAPedia.com we discuss different types of heating systems (octopus furnaces, forced air heating systems, steam boilers, forced hot water boilers, high efficiency systems) and fuel types (coal, oil, gas) as an aid in determining the age of a home or other building. Heat pumps are discussed at AIR CONDITIONING & HEAT PUMP SYSTEMS

Manufacturers & brands of HVAC Equipment and Parts identified and decoded in the CDA Technical Reference Guide include about 128 different brands of equipment sold in North America

Aaon, Inc., Ack-O-Matic ,Aero Burners, Aero Environmental, Airco, Airtemp and Tempmatic, Aitons' Equipment - APCO, Allanson Transformers, Amalgamated Electric, Amana, American Standard, American Standard Water Heater Group, Amtrol, Anthes, APCO, ARCO Air, Arkla Industries, Armstrong Air Conditioning Co., S.A. Armstrong, Baltimore Aircoil of Canada, Bard, Bell & Gossett, Borg-Warner, Bradford White, Bristol Compressors, Bryant manufacturing Co. of Indianapolis, Buffalo Package Equipment, Bulloch, Burke Water System Industries, Burnham Corporation, Canadian Tire Corporation, Carlyle Compressor Company, Carrier, Chromalox Canada, Chrysler, Clare Brothers, Clare Mega Save, Clare HECLA, Clawsey-Sohrt Manufacturing Co., Climate Control Products, Climate Master, Climatrol, Coleman, Comfort Aire, Copeland, Copelaweld Compressors, Crane, Davie Environmental Equipment, Day-Nite, DMO Industries, Ducane Heating Division, Dunham Bush, Duomatic, Economite, Elect-Aire, Electric Apparatus COmpany, Elliot, Emerson Electric Company, Enmar Enmar Systems, Envirotron, Esso, Evcon Industries, F.P. Industries, Fairbanks Morse, Fedders, Fess, Findlays Limited, Flamemaster, Fleetline, Florida Heat Pump Manufacturing, FMC Corporation, FP Industries, Franklin Electric Company, Frick, Friedrich, Frigidaire, Frigiking, Fuel Master Burners, G.M.L. Manufacturing, GSW Inc., Galais Manufacturer, Galaxy Boilers, General Controls (ITT), General Electric, Gilbarco, Gilbert and Barker, Goettl, Good Cheer, Goodman, Grimsby Stove and Furnace Ltd., Heat Controller Inc., Heil, Hill York, Hitachi, Homart, Honeywell, Howard Furnace and Boilers, Howell Electric Motors Company, Hydrotherm Inc., I.C. Burners, ITT, Inglis, Inter City Gas (I.C.G.), International, International Comfort Products, Intertherm, Iron Fireman, Janitrol Heating and Air Cooling Conditioning, John Wood Co., Johnson Air Ease, Keeprite, kenmore, Koldwave, Kool-Fire, LG, The Arthur S. Leitch Co., Lennox Industries, Lincoln, Louis Allis Company, Luxaire, Magic Chef Air Conditioning Co., Mgnatec, Marathon Electric, Marcus Transformer, Marley Cooling Tower, Marvair, McLary, McQuay International, Mestek, Metzger, Metropolitan Oil and Gas Industries, Mid Continent Metal Products Co., Miller, Mitsubishi, Modine, Mueller, N'Furno, Nordyne, Norseman Boilers, Oakwood Iron Works (OIW), Olsen, Payne, Pendell Boiler Ltd., Philco, Powermatic, Precision Boilers, Preston, Pyreco, Raypak or Raypak, RBI Water Heaters, Refcan, Reznor ITT, Rheem, Roberts Gordon, RUUD, Sanyo, SJC Corporation, Scarboro Pump Manufacturing Co., Sears, Sears Roebuck, Severn Boiler, Simpsons-Sears, Shell, Singer, Slant Fin Ltd., A.O. Smith, H.B. Smith Co., Smith Boilers, Snyder General Corp., Spacepak, Spencer Boilers, State Industries, Sterling HVAC Products, Sun Dial Manufacturing Inc., Sunscan Compressors, TACO (Canada), TACO, Tappan, TECO, Techumseh Compressors, Teledyne Laars, Tempmatic, Temprite, Tempstar, Thermo Pride, Trane, Typhoon, Unitary Products, viessman, Viking, Warden King, Water Furnace, Watts Regulator Co., Weben jarco, Weil-McLain, Westinghouse, Whirlpool, White-Rodgers, Wood, Worthington Air Coils Ltd., York - Borg Warner.

How to Use Heating Equipment as Indicators of Building Age

PHOTO of an Octopus heating furnace, originally coal fired, converted to natural gas fuel.Indoor heating methods by historic periods or years: (adding date ranges is continuing for the list below - Contact Us to contribute).

Illustration of a Warn Air Heating System Using a Gravity Furnace

Our photo (left) shows a gravity warm-air "octopus" furnace; in its earliest version these furnaces, installed in the late 1800's in the U.S. were coal fired; many were later converted to oil.

Gravity furnaces rely on natural convection (warm air rises) to deliver heat to the occupied space. There is no blower fan in the system. In their simplest design, the gravity furnace system included no ductwork whatsoever. Rather a large grate was provided in the building floor just above the furnace itself. In a multi-story house, heat rose to upper floors by passing up the stairwell or through open registers in first floor ceilings.

The gravity furnace we show at left was a more advanced design in which an "octopus" of duct work "arms" delivered heat directly to individual areas of the building.

The furnace in our photo is taking much of its "return air" from the basement - a very expensive way to heat a home. Earlier models eschewed ductwork and instead fed heat into the first floor of the building through a large central grate in the floor immediately above the furnace.

  • Central fireplaces, no chimneys
  • Indoor fireplaces, chimney in building or on exterior building wall
  • Free-standing wood-burning stoves, the Franklin Stove
  • Coal burning free-standing stoves;
  • Kerosene stoves
  • Coal fired octopus furnaces and steam boilers (photograph above) 1850 - 1930. Some of these heaters have continued into contemporary use after having converted to oil-burners.

Audel's Oil Buerner Guide (C) Daniel Friedman

  • Oil burners: different types of oil burners, coal conversions, low speed, high speed, high efficiency. Audel's 1946 Oil Burner Guide originally sold for $1.00 U.S. and includes photos and sketches of its generation of oil heating burners, boilers, furnaces, radiators, steam and hydronic systems, as well as control devices. Frank Graham's no-heat diagnostic steps are still useful today. Quotations from this wonderful text appear on other articles at InspectAPedia.
  • Oil-fired furnaces, hydronic (hot water) boilers, steam boilers
  • Gas-fired furnaces, boilers, steam boilers - see AGE of HEATERS, BOILERS, FURNACES - AGE of heating equipment, boilers, furnaces by decoding data tags
  • Electric furnaces and heating boilers
  • Geothermal hot water heating systems (Iceland)
  • Heat pumps - see-AGE of AIR CONDITIONERS & HEAT PUMPS how to read data tags to decode the age

If you don't know what kind of heat your building uses, we explain how to figure out the answer at HEATING SYSTEM TYPES.

If your heating system is not working properly, see NO HEAT - BOILER or NO HEAT - FURNACE.

Antique Gas-Fired Floor & Wall Heater

Royal Metal Works gas-fired floor heater (C) InspectAPedia GLReader Question: Royal Heater in-floor gas fired heater history

I just bought a home in California. It has a dual sided, vent less, gas floor heater.

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The only name I see is " Royal Heater". there are 2 valves; one for burner, one for pilot.

You need a key to turn them. On top of the unit is a view finder cap. Inside it looks like a 3 burner pilot

. I have attached photos of it. I'm trying to find any information on it. thank you.

[This particular heater] works beautifully and has been inspected. I want to find a operator's manual so I can maintain it.
- G.L., 16 Jan 2015

Reply: history of Royal Metal Works gas fired floor heaters in California


The Royal brand in-floor gas heaters were originally designed in California in the late 1920's - we have a patent (Publication No. US1666367 A) by Louis Clausing (Burlingame CA) assigned to the Royal Metal Works (his own company held in partnership with Max Schwartz0 describing an earlier version of the product dated 1928: "Heating device." U.S. Patent 1,666,367, issued April 17, 1928.

Your photos below illustrate the interals of this floor-wall gas heater.

Royal Metal Works gas-fired floor heater (C) InspectAPedia GL Royal Metal Works gas-fired floor heater (C) InspectAPedia GL

That that company was Royal Metal Works, 238 Van Ness Ave, in San Francisco, CA. That patent was cited by other product patents between 1943 and 1982.

Below at left your photo shows the gas controls including main valve (left) and pilot valvce (right-hand stem). At below right you've shown the pilot flame (I think).

Royal Metal Works gas-fired floor heater (C) InspectAPedia GL Royal Metal Works gas-fired floor heater (C) InspectAPedia GL

The company filed just three patents, two for heaters and one for metal bending:


  • Publication No. US1808019 A - an interesting method for bending corrugated metal - 1931 (filed 1929) and perhaps involved in the manufacture of the heaters in the earlier patents.

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Royal Metal Works Gas Heater 1928 Patent (C) InspectApedia Royal Metal Works Gas Heater 1928 Patent (C) InspectApedia

There is presently a [different] California Royal Metal Company (in fact several of them)
who might be able to give you more historical data, is a sheet metal fabricator whose business was established in 1981 but who may have known of the older Royal Metal Works who made your heater:

Royal Metal
Ted Rieck Enterprises Inc,
1228 South Wright St
Santa Ana, CA 92705
Phone: (714) 542-4763
Web: Royalmetal.com

Unless you object, I'll add your photos to data we have at InspectApedia and will leave you anonymous (our default) unless you let me know that you want to be identified. That may attract comment from other readers who have similar products.

I'll attach the documents of interest to this article.

Watch out: I would not assume that the heater you have is safe to use without both a thorough visual inspection and testing for gas leaks as burning LP or natural gas in a defective appliance can produce fatal carbon monoxide gas. I would suspect that your device may also lack safety features of modern gas heaters. If you are going to ignore my timid warnings then at least be sure you have working CO and smoke detectors properly located and installed.

Other antique wall heating convectors are shown at WALL CONVECTORS HVAC



Continue reading at AGE of a BUILDING or select a topic from the More Reading links shown below.


Or see Lennox HVAC products Age PDF

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AGE of HEATERS, BOILERS, FURNACES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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