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Here are some other facts on how it works: Old cast-iron radiators, very often in Victorian splendor, stand guard over the chills of winter, and many homeowners hate to part with these beauties. Other homes have heating systems that literally disappear beneath the surfaces of the rooms as radiant panels. Just about anything is (and always has been) possible with hydronics.

Older cast-iron radiators, the sort used on "one-pipe" steam heat, have nipples only across the bottom portion of the individual radiator sections because steam is lighter than air. When the steam enters the bottom of a radiator it flows upward into the radiator sections, pushing the air from a vent.

Hot-water radiators, on the other hand, have nipples across both the upper and lower portion of the radiator sections. Even though hot water rises, it doesn't move as quickly as steam. The double set of nipples encourages better circulation of the hot water through the radiator.

Around 1905, when "two-pipe" steam became popular, contractors began to use hot-water radiators on their steam systems as well, and those old steam radiators with their single set of bottom nipples soon became obsolete. Several manufacturers continue to make freestanding cast-iron radiators with the upper and lower push nipples, however.

And some more information on its origins (originally found at

It is commonly claimed that the Romans invented central heating, but the Samara Heating company did some research which it said showed the radiator itself first appeared in 1855 in the then Russian capital, St Petersburg.

Its inventor, an ethnic German of Italian origin named Franz San-Galli, named it the "hot box" and patented it in Germany and the US.

Request for Specifics[edit]

I generally like this article, but I would appreciate more specifics.

Under "Automobiles," the article states:

"Between the engine and the radiator lies the thermostat, a temperature operated valve. It remains closed, restricting coolant flow, until the engine reaches the thermostat's activation temperature. This arrangement allows the engine temperature to be maintained in the ideal operating range." [Bolding added.]

What is the "ideal operating range" of temperatures? Do different types of engine (e.g. Gasoline, E85, Diesel, Propane/LPG, Natural Gas, Gasoline-Electric Hybrid) have different "ideal operating ranges"?

For a standard petrol car engine the ideal operating temperature is around 82C. Does anyone know the power transfer capacity of a radiator? I roughly guess that it is 20kW / (80C - 20C) = 340W/K but I can't find any hard figures. --njh 01:21, 10 November 2006 (UTC)

Another point that seems unclear to me: is "ethylene glycol (a.k.a. antifreeze)" added only to ensure cold weather performance, or also to make heat transfer more efficient in any weather?

I believe that Ethylene glycol and now Propylene glycol are used mainly to stop freezing. Boiling point elevation is more easily done with pressure valves, both chemicals reduce the water's heat capacity and increase the viscosity (reducing the conduction rate). They might help with wetting? --njh 01:21, 10 November 2006 (UTC)

Finally, it would be nice to add citations for the stated facts, as well as sources of additional information.

Thanks in advance for your help.—Preceding unsigned comment added by (talkcontribs)

  • The 'ideal' temperature is a bit misleading, because engine temperature (like so many other engine parameters) is a compromise. A cooler engine will produce more power, while a hotter engine may have lower emissions. This is probably too in-depth for an article about radiators, so I'll change the 'ideal' into 'design' temperature.
  • Also, the article seems to refer to the thermostat as either 'open' or 'closed', which isn't correct. The thermostat opens just enough to maintain the engine at the design temperature. How far it opens, depends on many factors (such as outside air temperature, air flow through the radiator and the amount of power (=heat) the engine is producing. I'll incorporate this into the article. -- Rpvdk 08:37, 19 October 2006 (UTC)
    • No, I dont believe this is quite correct. While the size of the thermostat's opening does vary slightly based on the temperature, generally it's considered either open or closed. This has to do with the fact that the valve is a wax-pellet design - once the target temperature is reached, the wax melts which opens the valve fully. Subsequent increases in temperature may open it slightly more, but not much. Try watching it in some water heated on your stove, it's kindof fun/interesting. 10:08, 3 December 2007 (UTC)

I think that the radiator artical should show how it heats the room as well as where it comes from. —Preceding unsigned comment added by (talk) 19:30, 30 April 2008 (UTC)

A useful article, but I also think more specifics would be helpful in relation to domestic (ie building) radiators:

  • what range of temperatures do they operate at?
  • How does this compare to the temperature of underfloor heating systems (generally lower temperature)?
  • What implications does this have for energy efficiency and choice of heat source (eg gas boiler vs ground source heat pump)?

Please: if anyone can help with the technical aspects of this, I think this article would be the better for it. (Or maybe there should be a new article on domestic thermodynamics!) HallfieldResident (talk) 09:49, 8 October 2008 (UTC)

bleeding home radiators[edit]

I have hot water baseboard heating and need to bleed the radiators because I hear a lot of gurgling when the heating comes on. Should the heat be turned up or off when I bleed the radiators?Markhoffman 23:27, 1 January 2007 (UTC)

Perhaps not a Wikipedia topic? But always nice to help: Afraid I'm not entirely sure what you mean by 'baseboard' but to purge air from a rad that is always (in theory) water filled, it doesn't matter if the heat is on or off. The rad valve control should be open but ideally have the system pump turned off (goes off when heating is off) - the water pressure will expel the air. On some systems, having the pump on could theoretically cause air to be sucked in rather than expelled... 20:38, 3 February 2007 (UTC)

Convectors in houses are properly called radiators ...[edit]

... for the simple reason that if you say "radiator", people will know what you mean and if you say "convector" almost no one will. Good luck finding "convector repair" in the Yellow Pages(TM).

Whether "radiators" actually work by radiation is beside the point. I'll probably fix the article in a spare moment. -Dmh 22:40, 8 January 2007 (UTC)

Water as the coolant liquid in automobile radiators[edit]

This article currently states that the coolant liquid used in automobile radiators is most often antifreeze. This might be true in locations where the winters are cold enough for the temperature to drop below freezing, but I think that in warmer climates, the usual practice is to just use plain water as the coolant liquid. I'm not knowledgeable enough about the subject to offer any authoritative information, but someone else should look into this. -Sky Blu 2 (talk) 00:15, 14 May 2008 (UTC)

I've tried to come up with a more general wording, hopefully this will help. ChrisHodgesUK (talk) 12:38, 4 February 2009 (UTC)

Silver "bulb" sticking out the side of the cast iron radiator[edit]

Anyone know what the silver "bulb" that's sticking out the side of the cast iron radiator is ? located here: it's on the left, about 2/3 of the way up. mine is labeled usav-884. another in the house is labeled usav-881. they have a dial on the top that can be turned from "closed" to "full open", and air seems to come out of it slowly, making a whistling, when the heat is on. Nqzero (talk) 19:26, 26 December 2008 (UTC)


The radiator is always a source of heat to its environment

This is wrong, domestic radiators are eg on themselves no continous source of heat; this is only when heated water is run trough it (the water being heated by a burner or electric heater elsewere in the system)


The following is a closed discussion of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the proposal was: Not Moved. Station1 (talk) 05:54, 15 October 2009 (UTC)

RadiatorRadiative heater — Radiator isn't a good article name, as anything which gives off radiation is a radiator. A simple stove for example also radiates heat. Also, a radiator doesn't specifically refer a device which emits thermal radiation; electrical, nuclear, ... radiation also counts; thus eg radio's, ... are also radiators. (talk) 13:02, 7 October 2009 (UTC)

  • Strong Oppose This article's content is strictly about "Radiators" as a term in popular usage (however it is mis-used), rather than "radiator" as an abstract concept. It would be wrong to apply a name to this article that differed from this.
The sub-article (i.e. not the article discussed here) radiator (heating) was previously moved to radiative heater (and then reverted). That move was made by User:KVDP, and as I see that you're also in Belgium, then might I ask if you're the same editor, posting anonymously, and putting forward a very similar move?
"Radiative heater" was a poor name for that article, for two reasons. Firstly it's a WP:NEO and has no common-use currency for this commonplace domestic appliance. I'm in the UK, I don't know how terminology in Belgium works, but call them "radiators" even if they work by convection. Secondly it's particularly mis-leading as it's just the wrong physical principle altogether.
If you wish to create an article called radiative heater and describe heating by radiative transfer, then please do so. If you want a general article on radiation, radiating devices or even radiators, then please do so (and please set up Radiator (disambiguation) if you do create Radiators).
Moving RadiatorRadiative heater though would create an article with an unrecognised neologism as a name, that isn't even about radiative process. Andy Dingley (talk) 13:52, 7 October 2009 (UTC)
  • Oppose As stated above no one uses the phrase "Radiative heater". On the other hand, the word "Radiator" is the name in common usage for the appliance. The DAB header is sufficiant. If there is still a problem with the present name then perhaps "Radiator (appliance)" would be better. A real problem to be addressed is that the articles Radiator (heating) and Radiator overlap enormously and need to be expanded to avoid a merge tag being added in the future. Jubilee♫clipman 15:39, 7 October 2009 (UTC)
  • Oppose an attempt to disambiguate something which is not ambiguous to fluent English speakers. The vast majority of the English-speaking world gets by with calling radiators radiators, no reason for anything different here. Knepflerle (talk) 22:43, 7 October 2009 (UTC)
  • Oppose. "Radiative heater" is nonsense. "Radiator" in common use means the item described at Radiator (heating), but the link to that article is not prominent, being some way down the page. This page (Radiator) could with not much effort be merged with Radiator (disambiguation). Sussexonian (talk) 03:28, 8 October 2009 (UTC)

Minefield energy??? Jon (talk) 21:04, 11 October 2009 (UTC)

The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

theoretical matters[edit]

The article could be improved a lot if it went into specifics about theoretical matters like efficiency. For example, if i wanted to design a radiator for use in space, i'd want to know how much thermal power would be transferred from a pipe, rod, or fin of a particular material, size, shape, and temperature into the interplanetary medium. I know from first principles that the answer will depend on things like surface area, temperature difference, and heat capacity. Some formula would really help, here. -- (talk) 16:34, 11 November 2009 (UTC)

Nice idea, but I think I'd want that in a sub article, and to keep this as a lightweight abstract across the topic.
A good article on Spacecraft heat management (heating and cooling, they're very closely related) would be a brilliant topic. Andy Dingley (talk) 16:49, 11 November 2009 (UTC)
I agree; heat management in satellites and spacecraft is a huge part of their design, and much of the relevant physics info is already tucked away on several Wikipedia pages. So a section in this article on first principles would be appropriate, and the nitty gritty details, which are substantial, would be in the sub-article(s). The main points to keep here, will be: that there are three properties of radiators: emissivity, absorptivity, and reflectivity; that watts per square metre are the SI units used for radiant emittance; that there is a fourth power relation to absolute temperature; and that the Stefan–Boltzmann constant is used to calculate it, as . See Thermal radiation#Formula. -- (talk) 23:39, 11 November 2009 (UTC)

what makes an efficient home radiator[edit]

I think this article could use some information, explained in simple terms, about what makes a home radiator design efficient, and why most radiators look a certain way. Obviously its called something to do with heat exchange and surface area, but what about water and steam flow? Many of the stranger new conceptual designs, for example from this design competition [1] claim their radiators are more efficient than older designs because they maximise surface area (one even uses a fractal space filling design based on that premise), but this ignores the mainly vertical and modular design of traditional home radiators. Or is the traditional design like that because of manufacturing constraints?--Yugyug (talk) 18:11, 5 March 2010 (UTC)

For starters, that would be best over at Radiator (heating)
Secondly, beware of WP:NOR. Find some prior discussion of efficiency and refer to that. This isn't the place to start such a synthesis. Andy Dingley (talk) 19:55, 5 March 2010 (UTC)

Thanks for your response. I don't intend to to add any original research, I just think that radiator design must follow some generally accepted guidelines, known to the engineers that build them. I would like to know what they are and think it would be interesting to include in the article. I can't find much online - searching with keywords like 'efficiency' tends to only uncover information about how to make existing designs more efficient (TRVs and reflector boards etc), not much about their design. And then searching with 'design' tends to bring up brands, styles, marketing pages etc. Is it the type of thing that would be included in engineering textbooks? —Preceding unsigned comment added by Yugyug (talkcontribs) 20:15, 6 March 2010 (UTC) ....forgot to sign before: --Yugyug (talk) 20:17, 6 March 2010 (UTC)

When a radiator is "inefficient", what happens to the lost energy? What about an electric space heater? Jeh (talk) 16:05, 13 April 2018 (UTC)
It's not delivered (by either convection or radiation) into the room containing the radiator. This is either because it's lost elsewhere in the system (heating underfloor pipe voids is of little value) or it required additional power from the circulating pump. An efficient radiator provides a lot of useful heating area, in a small overall size, with little restriction in flow. As heating systems are also operated intermittently (their ability to heat rapidly from cold often requires them to be somewhat oversized), then the thermal mass of the radiator itself can be a drawback. Inefficient radiators provide either low surface area (so the "useless" piping surface represents a greater proportion of the system surface for losing heat; such as early cast-iron sectional radiators did. Or else they restrict flow, requiring more energy to pump the system.
It's easy to say that "heating systems are 100% efficient" because their losses are as heat anyway, but a system design approach, taking effective heat delivered to where it's needed, is more fussy. Andy Dingley (talk) 18:27, 13 April 2018 (UTC)


I added the copyediting tag for the first three sections, which are terribly written: run-on sentences, lack of punctuation, and bad structure. I suggest rewriting them entirely. -- (talk) 15:33, 13 April 2018 (UTC)